bluuebunny/crossref_metadata_2025 huggingface dataset:
Episodic total ozone minima and associated effects on heterogeneous chemistry and lower stratospheric transport
Authors: Rood Richard B. , Nielsen J. Eric , Stolarski Richard S. , Douglass Anne R. , Kaye Jack A. , Allen Dale J.
Published: February 2012

A description of the January 31, 1989, ozone minihole over Stavanger, Norway, is given on the basis of three‐dimensional model simulations. This minihole is typical (though of large magnitude) of many transient events in the lower stratosphere that arise because of cyclonic‐scale disturbances in the troposphere. The ozone reduction is a short‐lived reversible dynamical event. However, through heterogeneous chemical processes there can be a significant transfer of chlorine from reservoir molecules to active radicals. This chemically perturbed air is defined as processed air, and it is found that a single event can produce enough processed air to reduce the HCl in the entire polar vortex. Chemical processing on clouds associated with transient events is shown to be a major source of processed air in the polar vortex in December before background temperatures are cold enough for more uniform heterogeneous conversion. In the model, intense cyclonic scales propagating close to the vortex edge and large planetary wave events (especially stratospheric warmings) are the major mechanisms of extra‐vortex transport. Only a small amount of processed air is found outside of the polar vortex. The processed air is a strong function of longitude, and it is virtually excluded from the Pacific Basin.
Input of atmospheric trace elements and mineral matter to the Yellow Sea during the spring of a low‐dust year
Authors: Gao Y. , Arimoto R. , Duce R. A. , Lee D. S. , Zhou M. Y.
Published: February 2012

Aerosol particle samples collected in Beijing, China, and Mallipo, South Korea, were analyzed by instrumental neutron activation to (1) determine the atmospheric concentrations of trace elements over the Yellow Sea and (2) to estimate the atmospheric deposition of selected trace elements to this region. The atmospheric concentrations of trace elements decreased from April to May at these two sampling sites, but the percentages of the concentration decreases varied among elements. A decrease in the concentrations of mineral aerosol with distance was modeled using an exponential decay pattern. The estimated atmospheric deposition of mineral aerosol to the Yellow Sea, based on the representative crustal elements, was 9 to 76 g m−2 yr−1. This flux is comparable to that for any coastal region studied to date, and it can account for 20–70% of the total input of mineral material to the Yellow Sea. The atmospheric deposition of pollutant metals to the Yellow Sea apparently is comparable to the atmospheric fluxes to several European seas and to coastal sites in North America.
Global average concentration and trend for hydroxyl radicals deduced from ALE/GAGE trichloroethane (methyl chloroform) data for 1978–1990
Authors: Prinn R. , Cunnold D. , Simmonds P. , Alyea F. , Boldi R. , Crawford A. , Fraser P. , Gutzler D. , Hartley D. , Rosen R. , Rasmussen R.
Published: February 2012

Atmospheric measurements at several surface stations made between 1978 and 1990 of the anthropogenic chemical compound 1,1,1‐trichloroethane (methyl chloroform, CH3CCl3) show it increasing at a global average rate of 4.4 ± 0.2% per year (1σ) over this time period. The measured trends combined with industrial emission estimates are used in an optimal estimation inversion scheme to deduce a globally averaged CH3CCl3 tropospheric (and total atmospheric) lifetime of 5.7 (+0.7, −0.6) years (1σ) and a weighted global average tropospheric hydroxyl radical (OH) concentration of (8.7 ± 1.0) × 105 radical cm−3 (1σ). Inclusion of a small loss rate to the ocean for CH3CCl3 of 1/85 year−1 does not affect the stated lifetime but lowers the stated OH concentration to (8.1 ± 0.9) × 105 radical cm−3 (1σ). The rate of change of the weighted global average OH concentration over this time period is determined to be 1.0 ± 0.8% per year (1σ) which has major implications for the oxidation capacity of the atmosphere and more specifically for methane (CH4), which like CH3CCl3 is destroyed primarily by OH radicals. Because the weighting strongly favors the tropical lower troposphere, this deduced positive OH trend is qualitatively consistent with hypothesized changes in tropical tropospheric OH and ozone concentrations driven by tropical urbanization, biomass burning, land use changes, and long‐term warming. We caution, however, that our deduced rate of change in OH assumes that current industry estimates of anthropogenic emissions and our absolute calibration of CH3CCl3 are accurate. The CH3CCl3 measurements at our tropical South Pacific station (Samoa) show remarkable sensitivity to the El Nino‐Southern Oscillation (ENSO), which we attribute to modulation of cross‐equatorial transport during the northern hemisphere winter by the interannually varying upper tropospheric zonal winds in the equatorial Pacific. Thus measurements of this chemical compound have led to the discovery of a previously unappreciated aspect of tropical atmospheric tracer transport.
Comparison of 2‐D model simulations of ozone and nitrous oxide at high latitudes with stratospheric measurements
Authors: Proffitt M. H. , Solomon S. , Loewenstein M.
Published: February 2012

A linear reference relationship between O3 and N2O has been used to estimate polar winter O3 loss from aircraft data taken in the lower stratosphere. Here we evaluate this relationship at high latitudes by comparing it with a two‐dimensional (2‐D) model simulation and with NIMBUS 7 satellite measurements. Although comparisons with satellite measurements are limited to January through May, the model simulations are compared during other seasons. The model simulations and the satellite data are found to be consistent with the winter O3 loss analysis. It is shown that such analyses are likely to be inappropriate during other seasons.
On the role of charged aerosols in polar mesosphere summer echoes
Authors: Cho John Y. N. , Hall Timothy M. , Kelley Michael C.
Published: February 2012

Submicron aerosols, as evidenced by the occurrence of polar mesospheric and noctilucent clouds, exist at heights from which polar mesosphere summer echoes (PMSE) are observed. We investigate the role of positively and negatively charged aerosols in the scattering processes proposed in the literature. These aerosols, if charged substantially, can account for the remarkably high radar reflectivity at both VHF and UHF by raising the electron Schmidt number through the ambipolar effect. A positively charged component may be responsible for enhanced UHF radar scatter by increasing the incoherent scatter power through a dressed dust effect, although such a process is not realistic as an explanation for VHF scatter during PMSE. Such an enhanced UHF scatter will be associated with extremely narrow backscatter spectra. We propose a model in which both negatively and positively charged aerosols are present to explain both the radar properties and the rocket probe observations of charged particle depletions. Finally, we point out that the Poker Flat 50‐MHz long‐term data, which contrary to accepted dynamical theory show average downward velocities in the summertime upper mesosphere, can be attributed to the fall speed of the aerosols responsible for PMSE.
On the use of Isaksen‐Luther method of computing photodissociation rates in photochemical models
Authors: Dvortsov Victor L. , Zvenigorodsky S. G. , Smyslaev S. P.
Published: February 2012

Isaksen's algorithm of the photolysis rate calculation in Luther's modification (I‐L method) is analyzed. The interpretations suggested by Thompson [1984] and Madronich [1982] are also considered. The accuracy of the I‐L method is tested by (1) evaluation of the transmittance and reflectance coefficients for a single homogeneous Rayleigh scattering layer against delta Eddington and discrete ordinate results and (2) comparison of I‐L and delta Eddington photolysis rates. These tests show that if the I‐L method is applied for calculation of twilight UV photolysis rates, its inaccuracy can exceed 50% (compare 10% according to the earlier estimations). The possible effect of such inaccuracy on model predictions is illustrated by comparing the results obtained by the same one‐dimensional PCM successively employing I‐L and delta Eddington radiation codes.
Carbon and hydrogen isotopic characterization of methane from wetlands and lakes of the Yukon‐Kuskokwim delta, western Alaska
Authors: Martens Christopher S. , Kelley Cheryl A. , Chanton Jeffrey P. , Showers William J.
Published: February 2012

The total methane flux to the troposphere from tundra environments of the Yukon‐Kuskokwim Delta is dominated by emissions from wet meadow tundra (∼75%) and small, organic‐rich lakes (∼20%). The mean δ13C value of methane diffusing into collar‐mounted flux chambers from wet meadow environments near Bethel, Alaska, was −65.82 ± 2.21‰ (±1 sigma, n = 18) for the period July 10 to August 10, 1988. Detritus‐rich sediments of Delta lakes, including margins of large lakes and entire submerged areas of smaller ones, are laden with gas bubbles whose methane concentration ranges from 11% to 79%. Lowest methane concentrations are found along heavily vegetated lake edge environments and highest through‐out organic‐rich, fibrous sediments of small lakes. A minimum ebullition flux estimated for the 5% of total Delta area comprised of small lakes ranges from 0.34 to 9.7 × 1010 g CH4 yr−1, which represents 0.6% to 17% of the total Delta methane emission. The δ13C and δD values of this ebullitive flux are −61.41 ± 2.46‰ (n = 38) and −341.8 ± 18.2‰ (n = 21), respectively. The methane in gas bubbles from two lakes is of modern, bomb carbon enriched, radiocarbon age. Gas bubble δ13C values varied from 2 to 5‰ seasonally, reaching heaviest values in midsummer, no such variations in δD values were observed. Combined isotope data reveal that higher δ13C values in heavily vegetated areas correlate with lower δD values, suggesting enhanced methane production via acetate fermentation. Spatial isotopic variations in lakes appear to be controlled by variations in production rather than oxidation processes.
Ground‐based microwave monitoring of stratospheric ozone
Authors: Parrish A. , Connor B. J. , Tsou J. J. , McDermid I. S. , Chu W. P.
Published: February 2012

A microwave instrument developed for operational measurements of ozone for the Network for Detection of Stratospheric Change is discussed. The instrument observes two spectral lines near 3 mm wavelength with a bandwidth of 630 MHz, allowing profile retrieval from 20 to 70 km. The observing technique and calibration procedures are described. The measurement forward model and retrieval algorithm are formulated. Preliminary comparisons with a co‐located ground‐based lidar and the SAGE II instrument are presented. The measurements are shown to typically agree to within 5 to 10%.
Ultraviolet radiation in the Arctic: The impact of potential ozone depletions and cloud effects
Authors: Tsay Si‐Chee , Stamnes Knut
Published: February 2012

An atmospheric radiation model is used to study the combined effects of ozone depletions/redistributions and particulate clouds on atmospheric heating/photolysis rates and ultraviolet radiation reaching the biosphere. Four types of particulate clouds prevalent in the summertime Arctic are considered: stratospheric aerosols, tropospheric aerosols (Arctic haze), cirrus clouds, and stratus clouds. The effects of ozone depletion and vertical redistributions of ozone are also examined. The main findings are as follows: (1) stratus clouds provide significant protection from ultraviolet radiation exposure, but while stratospheric aerosols imply increased UVB exposure, Arctic haze results in a decrease; (2) a redistribution of ozone from the stratosphere to the troposphere tends to decrease UV exposure, but for low solar elevations an increase may occur; (3) a 20% ozone depletion leads to about 0.4 K/d cooling in the lower stratosphere, while redistribution of ozone from the stratosphere to the troposphere implies a warming of about 0.015 K/d in the upper troposphere; (4) stratus clouds may cause a large warming in the middle and upper stratosphere (0.8 K/d); (5) clouds have little effect on ozone photolysis leading to O(1D) production at altitudes higher than 25 km; (6) for ozone photolysis leading to O(3P) production photolysis rates may increase by 50% or more throughout the atmosphere due to multiple scattering by stratus clouds.
Measurements of nitric acid and aerosol nitrate at the Mauna Loa Observatory during the Mauna Loa Observatory Photochemistry Experiment 1988
Authors: Norton R. B. , Carroll M. A. , Montzka D. D. , Hübler G. , Huebert B. J. , Lee G. , Warren W. W. , Ridley B. A. , Walega J. G.
Published: February 2012

Ambient air concentrations of nitric acid vapor and aerosol nitrate were measured above the remote North Pacific between May 1 and June 5, 1988, during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). Nighttime (free tropospheric) mean values were 30 pptv nitrate aerosol and 103 pptv nitric acid. Daytime values, representative of island‐modified marine boundary layer air, averaged 60 pptv aerosol and 130 pptv nitric acid. The measurements were generally consistent with previous measurements in the remote North Pacific including free tropospheric measurements of nitric acid during NASA's Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation (GTE/CITE 2). MLOPEX observations are smaller than model HNO3/NOx ratios. However, the magnitude of this discrepancy is obscured by uncertainties, mainly in the model OH concentration and nitric acid photolysis rates. Nonetheless, large observed variations in the HNO3/NOx ratio likely indicate significant loss of nitric acid, at least part of the time, by some process in addition to vapor phase photolysis and destruction by OH. Several processes are considered, but no firm conclusion is reached.
The measurement of tropospheric OH by long path absorption 1. Instrumentation
Authors: Mount George H.
Published: February 2012

The determination of the concentration of OH in the Earth's troposphere is of fundamental importance to an understanding of the chemistry of the lower atmosphere. Many experiments to measure OH concentration have been performed in recent years; very few of these experiments have produced significant results. In particular, because of the extremely low amount of OH in the clean troposphere (several tenths parts per trillion by volume at summertime local noon), none of the experiments performed have attained the sensitivity limit necessary to test the photochemical theories of OH and its temporal behavior. Described here is an experiment utilizing a laser source and very high resolution ultraviolet absorption spectroscopy to measure the concentration of OH in a clean environment at a measured sensitivity limit of approximately 5 × 105 cm−3 (0.01 pptv) with an integration time of several minutes. This limit is substantially below predicted noontime OH concentrations and should be low enough to provide a rigorous test of photochemical theories of hydroxyl formation. This paper describes the instrumentation developed to make the measurements.
Tropical boundary layer equilibrium in the last ice age
Authors: Betts Alan K. , Ridgway W.
Published: February 2012

A radiative‐convective boundary layer model is used to assess the effect of changing sea surface temperature, pressure, wind speed, and the energy export from the tropics on the boundary layer equilibrium equivalent potential temperature. It remains difficult to reconcile the observations that during the last glacial maximum (18,000 yr BP) the snowline on the tropical mountains fell 950 m, while the tropical sea surface temperatures fell only 1–2 K.
Variation in energy balance components from six sites in a native prairie for three years
Authors: Pritschen Leo J. , Qian Ping
Published: February 2012

Six automatic stations were used to evaluate the surface energy and radiation balances on a native prairie near Manhattan, Kansas, using the Bowen ratio technique for a total of 300 days. Data were taken during the periods from May 26 to October 16, 1987, May 10 to September 18, 1988, and July 21 to August 13, 1989. The station site locations were selected to represent burned and unburned treatments on ridges, valley bottoms, and slopes with various aspects. The measured variables were (1) air and wet bulb temperatures at two heights, (2) net radiation, (3) solar radiation (up and down), (4) total hemispherical radiation (up and down), (5) diffuse radiation, (6) soil heat flow and soil temperature, (7) wind speed, (8) wind direction, and (9) precipitation. Energy balance components at the sites were compared for the 3 years. The variation between sites and years was small, even though some sites were as much as 10 km apart and the years had different rainfall amounts. The average values for the four summer intensive field campaigns (IFCs) were as follows: albedo, 0.2; ratio of net radiation to solar radiation, 62%; evaporation equivalent, 4 mm d−1; Bowen ratio, 0.32; evaporation fraction, 70%; and the ratio of evaporation to solar energy, 40%. These values were different for the fall IFC. The latent and sensible heat fluxes were more variable than the radiation terms reflecting soil moisture differences between IFCs.
Area‐averaged surface fluxes and their time‐space variability over the FIFE experimental domain
Authors: Smith E. A. , Hsu A. Y. , Crosson W. L. , Field R. T. , Fritschen L. J. , Gurney R. J. , Kanemasu E. T. , Kustas W. P. , Nie D. , Shuttleworth W. J. , Stewart J. B. , Verma S. B. , Weaver H. L. , Wesely M. L.
Published: February 2012

The underlying mean and variance properties of surface net radiation, soil heat flux, and sensible‐latent heat fluxes are examined over the densely instrumented grassland region encompassing the First ISLSCP Field Experiment (FIFE). Twenty‐two surface flux stations at 20 sites were deployed during the four 1987 intensive field campaigns (IFCs). Flux variability is addressed together with the problem of scaling up to area‐averaged fluxes. Successful parameterization of area‐averaged fluxes in atmospheric models is based on accounting for internal spatial and temporal scales correctly. Mean and variance properties of fluxes are examined in both daily and diurnally averaged frameworks. Results are compared and contrasted for clear and cloudy situations and checked for the influence of surface‐induced biophysical controls (burn and grazing treatments) and topographic controls (slope factors and aspect ratios). Examination of the sensitivity of domain‐averaged fluxes to different averaging procedures demonstrates that this may be an important consideration. The results reveal six key features of the 1987 surface fluxes: (1) cloudiness variability and ample rainfall throughout the growing season led to near‐consistency in flux magnitudes during the first three IFCs; (2) burn treatment, grazing conditions, and topography have clearly delineated influences on the diurnal cycle flux amplitudes but do not alter the evaporative fraction significantly; (3) cloudiness is the major control on flux variability in terms of both mean and variance properties but has little impact on the Bowen ratio or evaporative fraction; (4) spatial weighting of fluxes based on a biophysicaltopographical cross stratification generates a measurable bias with respect to straight arithmetic averaging (up to 20 W m−2 in available heating); (5) structure function analysis demonstrates significant underlying spatial autocorrelation structure in the fluxes, but the observed distance dependence is due to cloudiness controls, not surface controls; (6) Monte Carlo analysis of high resolution vegetation indices obtained from SPOT satellite measurements suggest that the mean domain amplitudes of the diurnal sensible and latent heat flux cycles can be biased up to 30–40 W m −2 by repositioning the 20 site locations within the experimental domain.
Evaluation of a technique for satellite‐derived area estimation of forest fires
Authors: Cahoon Donald R. , Stocks Brian J. , Levine Joel S. , Cofer Wesley R. , Chung Charles C.
Published: February 2012

Satellite data have been used increasingly during the past few years to examine burning around the globe. One such satellite instrument, the advanced very high resolution radiometer (AVHRR), has been found useful for the location and monitoring of both smoke and fires because of the daily observations, the large geographical coverage of the imagery, the spectral characteristics of the instrument, and the spatial resolution of the instrument. Earlier studies using AVHRR imagery have focused on locating and monitoring fires and studying the characteristics of smoke. This paper will discuss the application of AVHRR data to assess the geographical extent of burning. Methods have been developed to estimate the surface area of burning by analyzing the surface area effected by fire with AVHRR imagery. Characteristics of the AVHRR instrument, its orbit, field of view, and archived data sets are discussed relative to the unique surface area of each pixel. The errors associated with this surface area estimation technique are determined using AVHRR‐derived area estimates of target regions with known sizes. This technique is used to evaluate the area burned during the Yellowstone fires of 1988.
Sources and distribution of NOx in the upper troposphere at northern mid‐latitudes
Authors: Ehhalt D. H. , Rohrer F. , Wahner A.
Published: February 2012

A simple quasi‐two‐dimensional model is used to study the zonal distribution of NOx. The model includes vertical transport in the form of eddy diffusion and deep convection, zonal transport by a vertically uniform wind, and a simplified chemistry of NO, NO2, and HNO3. The NOx sources considered are surface emissions (mostly from the combustion of fossil fuel), lightning, aircraft emissions, and downward transport from the stratosphere. The model is applied to the latitude band of 40° to 50°N during the month of June; the contributions to the zonal NOx distribution from the individual sources and transport processes are investigated. The model predicted NOx concentration in the upper troposphere is dominated by air lofted from the polluted planetary boundary layer over the large industrial areas of eastern North America and Europe. Aircraft emissions are also important and contribute on average 30%. Stratospheric input is minor about 10%, less even than that by lightning. The model provides a clear indication of intercontinental transport Of NOx and HNO3 in the upper troposphere. Comparison of the modeled NO profiles over the western Atlantic with those measured during STRATOZ III in 1984 shows good agreement at all altitudes.
Low boreal wetlands as a source of atmospheric methane
Authors: Roulet Nigel T. , Ash Rosemary , Moore Tim R.
Published: February 2012

Boreal wetlands are thought to be a large source of atmospheric methane, but this idea is based on very few measurements. Thus a regional survey in the low boreal forest region of central Ontario, Canada, consisting of 24 sites over 12 wetlands and 3 beaver ponds was conducted to determine the temporal and spatial trends in emissions and the net annual methane (CH4) flux. Conifer swamps represented nearly 50% of the wetland coverage, but emit a small amount of CH4 (seasonal means < 8 mg m−2 d−1). The significant emitters of CH4, in order from highest to lowest seasonal means, were beaver ponds (30–90 mg m−2 d−1), thicket swamps (0.1–88 mg m−2 d−1), and bogs (6–21 mg m−2 d−1). Mixed swamps, marshes, and fens emitted very little CH4 (< 3 mg m−2 d−1). Moisture saturation was the key determinant of high emissions, and when satisfied, differences in emissions could be explained by peat and sediment temperatures. On the basis of the areal extent of wetlands from peatland inventories we calculate that the low boreal region of Canada contributes approximately 0.15Tg CH4 yr−1 to the atmosphere. This is an order of magnitude lower than the flux would be using the estimate of Aselmann and Crutzen (1989) for the same boreal region.
Total reactive oxidized nitrogen (NOy) in the remote Pacific troposphere and its correlation with O3 and CO: Mauna Loa Observatory Photochemistry Experiment 1988
Authors: Hübler G. , Montzka D. D. , Norton R. B. , Murphy P. C. , Fehsenfeld F. C. , Liu S. C. , Ridley B. A. , Walega J. G. , Atlas E. , Grahek F. E. , Heidt L. E. , Merrill J. , Huebert B. J. , Bodhaine B. A.
Published: February 2012

As part of the Mauna Loa Observatory Photochemistry Experiment (MLOPEX) total reactive oxidized nitrogen (NOy) was measured during May and early June of 1988 at the Mauna Loa Observatory, the NOAA‐Geophysical Monitoring for Climatic Change Baseline Monitoring Station, located at 3.4‐km elevation on the island of Hawaii. Gold catalytic surface conversion of individual reactive oxidized nitrogen species to NO and subsequent quantification of the NO by NO/O3 chemiluminescence was used to measure the NOy mixing ratio. The NOy abundance at the site was governed by the local downslope/upslope wind systems as well as synoptic‐scale transport. With some exceptions, downslope wind brought air representative of the free troposphere, while upslope winds transported air from below the trade wind inversion to the site. The upslope air masses could be a mix of marine boundary layer air and free tropospheric air modified by anthropogenic and natural emissions from island sources. It was possible to identify free tropospheric air in the downslope flow through meteorological and chemical tracers. Reflecting the remote location, low NOy mixing ratios with median values of 262 and 239 pptv were found in free tropospheric and upslope air masses, respectively. The median NOy levels in free tropospheric air are consistent with airborne NOy measurements made during NASA's Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation (CITE 2) program over the northeastern Pacific Ocean at corresponding altitudes. The median NOy values in upslope flow are significantly higher than those measured in the remote marine boundary layer during CITE 2, reflecting probably the influence of island source and/or mixing of free tropospheric air with boundary layer air. The low correlation found between NOy and tracers of anthropogenic sources, such as carbon monoxide, tetrachloroethylene, and n‐propyl nitrate, in free tropospheric air samples is consistent with a stratospheric or upper tropospheric source for NOy. Simultaneous particulate nitrate (NO3−) measurements suggest that at times not all aerosol NO3− was quantitatively converted to NO by the Au‐surf ace converter technique. These episodes were usually found during upslope flow and were characterized by high sodium concentrations, suggesting that possibly the sodium nitrate contained in these aerosols was not converted efficiently by the Au converter.
Composition measurements of the 1989 Arctic winter stratosphere by airborne infrared solar absorption spectroscopy
Authors: Toon G. C. , Farmer C. B. , Schaper P. W. , Lowes L. L. , Norton R. H.
Published: February 2012

Simultaneous measurements of the stratospheric burdens of H2O, HDO, OCS, CO2, O3, N2O, CO, CH4, CF2Cl2, CFCl3, CHF2Cl, C2H6, HCN, NO, NO2, HNO3, ClNO3, HOCl, HCl, and HF were made by the Jet Propulsion Laboratory MkIV interferometer on board the NASA DC‐8 aircraft during January and early February 1989 as part of the Airborne Arctic Stratosphere Experiment (AASE). Data were acquired on 11 flights at altitudes of up to 12 km over a geographic region covering the NE Atlantic Ocean, Iceland, and Greenland. Analyses of the chemically active gases reveal highly perturbed conditions within the vortex. The ClNO3 abundance was chemically enhanced near the edge of the vortex but was then depleted inside. HCl was chemically depleted near the vortex edge and became even more depleted inside. In fact, by late January deep inside the vortex, HCl was either completely removed up to 27‐km altitude, or partially removed to an even greater altitude. NO2 was also severely depleted inside the vortex. In contrast to Antarctica, H2O and HNO3 were both more abundant inside the vortex than outside. While for H2O this is solely a consequence of descent (without accompanying dehydration), HNO3 additionally shows evidence for chemical enhancement inside the vortex. One exception to the high HNO3 abundances inside the vortex occurred on January 31 when stratospheric temperatures above the aircraft fell below 190 K. However, following this event, HNO3 burdens fully recovered, suggesting that if the loss on January 31 was due to temporary freeze‐out of HNO3, the resulting particles reevaporated above 12 km. Taken together, these results suggest that although the Arctic vortex did not get cold enough to produce any dehydration, nor as vertically extensive denitrification as occurred in Antarctica, nevertheless, enough heterogeneous chemistry still occurred to convert over 90% of the inorganic chlorine to active forms in the 14‐ to 27‐km altitude range by early February 1989.
Evidence for subsidence in the 1989 Arctic winter stratosphere from airborne infrared composition measurements
Authors: Toon G. C. , Farmer C. B. , Schaper P. W. , Lowes L. L. , Norton R. H. , Schoeberl M. R. , Lait L. R. , Newman P. A.
Published: February 2012

Simultaneous measurements of the stratospheric burdens of CO2, HCN, N2O, CH4, OCS, CF2Cl2, CFCl3, CHF2Cl and HF were made by the Jet Propulsion Laboratory MkIV interferometer on board the NASA DC‐8 aircraft during January and early February 1989 as part of the Airborne Arctic Stratosphere Experiment. Data were acquired on 11 flights at altitudes of up to 12 km over a geographic region covering the NE Atlantic Ocean, Iceland and Greenland. The results obtained show large variations in the burdens of these tracers due to the effects of transport. The tropospheric source gas burdens were reduced inside the polar vortex, suggesting that the air had subsided with respect to the surrounding mid‐latitude air. Increased HF burdens inside the vortex support this interpretation. The results obtained from the different tracers are highly consistent with each other and indicate that in the 15‐ to 20‐km altitude range inside the vortex, surfaces of constant volume mixing ratio were located some 5–6 km lower in absolute altitude than outside the vortex. The results also indicate that the magnitude of this subsidence increases with altitude. These conclusions are consistent with other measurements.
Intercomparison and interpretation of surface energy fluxes in atmospheric general circulation models
Authors: Randall D. A. , Cess R. D. , Blanchet J. P. , Boer G. J. , Dazlich D. A. , Del Genio A. D. , Deque M. , Dymnikov V. , Galin V. , Ghan S. J. , Lacis A. A. , Le Treut H. , Li Z.‐X. , Liang X.‐Z. , McAvaney B. J. , Meleshko V. P. , Mitchell J. F. B. , Morcrette J.‐J. , Potter G. L. , Rikus L. , Roeckner E. , Royer J. F. , Schlese U. , Sheinin D. A. , Slingo J. , Sokolov A. P. , Taylor K. E. , Washington W. M. , Wetherald R. T. , Yagai I. , Zhang M.‐H.
Published: February 2012

We have analyzed responses of the surface energy budgets and hydrologic cycles of 19 atmospheric general circulation models to an imposed, globally uniform sea surface temperature perturbation of 4 K. The responses of the simulated surface energy budgets are extremely diverse and are closely linked to the responses of the simulated hydrologic cycles. The response of the net surface energy flux is not controlled by cloud effects; instead, it is determined primarily by the response of the latent heat flux. The prescribed warming of the oceans leads to major increases in the atmospheric water vapor content and the rates of evaporation and precipitation. The increased water vapor amount drastically increases the downwelling infrared radiation at the Earth's surface, but the amount of the change varies dramatically from one model to another.
Atmospheric sulfur dioxide at Mauna Loa, Hawaii
Authors: Luria Menachem , Boatman Joe F. , Harris Joyce , Ray John , Straube Tim , Chin John , Gunter Ruth L. , Herbert Gary , Gerlach Terrance M. , Van Valin Charles C.
Published: February 2012

Measurements of sulfur dioxide (S02) were made at the National Oceanic and Atmospheric Administration's Mauna Loa Observatory in Hawaii, during a 12‐month period beginning in December 1988. SO2 concentrations varied from background levels of less than 0.05 ppbv to a maximum of 50 ppbv, during episodes that lasted from 2 to 24 hours. Emissions from the Kilauea crater, approximately 35 km southeast of the observatory at an elevation of about 1000 m above sea level (asl), and the current eruption at Puu O′o 50 km east‐southeast, are the most likely sources for the higher concentrations. These episodes occurred 10–25 times each month, mostly during the day; peak concentrations were usually recorded at mid‐day. The SO2 concentrations can be grouped into three periods; low (June–September), high (October–January) and intermediate (February–May). A clear diurnal cycle of SO2 concentration exists throughout the year, although day‐night changes were greatest during October–January and were barely detectable during the June–September period. The highest SO2 concentrations were recorded when the predominant wind direction was northerly to northwesterly, even though the apparent sources are in the southeastern sector. Nighttime concentrations were usually at background levels; however, many exceptions were observed. A few cases of higher than background SO2 were observed when free tropospheric (FT) conditions were identified. The possibility that long‐range transport was the cause for elevated SO2 concentrations under FT conditions was examined using air mass back trajectories analyses. The highest nighttime SO2 concentrations, under FT conditions, were observed during periods with slow easterly trajectories, and the lowest concentrations were found during westerly flows. Twenty‐four nighttime free tropospheric events were recorded when the SO2 concentration exceeded 0.2 ppbv. During 18 of these episodes, unusually high CO2 concentrations were observed.
FIFE atmospheric boundary layer budget methods
Authors: Betts A. K.
Published: February 2012

The budget methods and the mixed layer model used to analyze the aircraft data from the First ISLSCP Field Experiment (FIFE) are outlined. The separation of the temporal and horizontal derivatives is discussed. Vector budgets for the mixed layer are presented on conserved variable diagrams. Theoretical solutions are given for the critical surface Bowen ratio, which produces no boundary layer moistening or equivalent potential temperature rise as a function of the Bowen ratio at the inversion. Improved measurement strategies are suggested.
Air‐surface exchange of H2O, CO2, and O3 at a tallgrass prairie in relation to remotely sensed vegetation indices
Authors: Gao W. , Wesely M. L. , Cook D. R. , Hart R. L.
Published: February 2012

Parameters derived from eddy correlation measurements of the air‐surface exchange rates of H2O, CO2, and O3 over a tallgrass prairie are examined in terms of their relationships with spectral reflectance data remotely sensed from aircraft and satellites during the four 1987 intensive field campaigns of the First ISLSCP Field Experiment (FIFE). The surface conductances gc were strongly modulated by photosynthetically active radiation received at the surface (K ↓ par) when the grass was green and well watered; mesophyll resistances were large for CO2 but negligible for H2O and O3. Seasonal changes of the surface conductances for a given level of K ↓ par were well correlated with changes in the simple ratio (SR) of canopy reflectances in the red and near‐infrared wave bands. A linear relationship in the form of gc = G0 + β(SR ‐ SR0), where SR0 ≈ 2 represents the simple ratio for senescent grass and G0 represents the corresponding nonstomatal conductance, fits the data fairly well and thus supports the results of modeling studies by Sellers (1985, 1987). In this relationship, G0 had values of near zero for H2O and CO2 and about 0.4 cm s−1 for O3. The slope β for large irradiation was about 0.08 cm s−1 for H2O and O3 and 0.03 cm s−1 for CO2. The inferred nonstomatal conductance had a small seasonal variability in comparison to the total canopy conductance.
Two‐dimensional model studies of the interannual variability of trace gases in the middle atmosphere
Authors: Chipperfield M. P. , Gray L. J.
Published: February 2012

A parameterization of the mechanisms believed to be responsible for the quasi‐biennial oscillation (QBO) in the zonal winds of the equatorial lower stratosphere has been included in an interactive dynamical‐radiative‐photochemical model of the atmosphere. As well as a QBO signal in the zonal wind, temperature, and ozone there are QBO signals in a range of other chemical species contained in the model. In the case of long‐lived tracers the QBO signal results from the direct effect of the QBO‐induced modification to the model circulation. The sign and magnitude of these QBO signals depend on the sign and strength of the vertical gradient of these long‐lived tracers in the lower stratosphere. For shorter‐lived species a QBO signal can result from the QBO in temperature or in trace gases controlling the species' production and loss. In many cases, much larger interannual variability is predicted for these short er‐lived species. Notably, NO2 and N2O5, whose chemistry is very temperature dependent, show very strong QBO signals. In the case of ozone the transition from dynamical control in the lower stratosphere to photochemical control at higher altitudes can be seen in its QBO signal. These predictions of interannual variability of trace species should be considered when analyzing and interpreting observational data, particularly when calculating year‐to‐year trends.
A comparison of total ozone data from satellite and ground‐based observations at northern latitudes
Authors: Heese Birgit , Barthel Knut , Hov Øystein
Published: February 2012

Ozone measurements from the Total Ozone Mapping Spectrometer on the Nimbus 7 satellite are compared with ground‐based measurements from five Dobson stations at northern latitudes to evaluate the accuracy of the TOMS data, particularly in regions north of 50°N. The measurements from the individual stations show mean differences from −2.5% up to +8.3% relative to TOMS measurements and two of the ground stations, Oslo and Longyearbyen, show a significant drift of +1.2% and +3.7% per year, respectively. It can be shown from nearly simultaneous measurements in two different wavelength double pairs at Oslo that at least 2% of the differences result from the use of the CC' wavelength double pair instead of the standard AD wavelength double pair. Since all Norwegian stations used the CC' wavelength double pair exclusively, a similar error can be assumed for Tromsø and Longyearbyen. A comparison between the tropospheric ozone content in TOMS data and from ECC ozonesonde measurements at Ny‐Ålesund and Bear Island shows that the amount of tropospheric ozone in the standard profiles used in the TOMS algorithm is too low, which leads to an error of about 2% in total ozone. Particularly at high solar zenith angles (>80°), Dobson measurements become unreliable. They are up to 20% lower than TOMS measurements averaged over solar zenith angles of 88° to 89°.
Stratospheric sulfate aerosol in and near the northern hemisphere polar vortex: The morphology of the sulfate layer, multimodal size distributions, and the effect of denitrification
Authors: Wilson J. C. , Stolzenburg M. R. , Clark W. E. , Loewenstein M. , Ferry G. V. , Chan K. R. , Kelly K. K.
Published: February 2012

Measurements were made of stratospheric sulfate aerosols using a passive cavity aerosol spectrometer and a condensation nucleus counter on a NASA ER–2 aircraft in the Airborne Arctic Stratospheric Experiment of 1989. The problems of representative and accurate sampling and particle evaporation were explicitly addressed in the design of the inlets and reduction of the data. The measurements suggest that the sulfate aerosol is bimodal in the polar vortex above the mass mixing ratio maximum in the sulfate layer. It appears that a nuclei mode of small, newly formed particles exists in this region. A stronger case is made for a nuclei mode in the upper few kilometers of the troposphere and in the lower few kilometers of the stratosphere. This mode is probably a global phenomenon occurring in all seasons. Comparison of denitrified and nondenitrified air suggests that denitrification removes some of the larger sulfate particles.
Variations in atmospheric methane at Mauna Loa Observatory related to long‐range transport
Authors: Harris Joyce M. , Tans Pieter P. , Dlugokencky Edward J. , Masarie Kenneth A. , Lang Patricia M. , Whittlestone Stewart , Steele L. Paul
Published: February 2012

Methane measurements, radon measurements, and air mass trajectories calculated for Mauna Loa Observatory (MLO) are examined to determine relationships among methane source/sink regions, flow patterns for MLO, and methane variations on the synoptic‐to‐seasonal scale. We present evidence that the methane seasonal cycle observed at MLO is in large part driven by seasonal variations in transport. Furthermore, the variability in methane mixing ratio at MLO is higher in winter than in summer because of greater variability in flow patterns. Ten‐day back trajectories are classified according to wind speed and direction using cluster analysis to determine six typical transport regimes. The methane data are then grouped according to transport cluster. The median methane mixing ratio corresponding to tradewind flow was 17.2 ppbv (parts per billion by volume) lower than that corresponding to strong westerly flow. This difference is attributed to transport from source/sink regions, flow across the methane latitudinal gradient, and seasonality of flow patterns. Case studies utilizing individual trajectories and radon measurements to determine probable air parcel origins illustrate the effects of long‐range transport on the methane mixing ratio at MLO. Changes in flow pattern from sink to source origins can result in a 50 ppbv rise in methane mixing ratio over a period of a few days. During winter, alternation of westerly winds, tradewinds and anticyclonically curving flows contributes to the large variability in the methane mixing ratio. During summer this variability is reduced with the cessation of strong westerly flows from methane source regions. In July and August, air parcels originate far from methane source regions and in the area of highest modeled OH concentration. At the same time, methane mixing ratios decrease to the lowest values for the year. In this way, the seasonality of flow patterns exerts a major influence on the observed seasonal cycle of methane at MLO.
Large‐scale variability of ozone and aerosols in the summertime Arctic and sub‐Arctic troposphere
Authors: Browell E. V. , Butler C. F. , Kooi S. A. , Fenn M. A. , Harriss R. C. , Gregory G. L.
Published: February 2012

Measurements of ozone (O3) and aerosol distributions were made with an airborne lidar system in the Arctic and sub‐Arctic during July–August 1988 as part of the NASA Global Tropospheric Experiment/Arctic Boundary Layer Expedition (ABLE 3A). Aerosol and O3 profiles were measured simultaneously above and below the Electra aircraft from near the surface to above the tropopause. In situ measurements of O3 mixing ratios and aerosol size distributions and number densities were also made on the aircraft. Many different atmospheric conditions were investigated on long‐range survey flights in the Arctic and on intensive flights over the tundra, ice, and marine regions near Barrow and Bethel, Alaska. The tropospheric composition at high latitudes was found to be strongly influenced by stratospheric intrusions. Regions of low‐aerosol scattering and enhanced O3 mixing ratios were correlated with descending air from the lower stratosphere. Over 37% of the troposphere along our flight track at latitudes >57°N had significantly enhanced O3 levels due to stratospheric intrusions, and in the 4‐ to 6‐km altitude range the tropospheric extent of the enhanced O3 exceeded 56%. Ozone mixing ratios of 80 ppbv at 6 km were common, with vertical O3 gradients of over 11 ppbv km−1 observed across the base of strong intrusions. In the mixed layer over the tundra, O3 was in the 25–35 ppbv range with a gradient of 5.5 ppbv km−1, while in continental polar air masses, the average gradient in the lower troposphere was 7.4 ppbv km−1, indicating more downward transport of O3 at higher latitudes. Due to the many forest fires that year, plumes from biomass burning sources were observed on several flights over Alaska. Plumes influenced about 10% of the air below 4 km, and in some photochemically active plumes, O3 was enhanced by 10–20 ppbv over ambient levels. Pollution plumes from industrial sources were infrequently observed; however, a few large plumes were found over the North Pacific with greatly enhanced aerosol scattering and with O3 levels exceeding 75 ppbv.
Ozone response to a CO2 doubling: Results from a stratospheric circulation model with heterogeneous chemistry
Authors: Pitari G. , Palermi S. , Visconti G. , Prinn R. G.
Published: February 2012

A spectral three‐dimensional model of the stratosphere has been used to study the sensitivity of polar ozone with respect to a carbon dioxide increase. The lower stratospheric cooling associated with an imposed CO2 doubling may increase the probability of polar stratospheric cloud (PSC) formation and thus affect ozone. We compare the ozone perturbation obtained with the inclusion of a simple parameterization for heterogeneous chemistry on PSCs to that relative to a pure homogeneous chemistry. In both cases the temperature perturbation is determined by a CO2 doubling, while the total chlorine content is kept at the present level. It is shown that the lower temperature may increase the depth and the extension of the ozone hole by extending the area amenable to PSC formation. It may be argued that this effect, coupled with an increasing amount of chlorine, may produce a positive feedback on the ozone destruction.
Stable isotope composition of waters in southeastern California: 2. Groundwaters and their relation to modern precipitation
Authors: Smith George I. , Friedman Irving , Gleason Jim D. , Warden Augusta
Published: February 2012

We compare isotopic data on modern groundwater recharge, estimated from a 7‐year collection of precipitation samples, with the isotopic compositions of 82 samples from wells and perennial springs collected in southeastern California. Over half the samples represent recharge that is considerably more depleted in deuterium (δD) than the lightest (winter) precipitation δD values now precipitating in nearby areas. Wells in the vicinity of irrigation canals fed from the Colorado River contain water whose δD resembles that of the irrigation canals, and wells adjacent to the Mojave River are recharged by Mojave River water. The remainder of the samples from the 17 hydrologic units discussed in this paper include one or more whose δD values are depleted in deuterium by at least 10‰ compared to recharge estimated from modern winter precipitation. A plot of δ18O versus δD for 56 wells and 22 springs shows substantial scatter (R2=0.66) and defines a slope of 4.9, which is lower than the slope of the Meteoric Water Line. This slope and the scatter of the data suggest these diverse waters were evaporated to different degrees before recharge, and they may also have exchanged oxygen with solid mineral phases. We interpret the fact that many groundwaters in this region have lower δD values than modem precipitation to indicate that recharge of many of the groundwater basins occurred during an earlier period, probably the late Pleistocene, when winters were colder, evaporation rates were lower, and precipitation was quantitatively greater and isotopically lighter.