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Anderson, B.E., G.L. Gregory, J.E. Collins Jr., G.W. Sachse, T.J. CONWAY, and G.P. Whiting. Airborne observations of spatial and temporal variability of tropospheric carbon dioxide. Journal of Geophysical Research 101(D1):1985-1997 (1996).

Fast response (5-s resolution) CO₂ measurements were recorded on two recent NASA-sponsored airborne atmospheric chemical survey missions: the summer/fall 1991 Pacific Exploratory Mission-West A (PEM-West A) and the winter 1992 Airborne Arctic Stratospheric Expedition II (AASE II). Both missions were conducted aboard the NASA Ames Research Center DC-8 aircraft and included sampling between the surface and 12-km altitudes over a wide range of latitudes and longitudes. In the following text, these data, along with simultaneous surface measurements from the NOAA flask sampling network, are examined to establish the vertical distribution and variability of CO₂ as a function of location and season. Results indicate that middle to upper tropospheric (>5 km altitude) CO₂ concentrations often differ considerably (>5 parts per million by volume in some cases) from values recorded at surface stations within the same geographic region. These differences are particularly notable at middle to high northern latitudes where midtropospheric concentration changes and seasonal cycles are generally delayed in time and highly damped in amplitude relative to surface observations.

Atlas, E., B. Ridley, J. Walega, J. Greenberg, G. Kok, T. Staffelbach, S. Schauffler, J. Lind, G. Hübler, R. Norton, GTE PEM-West Science Team, E. DLUGOKENCKY, J. ELKINS, S. OLTMANS, G. Mackay, and D. Karecki. A comparison of aircraft and ground-based measurements at Mauna Loa Observatory, Hawaii, during GTE PEM-West and MLOPEX 2. Journal of Geophysical Research 101(D9):14,599-14,612 (1996).

During October 19-20, 1991, one flight of the NASA Global Tropospheric Experiment (GTE) Pacific Exploratory Mission (PEM-West A) mission was conducted near Hawaii as an intercomparison with ground-based measurements of the Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2) and the NOAA Climate Modeling and Diagnostics Laboratory (CMDL). Ozone, reactive nitrogen species, peroxides, hydrocarbons, and halogenated hydrocarbons were measured by investigators aboard the DC-8 aircraft and at the ground site. Lidar cross sections of ozone revealed a complex air mass structure near the island of Hawaii which was evidenced by large variation in some trace gas mixing ratios. This variation limited the time and spatial scales for direct measurement intercomparisons. Where differences occurred between measurements in the same air masses, the intercomparison suggested that biases for some trace gases was due to different calibration scales or, in some cases, instrumental or sampling biases. Relatively large uncertainties were associated with those trace gases present in the low parts per trillion by volume range. Trace gas correlations were used to expand the scope of the intercomparison to identify consistent trends between the different data sets.

Battle, M., M. Bender, T. Sowers, P.P. TANS, J.H. BUTLER, J.W. ELKINS, J.T. Ellis, T. CONWAY, N. ZHANG, P. LANG, and A.D. CLARK. Atmospheric gas concentrations over the past century measured in air from firn at the South Pole. Nature 383:231-235 (1996).

The extraction and analysis of air from the snowpack (firn) at the South Pole provides atmospheric concentration histories of biogenic greenhouse gases since the beginning of the present century which confirm and expand on those derived from studies of air trapped in ice cores. Furthermore, calculations based on the inferred atmospheric concentrations of oxygen and carbon dioxide indicate that--in contrast to the past few years--the terrestrial biosphere was neither a source nor sink of CO₂ between ~1977 and 1985.

Beine, H.J., D.A. Jaffe, D.R. Blake, E. Atlas, and J. HARRIS. Measurements of PAN, alkyl nitrates, ozone, and hydrocarbons during spring in interior Alaska. Journal of Geophysical Research 101(D7):12,613-12,619 (1996).

Measurements of the atmospheric mixing ratios of ozone, peroxyacetylnitrate (PAN), hydrocarbons, and alkyl nitrates were made in a boreal forest ecosystem in the interior of Alaska from March 15 to May 14, 1993. During this period the mixing ratios of PAN, alkyl nitrates, and nonmethane hydrocarbons (NMHCs) generally decreased due to the influence of both meteorology and OH removal. Mean mixing ratios of ozone, PAN, C₂-C₆ alkyl nitrates, and total C₂-C₅ NMHC during southerly flow periods were 24.4 parts per billion (ppbv), 132.1 parts per trillion (pptv), 34 pptv, and 8.2 ppbCv, respectively, During a short period of northerly flow, mixing ratios of PAN and total NMHC were approximately 2 times the southerly flow mixing ratios. PAN is correlated with ozone, and alkyl nitrates are correlated with alkanes PAN and ozone mixing ratios exhibit similar diurnal variations on a number of days with an early morning minimum and afternoon maximum. This is likely due to a diurnal cycle in the boundary layer-free troposphere exchange and loss processes in the boundary layer for both O₃ and PAN. Higher molecular weight (mw) hydrocarbons and alkyl nitrates are observed to decrease more quickly than the lower mw hydrocarbons, consistent with removal by OH as the primary loss process.

BODHAINE, B.A. Aerosol measurements during the Mauna Loa Photochemistry Experiment 2. Journal of Geophysical Research 101(D9):14,757-14,765 (1996).

Aerosol measurements have been made continuously at Mauna Loa Observatory (MLO) from 1974 to the present. Condensation nucleus (CN) concentration has been measured using automatic CN counters, and aerosol scattering extinction (s_sp) has been measured using a four-wavelength nephelometer. The Mauna Loa Observatory Photochemistry Experiment (MLOPEX) was conducted in 1991-1992 to study intensively many important variables in the field of atmospheric chemistry. Because of a strong diurnal cycle in nearly everything measured at MLO, caused by an upslope-downslope wind system, it is important to develop data-editing criteria that can safely identify background conditions as opposed to other conditions when the site may be contaminated by local sources. Ordinarily, background conditions occur during nighttime downslope wind conditions, and contaminated conditions occur during daytime upslope wind conditions. However, occasionally unusual weather conditions or contamination caused by a local source such as the Mauna Loa caldera can confuse the issue. It is recommended that background aerosol data be chosen during 0000-0800 Hawaiian standard time (HST) to generally avoid upslope wind conditions, and that wind direction and speed, CN, and SO₂ data be used if available to further eliminate local pollution episodes. In addition, all data should be examined by a human editor, if possible, in order to recognize certain episodes that many not fit automated criteria.

BODHAINE, B.A. Central Antarctica: atmospheric chemical composition and atmospheric transport. In Chemical Exchange Between the Atmosphere and Polar Snow, E.W. Wolff and R.C. Bales (eds.). NATO ASI Series I, 43:145-172, Springer-Verlag, Berlin (1996).

No abstract.

BODHAINE, B.A., R.L. McKenzie, P.V. Johnston, D.J. HOFMANN, E.G. DUTTON, R.C. SCHNELL, J.E. BARNES, S.C. RYAN, and M. Kotkamp. New ultraviolet spectroradiometer measurements at Mauna Loa Observatory. Geophysical Research Letters 23(16):2121-2124, 1996.

A research-grade scanning UV spectroradiometer was installed at Mauna Loa Observatory (MLO), Hawaii, in July 1995. This instrument, built around a commercially available double monochromator, is interfaced with a PC to provide automatic control and data acquisition. The spectral range sampled by the instrument is 290-450 nm, and the bandpass is about 1 nm. A complete scan requires about 200 seconds and is performed every 5 degrees of solar zenith angle (SZA) during daylight hours. Calibration is performed on site at 6-month intervals using a 1000-W standard quartz-halogen FEL lamp with calibration traceable to NIST. The UV irradiances measured at MLO are much more intense than at low altitude mid-latitude locations. For observations at a SZA of 45°, the erythemally weighted UV can exceed 18 mW cm^-2, which is approximately 15-20% greater than the maxima seen at Lauder, New Zealand, for similar ozone amounts. The difference is primarily due to the higher altitude at MLO. For overhead sun conditions at MLO, erythemal UV can exceed 45 mW cm^-2, which to our knowledge is the highest recorded anywhere at the Earth's surface. UV irradiance is strongly correlated (inversely) with Dobson spectrophotometer total ozone measurements at MLO, with higher correlations at shorter wavelengths. The radiative amplification factor (RAF) for erythema at MLO is about 1.44 ± 0.46 at SZA 45°. Using ozone retrievals from the UV spectra themselves, the deduced RAF for erythema is 1.26 ± 0.38. The RAF's for erythema at SZA 60° are similar, and in agreement with other determinations within the limits of experimental uncertainty.

BUTLER, J.H. Scientific uncertainties in the budget of atmospheric methyl bromide. Atmospheric Environment 30(7):i-iii (1996).

No abstract.

BUTLER, J.H., and J.M. Rodriguez. Methyl bromide in the atmosphere. In The Methyl Bromide Issue, C.H. Bell, N. Price, and B. Chakrabarati (eds.). Wiley & Sons, New York, 27-90 (1996).

No abstract.

Chang, A.Y., R.J. Salawitch, H.A. Michelsen, M.R. Gunson, M.C. Abrams, R. Zander, C.P. Rinsland, J.W. ELKINS, G.S. DUTTON, C.M. VOLK, C.R. Webster, R.D. May, D.W. Fahey, R.-S. Gao, M. Loewenstein, J.R. Podolske, R.M. Stimpfle, D.W. Kohn, M.H. Proffitt, J.J. Margitan, K.R. Chan, M.M. Abbas, A. Goldman, F.W. Irion, G.L. Manney, M.J. Newchurch, and G.P. Stiller. A comparison of measurements from ATMOS and instruments aboard the ER-2 aircraft: Halogenated gases. Geophysical Research Letters 23(17):2393-2396 (1996).

We compare volume mixing ratio profiles of N₂O, CFC-11, CFC-12, CCl₄, SF₆, and HC1 in the midlatitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS-3 Space Shuttle Mission with in situ measurements acquired from the NASA ER-2 aircraft during November 1994. Good agreement is found between ATMOS and in situ correlations of [CFC-11], [CFC-12], and [SF₆] with [N₂O]. ATMOS measurements of [CCl₄] are 15% high compared to ER-2 data, but agree within the systematic uncertainties. ATMOS observations of [HC1] vs. [N₂O] are within ~10% of ER-2 data for [HC1] > 1 ppbv, but exceed in situ measurements by larger fractional amounts for smaller [HC1]. ATMOS measurements of [C1ONO₂] agree well with values inferred from in situ observations of [C1O], [NO], and [O₃]. The sum of [HC1] and [C1ONO₂] observed by ATMOS, supplemented by a minor contribution from [C10] estimated with a photochemical model, is consistent with the levels of inorganic chlorine inferred from in situ measurements of chlorine source gases.

Chang, A.Y., R.J. Salawitch, H.A. Michelsen, M.R. Gunson, M.C. Abrams, R. Zander, C.P. Rinsland, M. Loewenstein, J.R. Podolske, M.H. Proffitt, J.J. Margitan, D.W. Fahey, R.-S. Gao, K.K. Kelly, J.W. ELKINS, C.R. Webster, R.D. May, K.R. Chan, M.M. Abbas, A. Goldman, F.W. Irion, G.L. Manney, M.J. Newchurch, and G.P. Stiller. A comparison of measurements from ATMOS and instruments aboard the ER-2 aircraft: Tracers of atmospheric transport. Geophysical Research Letters 23(17):2389-2392 (1996).

We compare volume mixing ratio profiles of N₂O, O₃, No_y, H₂O, CH₄, and CO in the midlatitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS-3 Space Shuttle Mission with in situ measurements acquired from the NASA ER-2 aircraft during November 1994. ATMOS and ER-2 observations of [N₂O] show good agreement, as do measured correlations of [O₃], [No_y], [H₂O], and [CH₄] with [N₂O]. Thus a consistent measure of hydrogen (H₂O, CH₄) content of the lower stratosphere is provided by the two platforms. The similarity of [No_y] determined by detection of individual species by ATMOS and the total [No_y] measurement on the ER-2 provides strong corroboration for the accuracy of both techniques. A 25% discrepancy in lower stratospheric [CO] observed by ATMOS and the ER-2 remains unexplained. Otherwise, the agreement for measurements of long-lived tracers demonstrates the ability to combine ATMOS data with in situ observations for quantifying atmospheric transport.

Deshler, T., B.J. JOHNSON, D.J. HOFMANN, and B. Nardi. Correlations between ozone loss and volcanic aerosol at altitudes below 14 km over McMurdo Station, Antarctica. Geophysical Research Letters 23(21):2931-2934 (1996).

Ozone and aerosol profiles over McMurdo Station, Antarctica (78°S), have been measured August �October for the years 1986-1995. This spans the development and decay of the recent perturbation to stratospheric aerosol caused by Pinatubo. Volcanic aerosol surface areas, in the 11-14 km region, peaked near 100 mm² cm^-3 in 1991, decaying to 20-30 mm² cm^-3 in 1992, 15-25 mm² cm^-3 in 1993, and to background levels of 4-8 mm² cm^-3 in 1994. Based on these measurements the volcanic aerosol signal persisted over Antarctica for three austral springs, implying an exponential decay rate of about 14 months. The aerosol below 14 km was correlated with previously unobserved ozone loss at these altitudes. Ozone loss rates of 5-15 ppb dy^-1 (0.3-0.5 DU dy^-1) were observed in the 10-12 and 12-14 km layers. Beginning in 1994, when the aerosol approached its pre-Pinatubo level, ozone loss diminished in the 12-14 km layer and was not observed in the 10-12 km layer.

DLUGOKENCKY, E.J., E.G. DUTTON, P.C. NOVELLI, P.P. TANS, K.A. MASARIE, K.O. Lantz, and S. Madronich, Changes in CH₄ and CO growth rates after the eruption of Mt. Pinatubo and their link with changes in tropical tropospheric UV flux. Geophysical Research Letters 23(20):2761-2764 (1996).

Trace gas measurements from air samples collected weekly at a globally-distributed network of sampling sites revealed sharp increases in the growth rates of CH₄ and CO in the tropics and high southern latitudes immediately following the eruption of Mt. Pinatubo on June 15, 1991. The eruption emitted ~20 Mt SO₂ into the lower stratosphere. Calculations made with a radiative transfer model show that UV actinic flux in the wavelength region 290-330 nm was attenuated by ~12% immediately after the eruption due to direct absorption by SO₂, and that it was perturbed for up to 1 year after the eruption due to scattering by sulfate aerosols. We suggest that the decreased UV flux decreased the steady-state [OH] and led to the observed anomalously large growth rates for CH₄ and CO during late 1991 and early 1992.

ELKINS, J.W., D.W. Fahey, J.M., GILLIGAN, G.S. DUTTON, T.J. BARING, C.M. VOLK, R.E. DUNN, R.C. MYERS, S.A. MONTZKA, P.R. WAMSLEY, A.H. HAYDEN, J.H. BUTLER, T.M. THOMPSON, T.H. SWANSON, E.J. DLUGOKENCKY, P.C. NOVELLI, D.F. HURST, J.M. LOBERT, S.J. Ciciora, R.J. Mc Laughlin, T.L. THOMPSON, R.H. Winkler, P.J. Fraser, L.P. Steele, and M.P. Lucarelli. Airborne gas chromatograph for in situ measurements of long-lived species in the upper troposphere and lower stratosphere. Geophysical Research Letters 23(4):347-350 (1996).

A new instrument, the Airborne Chromatograph for Atmospheric Trace Species IV (ACATS-IV), for measuring long-lived species in the upper troposphere and lower stratosphere is described. Using an advanced approach to gas chromatography and electron capture detection, the instrument can detect low levels of CFC-11 (CCl₃F), CFC-12 (CCl₂F₂), CFC-113 (CCl₂F-CClF₂), methyl chloroform (CH₃CCl₃), carbon tetrachloride (CCl₄,), nitrous oxide (N₂O), sulfur hexafluoride (SF₆), halon-1211 (CBrClF₂), hydrogen (H₂), and methane (CH₄) acquired in ambient samples every 180 to 360 s. The instrument operates fully-automated onboard the NASA ER-2 high-altitude aircraft on flights lasting up to 8 hours or more in duration. Recent measurements include 24 successful flights covering a broad latitude range (70.1°S - 61.1°N) during the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA) campaign in 1994.

Erickson, D.J. III, P.J. Rasch, P.P. TANS, P. Friedlingstein, P. Ciais, E. Maier-Reimer, K. Six, C.A. Fischer, and S. Walters. Journal of Geophysical Research 101(D10):15,079-15,097 (1996).

A global three-dimensional atmospheric model, the NCAR CCM2 general circulation model, has been adapted to study the hourly to yearly variability of CO₂ in the atmosphere. Features of this CCM2-based model include high spatial resolution (2.8° 2.8° latitude/longitude), 18 vertical levels, a 15-min time step, and an explicit, nonlocal atmospheric boundary layer parameterization. The surface source/sink relationships used include exchange with the ocean, the terrestrial biosphere, biomass burning, and fossil fuel release of CO₂. The timing and magnitude of the model seasonal cycle are compared to observational data for 28 sites. The seasonal cycle of atmospheric CO₂ is generally well predicted by the model for most of the northern hemisphere, but estimates of the amplitude of the seasonal cycle in the southern hemisphere are overpredicted. To address this aspect more rigorously, we have used the monthly surface ocean pCO₂ maps created by the Max-Planck-Hamburg ocean general circulation model to assess the ocean seasonality on the atmospheric surface CO₂ seasonality. The globally-averaged interhemispheric gradient in atmospheric CO₂ concentrations, as computed with the chosen source/sink distributions, is a factor of two, too high compared to data, and selected longitudinal bands may be up to 50% higher than the zonal mean. The high temporal resolution of this model allows the infrequent yet real extrema in atmospheric CO₂ concentrations to be captured. The vertical attenuation of the seasonal cycle of atmospheric CO₂ is well simulated by the boundary layer/free troposphere interaction in the model in the northern hemisphere. Conversely, an increasing amplitude of the seasonal cycle aloft is found in the midlatitude southern hemisphere indicating interhemispheric transport effects from north to south. We use two different models of the terrestrial biosphere to examine the influence on the computed seasonal cycle and find appreciable differences, especially in continental sites. A global three-dimensional chemical transport model is used to assess the production of CO₂ from the oxidation of CO throughout the volume of the atmosphere. We discuss these CO + OH CO₂ + H results within the context of inverse model approaches to ascertaining the global and regional source/sink patterns of CO₂. Deficiencies in the model output as compared to observational data are discussed within the context of guiding future research.

Froidevaux, L., W.G. Read, T.A. Lungu, R.E. Cofield, E.F. Fishbein, D.A. Flower, R.F. Jarnot, B.P. Ridenoure, Z. Shippony, J.W. Waters, J.J. Margitan, I.S. McDermid, R.A. Stachnik, G.E. Peckham, G. Braathen, T. Deshler, J. Fishman, D.J. Hofmann, and S.J. OLTMANS. Validation of UARS Microwave Limb Sounder ozone measurements. Journal of Geophysical Research 101(D6):10,017-10,060 (1996).

This paper describes the validation of ozone data from the Upper Atmosphere Research Satellite (UARS) Microwave Limb Sounder (MLS). The MLS ozone retrievals are obtained from the calibrated microwave radiances (emission spectra) in two separate bands at frequencies near 205 and 183 GHz. Analyses described here focus on the MLS Version 3 data (the first set of files made publicly available). We describe results of simulations performed to assess the quality of the retrieval algorithms in terms of both mixing ratio and radiance closure. From actual MLS observations, the 205-GHz ozone retrievals give better closure (smaller radiance residuals) than that from the 183-GHz measurements and should be considered more accurate from the calibration aspects. However, the 183-GHz data are less noise limited in the mesosphere and can provide the most useful scientific results in that region. We compare the retrieved 205-GHz ozone profiles in the middle to lower stratosphere to ozonesonde measurements at a wide range of latitudes and seasons. Ground-based lidar data from Table Mountain, California, provide a good reference for comparisons at higher altitudes. Based on these analyses, comparisons with balloon-borne measurements and others, as well as a detailed budget of estimated uncertainties, MLS results appear to be generally of high quality with some biases worth mentioning. Results for the lowermost stratosphere (~ 50 to 100 hPa) are still in need of improvement. A set of estimated precision and accuracy values is derived for the MLS ozone data sets. We also comment on recent updates in the retrieval algorithms and their impact on ozone values.

Gonzalez Jorge, H., and J.A. OGREN. Sensitivity of retrieved aerosol properties to assumptions in the inversion of spectral optical depths. Journal of the Atmospheric Sciences 53(24):3669-3683 (1996).

The uncertainties of integral aerosol properties calculated using aerosol size distributions retrieved from multiwavelength observations of aerosol optical depth have been determined for a variety of typical atmospheric aerosol size distributions and refractive indices. The results suggest that more information about the aerosol composition, as well as more information about the sizes that are less efficient, in the optical sense, is needed to improve the shape of the retrieved size distributions. All the calculations in this paper assume spherical homogeneous particles. The sensitivity results refer to these conditions. The moments of the retrieved size distributions are systematically underestimated and errors can be as large as -82%, -30%, and-35% for the total number of particles, the total surface, and the total volume, respectively. The errors in the mass scattering efficiency, the effective radius, and the total volume depend very much on whether the actual volume size distribution is monomodal or bimodal. For a known refractive index, the total scattering coefficient, the hemispherical backscattering coefficient, and the extinction coefficient, as well as the hemispheric backscattering to total scattering ratio and the asymmetry factor, are obtained with absolute values for the average errors less than 4%. Similar behavior was expected for cases with uncertainty in the refractive index, especially for parameters defined by the ratio of two integral properties. However, it turns out that the hemispheric backscattering coefficient and the hemispheric backscattering to total scattering ratio were poorly retrieved, reaching errors of 29% in several cases, while the asymmetry factor was very well recovered with absolute values of the average errors always under 7%. When the wavelength dependence of the refractive index is included, the retrieved size distribution is very unrealistic, with average errors in the hemispheric backscattering coefficients and the hemispheric backscattering to total scattering ratio around 30% at some wavelengths. However, even in this case the errors in the retrieved asymmetry factor stay under 8%. Thus, for spherical and homogeneous particles, the spectral optical depth data can be used to determine the asymmetry factor with little sensitivity to the assumptions in the calculations. Furthermore, the retrieved size distribution can be used as an intermediate step to extrapolate one set of optical properties from another set of optical properties.

HOFMANN, D.J. Recovery of Antarctic ozone hole. Nature 384:222-223 (1996).

No abstract.

HOFMANN, D.J. The 1996 Antarctic ozone hole. Nature 383:129 (1996).

No abstract.

HOFMANN, D.J., J.T. PETERSON, and R.M. ROSSON (eds.). Climate Monitoring and Diagnostics Laboratory No. 23 Summary Report 1994-1995. NOAA Environmental Research Laboratories, Boulder, CO 161 pp. (1996).

No abstract.

HOFMANN, D.J., S.J. OLTMANS, G.L. KOENIG, B.A. BODHAINE, J.M. HARRIS, J. A. LATHROP, R.C. SCHNELL, J. BARNES, J. CHIN, D. KUNIYUKI, S. RYAN, R. UCHIDA, A. YOSHINAGA, P.J. Neale, D.R. Hayes, Jr., V.R. Goodrich, W.D. KOMHYR, R.D. EVANS, B.J. JOHNSON, D.M. QUINCY, and M. CLARK. Record low ozone at Mauna Loa Observatory during winter 1994-1995: A consequence of chemical and dynamical synergism? Geophysical Research Letters 23(12):1533-1536 (1996).

During two days in late December 1994, total ozone measured at the Mauna Loa Observatory on the island of Hawaii, dropped below 200 Dobson Units (DU) for the first time since ozone measurements began at this site over 30 years ago. Total ozone values this low have not previously occurred over populated areas except on rare occasions when the edges of the springtime Antarctic ozone hole temporarily pass over the southern tip of Argentina. The monthly total ozone average for January 1995 was 216 DU, about 14% below the 1964-1981 baseline value. Ultraviolet radiation measured at Mauna Loa on clear days during this period increased inversely with ozone as expected, more than tripling in relative intensity at 295 nm. The normal annual minimum in total ozone occurs in winter at Mauna Loa; however, some winters experience considerably lower values than others. This was the case during the winter of 1994-1995. Although the general decline in global ozone, which began about 1980 and also appears in the Mauna Loa record, may be related to chemical ozone depletion, the unusually low values during some winters at Mauna Loa appear to be related to ozone transport from the tropics, and the timing of phase transitions of the QBO. This analysis provides an accurate method of forecasting low-ozone, high-UV winters in Hawaii.

HOFMANN, D.J., and S. Solomon. Observations and interpretation of changes in stratospheric ozone following the Pinatubo eruption. In The Mount Pinatubo Eruption Effects on the Atmosphere and Climate, G. Fiocco, D. Fuá, and G. Visconti (eds.). NATO ASI Series, 142:177-188, Springer-Verlag, Berlin (1996).

No abstract.

HURST, D.F., W.T. Griffith, and G.D. Cook. Trace-gas emissions from biomass burning in Australia. In Biomass Burning and Global Change, Vol. 2, J.S. Levine (ed.), pp. 787-792, MIT Press, Cambridge, Mass. (1996).

No abstract.

Keeling, C.D., J.F.S. CHIN, and T.P. Whorf. Increased activity of northern vegetation inferred from atmospheric CO₂ measurements. Nature 382:146-149 (1996).

Throughout the Northern Hemisphere the concentration of atmospheric carbon dioxide rises in winter and declines in summer, mainly in response to the seasonal growth in land vegetation. In the far north the amplitude of the seasonal cycle, peak to trough, is between 15 and 20 parts per million by volume. The annual amplitude diminishes southwards to about 3 p.p.m. near the equator, owing to the diminishing seasonality of plant activity towards the tropics. In spite of atmospheric mixing processes, enough spatial variability is retained in the seasonal cycle of CO₂ to reveal considerable regional detail in seasonal plant activity. Here we report that the annual amplitude of the seasonal CO₂ cycle has increased by 20%, as measured in Hawaii, and by 40% in the Arctic, since the early 1960s. These increases are accompanied by phase advances of about 7 days during the declining phase of the cycle, suggesting a lengthening of the growing season. In addition, the annual amplitudes show maxima which appear to reflect a sensitivity to global warming episodes that peaked in 1981 and 1990. We propose that the amplitude increases reflect increasing assimilation of CO₂ by land plants in response to climate changes accompanying recent rapid increases in temperature.

Key, J.R., R.A. Silcox, and R.S. STONE. Evaluation of surface radiative flux parameterizations for use in sea ice models. Journal of Geophysical Research 101(C2):3839-3849 (1996).

The surface radiation budget of the polar regions strongly influences ice growth and melt. Thermodynamic sea ice models, therefore, require accurate, yet computationally efficient methods of computing radiative fluxes. In this study a variety of simple parameterizations of downwelling shortwave and longwave radiation fluxes at the Arctic surface are examined. Parameterized fluxes are compared to in situ measurements over an annual cycle. Results suggest that existing parameterizations can estimate the downwelling shortwave flux to within 2% in the mean, with a root-mean-square error (RMSE) of about 4% for clear skies and 21% for cloudy conditions. Parameterized longwave fluxes are accurate to within 1% in the mean, with RMSE values of 6% for both clear and cloudy skies. On the basis of these results, two parameterization schemes are recommended to estimate radiation forcings in sea ice models for Arctic applications.

Kirchhoff, V.W.J.H., N.J. Schuch, D.K. Pinheiro, and J.M. HARRIS. Evidence for an ozone hole perturbation at 30° South. Atmospheric Environment 30(9):1481-1488 (1996).

A relatively strong stratospheric column ozone decrease was observed in the south of Brazil (29.5°S) in 1993, at the end of October. This ozone decrease was observed when the normal behavior of the ozone column at low latitudes, in Brazil, reaches its yearly maximum, so that a decrease of ozone during this time period is unexpected. The local observations were made by two different measurement techniques. Two independent ground-based Brewer spectrophotometers documented strong column ozone decreases in the south of Brazil in 1993. The vertical distribution of ozone was observed with ozone-soundings, showing a uniform ozone decrease at all heights in the stratosphere, and very low ozone in the lower stratosphere, which has been shown to be characteristic of Antarctic ozone in Spring. TOMS ozone data, representing a third observational technique, averaged over small latitude-longitude bands, correlate very well with the local observations, which leaves no doubt that the observed ozone decreases in the south of Brazil during October 1993 were real. Also, the observed ozone decreases may be considered large, since for comparison, the local seasonal variation is at most of the order of 30 Dobson Units (DU), whereas one of the October decreases measured about 60 DU. There seems to be no physical or chemical mechanism at low latitudes, that could account for such a large and fast perturbation in the stratosphere. On the other hand, inspection of the TOMS total ozone data maps, on the days of the above observations, show a distinct link between the Antarctic ozone hole latitudes, reaching out to the north in a curved path, and touching tropical latitudes over a narrow belt. Trajectory analyses confirm that for days of low ozone in Santa Maria, Brazil, the air masses at 20 and 25 km height have an Antarctic origin.

Kley, D., P.J. Crutzen, H.G. Smit, H. VÖMEL, S.J. OLTMANS, H. Grassl, and V. Ramanathan. Observations of near-zero ozone concentrations over the convective Pacific: Effects on air chemistry. Science 274:230-233 (1996).

A series of measurements over the equatorial Pacific in March 1993 showed that the volume mixing ratios of ozone were frequently well below 10 nanomoles per mole both in the marine boundary layer (MBL) and between 10 kilometers and the tropopause. These latter unexpected results emphasize the enormous variability of tropical tropospheric ozone and hydroxyl concentrations, which determine the oxidizing efficiency of the troposphere. They also imply a convective short circuit of marine gaseous emissions, such as dimethyl sulfide, between the MBL and the uppermost troposphere, leading, for instance, to sulfate particle formation.

Lahoz, W.A., M.R. Suttie, L. Froidevaux, R.S. Harwood, C.L. Lau, T.A. Lungu, G.E. Peckham, H.C. Pumphrey, W.G. Read, Z. Shippony, R.A. Suttie, J.W. Waters G.E. Nedoluha, S.J. OLTMANS, J.M. Russell III, and W.A. Traub. Validation of UARS microwave limb sounder 183 GHz H₂O measurements. Journal of Geophysical Research 101(D6):10,129-10,149 (1996).

The Upper Atmosphere Research Satellite (UARS) microwave limb sounder (MLS) makes measurements of thermal emission at 183.3 GHz which are used to infer the concentration of water vapor over a pressure range of 46-0.2 hPa (~20 to ~60 km). We provide a validation of MLS H₂0 by analyzing the integrity of the measurements, by providing an error characterization, and by comparison with data from other instruments. It is estimated that version 3 MLS H₂0 retrievals are accurate to within 20-25% in the lower stratosphere and to within 8-13% in the upper stratosphere and lower mesosphere. The precision of a single profile is estimated to be ~0.15 parts per million by volume (ppmv) in the midstratosphere and 0.2 ppmv in the lower and upper stratosphere. In the lower mesosphere the estimate of a single profile precision is 0.25-0.45 ppmv. During polar winter conditions, H₂0 retrievals at 46 hPa can have a substantial contribution from climatology. The vertical resolution of MLS H₂0 retrievals is ~ 5 km.

LOBERT, J.M., J.H. BUTLER, L.S. GELLER, S.A. YVON, S.A. MONTZKA, R.C. MYERS, A.D. CLARKE, and J.W. ELKINS. BLAST94, Bromine Latitudinal Air/Sea Transect 1994: Report on oceanic measurements on methyl bromide and other compounds. NOAA Technical Memorandum ERL CMDL-10, 39 pp. (1996).

The Nitrous Oxide and Halocompounds (NOAH) division of NOAA/CMDL participated in two research cruises in 1994 for the Bromine Latitudinal Air/Sea Transect project. Frequently collected CH₃Br data from these expeditions constitute the largest data set for oceanic CH₃Br to date, and the first solid estimate of oceanic emission, production, and degradation of the compound. Our conclusion from these studies is that the ocean is probably not a net source of CH₃Br, but rather a net sink. Although CH₃Br is both produced and consumed everywhere in the surface ocean, the rate of consumption exceeds that of production in most waters sampled. Exceptions were coastal and coastally influenced waters, which were typically supersaturated, and areas of open ocean upwelling, where CH₃Br saturations were close to zero. About 80% of the ocean are undersaturated in CH₃Br, representing a net annual sink of 8-22 Gg y^-1. In addition to conducting two research cruises, we investigated potential contamination effects from sampling flasks and potential analytical artifacts from GC/ECD systems, developed a calibration scale for atmospheric and oceanic CH₃Br and a global, finite-increment model for more precisely estimating the partial lifetime of atmospheric CH₃Br with respect to oceanic losses. CH₃Br data from the second cruise indicate that our conclusions from the first expedition were qualitatively and quantitatively accurate. The latter results give greater strength to the global extrapolations of the first data set. Our best estimate of the partial lifetime of atmospheric CH₃Br with respect to oceanic losses is 2.7 (2.4-6.5) y. This range was derived from a 40 year, global data set of sea surface temperatures and windspeeds. Data from the two expeditions suggest a shorter lifetime of CH₃Br on the order of 2.4 y. The difference between the two estimates is due to the high windspeeds encountered during the cruises. Our estimate of the atmospheric lifetime, based upon combined atmospheric and oceanic losses, is now 1.0-1.1 y, compared to earlier estimates of 1.8-2.1 y when the ocean was considered an insignificant sink and tropospheric OH concentrations were underestimated by 15%. The oceanic sink correspondingly lowers the ODP for CH₃Br by about one-third. Work on the sampling and analytical uncertainties has revealed significant problems with the measurement of CH₃Br in flasks, which have been used historically for virtually all previous measurements of CH₃Br in the atmosphere. Whereas results from the shipboard system were free of sample storage effects and both the shipboard and the laboratory-based GC/MS systems were free of problems with co-eluting compounds, our results in analyzing flasks from the first expedition show that CH₃Br in flasks often is unstable and will increase or decrease with time. In addition, we found that results for CH₃Br determined by GC/ECD can be compromised by some GC configurations.

MC INTOSH, C.M., E.J. DLUGOKENCKY, P.M. LANG, and K.A. MASARIE. Atmospheric CH₄ seasonal cycles and latitude gradient from the NOAA CMDL cooperative air sampling network. NOAA Technical Memorandum ERL CMDL-11 79 pp. (1996).

Methane has been measured in air samples collected as part of the NOAA CMDL Carbon Cycle Group Cooperative Air Sampling Network since 1983. The data from each site are used to determine two important parameters that are useful in constraining the global CH₄ budget: seasonal cycles and the latitude gradient. Average seasonal cycles are determined using 2 to 13 years of data, depending on the site. The average latitude gradient is determined as the annually averaged mixing ratios for each site minus the annual average at the South Pole. Seasonal cycles and the latitude gradient are tabulated and shown graphically. Interannual variations in both parameters are quantified as standard deviations.

Merrill, J.T., J.L. Moody, S.J. OLTMANS, and H. Levy II. Meteorological analysis of tropospheric ozone profiles at Bermuda. Journal of Geophysical Research 101(D22):29,201-29,211 (1996).

As part of the North Atlantic Regional Experiment (NARE) a number of ozonesonde profiles were obtained from Bermuda during the spring and summer of 1993. We present meteorological case studies of two instances of elevated O₃ mixing ratio in the middle and upper troposphere which took place during the summer. The ozonesonde profile of July 9, 1993, indicated ozone mixing ratios exceeding 100 parts per billion by volume (ppbv) from ~5 km to above 15 km above sea level. A series of profiles for August 2-4 indicated elevated ozone in a layer which initially extended from 8 to 9 km and thickened to cover the 8- to 14-km range. Isentropic trajectories lead back to potential source areas over North America 2 to 5 days prior to the events. Objective analyses based on radiosonde data demonstrate that the air masses, as indicated by the trajectories, pass through areas of elevated isentropic potential vorticity located in troughs in the tropopause-level geopotential height field. The conformation and temporal development suggest that active planetary wave breaking was responsible for stratosphere-troposphere exchange in these systems. These results suggest an important role for O₃ of stratospheric origin in the western North Atlantic Ocean area, transported into the troposphere upstream over or near North America. It is notable that these events took place in the summer months of July and August, when such events had been considered unlikely.

Minschwaner, K., A.E. Dessler, J.W. ELKINS, C.M. VOLK, D.W. Fahey, M. Loewenstein, J.R. Podolske, A.E. Roche, and K.R. Chan. Bulk properties of isentropic mixing into the tropics in the lower stratosphere. Journal of Geophysical Research 101(D5):9433-9439 (1996).

Timescales for mixing of midlatitude air into the tropical lower stratosphere are deduced from observations of long-lived tracers N₂O and CCl₃F. Bulk mixing between tropical and midlatitude regions is assumed to be isentropic and relatively slow compared with local mixing within each region. The mean value of the mixing timescale ranges from 12 to 18 months near 20 km. There is a tendency for shorter mixing times at higher and lower altitudes, although vertical profiles of mixing cannot be definitively established by the data. A more robust quantity is given by the fraction of midlatitude air entrained into the tropical upwelling region. Implied mixing fractions exceed 50% above 22 km.

MONTZKA, S.A., J.H. BUTLER, R.C. MYERS, T.M. THOMPSON, T.H. SWANSON, A.D. CLARKE, L.T. LOCK, and J.W. ELKINS. Decline in the tropospheric abundance of halogen from halocarbons: Implications for stratospheric ozone depletion. Science 272, 1318-1322, (1996).

Analyses of air sampled from remote locations across the globe reveal that tropospheric chlorine attributable to anthropogenic halocarbons peaked near the beginning of 1994 and was decreasing at a rate of 25 ± 5 parts per trillion per year by mid 1995. Although bromine from halons was still increasing in mid-1995, the summed abundance of these halogens in the troposphere is decreasing. To assess the effect of this trend on stratospheric ozone, estimates of the future stratospheric abundance of ozone-depleting gases were made for midlatitude and polar regions on the basis of these tropospheric measurements. These results suggest that reactive chlorine and bromine will reach a maximum in the stratosphere between 1997 and 1999 and will decline thereafter if limits outlined in the adjusted and amended Montreal Protocol on Substances That Deplete the Ozone Layer are not exceeded in future years.

MONTZKA, S.A., R.C. MYERS, J.H. BUTLER, J.W. ELKINS, L.T. LOCK, A.D. CLARKE, A.H. GOLDSTEIN. Observations of HFC-134a in the remote troposphere. Geophysical Research Letters 23(2):169-172 (1996).

Hydrofluorocarbon-134a (CF₃CH₂F) has been detected and quantified in air samples collected at remote, globally dispersed locations. Using gas chromatography and mass spectrometry detection techniques, we have observed increases for HFC-134a throughout the global troposphere from <50 fmol mol^-1 (ppq) in the late 1980s to 1.6 pmol mol^-1 (ppt) in mid-1995. Results obtained from samples collected during two cruises in 1994 indicate that mixing ratios more than doubled during that year. Increases observed globally from early 1994 through mid-1995 are consistent with exponential growth at ~100% yr^-1.

Moody, J.L., J.C. Davenport, J.T. Merrill, S.J. OLTMANS, D.D. Parrish, J.S. Holloway H. Levy II, G.L. Forbes, M. Trainer, and M. Buhr. Meteorological mechanisms for transport O₃ over the western North Atlantic Ocean: A case study for August 24-29, 1993. Journal of Geophysical Research 101(D22):29,213-29,227 (1996).

A large-scale view of O₃ transport over the western North Atlantic Ocean (WNAO) in summer illustrates distinct sources of O₃, and separate transport mechanisms are important at different vertical levels in the troposphere. The week-long period presented covers a sequence of O₃ sondes released from Bermuda and encompasses two surface O₃ events in the month-long NARE intensive. O₃ and CO peaked at Chebogue Point on the evening of August 25 and after midnight on the morning of August 28. At Sable Island, peaks occurred during early morning of August 26 and late morning of August 28. These events occurred under W-SW winds associated with advancing low-pressure systems that transported anthropogenic pollutants over the WNAO. The concentrations dropped with the passage of a trough or a cold front. Evidence suggests the surface was occasionally isolated from polluted air during favorable transport with pollutants lifted in warm sector flow riding over a wedge of cool, thermodynamically stable air. In addition to surface O₃, the O₃-sonde profile over Bermuda on the morning of August 27 showed a deep layer of O₃ from 6 to 12 km. Using back trajectories and two tracers (isentropic potential vorticity and water vapor), we illustrate that stratospheric ozone exchanged into the upper troposphere in conjunction with surface cyclogenesis was advected through the middle to upper troposphere over the midlatitudes with the potential to reach lower altitudes through subsidence in regions of anticyclonic motion.

Munger, J.W., S.C. Wofsy, P.S. BAKWIN, S.-M. Fan, M.L. Goulden, B.C. Daube, A.H. Goldstein, K.E. Moore, and D.R. Fitzjarrald. Atmospheric deposition of reactive nitrogen oxides and ozone in a temperate deciduous forest and a subarctic woodland 1. Measurements and mechanisms. Journal of Geophysical Research 101(D7):12,639-12,657 (1996).

We present 5 years of NO_y and O₃ eddy flux and concentration measurements and NO_x concentration measurements at Harvard Forest (1990-1994), a mixed deciduous forest in central Massachusetts, and 2 months of data for a spruce woodland near Schefferville, Quebec, during the NASA ABLE3B/Northern Wetlands Study (1990). Mean midday values of net dry NO_y flux from atmosphere to canopy were 3.4 and 3.2 mole m^-2 hr^-1 at Harvard Forest in summer and winter, respectively, and 0.5 mole m^-2 h^-1 at Schefferville during summer. Nighttime values were 1.3, 2.0, and 0.15 mole m^-2 hr^-1, respectively. For 1990-1994, the net annual dry deposition of nitrogen oxides was 17.9 mmole m^-2 yr^-1 (2.49 kgN ha^-1 y^-1). Oxidized species such as HNO₃ dominated N deposition, with minor contributions from direct deposition of NO₂. Emissions of NO from the forest soil were negligible compared to deposition. Comparison of No_ydeposition at Harvard Forest and Schefferville and analysis of the dependence on meteorological parameters show that anthropogenic sources dominate the nitrogen oxide inputs over much of North America. Heterogeneous reactions account for >90% of the conversion of NO₂ to HNO₃ in winter, leading to rates for dry deposition of NO_y similar to fluxes in summer despite 10-fold decrease in OH concentrations. In summer, formation of HNO₃ by heterogeneous reactions (mainly at night) could provide 25-45% of the NO₂ oxidation.

Newman, P.A., L.R. Lait, M.R. Schoeberl, M. Seablom, L. Coy, R. Rood, R. Swinbank, M. Proffitt, M. Loewenstien, J.R. Podolski, J.W. ELKINS, C.R. Webster, R.D. May, D.W. Fahey, G.S. DUTTON, and K.R. Chan. Measurements of polar vortex air in the midlatitudes. Journal of Geophysical Research 101(D8):12,879-12,891 (1996).

The Stratospheric Photochemistry, Aerosols, and Dynamics Expedition (SPADE) was conducted in the spring of 1993 from Moffett Field, California (NASA Ames Research Center), utilizing the NASA high-altitude ER-2 aircraft. These northern midlatitude aircraft flights showed laminae containing high ozone concentrations, traceable to the April 1993 polar vortex breakup and corroborated by laminae of other trace gases such as CFCs, CH₄, N₂O, and CO₂. These laminae are clearly traceable as polar vortex breakup fragments using Rossby-Ertel's potential vorticity and isentropic trajectory calculations. Laminae in stratospheric ozone profiles are commonly observed in the northern hemisphere from fall to spring, and are hypothesized to originate from very low frequency transverse waves, and/or via Rossby wave breaking. On the basis of these results, the ozone laminae observed during SPADE were a result of Rossby wave breaking during the breakdown of the polar vortex. In addition, it is shown that conventional once-per-day meteorological analyses were adequate for representing the transport of this material into the lower stratosphere midlatitudes over the course of the spring vortex breakup.

OLTMANS, S.J., D.J. HOFMANN, J.A. LATHROP, J.M. HARRIS, W.D. KOMHYR, and D. KUNIYUKI. Tropospheric ozone during Mauna Loa Observatory Photochemistry Experiment 2 compared to long-term measurements from surface and ozonesonde observations. Journal of Geophysical Research 101(D9):14,569-14,580 (1996).

Continuous surface ozone measurements have been made at Mauna Loa Observatory (MLO) for 20 years. In addition, weekly ozone profile measurements using balloonborne ozonesondes have been carried out from Hilo, Hawaii, since 1985. These long-term records are compared with data obtained during the MLOPEX 2 period from September 1991 to August 1992. Ozone behavior at the observatory level (~3.4 km) during autumn and winter of 1991-1992 was similar to that found during the period 1980-1990. In spring and summer 1992, however, there were several significant differences from the long-term behavior. During March and April 1992, there was about 10% more ozone than the long-term average, and the variability was less than half of what is seen normally. These characteristics are associated with strong flow from the north and west. Both June and July 1992 saw periods of elevated ozone with the June average 20% higher than normal. During the more limited sampling (weekly profiles) when ozonesonde measurements were made, the 1992 spring enhancement was particularly pronounced at 500 mbar (~6 km), while during the summer the larger than normal concentrations were at 700 mbar (~3.5 km). In the upper troposphere, on the other hand, spring ozone amounts in 1992 were much below normal with only about half the ozone usually seen in the 12- to 15-km region. The ozone profiles are discussed in terms of the representativeness of the MLO surface measurements in characterizing the free troposphere ozone behavior at both the altitude of the observatory as well as other heights in the atmosphere. During the winter and spring, the MLO measurements are often representative of behavior over a broad depth of the troposphere (3-10 km). In the summer and autumn the MLO observations are more characteristic of free tropospheric conditions at or near the observatory level.

OLTMANS, S.J., H. Levy II, J.M. HARRIS, J.T. Merrill, J.L. Moody, J.A. LATHROP, E. Cuevas, M. Trainer, M.S. O'NEILL, J.M. Prospero, H. VÖMEL, and B.J. JOHNSON. Summer and spring ozone profiles over the North Atlantic from ozonesonde measurements. Journal of Geophysical Research 101(D22):29,179-29,200 (1996).

Ozone profiles obtained by near-daily ozonesonde observations during campaigns at several sites in the North Atlantic are used to construct time-height cross sections of ozone concentration through the troposphere. Strong day-to-day ozone variability on the scale of synoptic meteorological disturbances is found both in the spring and in the summer throughout much of the troposphere. Layers of high ozone concentration (~100 ppb) are frequently seen in the middle and upper troposphere and are invariably associated with transport characteristics that strongly support a stratospheric source for these layers. Regions of low ozone (<40 ppb) are seen in the middle and upper troposphere associated with higher relative humidity. The connection of these events with low surface mixing ratios suggests that convective processes mix air low in ozone up through the troposphere. Vertical layering of ozone mixing ratio, which is seen at all of the observing locations, is a result of differing sources of air in the different layers.

Parungo, F., Y. Kim, C. Zhu, J. HARRIS, R. SCHNELL, X. Li, D. Yang, X. Fang, P. Yan, X. Yu, M. Zhou, Z. Chen, F. Qian, and K. Park. Asian dust storms and their effects on radiation and climate, Part II. STC Technical Report 2959, 80 pp., Science and Technology Corporation, Hampton, VA (1996).

No abstract.

Parungo, F., R. SCHNELL, A. YOSHINAGA, L. PAJO, Y. Kim, C.-J. Zhu, J. HARRIS, B. BODHAINE, M. Zhou, Z. Chen, X. Li, D. Yang, X. Fang, P. Yan, X. Yu, and K. Park, Asian dust storms and their effects on radiation and climate, Part III. Science and Technology Corporation Technical Report 3111, 95 pp., Hampton, VA (1996).

No abstract.

Planet, W.G., A.J. Miller, J.J. DeLuisi, D.J. HOFMANN, S.J. OLTMANS, J.D. Wild, I.S. McDermid, R.D. McPeters, and B.J. Connor. Comparison of NOAA-11 SBUV/2 ozone vertical profiles with correlative measurements. Geophysical Research Letters 23(3):293-296 (1996).

Vertical profiles of ozone have been determined from observations with the Solar Backscatter Ultraviolet (SBUV/2) instrument on the NOAA-11 operational satellite. These observations began in January 1989 and continue to early 1995. Comparisons have been made with selected sets of ozone vertical profiles derived from an ensemble of satellite and land-based measurements. These include: (1) lidar and microwave measurements performed at Table Mountain, CA. (2) Umkehr observations with a mid-northern latitude set of Dobson spectrophotometers. (3) balloon ozonesondes launched from Boulder, CO. (4) measurements with the NASA SBUV on Nimbus-7. Overall, the SBUV/2 profiles within the altitude range of 1-20 mb agree with the other measurements to about 5% with a -3 to -5% bias, the SBUV/2 values being lower. This level of agreement is consistent with the expected performance of the SBUV/2 instrument based on an extensive characterization of the instrument both in pre-launch calibration and in-orbit performance and also with current understanding of the test optical components used in pre-flight calibration.

Russell, P.B., J.M. Livingston, R.F. Pueschel, J.J. Bauman, J.B. Pollack, S.L. Brooks, P. Hamill, L.W. Thomason, L.L. Stowe, T. Deshler, E.G. DUTTON, and R.W. Bergstrom. Global to microscale evolution of the Pinatubo volcanic aerosol derived from diverse measurements and analyses. Journal of Geophysical Research 101(D13):18,745-18,763 (1996).

We assemble data on the Pinatubo aerosol from space, air, and ground measurements, develop a composite picture, and assess the consistency and uncertainties of measurement and retrieval techniques. Satellite infrared spectroscopy, particle morphology, and evaporation temperature measurements agree with theoretical calculations in showing a dominant composition of H₂SO₄-H₂O mixture, with H₂SO₄ weight fraction of 65-80% for most stratospheric temperatures and humidities. Important exceptions are (1) volcanic ash, present at all heights initially and just above the tropopause until at least March 1992, and (2) much smaller H₂SO₄ fractions at the low temperatures of high-latitude winters and the tropical tropopause. Laboratory spectroscopy and calculations yield wavelength- and temperature-dependent refractive indices for the H₂SO₄-H₂O droplets. These permit derivation of particle size information from measured optical depth spectra, for comparison to impactor and optical-counter measurements. All three techniques paint a generally consistent picture of the evolution of R_eff, the effective radius. In the first month after the eruption, although particle numbers increased greatly, R_eff outside the tropical core was similar to pre-eruption values of ~0.1 to 0.2 mm, because numbers of both small (r<0.2 mm) and large (r>0.6 mm) particles increased. In the next 3-6 months, extracore R_eff increased to -0.5 mm, reflecting particle growth through condensation and coagulation. Most data show that R_eff continued to increase for ~1 year after the eruption. R_eff values up to 0.6-0.8 mm or more are consistent with 0.38-1 mm optical depth spectra in middle to late 1992 and even later. However, in this period, values from in situ measurements are somewhat less. The difference might reflect in situ undersampling of the very few largest particles, insensitivity of optical depth spectra to the smallest particles, or the inability of flat spectra to place an upper limit on particle size. Optical depth spectra extending to wavelengths l >1 mm are required to better constrain R_eff, especially for R_eff>0.4 mm. Extinction spectra computed from in situ size distributions are consistent with optical depth measurements; both show initial spectra with l_max £ 0.42 mm, thereafter increasing to 0.78 l_max £ 1 mm. Not until 1993 do spectra begin to show a clear return to the pre-eruption signature of l_max £ 0.42 mm. The twin signatures of large R_eff (>0.3 mm) and relatively flat extinction spectra (0.4-1 mm) are among the longest-lived indicators of Pinatubo volcanic influence. They persist for years after the peaks in number, mass, surface area, and optical depth at all wavelengths £ 1 mm. This coupled evolution in particle size distribution and optical depth spectra helps explain the relationship between global maps of 0.5- and 1.0-mm optical depth derived from the Advanced Very High Resolution Radiometer (AVHRR) and Stratospheric Aerosol and Gas Experiment (SAGE) satellite sensors. However, there are important differences between the AVHRR and SAGE midvisible optical thickness products. We discuss possible reasons for these differences and how they might be resolved.

SCHNELL, R.C. Airflow over the island of Hawaii. Hawaii Medical Journal 55:44-45 (1996).

No abstract.

Seinfeld, J.H., R. Charlson, P.A. Durkee, D. Hegg, B.J. Huebert, J. Kiehl, M. P. McCormick, J.A. OGREN, J.E. Penner, V. Ramaswamy, J.H. and W.G.N. Slinn. A Plan for a Research Program on Aerosol Radiative Forcing and Climate Change. National Academy Press, Washington, D.C., 161 pp. (1996).

No abstract.

STONE, R., T. MEFFORD, E. DUTTON, D. LONGENECKER, B. HALTER, and D. ENDRES. Barrow, Alaska, surface radiation and meteorological measurements: January 1992 to December 1994. NOAA Data Report ERL-CMDL-11 81 pp. (1996).

Measured surface radiation budget (or balance) components with daily and monthly time resolution are presented for the Barrow, Alaska, Observatory (BRW) operated by the Climate Monitoring and Diagnostics Laboratory (CMDL) of NOAA. CMDL's monitoring program and the data reduction and summary procedures are described. Tables and corresponding plots are presented showing annual cycles of several measured and derived radiation variables for three years, 1992, 1993, and 1994. In addition, ancillary meteorological data are included, which are useful for interpreting the radiation measurements and how they vary on time scales of days to years. It is found that each year there is a net gain of surface radiation at BRW from the end of April until mid-September that peaks during July. Once snow covers the tundra in the autumn, the net surface radiation balance becomes negative until solar gain again exceeds the net loss of terrestrial radiation the following spring. Net radiative loss is greatest during November, December, or January depending on the response to changing meteorological conditions. Transitory events can influence the record quite dramatically on short time scales. Possible trends in cloudiness and/or in sea ice concentration in the Arctic Ocean may be affecting the radiation regime of BRW on longer time scales. Preliminary analysis suggests that the year-to-year variability of parameters that characterize BRW's climate is significant. Radiation and meteorological observations continue to be made at BRW in an effort to establish a long-term, comprehensive data set. Continuous monitoring will provide opportunities to detect climate change in this region of the Arctic to validate remotely sensed geophysical parameters and to improve parameterization schemes used in models to simulate the climate of this region.

TANS, P.P., P.S. BAKWIN, and D.W. GUENTHER. A feasible Global Carbon Cycle Observing System: A plan to decipher today's carbon cycle based on observations. Global Change Biology 2:309-318 (1996).

A design is presented to continuously monitor the transfers of carbon between the atmosphere and the terrestrial biosphere and oceans on large spatial scales. A consideration of the expected signal-to-noise suggests that a very cost effective method is to perform repeated measurements of the mixing ratios of trace gases in the atmospheric column at an increased number of sites compared to the present geographical coverage. This can be accomplished with existing technology, provided that more automation is applied to the sampling process as well as to the analytical procedures. The resulting data will be crucial to test extrapolations based on direct flux measurements to regional and global scales.

VOLK, C.M., J.W. ELKINS, D.W. Fahey, R.J. Salawitch, G.S. DUTTON, J.M. GILLIGAN, M.H. Proffitt, M. Loewenstein, J.R. Podolske, K. Minschwaner, J.J. Margitan, K.R. Chan. Quantifying transport between the tropical and midlatitude lower stratosphere. Science 272:1763-1768 (1996).

Airborne in situ observations of molecules with a wide range of lifetimes (methane, nitrous oxide, reactive nitrogen, ozone, chlorinated halocarbons, and halon-1211), used in a tropical tracer model, show that midlatitude air is entrained into the tropical lower stratosphere within about 13.5 months; transport is faster in the reverse direction. Because exchange with the tropics is slower than global photochemical models generally assume, ozone at midlatitudes appears to be more sensitive to elevated levels of industrial chlorine than is currently predicted. Nevertheless, about 45 percent of air in the tropical ascent region at 21 kilometers is a mid-latitude origin, implying that emissions from supersonic aircraft could reach the middle stratosphere.

YVON, S.A., and J.H. BUTLER. An improved estimate of the oceanic lifetime of atmospheric CH₃Br. Geophysical Research Letters 23(1):53-56 (1996).

Previous estimates of the partial atmospheric lifetime of CH₃Br with respect to degradation in the ocean have not fully accounted for co-variation of sea-surface and boundary layer properties. Here we substantially reduce uncertainty in this calculation by using a coupled, ocean-atmosphere box model and a tightly gridded data set of oceanic and atmospheric properties. The best estimate of the partial atmospheric lifetime of CH₃Br with respect to the ocean is 2.7 y with a possible range, due mainly to the choice of computational procedures for critical terms, of 2.4 to 6.5 y. This range is about one-third of that estimated previously. The total atmospheric lifetime, based upon oceanic, atmospheric, and proposed soil losses with all of their uncertainties, is 0.8 (0.6 to 1.4) y. Only 28% of this total uncertainty is attributable to the uncertainty in oceanic loss.

YVON, S.A., J.M.C. Plane, C.-F. Nien, D.J. Cooper, and E.S. Saltzman. Interaction between nitrogen and sulfur cycles in the polluted marine boundary layer. Journal of Geophysical Research 101(D1):1379-1386 (1996).

Simultaneous measurements are reported of the nitrate radical (NO₃), nitrogen dioxide (NO₂), ozone (O₃), and dimethylsulfide (DMS) in the nighttime marine boundary layer over Biscayne Bay in South Florida. These field observations are analyzed and used to initialize a boundary layer box model which examines the relative importance of the various sinks for NO_x in the marine boundary layer. The results show that the observed lifetime of NO₃ (6 min.) is probably controlled both by the loss of nitrogen pentoxide (N₂O₅) to reaction with water vapor and aerosols and by the reaction between NO₃ and DMS. The model is then extended to investigate the loss of nitrogen oxides from an air parcel that remains in the boundary layer with a constant sea-to-air DMS flux for several days. The principal conclusions are (1) that DMS is a much more important sink for NO₃ at lower NO₂ levels and (2) that the reaction between NO₃ and DMS is an important sink for DMS in the marine boundary layer and could exceed that of the daytime removal by OH.

YVON, S.A., and E.S. Saltzman. Atmospheric sulfur cycling in the tropical Pacific marine boundary layer (12°S, 135°W): A comparison of field data and model results 2. Sulfur dioxide. Journal of Geophysical Research 101(D3):6911-6918 (1996).

The atmospheric chemistry of sulfur dioxide over the tropical South Pacific Ocean is investigated by using results from field measurements and numerical models. Simultaneous real time measurements of sulfur dioxide and its biogenic precursor dimethylsulfide were made at 12°S, 135°W for a 6-day period from March 3 through March 9, 1992. The mean SO₂ and DMS mole fractions were 71 ± 56 pmol mol^-1 (1) and 453 ± 93 pmol mol^-1 (1) respectively. These concentrations are compared to those predicted by a time-dependent photochemical box model of the marine boundary layer. Model estimates of the yield of SO₂ from DMS oxidation range from 27% to 54%. Even with low yields, DMS is the dominant source of SO₂ in this region. Estimates of vertical entrainment velocities based on the tropospheric ozone budget suggest that vertical entrainment is a minor source of SO₂. The relative rates of various loss mechanisms for SO₂ are dry deposition to the sea surface (58%), in-cloud oxidation (9%), OH oxidation (5%), and uptake by sea-salt aerosols (28%).

YVON, S.A., E.S. Saltzman, D.J. Cooper, T.S. Bates, and A.M. Thompson. Atmospheric sulfur cycling in the tropical Pacific marine boundary layer (12°S, 135°W): A comparison of field data and model results 1. Dimethylsulfide. Journal of Geophysical Research 101(D3):6899-6909 (1996).

Shipboard measurements of atmospheric and seawater DMS were made at 12°S, 135°W for 6 days during March 1992. The mean seawater DMS concentration during this period was 4.1 0.45 nM (1, n = 260) and mean atmospheric DMS mole fraction was 453 93 pmol mol^-1 (1 n = 843). Consistent atmospheric diel cycles were observed, with a nighttime maximum and daytime minimum and an amplitude of approximately 85 pmol mol-1. Photochemical box model calculations were made to test the sensitivity of atmospheric DMS concentrations to the following parameters: (1) sea-to-air flux, (2) boundary layer height, (3) oxidation rate, and (4) vertical entrainment velocities. The observed relationship between the mean oceanic and atmospheric DMS levels require the use of an air-sea exchange coefficient which is at the upper limit end of the range of commonly used parameterizations. The amplitude of the diel cycle in atmospheric DMS is significantly larger than that predicted by a photochemical model. This suggests that the sea-to-air DMS flux is higher than was previously thought, and the rate of daytime oxidation of DMS is substantially underestimated by current photochemical models of DMS oxidation.

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