COSPAR International Reference Atmosphere Research Articles

The operational and research DTM-2020 thermosphere models

Aims: The semi-empirical Drag Temperature Models (DTM) predict the Earth’s thermosphere’s temperature, density, and composition, especially for orbit computation purposes. Two new models were developed in the framework of the H2020 Space Weather Atmosphere Models and Indices (SWAMI) project. The operational model is driven by the trusted and established F10.7 andKpindices for solar and geomagnetic activity. The so-called research model is more accurate, but it uses the indices F30 and the hourly Hpo, which are not yet accredited operationally.Methods: The DTM2020 models’ backbone comprises GOCE, CHAMP, and Swarm A densities, processed by TU Delft, and Stella processed in-house. They constitute the standards for absolute densities, and they are 20–30% smaller than the datasets used in the fit of DTM2013. Also, the global daily mean TLE densities at 250 km, spanning four solar cycles, were now used to improve solar cycle variations. The operational model employs the same algorithm as DTM2013, which was obtained through fitting all data in our database from 1967 to 2019. Because of the Hpo index, which is not available before 1995, the coefficients linked to the geomagnetic activity of the research model are fitted to data from 2000 to 2019. The algorithm was updated to take advantage of the higher cadence of Hpo. Both models are assessed with independent data and compared with the COSPAR International Reference Atmosphere models NRLMSISE-00, JB2008, and DTM2013. The bias and precision of the models are assessed through comparison with observations according to published metrics on several time scales. Secondly, binning of the density ratios are used to detect specific model errors.Results: The DTM2020 densities are on average 20–30% smaller than those of DTM2013, NRLMSISE-00, and JB2008. The assessment shows that the research DTM2020 is the least biased and most precise model compared to assimilated data. It is a significant improvement over DTM2013 under all conditions and at all altitudes. This is confirmed by the comparison with independent SET HASDM density data. The operational DTM2020 is always less accurate than the research model except at 800 km altitude. It has comparable or slightly higher precision than DTM2013, despite using F10.7 instead of F30 as solar activity driver. DTM, and semi-empirical models in general, can still be significantly improved on the condition of setting up a more complete and consistent total density, composition, and temperature database than available at this time by means of a well-conceived observing system.

Rayleigh Lidar observed atmospheric temperature characteristics over a western Indian location: intercomparison with satellite observations and models

General characteristics of sub-tropical middle atmospheric temperature structure over a high altitude station, Mt. Abu (24.5°N, 72.7°E, altitude ~1670 m, above mean sea level (amsl)) are presented using about 150 nights observational datasets of Rayleigh Lidar. The monthly mean temperature contour plot shows two distinct maxima in the stratopause region (~45–55 km), occurring during February-March and September-October, a seasonal dependence similar to that reported for mid- and high-latitudes respectively. Semi-Annual Oscillation (SAO) are stronger at an altitude ~60 km in the mesospheric temperature in comparison to stratospheric region. A comparison with the satellite (Halogen Occultation Experiment, (HALOE)) data shows qualitative agreement, but quantitatively a significant difference is found between the observation and satellite. The derived temperatures from Lidar observations are warmer ~2–3 K in the stratospheric region and ~5–10 K in the mesospheric region than temperatures observed from the satellite. A comparison with the models, COSPAR International Reference Atmosphere (CIRA)-86 and Mass Spectrometer Incoherent Scatter Extended (MSISE)-90, showed differences of ~3 K in the stratosphere and ~5–10 K in the mesosphere, with deviations somewhat larger for CIRA-86. In most of the months and in all altitude regions model temperatures were lower than the Lidar observed temperature except in the altitude range of 40–50 km. MSISE-90 Model temperature overestimates as compared to Lidar temperature during December-February in the altitude region of 50–60 km. In the altitude region of 55–70 km both models deviate significantly, with differences exceeding 10–12 K, particularly during equinoctial periods. An average heating rate of ~2.5 K/month during equinoxes and cooling rate of ~4 K/month during November-December are found in altitude region of 50–70 km, relatively less heating and cooling rates are found in the altitude range of 30–50 km. The stratospheric temperature derived from the Lidar and columnar ozone observed by the Total Ozone Mapping Spectrometer (TOMS) over Mt. Abu shows good correlation (r 2 = 0.61) and indicates the association of ozone with the temperature.

Characterizing polar atmospheres and their effect on Rayleigh‐scattering optical depth

A large set of radiosoundings was analyzed to study the dependence of Rayleigh‐scattering optical depth (ROD) on pressure and temperature features of the polar clear‐sky atmosphere. This set consists of 1320 radiosoundings, launched throughout the year at six Arctic sites, and of 940 radiosoundings launched at five Antarctic sites. The vertical profiles of pressure, temperature, and relative humidity given by these radiosoundings were corrected for lag errors and dry biases and then completed up to 120 km altitude, using COSPAR International Reference Atmosphere (CIRA) monthly vertical profiles of pressure and temperature, water vapor mixing ratio data derived from various satellite observations, and standard CO2 vertical profile relative to 2007, when the ground‐level concentration was 380 ppmv. Calculations of the volume Rayleigh‐scattering coefficient were made for all the radiosoundings to study its seasonal variations with height due to pressure and temperature changes occurring in the troposphere and stratosphere. It was found that the surface‐level pressure and temperature conditions can account to a large extent for these seasonal effects. Therefore, average spectral evaluations of ROD were made at 88 selected wavelengths from 0.20 to 4.0 μm for all the radiosoundings, subdivided into eight latitude/altitude site classes, representing 70°N, 75°N, 80°N, 70°S, 75°S, 80°S, and 90°S latitudes, for which the average ground values of air pressure pa and air temperature Ta were defined. The dependence of ROD on the daily ground‐level values of air pressure po and air temperature To measured at each site can be accounted for by using an algorithm in which the pressure dependence is given with good approximation by ratio (po/pa), and the temperature linear dependence is expressed by the difference (Ta − To) multiplied by a spectral slope coefficient k(λ) which varies by site classification. This algorithm was estimated to provide values of ROD with accuracy within ±0.5% at the six sea‐level Arctic sites, ±0.5% at the three Antarctic coastal sites, and ±0.7% at the two Antarctic Plateau sites (Dome C and South Pole). When used to analyze the Sun photometer measurements, the present evaluations of ROD are estimated to provide aerosol optical depth values at visible wavelengths with relative errors of 1%–2% at the Arctic sites, 1%–4% at the coastal Antarctic sites, and 3%–13% at the Antarctic Plateau sites, for background aerosol extinction conditions.

Observations of equatorial mesospheric winds over Cariri (7.4° S) by a meteor radar and comparison with existing models

Abstract. Mesospheric winds observed with a meteor radar at Cariri (7.4° S, 36.5° W), Brazil, during the period of July 2004 to June 2005, show a clear semiannual oscillation known as the Mesospheric Semiannual Oscillation (MSAO), which maximizes in the zonal mean wind mainly at 82 km, with amplitude decreasing with height. Maximum westward winds for the MSAO occurred in March and September. The meridional wind, on the other hand, presented a clear annual variation maximizing in December. On average, the amplitude of the meridional MSAO was smaller than the zonal MSAO component. Comparison with models shows on occasions that there are significant differences between the observed winds and the CIRA (Cospar International Reference Atmosphere) and HWM93 (Horizontal Wind Model) models. In addition, diurnal and semidiurnal parameters were calculated and compared to the GSWM model. Other results observed during one year of data are presented in this work.

Improved cosmic ray ionization model for the system ionosphere–atmosphere—Calculation of electron production rate profiles

The effects of galactic cosmic rays (CRs) in the middle atmosphere are considered in this work. We take into account the CR modulation by solar wind and the anomalous CR component also. In fact, CRs determine the electric conductivity in the middle atmosphere and influence the electric processes in itin this way. CRs introduce solar variability in the terrestrial atmosphere and ozonosphere—because they are modulated by solar wind. A new analytical approach for CR ionization by protons and nuclei with charge Z in the lower ionosphere is developed in this paper. For this purpose, the ionization losses (d E/d h) according to the Bohr–Bethe–Bloch formula for the energetic charged particles are approximated in three different energy intervals. More accurate expressions for CR energy decrease E( h) and electron production rate profiles q( h) are derived. The obtained formulas allow comparatively easy computer programming. q( h) is determined by the solution of a 3D integral with account of geomagnetic cut-off rigidity. The integrand in q( h) gives the possibility for application of adequate numerical methods—in this case Gauss quadrature, for the solution of the mathematical problem. Computations for CR ionization in the middle atmosphere are made. In this way the process of interaction of CR particles with the upper and middle atmosphere are described much more realistically. The full CR composition is taken into account: protons, helium ( α-particles), light L, medium M, heavy H and very heavy VH group of nuclei. All computations are made for geomagnetic cut-off rigidity R=1 GV in the altitude interval 15–120 km. The COSPAR International Reference Atmosphere CIRA’86 is applied in the computer program for the neutral density and scale height values. The proposed improved CR ionization model will contribute to the quantitative understanding of solar–atmosphere relationships.

A fast radiative transfer model for SSMIS upper atmosphere sounding channels

Special Sensor Microwave Imager/Sounder (SSMIS) on board the Defense Meteorology Satellite Program (DMSP) F‐16 satellite probes the atmospheric temperature from surface to 100 km. SSMIS channels 19–22 are significantly affected by Zeeman splitting, which is dependent on the Earth’s magnetic field. Thus, in satellite data assimilation or retrieval systems, SSMIS brightness temperatures and their Jacobians (or gradient with respect to temperature) must be computed with a fast radiative transfer (RT) scheme that takes into account the Zeeman‐splitting effect. In this study, an averaged transmittance within the channel frequency passbands is parameterized and predicted with atmospheric temperature, geomagnetic field strength, and the angle between the geomagnetic field vector and the electromagnetic wave propagation direction. The coefficients of predictors are trained with a line‐by‐line (LBL) radiative transfer model that accurately computes the monochromatic transmittances at fine frequency steps within each passband. The new radiative transfer scheme is compared to the results from the line‐by‐line model for the dependent and independent data sets. It is shown that the differences between the two models are well below the instrument noise levels but the new scheme is much faster. It is also shown that the SSMIS measurements agree well with the simulations that are based on the atmospheric profiles from the sounding of the atmosphere using broadband emission radiometry (SABER) on the Thermosphere‐lonosphere‐Mesosphere Energetics and Dynamics satellite and the COSPAR international reference atmosphere (CIRA) model.

Trace constituent updates in the Marshall engineering thermosphere and global reference atmospheric model

Global reference atmospheric model (GRAM-99) is an engineering-level model of Earth’s atmosphere. It provides both mean values and perturbations for density, temperature, pressure, and winds, as well as monthly and geographically varying trace constituent concentrations. From 0 to 27 km, GRAM thermodynamics and winds are based on National Oceanic and Atmospheric Administration Global Upper Air Climatic Atlas (GUACA) climatology. Above 120 km, GRAM is based on the NASA Marshall engineering thermosphere (MET) model. In the intervening altitude region, GRAM is based on middle atmosphere program (MAP) climatology that also forms the basis of the 1986 COSPAR International reference atmosphere (CIRA). Atmospheric composition is represented in GRAM by concentrations of both major and minor species. Above 120 km, MET provides concentration values for N 2, O 2, Ar, O, He, and H. Below 120 km, represented species also include H 2O, O 3, N 2O, CO, CH 4, and CO 2. At 34th COSPAR a comparison was made between GRAM constituents below 120 km and those provided by Naval Research Laboratory (NRL) climatology. No current need to update GRAM constituent climatology in that height range was identified. This report examines GRAM/MET constituents between 100 and 1000 km altitudes. Internal discrepancies are noted between GRAM/MET constituent number densities and mass density or molecular weight. Near 110 km altitude, there is up to about 25% discrepancy between MET number density and mass density (with mass density being valid and number densities requiring adjustment). Near 700 km altitude there is also up to about 25% discrepancy between MET number density and mean molecular weight (with molecular weight requiring adjustment). In neither case are MET mass density estimates invalidated. The discrepancies have been traced to MET subroutines SLV (which affects 90–170 km height range) and SLVH (which affects helium above 440 km altitude). With these discrepancies corrected, results are presented to illustrate GRAM/MET constituent mole fractions in terms of height-latitude cross-sections from 100 to 1000 km altitude, and latitude–longitude “maps” at 450 km. Plans are discussed for an update of MET and GRAM to correct these constituent inconsistencies, and to incorporate several new thermospheric model features.

Temperatures and horizontal winds in the Antarctic summer mesosphere

A series of 26 meteorological rockets (“falling spheres,” FS) were launched in January and February 1998 from the Antarctic research station Rothera (68°S, 68°W). These flights gave densities and temperatures below ∼93 km and horizontal winds below ∼75 km, respectively. The lowest altitude is approximately 35 km. The instrumental technique is identical to the one applied in similar studies in the Northern Hemisphere (NH). In this paper, we summarize the experimental results and compare them with climatologies in the NH summer and with empirical models. We concentrate on the mesosphere. In January, temperatures in the upper mesosphere are very low (<135 K) and are very similar to the NH. In February, temperatures increase substantially, certainly more than in the corresponding time period in the NH. The zonal winds show a similar behavior: SH/NH values are very similar in January/July but differ in February/August. This indicates that (at least in 1998) the seasonal transition from summer to winter occurs earlier in the SH compared to the NH. Mass densities are generally similar in both hemispheres. The difference is less than 2–6% and shows a seasonal variation similar to temperatures and zonal winds. Our experimental results at Rothera differ significantly from empirical reference atmospheres such as the COSPAR International Reference Atmosphere (CIRA). For example, in the upper mesosphere our mass densities are up to 35–40% smaller compared to CIRA. Such differences can be important, for example, when modeling the sedimentation of ice particles leading to noctilucent clouds (NLC) and polar mesosphere summer echoes (PMSE). Furthermore, zonal winds in the mesosphere in January/July in the SH/NH are very similar in our measurements but different in CIRA. Recent lidar and radar measurements of NLC at Rothera and PMSE at Davis (68.6°S), respectively, show very similar mean altitudes compared to the NH supporting the similarity of the thermal structures in both hemispheres in January/July.

Earth global reference atmospheric model (GRAM-99) and trace constituents

Global reference atmospheric model (GRAM-99) is an engineering-level model of the Earth's atmosphere. It provides both mean values and perturbations for density, temperature, pressure, and winds, as well as monthly- and geographically-varying trace constituent concentrations. From 0 to 27 km altitude, thermodynamics and winds are based on National Oceanic and Atmospheric Administration Global Upper Air Climatic Atlas (GUACA) climatology. Above 120 km altitude, GRAM is based on the NASA Marshall Engineering Thermosphere (MET) model. In the intervening altitude region, GRAM is based on Middle Atmosphere Program (MAP) climatology that also forms the basis of the 1986 COSPAR International Reference Atmosphere (CIRA). MAP data in GRAM are augmented by specially derived longitude variation climatology. Atmospheric composition is represented in GRAM by concentrations of both major and minor species. Above 120 km, MET provides concentration values for N 2, O 2, Ar, O, He, and H. Below 120 km, species represented also include H 2O, O 3, N 2O, CO, CH 4, and CO 2. Water vapor in GRAM is based on a combination of GUACA, Air Force Geophysics Laboratory (AFGL), and NASA Langley Research Center climatologies. Other constituents below 120 km are based on a combination of AFGL and MAP/CIRA climatologies. This report presents results of comparisons between GRAM constituent concentrations and those provided by Naval Research Laboratory (NRL) climatology. GRAM and NRL concentrations were compared for seven species (CH 4, CO, CO 2, H 2O, N 2O, O 2, and OH 3) for months January, April, July, and October, over height range 0–115 km, and latitudes −90° to + 90° at 10° increments. Average GRAM-NRL correlations range from 0.878 (for CO) to 0.975 (for OH 3), with an average over all seven species of 0.936 (SD 0.049).

First in situ temperature measurements in the summer mesosphere at very high latitudes (78°N)

A total of 24 temperature profiles from ∼92 to 55 km were obtained from falling sphere flights in Longyearbyen (Svalbard, 78°N) from 16 July to 14 September 2001. The thermal structure of the upper mesosphere during the summer season (here from mid‐July to 23 August) is characterized by very low temperatures and little variability. The mesopause temperature decreases slightly from ∼130 K in mid‐July to 126–128 K in late July/beginning of August. The mesopause altitude in summer is ∼89 km. Compared to 10° further south (69°N, Andøya), the mesopause temperature is very similar in mid‐July but is significantly colder by 6–8 K in the second half of July and in August. Part of this difference (especially in late August) is due to the later transition from summer to winter in Longyearbyen. The mesopause altitude is higher by approximately 1 km at Longyearbyen compared to Andøya. At 82 km, the temperature in summer is very close to 150 K, very similar to other Arctic and Antarctic stations (“equithermal submesopause”). The temperatures in the upper mesosphere are significantly lower compared to COSPAR International Reference Atmosphere (CIRA, 1986) by up to 20 K. Assuming model water vapor concentrations, we derived the degree of saturation of water vapor (S). In summer, there is an extended altitude range (82–92 km) with supersaturation (S > 1). Occasionally, very high supersaturation was derived (S > 100). Our temperature measurements are in general agreement with the occurrence morphology of polar mesosphere summer echoes (PMSE). However, double layered structures frequently observed in PMSEs are not a prominent feature of the temperatures in the upper mesosphere.

Improved Mapping of Tropospheric Delays

The authors compare several methods to map the a priori tropospheric delay of global positioning system (GPS) signals from the zenith direction to lower elevations. This is commonly achieved with so-called mapping functions. Dry mapping functions are applied to the hydrostatic delay; wet mapping functions are used to map the zenith wet delay to lower elevation angles. The authors compared the following mapping techniques against raytraced delays computed for radiosonde profiles under the assumption of spherical symmetry: (a) the Niell mapping function; (b) mapping through the COSPAR International Reference Atmosphere with added water vapor climatology; (c) the same as b with added use of surface meteorological temperature, pressure, and humidity; and (d) use of the numerical reanalysis model of the National Centers for Environmental Prediction–National Center for Atmospheric Research. Based on comparisons with all available global radiosondes (∼1000 per day), for every fifth day of 1997 (73 days), the authors found that dry mapping based on method d performs 2–3 times better than a for elevations 15° and below. The authors further report that b and c perform better dry mapping than a, with an improvement of ∼50%. Smaller improvements are also shown for wet delay mapping by b, c, and d as compared to a. At 5° and below, the Niell dry mapping function has biases that vary with season by 1%, and it displays significant systematic errors (2%–4% at 5° elevation) between 30° and 90° southern latitude during the northern winter months. It is concluded that the most demanding meteorological and geodetic GPS applications should use location- and time-specific “direct” mapping functions such as b, c, or d rather than parameterized functions, especially if low elevation observations are used. The authors describe how this improved mapping can be implemented in GPS analysis software.

Simultaneous measurements of temperature in the upper mesosphere with an Ebert‐Fastie Spectrometer and a VHF meteor radar on Svalbard (78°N, 16°E)

From the 14th of November to the 21st of November 1999 measurements of the upper mesospheric temperatures were performed on Svalbard (78°N, 16°E). Both the SOUSY Svalbard Radar and a one meter focal length Ebert‐Fastie spectrometer were used, the first instrument measured the decay and phase changes of meteor echoes, and the latter measured the OH(6–2) rotational spectrum. These allowed us to deduce themperature estimates at 80–90 km altitude. Due to the differences in the height of the measurements the temperatures were compared on the background of the temperature profile according to the COSPAR International Reference Atmosphere and reasonable agreement was found.

Two‐day wave structure and mean flow interactions observed by radar and High Resolution Doppler Imager

Data obtained with four MF and meteor radars at equatorial and subtropical sites and with the High Resolution Doppler Imager (HRDI) instrument aboard the UARS satellite were used to examine the structure, wave‐mean flow interactions, and potential sources of the 2‐day wave in the middle atmosphere during three southern hemisphere summers. The three wave events were highly transient, having typical durations of 20 to 30 days and exhibiting modulation at shorter periods. Temporal variations were found to exhibit good correlations between radar and HRDI data. Radar and HRDI data were used to estimate those components of the Eliassen‐Palm flux that could be assessed with these data. Meridional fluxes of momentum and heat were computed using HRDI data and agree reasonably with the momentum fluxes computed from radar data at discrete locations. These fluxes were found to exhibit consistent latitudinal structures each year, suggesting systematic wave excitation and wave‐mean flow interactions. Meridional momentum flux gradients were seen to be anticorrelated with zonal wind accelerations in a manner consistent with wave forcing of the large‐scale circulation. The apparent wave‐mean flow interactions suggest that the 2‐day wave could be a transient response to baroclinic instability of the summer hemisphere mesospheric jet. A calculation of the meridional gradient of quasi‐geostrophic potential vorticity using HRDI winds and the COSPAR International Reference Atmosphere (CIRA 1986) temperatures exhibits a region of instability in the lower and middle mesosphere extending into subtropical latitudes and provides additional evidence of a possible source of this motion via baroclinic instability of the summer hemisphere jet structure.

Comparing upper tropospheric and lower stratospheric temperatures: Microwave sounding unit, radiosonde, COSPAR International Reference Atmosphere, and National Center for Environmental Prediction/National Center for Atmospheric Research reanalysis monthly mean climatologies

Climate‐modeling groups are having to assess their models' temperatures at high, thinly observed altitudes in order to investigate near‐tropopause forcings with confidence. To support such analyses, the microwave sounding unit (MSU), GFDL/Oort radiosonde, COSPAR International Reference Atmosphere (CIRA), and new 13‐year National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis Project climatologies are intercompared herein in terms of their monthly mean microwave brightness temperatures Tb. In the lower stratosphere these climatologies agree extremely well. Small differences between NCEP/NCAR and MSU Tb centered at about 80 mbar amount to ≤2 K year round across the tropics and ≤5 K in southern winter polar latitudes. Artificial land‐ocean outlines ≤2 K do appear in maps of the NCEP/NCAR lower stratospheric Tb between 30°S and 30°N. This NCEP/NCAR land‐ocean Tb distinction may be due to sparseness of inputed radiosonde data at lower stratospheric heights not compensated for by satellite retrievals in the NCEP/NCAR assimilation process. In the upper troposphere, good agreement again occurs between the GFDL radiosonde, the CIRA, and the NCEP/NCAR reanalysis Tb. However, the experimental MSU channel 3R climatology has markedly cooler upper tropospheric Tb. Coolness peaks at over 6 K across low latitudes and diminishes to a few kelvins at polar latitudes with little seasonal dependence. The cool bias of the MSU channel 3R is likely due to a combination of channel 3 receiver drift and limb‐darkening problems. Latitudinal correction terms are suggested for this experimental, but valuable, MSU product based on comparisons with calculated NCEP/NCAR reanalysis Tb.

Numerical simulations of gravity waves imaged over Arecibo during the 10‐day January 1993 campaign

Recently, measurements were made of mesospheric gravity waves in the OI (5577 Å) nightglow observed from Arecibo, Puerto Rico, during January 1993 as part of a special 10‐day campaign. Clear, monochromatic gravity waves were observed on several nights. By using a full‐wave model that realistically includes the major physical processes in this region, we have simulated the propagation of two waves through the mesopause region and calculated the O(1S) nightglow response to the waves. Mean winds derived from both UARS wind imaging interferometer (WINDII) and Arecibo incoherent scatter radar observations were employed in the computations as were the climatological zonal winds defined by COSPAR International Reference Atmosphere 1990 (CIRA). For both sets of measured winds the observed waves encounter critical levels within the O(1S) emission layer, and wave amplitudes, derived from the requirement that the simulated and observed amplitudes of the O(1S) fluctuations be equal, are too large for the waves to be gravitationally stable below the emission layer. Some of the model coefficients were adjusted in order to improve the agreement with the measurements, including the eddy diffusion coefficients and the height of the atomic oxygen layer. The effect of changing the chemical kinetic parameters was investigated but was found to be unimportant. Eddy diffusion coefficients that are 10 to 100 times larger than presently accepted values are required to explain most of the observations in the cases that include the measured background winds, whereas the observations can be modeled using the nominal eddy diffusion coefficients and the CIRA climatological winds. Lowering the height of the atomic oxygen layer improved the simulations slightly for one of the simulated waves but caused a less favorable simulation for the other wave. For one of the waves propagating through the WINDII winds the simulated amplitude was too large below 82 km for the wave to be gravitationally stable, in spite of the adjustments made to the model parameters. This study demonstrates that an accurate description of the mean winds is an essential requirement for a complete interpretation of observed wave‐driven airglow fluctuations.

Variability in the mesosphere observed by the Nimbus 6 pressure modulator radiometer

The pressure modulator radiometer flew aboard Nimbus 6, collecting radiance data from June 1975 until June 1978. These data have been processed to yield daily temperatures, geopotential heights, and balance wind estimates from the stratosphere and mesosphere (30–85 km) for the entire period. We use these data to examine the variability of both the zonal‐mean and the nonzonal disturbances present in the data. In terms of the zonal‐mean, we show that the COSPAR International Reference Atmosphere (1986), developed from these data, can be misleading in the mesosphere due to the underlying interannual variability and the merging with other data sets. Daily variability of the zonal‐mean flow is examined, and these data show strong evidence of coupling between the stratosphere and mesosphere for such variations. We also find evidence for significant coupling of wave‐like events in the stratosphere and the mesosphere but that not all such disturbances seen in the mesosphere are due to simple propagation from below. Space‐time spectral analysis is used to search for traveling planetary waves: Results show a weak 5‐day normal mode present in the Equinox seasons, which appears to correspond to the first symmetric mode predicted by theory. These data also show clear evidence of the 4‐day wave in all three southern winters examined and are consistent with the hypothesis that this mode grows due to instability of the background zonal flow.

High-pulse-repetition-frequency lidar system using a single telescope for transmission and reception

The design, construction, and operation of a stratospheric Rayleigh lidar system is outlined. The lidar system was designed to operate as a Doppler lidar; however, for the first stage of the project it was set up to operate in a manner similar to a more conventional stratospheric Rayleigh lidar. This system includes a number of unique design features, including a high-pulse-repetition-frequency laser and the use of a single 1-m-diameter telescope for transmission of the laser pulse and reception of the backscattered light. An associated high-speed rotating shutter system switches the optical system from the transmission to the reception mode. The system was operated at Adelaide, Australia (35° S, 138° E). Scattering ratio and temperature profiles are calculated for data collected during the period from 10 March 1992 to 11 May 1993. The scattering ratio profiles clearly show the reduction in the scattering from the stratospheric aerosol layer. This is due to the removal of the aerosol injected by the eruption of Mt. Pinatubo. The measured relative density profiles show very good agreement with the Cospar international reference atmosphere model densities, as do the temperature profiles calculated from these.

POAM II: Early results and comparisons with the COSPAR International Reference Atmosphere ozone models

NRL's Polar Ozone and Aerosol Measurement Experiment (POAM II) makes solar occultation measurements through the earth's atmospheric limb to provide the distribution of atmospheric aerosols, PSC's, and several molecular species critical for understanding ozone chemistry in the polar stratosphere. The early results from POAM II are presently being validated against in situ balloon borne instruments and remote sensing measurements from both the surface and other satellite platforms. The monthly zonal mean profiles of the POAM II results will be compared with the CIRA (COSPAR International Reference Atmosphere) ozone models.

Improved ozone reference models for the COSPAR International Reference Atmosphere

Improved ozone reference models for the COSPAR International Reference Atmosphere

Comparison of models of middle atmosphere composition with observations

This is a review of some of the more recently published comparisons of models with middle atmosphere trace species measurements. The extent to which models emulate the actual chemical composition of the atmosphere is delineated by emphasizing areas where models have done poorly, or are in disagreement with each other, rather than areas where there is good agreement between models and measurements. The trace species discussed are primarily N 2O, HNO 3, NO 2, NO, NO 3, N 2O 5, HCl, ClONO 2, ClO, and ozone. It is hoped that these remarks on the relation of model results to the existing measurements will aid in the preparation of the future COSPAR International Reference Atmosphere of Trace Species.