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Angevine, W.M., P.S. BAKWIN, and K.J. Davis. Wind profiler and RASS measurements compared with measurements from a 450-m-tall tower. Journal of Atmospheric and Oceanic Technology 15:818-825 (1998).

A 915-MHz boundary layer wind profiler with radio acoustic sounding system (RASS) was sited 8 km from a very tall (450 m) television transmitting tower in north-central Wisconsin during the spring, summer, and autumn of 1995. The profiler measured wind means and variances, and the RASS attachment measured virtual temperature. These quantities are compared to measurements from cup and sonic anemometers and a thermometer/hygrometer at 396 m above ground level on the tower. The precision of hour-averaged profiler winds is better than 1 m s-1, and the precision of the RASS virtual temperature is better than 0.9 K. Corrections to the virtual temperature measured by the RASS are discussed, and a new virtual temperature retrieval method is proposed. Vertical velocity variance correlation is similar to a previous study, and the fact that bias is small indicates that the calculation method used is reliable.
Bacmeister, J.T., V. Kuell, D. Offermann, M. Riese, J.W. ELKINS. Intercomparison of satellite and aircraft observations of ozone, CFC-11, and Noy using trajectory mapping. Journal of Geophysical Research 104(D13):16,379-16,390 (1999).

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) satellite measured global distributions of over 15 trace constituents at high horizontal resolution. The CRISTA mission began shortly before the end of the Airborne Southern Hemisphere Ozone Experiment and Measurements to Assess the Effects of Stratospheric Aircraft (ASHOE/MAESA) airborne measurement campaign. CRISTA measurements of ozone, CFC-11, and HNO3 are available below 20 km, in the altitude range sampled by the ER-2 aircraft during ASHOE/MAESA. However, the time separation between the two missions makes a direct comparison of the data impossible. In this study, trajectory techniques are used to compare CRISTA measurements to ozone, CFC-11, and HNO3 with ER-2 measurements taken during the last two flights of ASHOE/MAESA on November 2 and 4, 1994. Visual comparison of CRISTA and ER-2 data from the November 4 flight is generally good. Mean tracer gradients across scales of ~1000 km, as well as absolute mixing ratios agree well with those measured from the ER-2. Correlation coefficients for coincident pairs of ER-2 and CRISTA measurements are between 0.68 and 0.80. The comparison for the November 2 flight is poor. We argue that the poor agreement for this flight may be due to both smaller CRISTA measurement density as well as rapid stretching in the air mass sampled by the ER-2 on November 2.
BAKWIN, P.S., Carbon Cycle, in The Encyclopedia of Geochemistry, C.P. Marshall and R.W. Fairbridge (eds.), pp. 65-67, Kluwer Academic, Boston, MA (1999).

The term "carbon cycle" refers to the transfer of carbon in various forms between the earth's biogeochemical reservoirs:the oceans, atmosphere, terrestrial biosphere and soils, and the geosphere. Carbon dioxide (CO2) in the atmosphere influences the earth's radiative balance, and therefore its surface temperature and climate. Geological evidence indicates that liquid water has existed on earth since at least 3.8 billion years ago, reflecting a remarkable degree of regulation of the climate over geological time, and the carbon cycle is believed to have played a central role (Kasting 1993). The concern that global climate change may result from recent and future increases in CO2 in the atmosphere, due to anthropogenic combustion of fossil fuels such as coal, oil and gas, has led to a heightened interest in understanding the global carbon cycle.
Bell, G.D., M.S. Halpert, C.F. Ropelewski, V.E. Kousky, A.V. Douglas, R.C. SCHNELL, and M.E. Gelman. Climate Assessment for 1998. Bull. Am. Meteorol. Soc. 80(5), 1999.

The global climate during 1998 was affected by opposite extremes of the ENSO cycle, with one of the strongest Pacific warm episodes (El Niño) in the historical record continuing during January-early May and Pacific cold episode (La Niña) conditions occurring from July-December. In both periods, regional temperature, rainfall, and atmospheric circulation patterns across the Pacific Ocean and the Americas were generally consistent with those observed during past warm and cold episodes. Some of the most dramatic impacts from both episodes were observed in the tropics, where anomalous convection was evident across the entire tropical Pacific and in most major monsoon regions of the world. Over the Americas, many of the El Niño-(La Niña-) related rainfall anomalies in the subtropical and extratropical latitudes were linked to an extension (retraction) of the jet streams and their attendant circulation features typically located over the subtropical latitudes of both the North Pacific and South Pacific. The regions most affected by excessive El Niño-related rainfall included (1) the eastern half of the tropical Pacific, including western Ecuador and northwestern Peru, which experienced significant flooding and mudslides; (2) southeastern South American, where substantial flooding was also observed; and (3) California and much of the central and southern United States during January-March and the central United States during April-June. El Niño-related rainfall deficits during 1998 included (1) Indonesia and portions of northern Australia; (2) the Amazon Basin, in association with a substantially weaker-than-normal South American monsoon circulation; (3) Mexico, which experienced extreme drought throughout the El Niño episode; and (4) the Gulf Coast states of the United States, which experienced extreme drought during April-June 1998. The El Niño also contributed to extreme warmth across North American during January-May. The primary La Niña-related precipitation anomalies included (1) increased rainfall across Indonesia, and a nearly complete disappearance of rainfall across the east-central equatorial Pacific; (2) above-normal rains across northwestern, eastern, and northern Australia; (3) increased monsoon rains across central America and Mexico during October-December; and (4) dryness across equatorial eastern Africa. The active 1998 North Atlantic hurricane season featured 14 named storms (9 of which became hurricanes) and the strongest October hurricane (Mitch) in the historical record. In Honduras and Nicaragua extreme flooding and mudslides associated with Hurricane Mitch claimed more than 11,000 lives. During the peak of activity in August-September, the vertical wind shear across the western Atlantic, along with both the structure and location of the African easterly jet, were typical of other active seasons. Other regional aspects of the short-term climate included (1) record rainfall and massive flooding in the Yangtze River Basin of central China during June-July; (2) a drier and shorter-then-normal 1997/98 rainy season in southern Africa; (3) above-normal rains across the northern section of the African Sahel during June-September 1998; and (4) a continuation of record warmth across Canada during June-November. Global annual mean surface temperatures during 1998 for land and marine areas were 0.56ºC above the 1961-90 base period means. This record warmth surpasses the previous highest anomaly of +0.43ºC set in 1997. Record warmth was also observed in the global Tropics and Northern Hemisphere extratropics during the year, and is partly linked to the strong El Niño conditions during January-early May.
BUTLER, J.H., M. Battle, M.L. Bender, S.A. MONTZKA, A.D. CLARKE, E.S. Saltzman, C.M. Sucher, J.P. Severinghaus, and J.W. ELKINS. A record of atmospheric halocarbons during the twentieth century from polar firn air. Nature 399:749-755 (1999).

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Measurements of trace gases in air trapped in polar firn (unconsolidated snow) demonstrate that natural sources of chlorofluorocarbons, halons, persistent chlorocarbon solvents and sulfur hexafluoride to the atmosphere are minimal or non-existent. Atmospheric concentrations of these gases, reconstructed back to the late nineteenth century, are consistent with atmospheric histories derived from anthropogenic emission rates and known atmospheric lifetimes. The measurements confirm the predominance of human activity in the atmospheric budget of organic chlorine, and allow the estimation of atmospheric histories of halogenated gases of combined anthropogenic and natural origin. The pre-twentieth-century burden of methyl chloride was close to that at present, while the burden of methyl bromide was probably over half of today's value.
ELKINS, J.W. Chlorofluorocarbons (CFCs), In Encyclopedia of Environmental Science, D.E. Alexander and R.W. Fairbridge (eds.), pp. 78-80, Kluwer Academic, Boston, MA (1999).

Chlorofluorocarbons (CFCs) are nontoxic, nonflammable chemicals containing atoms of carbon, chlorine, and fluorine. They are used in the manufacture of aerosol sprays, blowing agents for foams and packing materials, as solvents, and as refrigerants. CFCs are classified as halocarbons, a class of compounds that contain atoms of carbon and halogen atoms. Individual CFC molecules are labeled with a unique numbering system. For example, the CFC number of 11 indicates the number of atoms of carbon, hydrogen, fluorine, and chlorine (e.g., CCl3F as CFC-11). The best way to remember the system is the "rule of 90" or add 90 to the CFC number where the first digit is the number of carbon atoms C, the second digit is the number of hydrogen atoms (H), and the third digit is the number of fluorine atoms (F). The total number of chlorine atoms (Cl) is calculated by the expression: Cl = 2(C+1) – H – F. In the example, CFC-11 has one carbon, no hydrogen, one fluorine, and therefore three chlorine atoms.
ELKINS, J.W., J.H. BUTLER, S.A. MONTZKA, T.M. THOMPSON, D.J. MONDEEL, L.T. LOCK, G.S. DUTTON, and M.R. PENDER. NOAA/CMDL measurements of trace halocompounds and nitrous oxide from flask samples and in situ instrument at Alert, in Canadian Baseline Program Summary of Progress to 1998, pp. 5-24-5-30, Atmospheric Environment Service, Environment Canada, Toronto, 1999.

We report the measurements of atmospheric N2O, CFC-11, CFC-12, CFC-113, halon-1211, halon-1301, halon-2402, SF6, HCFC-22, HCFC-141b, HCFC-142b, and HFC-134a collected from flask samples at Alert. These observations are compared to values measured from other sites in the NOAA/CMDL N2O and halocompound flask network. We also describe our measurement system for monitoring atmospheric N2O and SF6 from an in situ instrument operated at Alert.
Gao, R.S., D.W. Fahey, L.A. DEL NEGRO, S.G. Donnelly, E.R. Keim, J.A. Neuman, E. Teverovskaia, P.O. Wennberg, T.F. Hanisco, E.J. Lanzendorf, M.H. Proffitt, J.J. Margitan, J.C. Wilson, J.W. ELKINS, R.M. Stimpfle, R.C. Cohen, C.T. McElroy, T.P. Bui, R.J. Salawiatch, S.S. Brown, A.R. Ravishankara, R.W. Portmann, M.K.W. Ko, D.K. Weisenstein, and P.A. Newman. A comparison of observations and model simulations of Nox/Noy in the lower stratosphere. Geophysical Research Letters 26(8):1153-1156 (1999).

Extensive airborne measurements of the reactive nitrogen reservoir (Noy) and its component nitric oxide (NO) have been made in the lower stratosphere. Box model simulations that are constrained by observations of radical and long-lived species and which include heterogeneous chemistry systematically underpredict the Nox (=NO + NO2) to NOy ratio. The model agreement is substantially improved if newly measured rate coefficients for the OH + NO2 and OH + HNO3 reactions are used. When included in 2-D models, the new rate coefficients significantly increase the calculated ozone loss due to Nox and modestly change the calculated ozone abundances in the lower stratosphere. Ozone changes associated with the emission of a fleet of supersonic aircraft are also altered.
Hintza, E.J., E. M. Weinstock, J.G. Anderson, R.D. May, and D.F. HURST. On the accuracy of in situ water vapor measurements in the troposphere and lower stratosphere with the Harvard Lyman-a hygrometer. Journal of Geophysical Research 104(D7):8183-8189 (1999).

In an effort to better constrain atmospheric water vapor mixing ratios and to understand the discrepancies between different measurements of water vapor in the stratosphere and troposphere, we have carefully examined data from the Harvard Lyman-a photofragment fluorescence hygrometer, which has flown on the NASA ER-2 aircraft from 1992 through 1998. The instrument is calibrated in the laboratory before and after each deployment, and the calibration is checked by direct absorption measurements in the troposphere. On certain flights, the ER-2 flew level tracks during which water vapor varied by up to 80 ppmv, under nearly constant atmospheric conditions. These flights provide a stringent test of our calibration via direct absorption and indicate agreement to within 3%. During the 1997 Photochemistry of Ozone Loss in the Arctic Region In Summer (POLARIS) mission, our Lyman-a instrument was compared with a new diode laser hygrometer from the Jet Propulsion Laboratory. Overall agreement was 5% during the June/July deployment and 1% for potential temperatures of 490 to 540 K. The accuracy of our instrument is shown to be ± 5%, with an additional offset of at most 0.1 ppmv. Data from this instrument, combined with simultaneous measurements of CH4 and H2, are therefore ideal for studies of the hydrogen budget of the lower stratosphere.
HURST, D.F., G.S. DUTTON, P.A. ROMASHKIN, P.R. Wamsley, F.L. MOORE, J.W. ELKINS, E.J. Hintsa, E.M. Weinstock, R.L. Herman, E.J. Moyer, D.C. Scott, R.D. May, and C.R. Webster. Closure of the total hydrogen budget of the northern extratropical lower stratosphere. Journal of Geophysical Research 104(D7):8191-8200 (1999).

Methane (CH4), molecular hydrogen (H2), and water vapor (H2O) were measured concurrently on board the NASA ER-2 aircraft during the 1995-1996 Stratospheric Tracers of Atmospheric Transport (STRAT) and 1997 Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) campaigns. Correlations between these three main hydrogen reservoirs in the northern extratropical lower stratosphere are examined to evaluate H2O production from CH4 and H2 oxidation. The expected ratio of stratospheric H2O production (PH2O) to CH4 destruction (LCH4) = 1.973 ± 0.003 is calculated from an evaluation of CH4 and H2 oxidation reactions and the relationship between H2 and CH4 mixing ratios measured during STRAT. Correlations between H2O and CH4 were tight and linear only for air masses with mean ages ³ 3.8 years, restricting this analysis predominantly to latitudes between 40° and 90°N and potential temperatures between 470 and 540 K. The mean observed DH2O/DCH4 (-2.15 ± 0.18) is in statistical agreement with the expected PH2O/L CH4. The annual mean stratospheric entry mixing ratio for H2O calculated from this slope is 4.0 ± 0.3 ppm. The quantity H2O + 2· CH4 is quasi-conserved at 7.4 ± 0.5 ppm in older air masses in the northern extratropical lower stratosphere. Significant departure of H2O + 2· CH4 from the mean value is a sensitive indicator of processes which influence H2O without affecting CH4, such as dehydration in a polar vortex or near the tropical tropopause. No significant trend is observed in ER-2 aircraft data for H2O + 2· CH4 in the lower stratosphere from 1993 through 1997.
Jobson, B.T., S.A. McKeen, D.D. Parrish, F.C. Fehsenfeld, D.R. Blake, A.H. Goldstein, S.M. Schauffler, and J.W. ELKINS. Trace gas mixing ratio variability versus lifetime in the troposphere and stratosphere: Observations.Journal of Geophysical Research 104(D13):16,091-16,113 (1999).

Several archived data sets have been reviewed to examine the relationship between mixing ratio variability and lifetime for hydrocarbon and halocarbon species in the troposphere and stratosphere. The dependence on lifetime was described by the power law relationship slnX = At-b, where slnX is the standard deviation of the 1n of the mixing ratios, A is a proportionality coefficient, and b is an exponent that relates to the dominance of sink terms in the regional variability budget. At the Harvard forest ground site, winter and summer data displayed the same lifetime dependence, t-0.18, which was significantly weaker than the t-0.5, dependence of remote tropospheric data, indicating that source terms dominated regional variability at Harvard. In addition, the ratio of summer to winter slnX values was found to be similar for all species except ethane, averaging 1.54 ± 0.04. This ratio is consistent with a factor of 11 seasonal changes in the species lifetimes, given a t-0.18 lifetime dependence. Stratospheric data displayed a stronger lifetime dependence than tropospheric trends, indicating a more dominant role for sink terms in describing spatial variability in this region of the atmosphere. We show that a unique power law relationship between slnX ratios for two species Xi and Xj and the kinetic slope of ln(Xi) versus ln(Xj) correlation plots is found to hold in both observations and theory. Thus knowledge of the coefficient b allows for a clearer understanding of the relationship between observed slopes of ln(Xi) versus ln(Xj) correlation plots and the ratio of the species lifetimes.
Kato, S., T.P. Ackerman, E.G. DUTTON, N. Laulainen, and N. Larson. A comparison of modeled and measured surface shortwave irradiance for a molecular atmosphere. Journal of Quantitative Spectroscopy Radiation Transfer 61(4):491-502 (1999).

We compare the downward diffuse and direct normal irradiance computed by a two-stream model with measurements taken at the Mauna Loa Observatory when the atmosphere was close to a molecular atmosphere. The modeled downward diffuse irradiance agrees with measurements taken by a shaded pyranometer within the uncertainty of the measurement. Therefore, the two-stream approximation is adequate for computing the downward diffuse irradiance in molecular atmosphere. This result also indicates that neglecting the state of polarization introduces a negligible error in the irradiance computation.
MONTZKA, S.A., J.H. BUTLER, J.W. ELKINS, T.M. THOMPSON, A.D. CLARKE, and L.T. LOCK. Present and future trends in the atmospheric burden of ozone-depleting halogens. Nature 398:690-694 (1999).

The burden of ozone-depleting chemicals in the lower atmosphere has been decreasing since 1994 as a result of the Montreal Protocol. Here we show how individual chemicals have influenced this decline in order to estimate how the burden could change in the near future. Our measurements of atmospheric concentrations of the persistent, anthropogenic chemicals that account for most ozone-depleting halogens in today's stratosphere show that the decline stems predominantly from the decrease in the atmospheric load of trichloroethane (CH3CCl3), a previously common cleaning solvent. The influence of this chemical on the decline has now peaked, however, and will become much smaller over the next 5 to 10 years. As this influence lessens, a decrease in the burden of ozone-depleting halogen will be sustained only if emissions of other halocarbons fall. Although emissions of most gases regulated by the Montreal Protocol have decreased substantially over the past 10 years, emissions of the potent ozone-deleting gas CBrClF2 (halon-1211) have remained fairly constant during this period despite stringent limits on production in developed countries since 1994. The consequent atmospheric accumulation of this halon is retarding the decline of ozone-depleting halogens in the atmosphere more than any other persistent gas.
NELSON, D.W., J. Hickey, N. WOOD, and E. DUTTON. Broadband direct solar beam measurements utilizing absolute cavity radiometers equipped with calcium fluoride windows. Preprint, 10th Conference on Atmospheric Radiation, Madison, WI, June 28-July 2, 1999, American Meteorological Society, Boston, MA, 205-207 (1999).

 

 No abstract.
Perry, K.D., T.A. Cahill, R.C. SCHNELL, and J.M. HARRIS. Long-range transport of anthropogenic aerosols to the National Oceanic and Atmospheric Administration baseline station at Mauna Loa Observatory, Hawaii. Journal of Geophysical Research 104(D15):18,521-18,533 (1999).

Size-segregated measurements of aerosol mass and composition are used to determine the composition and seasonal variations of natural and anthropogenic aerosols at Mauna Loa Observatory (MLO) from 1993 through 1996. Although the springtime transport of Asian dust to MLO is a well-documented phenomenon, this study shows that fine anthropogenic aerosols, including sulfur, black carbon, and enriched trace metals such as As, Cu, Pb, and Zn, are also routinely transported to MLO each spring. It is estimated that at least one third of the sulfate measured at MLO during the spring is anthropogenic. In addition, indirect measurements indicate that the organic aerosol concentrations are often comparable to the sulfate concentrations. This study also combines size- and time-resolved aerosol composition measurements with isentropic, backward air-mass trajectories and gas measurements of 222Rn, CH4, CO, and CO2 to identify some potential source regions of the anthropogenic aerosols. Three types of long-range transport episodes are identified: (1) anthropogenic aerosols mixed with Asian dust, (2) Asian pollution with relatively small amounts of soil dust, and (3) biomass burning emissions from North America. This study shows that anthropogenic aerosols and gases can be efficiently transported to MLO from both Asia and North America during the spring.
Polissar, A.V., P.K. Hopke, P. Paatero, Y.J. Kaufmann, D.K. Hall, B.A. BODHAINE, E.G. DUTTON, and J.M. HARRIS. The aerosol at Barrow, Alaska: Long-term trends and source locations. Atmospheric Environment 33:2441-2458 (1999).

Aerosol data consisting of condensation nuclei (CN) counts, black carbon (BC) mass, aerosol light scattering (SC), and aerosol optical depth (AOD) measured at Barrow, Alaska, from 1977 to 1994 have been analyzed by three-way positive matrix factorization (PMF3) by pooling all of the different data into one large three-way array. The PMF3 analysis identified four factors that indicate four different combinations of aerosol sources active throughout the year in Alaska. Two of the factors (F1, F2) represent Arctic haze. The first Arctic haze factor F1 is dominant in January-February while the second factor F2 is dominant in March-April. They appear to be material that is generally ascribed to long-range transported anthropogenic particles. A lower ratio of condensation nuclei to scattering coefficient loadings is obtained for F2 indicating large particles. Factor F3 is related to condensation nuclei. It has an annual cycle with two maxima, March and July-August indicating some involvement of marine biogenic sources. The fourth factor F4 represents the contribution to the stratospheric aerosol from the eruptions of El Chichon and Mt. Pinatubo. No significant long-term trend for F1 was detected while F2 shows a negative trend over the period from 1982 to 1994 but not over the whole measurement period. A positive trend of F3 over the whole period has been observed. This trend may be related to increased biogenic sulfur production caused by reductions in the sea-ice cover in the Arctic and/or an air temperature increase in the vicinity of Barrow. Potential source contribution function (PSCF) analysis showed that in winter and spring during 1989 to 1993 regions in Eurasia and North America are the sources of particles measured at Barrow. In contrast to this, large areas in the North Pacific Ocean and the Arctic Ocean contributed to observed high concentrations of CN in the summer season. Three-way positive matrix factorization was an effective method to extract time-series information contained in the measured quantities. PSCF was useful for the identification of possible source areas and the potential pathways for the Barrow aerosol. The effects of long-distance transport, photochemical aerosol production, emissions from biogenic activities in the ocean, and volcanic eruptions on the aerosol measurements made at Barrow were extracted using this combined methodology.
SHERIDAN, P.J, and J.A. OGREN. Observations of the vertical and regional variability of aerosol optical properties over central and eastern North America. Journal of Geophysical Research 104(D14):16,793-16,805 (1999).

Aerosol optical properties were measured in situ from a research aircraft during three recent field experiments in the central and eastern parts of North America as well as over areas of the western Atlantic Ocean. Regional and vertical variability of the aerosol properties for boundary layer and free tropospheric air were determined. In general, the differences between distributions of aerosol properties measured at low (planetary boundary layer) and high (free troposphere) altitudes were small but statistically significant at the 3% level or better. However, most of the aerosol optical thickness of the layers studied (~5 km down to ~100 m) was encountered in the lowest 1 km of each layer. As a result, the near-surface measurements of aerosol optical properties adequately represented the portion of the lower column that dominates the radiative effects. The estimated error encountered by using near-surface aerosol measurements to calculate the layer forcing was typically <10%.
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