bluuebunny/crossref_metadata_2025 huggingface dataset:
Conditional sampling, bursting, and the intermittent structure of sensible heat flux
Authors: Katul Gabriel G. , Albertson John , Parlange Marc , Chu Chia‐Ren , Stricker Han
Published: February 2004

Sensible heat flux measurements were carried out to examine the characteristics related to frequency and duration of extreme flux events above a desert surface. First, the flux bursts were identified by a modified hyperbolic hole “quadrant analysis” in which the threshold criterion depends on the mean and standard deviation of the flux time statistics. Second, the frequency distribution of the extreme flux burst length was examined. It was found that the frequency distribution of the burst length is well approximated by two‐parameter power laws which account for two distinct types of bursting phenomena: one is organized, coherent, and has a relatively long duration, while the other is short lived, less organized, and has a relatively short duration. Linear regression analysis was used to determine the two power exponents of the burst length probability density function. Both exponents compare favorably with other reported measurements on concentration bursting in dispersing plumes from an elevated source. The cutoff burst length from one power law to the next also matches other studies. A strong correlation between bursting frequency and flux integral time scales was observed under a variety of atmospheric stability and surface wetness conditions. This strong correlation suggested a relationship between atmospheric stability and the mean time interval between bursts. It was found that the variation in the interval between bursts for the dynamic and dynamic convective sublayers is strongly related to the variation in stability. This was not the case for near‐convective and stable atmospheric conditions.
Seasonal variation of gravity wave activity in the lower atmosphere observed with the MU radar
Authors: Murayama Y. , Tsuda T. , Fukao S.
Published: February 2004

In this paper we analyzed the seasonal variation of gravity wave activity in the troposphere and lower stratosphere (5–25 km) as revealed by monthly observations with the MU radar between December 1985 and December 1989. In the lower stratosphere, wind velocity variance due to gravity waves with periods of 5 min‐21 hours showed a clear annual variation with a maximum in winter and a minimum in summer, agreeing fairly well with the seasonal variation of the jet stream intensity. This suggests that the excitation of gravity waves is closely related to the behavior of the background mean winds. The specific kinetic energy per unit volume of short‐period gravity waves (ground‐based period of 5 min‐2 hours) was enhanced in winter and spring, its peak in the profile being located near the peak of the jet stream (∼12 km). On the other hand, the kinetic energy of the long‐period (2–21 hours) component showed clear annual variation with a winter maximum and a summer minimum in the middle troposphere and lower stratosphere. The kinetic energy of the long‐period component was smaller in the lower stratosphere than in the troposphere, which did ot seem to penetrate the lower stratosphere. In the short‐period component the ratio of the horizontal to the vertical wind variances near the jet peak height was observed to be large in winter and small in summer, probably due to the seasonal variation of the Brunt‐Väisälä frequency. The wind variance ratio for the long‐period component in the upper troposphere and lower stratosphere was greatly reduced in winter, possibly due to the Doppler shifting of gravity waves. The vertical flux of zonal momentum for the 5 min‐ to 21‐hour period component showed negative values in the upper troposphere and lower stratosphere, implying that the upward propagating gravity waves in the lower stratosphere mostly traveled westward relative to the background wind. We did not find any significant seasonal variations in the vertical flux of meridional momentum.
Horizontal variability of temperature, specific humidity, and cloud liquid water as derived from spaceborne observations
Authors: Tjemkes Stephen A. , Visser Marijke
Published: February 2004

In an effort to assess the information content of spaceborne data wavenumber spectra of temperature, moisture and cloud liquid water are calculated from high‐resolution infrared sounder (HIRS), as archived in the International Satellite Cloud Climatology Project ‐ TIROS‐N operational vertical sounder (ISCCP‐TOVS) data set and special sensor microwave/imager (SSM/I) observations. The region under consideration is the southern hemispheric storm track, defined as the region extending from 38° to 58°S. The observational period is July 1989. In general, we find that the ISCCP‐TOVS temperature spectrum has two distinct regimes, one where it follows a m−3, and one where it follows m−5/3 power law. These results are consistent with theoretical results for enstrophy and inverse energy cascade respectively in two‐dimensional turbulence. The ISCCP‐TOVS specific humidity spectra are more difficult to interpret. There is some indication that especially for layers near the surface, these spectra has two regimes similar to the tempererature spectra, but this is not unambiguous. For layers in the upper troposphere or lower stratosphere, the m−3 regime is not visible. The spatial variance and the shape of the columnar water vapor spectrum derived from these two sources are very similar. Some differences exists, at high wavenumber domain, but this could be the result of the employed method to construct the SSM/I daily mean distribution. Finally, there is some indication that the cloud liquid water spectrum follows the theoretical spectrum for the diffusion of a passive admixture in two‐dimensional turbulence.
Biogenic sulfur emissions and aerosols over the tropical South Atlantic: 1. Dimethylsulfide in sea water and in the atmospheric boundary layer
Authors: Andreae Tracey W. , Andreae Meinrat O. , Schebeske Günther
Published: February 2004

We measured dimethylsulfide (DMS) in air (DMSa) and surface seawater (DMSw) on board the R/V Meteor during February–March 1991 on the tropical South Atlantic. Samples for the determination of DMSa were taken through a fluorinated ethylene/propylene Teflon inlet ≈33 m above sea level, preconcentrated by adsorption onto gold wool in quartz tubes, and analyzed by gas chromotography with flame photometric detection. The DMSa instrument is fully automated, providing improved precision, and processes up to four samples per hour. Over most of the cruise track, which followed the 19°S parallel between Brazil and Africa, DMSw, was significantly correlated to climatologically averaged chlorophyll concentrations obtained from coastal zone color scanner data, suggesting that remote sensing may be useful for estimating seawater DMS levels at least in some ocean regions. The cruise track proceeded from waters of low roductivity (off the coast of Brazil and in the subtropical gyre) to higher productivity (the Benguela Current and the upwelling region off Namibia and Angola); meteorological conditions were steady with consistent easterly winds. DMS values for air and water were low (≈ 50 ppt and 1–2 nmol L−1, respectively) in the areas of low productivity and increased simultaneously (≈ 100–300 ppt and 3–15 nmol L−1) as productivity increased. DMS sea‐to‐air fluxes (average 7.3 μmol m−2 d−1) were calculated based on different parameterizations; for the study region the differences between the results obtained from the different models were minor. DMSa was strongly correlated to its emission flux from the sea surface as estimated from DMSw and meteorological parameters. This suggests that the air/sea transfer parameterizations used are suitable for providing estimates of DMS flux from the oceans.
A two‐dimensional global study of tropospheric ozone production
Authors: Strand Asbjørn , Hov Ø.
Published: February 2004

The ozone production in the troposphere has been studied by means of a zonally averaged model which consists of a two‐dimensional transport model, a description of the emissions, wet and dry deposition, and chemical processes of importance for the ozone production in the troposphere. The transport model describes a closed circulation in the meridional plane below 10 hPa and has a resolution and a numerical solution which compares favorable with earlier two‐dimensional studies. The transport model also takes into account the fast vertical mixing in convective clouds and in frontal circulation. The production of nitrogen oxides by lightning has been coupled to the convection parameterization by assuming that the nitrogen oxides are transported vertically in the thunder clouds and released at the altitudes where boundary layer air entrained in the convective cells is released. Comparisons with observations indicate that the model is able to reproduce the seasonal variation of ozone in the meridional plane quite realistically. The calculated distributions of the chemical species which determine tropospheric ozone also compare well with measurements. The model estimated an annually averaged production of ozone in the troposphere over the northern hemisphere of 16.6×1010 molecules/cm2/s and over the southern hemisphere of 5.1×1010 molecules/cm2s. The annually and globally averaged dry deposition is 14.9×1010 molecules/cm2/s, and the corresponding injection from the stratosphere is 4.1×1010 molecules/cm2/s. A 50% reduction of the man‐made emissions from the industrialized society of nitrogen oxides resulted in a reduction in the ozone production of 2.9×1010 molecules/cm2/s in the lower troposphere over the northern hemisphere during the period of maximum photochemical production, June–August. The corresponding production decrease due to a 50% reduction of the emissions of volatile organic compounds and carbon monoxide from the same source, however, was 1.6×1010 molecules/cm2/s. Elsewhere, the effects of reductions are less significant due to smaller influence of man‐made emissions.
The total mass of the atmosphere
Authors: Trenberth Kevin E. , Guillemot Christian J.
Published: February 2004

Accurate but approximate formulae for determining the mass of the atmosphere in terms of the surface pressure ps are derived and applied to globally analyzed data from the European Centre for Medium‐Range Weather Forecasts (ECMWF) for 1985 through 1993. The formulae take into account effects of the shape of the Earth and variations in gravity with latitude and height. Variations in total mass occur because of changes in the water vapor loading of the atmosphere. Independent computations are made of the surface pressure due to water vapor pw, which is proportional to the precipitable water, using the ECMWF analyses of specific humidity. Spurious trends in both the mass of dry air and the atmospheric moisture are found to arise from changes in the analysis system at ECMWF, confounding attempts to seek real trends associated with climate change. For the recent 4‐year period 1990 to 1993 the mean annual ps was 984.76 mbar with a maximum in July of 984.98 mbar and a minimum in December of 984.61 mbar which correspond to a total mean mass of the atmosphere of 5.1441×1018 kg with a range of 1.93×1015 kg throughout the year associated with changes in water vapor in the atmosphere. The global mean pw for 1985–1993 is 2.58 mbar, but values are 5 to 10% lower after mid‐1992. Using the Special Sensor Microwave Imager data to make adjustments, the best estimate of the annual global pw is 2.4 mbar, corresponding to ∼2.5 cm of precipitable water. The total atmospheric moisture as given by pw varies with an annual cycle range of 0.36 mbar, a maximum in July, and a minimum in December. Thus the mean mass of water vapor is 1.25×1016 kg and the dry air mass is 5.132×1018 kg, corresponding to a mean surface pressure of 982.4 mbar. Overall uncertainties are ∼0.1 mbar or 0.5×1015 kg in total mass and about double those values for atmospheric moisture content. As well as the global means, hemispheric mean values and meridional profiles of ps and pw are presented for the mean annual cycle and as latitude‐time series to show the interannual and longer‐term variability.
Lightning return stroke model with height‐variable discharge time constant
Authors: Thottappillil Rajeev , Uman Martin A.
Published: February 2004

A new lightning return stroke model is proposed in which the lightning channel, previously charged by the leader, is exponentially discharged with the discharge time constant being a general function of height. The new model is both more general and more physically reasonable than the Diendorfer‐Uman model (Diendorfer and Uman, 1990) and its modification by Thottappillil et al. (1991). In the new model a single height‐variable discharge time constant is used instead of the two height‐invariant discharge time constants used for natural lightning in the Diendorfer‐Uman model. As an illustration of the use of the new model, the measured electric fields for three triggered lightning return strokes about 5‐km distant are compared with the fields calculated from the model, using simultaneously measured channel base current and return stroke speed as inputs to the model.
Determination of the dry deposition flux of SO2 using cosmogenic 35S and 7Be measurements
Authors: Tanaka N. , Turekian K. K.
Published: February 2004

The radionuclides 35S (half‐life = 87 days) and 7Be (half‐life = 53 days) are produced in the atmosphere by cosmic rays. The former quickly becomes gaseous 35SO2 while 7Be is directly associated with aerosols. The production rates of both nuclides increase virtually exponentially with increasing altitude. Conversion of 35SO2 to particulate 35SO4 is effected by oxidation after which, like 7Be, it is subject to removal by precipitation in the troposphere. The 35SO2 is also removed from the gaseous state by solution and oxidation in water droplets (clouds) and, at the planetary surface, through “dry deposition” (i.e., oxidation on plant and other surfaces). The kinetics controlling removal of 35SO2 also operate on SO2 in the atmosphere from natural and pollution sources. Through measurements of 35SO2,35SO4, 7Be, SO2 and SO4 in air samples in the boundary layer and the wet precipitation fluxes of the 35SO4, 7Be, and SO4 integrated over monthly intervals, we have established the following parameters at New Haven, Connecticut for 1992. Based on the 7Be balance the average effective height of the troposphere, Ht, varies from 13 km for the winter months to 17 through 21 km for the spring and summer months. The height of the surface reactive “boundary” layer, Hb, is about 0.5 km for all but the month of August. By optimization procedures, best solutions were obtained for scavenging coefficients for both the free troposphere and the surface reactive layer together with the dry deposition coefficient and the mean residence time of air in the surface reactive layer. The highest fraction of dry deposition flux to total S flux occurred in the fall and winter. The weighted average for the entire year is 0.25.
Equatorial Kelvin wave variability during 1992 and 1993
Authors: Canziani Pablo O. , Holton James R. , Fishbein Evan , Froidevaux Lucien
Published: February 2004

Temperature and ozone data from the Microwave Limb Sounder (MLS) instrument on UARS are used to analyze the variability of Kelvin wave activity during the first two years of the UARS mission. The analysis is carried out using the asynoptic mapping technique. Time frequency plots for zonal wavenumbers 1 and 2, at two heights representing the middle stratosphere and the stratopause, respectively, are used to analyze the temporal variability of the waves, and its possible relationship to the equatorial quasi‐biennial oscillation (QBO) and semiannual oscillation (SAO). Kelvin wave activity reaches a maximum during the solstice seasons and almost disappears during the equinoxes, in agreement with previous studies. Eastward propagating variance is estimated for wave periods from 4 to 20 days, at all UARS pressure surfaces currently available for MLS. The semiannual modulation of variance is observed to extend down to the lower limits of the height ranges of the temperature and ozone retrievals. Furthermore, a superposed QBO modulation is detected up to the stratopause. Comparison between the variance in eastward propagating waves and the mean zonal wind shows a possible participation of kelvin waves in the forcing of the QBO. At the stratopause the role of Kelvin waves in forcing the SAO appears to be limited, in agreement with previous results. Between the 21‐hPa and 4.6‐hPa surfaces there appears to be a transition zone where there is no clear relationship between Kelvin wave activity and mean zonal flow acceleration.
Lidar measurements of stratospheric ozone during the STOIC campaign
Authors: McGee Thomas J. , Ferrare Richard A. , Whiteman David N. , Butler James J. , Burris John F. , Owens Melody A.
Published: February 2004

The NASA Goddard Space Flight Center's Stratospheric Ozone Lidar Trailer Experiment participated in the Stratospheric Ozone Intercomparison Campaign (STOIC) at Table Mountain, California, from July 20 to August 2, 1989. From 20 to 39 km the average Goddard Space Flight Center (GSFC) profile agreed with the STOIC reference profile to better than 5%. The STOIC reference profile was generated by averaging all profiles from the eight participating instruments. In this same altitude region the GSFC and the Jet Propulsion Laboratory lidar average profiles also agreed to better than 5%. Similar results were found for an intercomparison of the lidar data with ozone data from ECC sondes launched from Table Mountain and from San Nicholas Island. The results of the intercomparison have led to a number of modifications to the GSFC lidar which have greatly improved the reliability of the ozone data, particularly at altitudes below 20 km and above 40 km.
Comparison between SAGE II and ISCCP high‐level clouds: 1. Global and zonal mean cloud amounts
Authors: Liao Xiaohan , Rossow William B. , Rind David
Published: February 2004

Global high‐level clouds identified in Stratospheric Aerosol and Gas Experiment II (SAGE II) occultation measurements for January and July in the period 1985 to 1990 are compared with near‐nadir‐looking observations from the International Satellite Cloud Climatology Project (ISCCP). Global and zonal mean high‐level cloud amounts from the two data sets agree very well, if clouds with layer extinction coefficients of <0.008 km−1 at 1.02 μm wavelength are removed from the SAGE II results and all detected clouds are interpreted to have an average horizontal size of about 75 km along the 200 km transmission path length of the SAGE II observations. The SAGE II results are much more sensitive to variations of assumed cloud size than to variations of detection threshold. The geographical distribution of cloud fractions shows good agreement, but systematic regional differences also indicate that the average cloud size varies somewhat among different climate regimes. The more sensitive SAGE II results show that about one third of all high‐level clouds are missed by ISCCP but that these clouds have very low optical thicknesses (<0.1 at 0.6 μm wavelength). SAGE II sampling error in monthly zonal cloud fraction is shown to produce no bias, to be less than the intraseasonal natural variability, but to be comparable with the natural variability at longer time scales.
Dynamical and radiative forcing of the summer mesopause circulation and thermal structure: 2. Seasonal variations
Authors: Luo Zhangai , Fritts David C. , Portmann Robert W. , Thomas Gary E.
Published: February 2004

We present in this paper an extension of the steady dynamical/radiative summer mesopause model by Fritts and Luo [this issue] to examine the variability of wave forcing required to account for the observed seasonal changes of temperature. The model employs dynamical forcing provided by gravity wave energy and momentum fluxes and divergence, including wave and turbulence effects, and radiative forcing describing solar heating of O2 and O3, local thermodynamic equilibrium (LTE) and non‐LTE cooling of O3 and CO2 and chemical heating due to Oχ and HOχ chemistry parameterized as Newtonian cooling. Strong sensitivity to dynamical and radiative forcing under steady conditions provides an ability to diagnose the temporal variability of dynamical forcing required to account for the observed departures from radiative and chemical equilibrium. The occurrence of minimum mesopause temperatures somewhat after summer solstice implies a similar lag in the maximum wave forcing and is consistent with the available momentum flux measurements and inferences based on the seasonal variations of the zonal mean winds. In particular, the rapid increase in mesopause temperature during August implies a rapid cessation of wave forcing accompanying the strong eastward acceleration of the mean flow during this interval.
The fate of atmospheric phosgene and the stratospheric chlorine loadings of its parent compounds: CCl4, C2Cl4, C2HCl3, CH3CCl3, and CHCl3
Authors: Kindler T. P. , Chameides W. L. , Wine P. H. , Cunnold D. M. , Alyea F. N. , Franklin J. A.
Published: February 2004

A study of the tropospheric and stratospheric cycles of phosgene is carried out to determine its fate and ultimate role in controlling the ozone depletion potentials of its parent compounds (CCl4, C2Cl4, CH3CCl3, CHCl3, and C2HCl3). Tropospheric phosgene is produced from the OH‐initiated oxidation of C2Cl4, CH3CCl3, CHCl3, and C2HCl3. Simulations using a two‐dimensional model indicate that these processes produce about 90 pptv/yr of tropospheric phosgene with an average concentration of about 18 pptv, in reasonable agreement with observations. We estimate a residence time of about 70 days for tropospheric phosgene, with the vast majority being removed by hydrolysis in cloudwater. Only about 0.4% of the phosgene produced in the troposphere avoids wet removal and is transported to the stratosphere, where its chlorine can be released to participate in the catalytic destruction of ozone. Stratospheric phosgene is produced from the photochemical degradation of CCl4, C2Cl4, CHCl3, and CH3CCl3 and is removed by photolysis and downward transport to the troposphere. Model calculations, in good agreement with observations, indicate that these processes produce a peak stratospheric concentration of about 25–30 pptv at an altitude of about 25 km. In contrast to tropospheric phosgene, stratospheric phosgene is found to have a lifetime against photochemical removal of the order of years. As a result, we find that a significant portion of the phosgene that is produced in the stratosphere is ultimately returned to the troposphere, where it is rapidly removed by clouds. This phenomenon effectively decreases the amount of reactive chlorine injected into the stratosphere and available for ozone depletion from phosgene's parent compounds; we estimate approximate decreases of 14, 3, 15, and 25% for the stratospheric chlorine loadings of CCl4, CH3CCl3, C2Cl4, and CHCl3, respectively. A similar phenomenon due to the downward transport of stratospheric COFCl produced from CFC‐11 is estimated to cause a 7% decrease in the amount of reactive chlorine injected into the stratosphere from this compound. Our results are potentially sensitive to a variety of parameters, most notably the rate of reaction of phosgene with sulfate aerosols. However, on the basis of the observed vertical distribution of COCl2, we estimate that the reaction of COCl2 with sulfate aerosol most likely has a γ< 5×10−5 and, as a result, has a negligible impact on the stratospheric chlorine loadings of the phosgene parent compounds.
Electrochemical concentration cell ozone soundings at two sites during the Stratospheric Ozone Intercomparison Campaign
Authors: Barnes Robert A. , Torres Arnold L.
Published: February 2004

The Stratospheric Ozone Intercomparison Campaign (STOIC) was designed to compare proposed instruments for the Network for the Detection of Stratospheric Change (NDSC) with established measurement techniques. Ground‐based measurements were conducted at Table Mountain, California (34.4°N, 117.7°W), and rocket profiles were made at San Nicolas Island, California (33.3°N, 119.5°W). In an effort to estimate site‐to‐site differences during the intercomparison, daily soundings were made with balloon‐borne electrochemical concentration cell (ECC) ozonesondes at the two sites. Comparisons have been made of the mean values for the soundings at each site. The soundings showed small temperature differences between the two sites with the nighttime Table Mountain measurements up to 2°K cooler than the daytime San Nicolas Island temperatures. Day/night temperature corrections based on the emissivity and absorptivity of the thermistors in the balloon instruments can account for these apparent temperature differences. Ozone partial pressure profiles from the ECCs have been used to estimate atmospheric ozone variability during STOIC. Above 20 km, the lowest altitude for the STOIC comparisons, the average data sets from both sites showed standard deviations that were at or below the estimated 5–6% profile‐to‐profile repeatability for the ozonesondes. This indicates that atmospheric ozone variability was only of the order of a few percent above 20 km during the 2 weeks of the STOIC campaign. Above 20 km the ozone partial pressures over the Table Mountain site averaged 2.0% lower than over San Nicolas Island.
Convective boundary layer mean depths and cloud geometrical properties obtained from volume imaging lidar data
Authors: Piironen Antti K. , Eloranta Edwin W.
Published: February 2004

This paper presents automatic methods for obtaining convective boundary layer mean depths, cloud base altitudes, cloud top altitudes, cloud coverages, and cloud shadows using the University of Wisconsin volume imaging lidar (VIL). These methods provide mesoscale observations representing the 70 km2 scanning area of the VIL. All data obtained with the VIL during the 1989 First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment are analyzed and the results are summarized. The reliability of these methods is verified by comparing the results with radiosonde profiles, satellite images, and visual estimates from range height indicator scans of the VIL.
Electrical structure and updraft speeds in thunderstorms over the southern Great Plains
Authors: Marshall Thomas C. , Rust W. David , Stolzenburg Maribeth
Published: February 2004

We have acquired 11 balloon soundings of the electric field and thermodynamics in large and sometimes severe and tornadic thunderstorms over the southern Great Plains. The ascent rates of the balloons were used to divide the soundings into weak and strong updrafts. All 11 soundings had magnitudes of charge densities and thicknesses of charge regions similar to those reported previously in small thunderstorms. The five weak‐updraft soundings had complex charge structures of 7–9 charge regions below 10 km altitude. The magnitude of the maximum measured electric field in these soundings was 100–150 k V m−1. The four soundings in strong updrafts had balloon ascent rates of at least 15 m s−1 for at least 1 km. These soundings had simpler electrical structures of 3–5 charge regions below 10 km altitude. Their maximum measured electric fields ranged from 85 to 130 kV m−1. The data may support an earlier hypothesis that charge is elevated in strong updrafts. In addition, the data may suggest that simpler charge structures are associated with proximity to strong updrafts rather than with different storm types.
Dynamical and radiative forcing of the summer mesopause circulation and thermal structure: 1. Mean solstice conditions
Authors: Fritts David C. , Luo Zhangai
Published: February 2004

We present here a simple eigenvalue model which illustrates the sensitivity of the mean circulation and thermal structure near the high‐latitude summer mesopause to dynamical and radiative processes under solstice conditions. Dynamical forcing is provided by gravity wave energy and momentum fluxes and their divergence which contribute both a zonal body force and implied turbulent heating and transport in the mesopause region. These profiles are chosen to be consistent with measurements of gravity wave fluxes and energy densities at high latitudes. Radiative forcing represents the effects of solar heating, non‐LTE CO2 cooling, and LTE O3 cooling below 70 km and is parameterized as a height‐dependent relaxation toward an equilibrium temperature profile accounting for both radiative and chemical influences. Gravity wave momentum flux divergence forces a mean vertical motion related to the meridional gradient of the density‐weighted momentum flux through the “downward control principle” and a mean meridional circulation required to balance the zonal body force. The model exhibits strong sensitivity to dynamical forcing and implies significant constraints on wave influences at mesopause altitudes. For plausible wave fluxes and energy densities, the model yields a mean vertical motion of ∼0.05 m s−1, a mean meridional jet of ∼10 to 15 m s−1, and a mesopause temperature of ∼130 K at Arctic latitudes, all of which are in good agreement with observations. The eigenvalue solution also yields estimates of the induced turbulent heating and vertical diffusion that may pose useful guidelines in modeling studies. Seasonal variations in the mesopause structure are the subject of a companion paper.
Gravity wave activity in the lower atmosphere: Seasonal and latitudinal variations
Authors: Allen Simon J. , Vincent Robert A.
Published: February 2004

A climatology of gravity wave activity in the lower atmosphere based on high‐resolution radiosonde measurements provided by the Australian Bureau of Meteorology is presented. These data are ideal for investigating gravity wave activity and its variation with position and time. Observations from 18 meteorological stations within Australia and Antarctica, covering a latitude range of 12°S – 68°S and a longitude range of 78°E–159°E, are discussed. Vertical wavenumber power spectra of normalized temperature fluctuations are calculated within both the troposphere and the lower stratosphere and are compared with the predictions of current gravity wave saturation theories. Estimates of important model parameters such as the total gravity wave energy per unit mass are also presented. The vertical wavenumber power spectra are found to remain approximately invariant with time and geographic location with only one significant exception. Spectral amplitudes observed within the lower stratosphere are found to be consistent with theoretical expectations but the amplitudes observed within the troposphere are consistently larger than expected, often by as much as a factor of about 3. Seasonal variations of stratospheric wave energy per unit mass are identified with maxima occurring during the low‐latitude wet season and during the midlatitude winter. These variations do not exceed a factor of about 2. Similar variations are not found in the troposphere where temperature fluctuations are likely to be contaminated by convection and inversions. The largest values of wave energy density are typically found near the tropopause.
An analysis of the Antarctic Halogen Occultation Experiment trace gas observations
Authors: Schoeberl Mark R. , Luo Mingzhao , Rosenfield Joan E.
Published: February 2004

Analysis of the version 16 Halogen Occultation Experiment (HALOE) CH4 data shows that this long‐lived trace gas is well correlated with potential vorticity (PV) computed from National Meteorological Center balanced winds. Analyzing late September and October 1992 data, we show that very low CH4 values are confined to the interior of a vortex edge defined by the maximum gradient in PV. The CH4 and HF time tendency is used to estimate the descent rate in the Antarctic vortex. After removing a component of the trend correlated with the HALOE sampling pattern, we compute the lower stratosphere vertical descent rates and net heating rates in the spring Antarctic vortex. Our computations of the spring Antarctic vortex heating rates give −0.5 to −0.1 K/day. Over the winter season, the overall lower stratospheric descent rate averages about 1.8–1.5 km/month. These computations are in line with radiative transfer estimates of the heating and descent rate. The HALOE data thus appear to be consistent with the picture of an isolated lower stratospheric Antarctic vortex.
Evolution of microwave limb sounder ozone and the polar vortex during winter
Authors: Manney G. L. , Froidevaux L. , Waters J. W. , Zurek R. W.
Published: February 2004

The evolution of polar ozone observed by the Upper Atmosphere Research Satellite Microwave Limb Sounder is described for the northern hemisphere (NH) winters of 1991/1992, 1992/1993, and 1993/1994 and the southern hemisphere (SH) winters of 1992 and 1993. Interannual and interhemispheric variability in polar ozone evolution are closely related to differences in the polar vortex and to the frequency, duration and strength of stratospheric sudden warmings. Ozone in the midstratospheric vortices increases during the winter, with largest increases associated with stratospheric warmings and a much larger increase in the NH than in the SH. A smaller NH increase was observed in 1993/1994, when the middle stratospheric vortex was stronger. During strong stratospheric warmings in the NH, the upper stratospheric vortex may be so much eroded that it presents little barrier to poleward transport; in contrast, the SH vortex remains strong throughout the stratosphere during wintertime warmings, and ozone increases only below the mixing ratio peak, due to enhanced diabatic descent. Ozone mixing ratios decrease rapidly in the lower stratosphere in both SH late winters, as expected from chemical destruction due to enhanced reactive chlorine. The interplay between dynamics and chemistry is more complex in the NH lower stratosphere and interannual variability is greater. Evidence has previously been shown for chemical ozone destruction in the 1991/1992 and 1992/1993 winters. We show here evidence suggesting some chemical destruction in late February and early March 1994. In the NH late winter lower stratosphere the pattern of high‐ozone values (typical of the vortex) seen in mid‐latitudes is related to the strength of the lower‐stratospheric vortex, with the largest areal extent of high ozone outside the vortex in 1994, when the lower stratospheric vortex is relatively weak, and the least extent in 1993 when the lower stratospheric vortex is strongest.
Radon 222 as a comparative tracer of transport and mixing in two general circulation models of the atmosphere
Authors: Genthon Christophe , Armengaud Alexandre
Published: February 2004

Radon 222 (222Rn) is used as a tracer to probe and intercompare transport, turbulent mixing, and convective mixing in the Laboratoire de Météorologie Dynamique (LMD) and Goddard Institute for Space Studies (GISS) atmospheric general circulation models (GCMs). Formulations for tracer transport and mixing and their control on the global distribution and time variability of 222Rn, as well as parameterizations for the continental surface source flux, are directly implemented into the two GCMs and run “in‐line.” Tracer formulations are largely inspired by climate variables (heat, moisture, momentum) formulations in the base GCMs. The comparison of model‐calculated 222Rn with observations of time (diurnal, seasonal, sporadic), variability, and spatial (horizontal, vertical) distribution shows partial agreement only. Uncertainties of the sources of 222Rn, in particular of the dependence of 222Rn emanation on soil freezing, are substantial, and the significance and reliability of some of the available observations are low. Model intercomparison is not subject to observation limitations, and it clearly indicates that the boundary layer is more homogeneously mixed in the LMD model, whereas deep convection is more efficient at carrying surface‐produced quantities to high tropospheric levels in the GISS model. Resolution also makes a large difference. The LMD model has a finer horizontal grid over most of the globe and is almost systematically better than the GISS model at reproducing sharp fluctuations of 222Rn and seasonal cycles. Our results support that 222Rn could provide an unequivocal absolute measure of the GCM's performances if a more comprehensive observational validation was available.
Evidence of seasonally dependent stratosphere‐troposphere exchange and purging of lower stratospheric aerosol from a multiyear lidar data set
Authors: Menzies Robert T. , Tratt David M.
Published: February 2004

Tropospheric and lower stratospheric aerosol backscatter data obtained from a calibrated backscatter lidar at Pasadena, California (34°N latitude) over the 1984–1993 period clearly indicate tightly coupled aerosol optical properties in the upper troposphere and lower stratosphere in the winter and early spring, due to the active midlatitude stratospheric‐tropospheric (ST) exchange processes occurring at this time of year. Lidar data indicate that during pre‐Pinatubo background conditions, the subsequent purging of the aerosol in the upper troposphere caused a significant reduction in the aerosol content throughout the 8–18 km altitude region in the early spring period. The post‐Pinatubo evidence of intense exchange in the winter and early spring is a significant increase in the upper tropospheric aerosol content, such that the backscatter levels reach values nearly equivalent to the enhanced backscatter levels existing in the lower stratosphere. The calculated stratospheric mass extrusion rate is consistent with a 45‐day lifetime of lower stratospheric aerosol during this part of the year, which implies that midlatitude ST exchange is a significant sink for stratospheric aerosol.
Carbon‐biosphere‐climate interactions in the last glacial maximum climate
Authors: Friedlingstein P. , Prentice K. C. , Fung I. Y. , John J. G. , Brasseur G. P.
Published: February 2004

The total carbon inventory in the terrestrial biosphere in the last glacial maximum (LGM), 18 kyr ago, is analyzed in a series of experiments that examine the sensitivity of the inventory to vegetation distribution and carbon dynamics. The results show that for most forest vegetation types, carbon densities for the LGM are within 10% of their present‐day values. Discrepancies between vegetation distributions simulated by two bioclimatic schemes are attributable to the assignation of vegetation types to climates with rare or no present‐day analog. The model experiments, combined with palynogical data for regions with no present‐day analog climate, yield to a decrease of 612±105 Gt C compared to present day.
Outgoing longwave radiation biases and their impacts on empirical orthogonal function modes of interannual variability in the tropics
Authors: Kayano Mary T. , Kousky Vernon E. , Janowiak John E.
Published: February 2004

The effects of different equator‐crossing times on the outgoing longwave radiation (OLR) data record are examined. A simple procedure proposed by Kousky and Kayano (1994) is used to reduce these effects. Large‐scale interannual modes of OLR within the tropics are determined by performing empirical orthogonal function analyses on OLR anomalies and on bias‐corrected OLR anomalies. Both analyses result in two physically meaningful leading modes, which describe different large‐scale anomalous features of the OLR related to the southern oscillation. A mode related to changes in the satellite observing system is found only in the analysis for the uncorrected OLR anomalies. Evidence is presented indicating that estimates of the mean daily OLR are affected by changes in the equator‐crossing times due either to the replacement of satellites or to long‐term drifts from the orbital plane during the lifetime of individual satellites.
A global model of natural volatile organic compound emissions
Authors: Guenther Alex , Hewitt C. Nicholas , Erickson David , Fall Ray , Geron Chris , Graedel Tom , Harley Peter , Klinger Lee , Lerdau Manuel , Mckay W. A. , Pierce Tom , Scholes Bob , Steinbrecher Rainer , Tallamraju Raja , Taylor John , Zimmerman Pat
Published: February 2004

Numerical assessments of global air quality and potential changes in atmospheric chemical constituents require estimates of the surface fluxes of a variety of trace gas species. We have developed a global model to estimate emissions of volatile organic compounds from natural sources (NVOC). Methane is not considered here and has been reviewed in detail elsewhere. The model has a highly resolved spatial grid (0.5°×0.5° latitude/longitude) and generates hourly average emission estimates. Chemical species are grouped into four categories: isoprene, monoterpenes, other reactive VOC (ORVOC), and other VOC (OVOC). NVOC emissions from oceans are estimated as a function of geophysical variables from a general circulation model and ocean color satellite data. Emissions from plant foliage are estimated from ecosystem specific biomass and emission factors and algorithms describing light and temperature dependence of NVOC emissions. Foliar density estimates are based on climatic variables and satellite data. Temporal variations in the model are driven by monthly estimates of biomass and temperature and hourly light estimates. The annual global VOC flux is estimated to be 1150 Tg C, composed of 44% isoprene, 11% monoterpenes, 22.5% other reactive VOC, and 22.5% other VOC. Large uncertainties exist for each of these estimates and particularly for compounds other than isoprene and monoterpenes. Tropical woodlands (rain forest, seasonal, drought‐deciduous, and savanna) contribute about half of all global natural VOC emissions. Croplands, shrublands and other woodlands contribute 10–20% apiece. Isoprene emissions calculated for temperate regions are as much as a factor of 5 higher than previous estimates.
Ground‐based measurements of water vapor in the middle atmosphere
Authors: Nedoluha Gerald E. , Bevilacqua Richard M. , Gomez R. Michael , Thacker D. L. , Waltman William B. , Pauls Thomas A.
Published: February 2004

We present measurements of the middle atmospheric water vapor mixing ratio profile obtained using the ground‐based Naval Research Laboratory water vapor millimeter‐wave spectrometer (WVMS) instrument at the Jet Propulsion Laboratory Table Mountain Observatory. The measurements cover a period of 262 days from January 23, 1992, to October 13, 1992. During this campaign it was possible to retrieve useful daily mixing ratio profiles for 186 days. We thus have a nearly continuous record of water vapor mixing ratios for altitudes from ≈35 to 75 km. The retrievals are obtained using the optimal estimation method. Details of the error analysis are presented, and a technique is introduced that reduces baseline effects and helps to estimate the baseline error. The high‐altitude (≳65 km) data show a sharp rise prior to the expected maximum near the summer solstice and a gradual decline in the following months. The mixing ratios generally peak between 55 and 65 km, at which point the mixing ratios are 6–7 parts per million by volume. The highest peaks occur in January, May, and October.
An explanation for anomalous lightning from forest fire clouds
Authors: Vonnegut B. , Latham D. J. , Moore C. B. , Hunyady S. J.
Published: February 2004

Experiments out of doors and in a wind tunnel show that when trees, vegetation, and other substances are burned in the open air, negative charge is released into the atmosphere under the influence of the fine weather electric field. The results indicate that the thunderclouds formed as the result of a forest fire have probably grown from air that contains negative, instead of the usual positive, fine weather space charge. Observations showing that cumulonimbus clouds formed over forest fires produced positive, instead of the usual negative, cloud‐to‐ground lightning, suggest that the electrification of these clouds may have been caused by one or more influence mechanisms.
Assessment of the quality of TOVS retrievals obtained with the 3I algorithm for Antarctic conditions
Authors: Köpken Christina , Heinemann Günther , Chédin Alain , Claud Chantal , Scott Noëlle A.
Published: February 2004

The quality of layer‐mean temperatures and humidities retrieved with the improved initialization inversion (3I) (version 2) algorithm from measurements of the TIROS operational vertical sounder (TOVS) radiometer has been studied for two summer periods in 1987 and 1990 in the Weddell Sea region (Antarctica) by means of collocations with radiosoundings, European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses and special sensor microwave/imager (SSM/I) retrievals. Appropriate corrections of the atmospheric transmission functions have been used for the two periods. A significant influence on the accuracy of the retrievals has been observed. Collocation statistics with radiosoundings for layer‐mean temperatures based on 160 cases show very satisfying results. The standard deviation is very close to the deviations expected from collocation errors alone, but an overall negative bias of the retrieved temperatures is observed. Considerably smaller biases in clear conditions suggest that the frequent cloudy situations are one reason. The atmospheric stability index derived from the retrievals corresponds well to the observations. However, surface inversions and inversions capping the boundary layer (being characteristics of the polar environment) cannot be resolved by the TOVS. Layer‐mean humidities and integrated water vapor content are calculated by the 3I algorithm with a good absolute accuracy and errors are comparable to those occurring at lower latitudes. But problems have been found in the ability to correctly retrieve varying water vapor contents in different situations which is caused by weak signals in the very dry Antarctic conditions. Comparisons of the total water vapor content to results based on SSM/I measurements show a good agreement between the two different instruments and retrieval methods. Comparisons of temperature and humidity retrievals to ECMWF analyses show a better correspondence between retrievals and analyses for 1990, related probably to model and assimilation system changes. The ECMWF analyses show deviations from radiosoundings comparable to those of the retrievals emphasizing the value of TOVS retrievals as an important source of information in this data‐sparse region.
Lidar estimation of stratospheric aerosol properties: Surface, volume, and extinction to backscatter ratio
Authors: Gobbi Gian Paolo
Published: February 2004

A method for estimating stratospheric aerosol surface area, volume, and extinction to backscatter ratio from single‐wavelength lidar measurements is presented. Functional relationships linking these variables are found on the basis of average scattering properties of a large set of aerosol distributions and compositions. The resulting model accounts for sulfate aerosol types, ranging from background to volcanic, in environmental conditions representative of most of the global lower stratosphere. Relevant errors range between 10 and 45% for surface area and between 15 and 35% for volume and extinction to backscatter ratio estimates. These values are slightly larger but comparable to those characterizing in situ particle counters. An extension of the method to the interpretation of both polar stratospheric cloud observations and satellite extinction measurements is discussed. The relationships between lidar backscatter at 532 nm and satellite extinction at 532 and at 1020 nm are evaluated.