Solar Mesosphere Explorer Research Articles

An Improved Lyman‐Alpha Composite

AbstractThe hydrogen Lyman‐alpha (Lyman α) line at 121.56 nm is the strongest solar vacuum ultraviolet emission line. Especially because of the impacts on planetary atmospheres, long‐term data sets of Lyman α are important for understanding solar and atmospheric processes. A revised composite data set of daily Lyman α values beginning in 1947 is constructed using measurements of Lyman α from Atmospheric Explorer E, Solar Mesospheric Explorer, Upper Atmosphere Research Satellite, and Solar Radiation and Climate Experiment. Gaps are filled using proxy models based on the Magnesium II index and the 10.7‐ and 30‐cm solar radio fluxes (F10.7 and F30).

Atomic hydrogen in the mesopause region derived from SABER: Algorithm theoretical basis, measurement uncertainty, and results

Atomic hydrogen (H) is a fundamental component in the photochemistry and energy balance of the terrestrial mesopause region (80–100 km). H is generated primarily by photolysis of water vapor and participates in a highly exothermic reaction with ozone. This reaction is a significant source of heat in the mesopause region and also creates highly vibrationally excited hydroxyl (OH) from which the Meinel band radiative emission features originate. Concentrations (cm−3) and volume mixing ratios of H are derived from observations of infrared emission from the OH (υ = 9 + 8, Δυ = 2) vibration-rotation bands near 2.0 µm made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. The algorithms for deriving day and night H are described herein. Day and night concentrations exhibit excellent agreement between 87 and 95 km. SABER H results also exhibit good agreement with observations from the Solar Mesosphere Explorer made nearly 30 years ago. An apparent inverse dependence on the solar cycle is observed in the SABER H concentrations, with the H increasing as solar activity decreases. This increase is shown to be primarily due to the temperature dependence of various reaction rate coefficients for H photochemistry. The SABER H data, coupled with SABER atomic oxygen, ozone, and temperature, enable tests of mesospheric photochemistry and energetics in atmospheric models, studies of formation of polar mesospheric clouds, and studies of atmospheric evolution via escape of hydrogen. These data and studies are made possible by the wide range of parameters measured simultaneously by the SABER instrument.

Ground-based radio observations to probe the ozone content in the meteor region

Radar studies of the plasma irregularities produced by meteoroid ablation provide a powerful diagnostic probe of the Earth's atmosphere. This role is especially important as an inexpensive route for studying several atmospheric processes in comparison with other remote sensing techniques or satellite measurements. Ozone concentration has been indirectly measured in the upper mesosphere/lower thermosphere region by the BLM (Bologna-Lecce-Modra) Forward Scatter (FS) meteor radar by the detection of meteoroids interacting with the Earth's atmosphere. Results of variations of mesospheric ozone concentration at different height levels and time scales were deduced in 1992-2000 from the cumulative duration distributions of overdense echoes. Data of the BLM radar obtained in the last millennium decade confi rm the existence of a secondary ozone layer at atmospheric heights of 85-90 km and show a gradual yearly depletion of the ozone content, similarly to the decrease measured in the eighties by the Solar Mesosphere Explorer (SME) satellite throughout consecutive years (Rusch et al., 1990). Radio observations show in addition large seasonal variations at middle latitudes where the abundance at a secondary ozone maximum at 85-90 km is found to be as much as a factor of two higher in spring months than that in summer months.

Ozone diurnal variations and mean profiles in the mesosphere, lower thermosphere, and stratosphere, based on measurements from SABER on TIMED

Ozone measurements from SABER on the TIMED satellite form a unique data set. They provide global information over the range of local solar times, from the lower stratosphere into the lower thermosphere, from the beginning of 2002, by one instrument. On the basis of zonal means of these data, we present new results from 20 to 100 km in altitude and from 48°S to 48°N in latitude, of ozone diurnal variations over 24 h in local solar time and over an annual cycle. While some of the results are new for the stratosphere, such comprehensive results for the mesosphere and lower thermosphere have not been available before. The diurnal variations generally become increasingly significant from the upper stratosphere into the lower thermosphere and provide information on the photochemistry of ozone and effects of transport over a diurnal cycle. Over most altitudes in the mesosphere and lower thermosphere (MLT), our estimates show the expected decrease in ozone after sunrise, with smaller variations during the day, and the increase near sunset. Outside of a small altitude near 80 km, the nighttime mixing ratios are generally larger than the daytime values. The diurnal variations themselves appear to exhibit variations over an annual cycle, including semiannual and annual variations. We compare the SABER results with data obtained about 10 years earlier by the MLS instrument on UARS, and with results by others based on data from HRDI on UARS, from the Solar Mesosphere Explorer (SME), from selected space shuttle experiments, and from ground‐based measurements. From the middle mesosphere to higher altitudes, departures from local thermodynamic equilibrium (non‐LTE) can be significant, and the uncertainties can be larger than those at lower altitudes.

Ozone quasi‐biennial oscillations (QBO), semiannual oscillations (SAO), and correlations with temperature in the mesosphere, lower thermosphere, and stratosphere, based on measurements from SABER on TIMED and MLS on UARS

The ozone and temperature measurements from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on the Thermosphere‐Ionosphere‐Mesosphere‐Energetics and Dynamics (TIMED) satellite form a unique set. They provide global information over the range of local solar times, from the lower stratosphere into the lower thermosphere, going back to 2002, by one instrument. On the basis of zonal means of these data, we present new results from 20 to 100 km in altitude and from 48°S to 48°N in latitude of ozone and temperature semiannual oscillations (SAO) and quasi‐biennial oscillations (QBO). While some of the results are new for the stratosphere, such results for the mesosphere and lower thermosphere (MLT) have not been available before. The SAO and QBO components are mostly symmetric with respect to the Equator. The correlations of ozone and temperatures provide the opportunity to study the relative effects of dynamics and chemistry. Our results show that the ozone oscillations are largely and positively correlated to those of the temperature below about 30 km and above 80 km, and mostly anti‐correlated with temperature between about 30 and 80 km. We compare with measurements made about 10 years earlier by the MLS instrument on UARS, and with results by others from the solar mesosphere explorer (SME) satellite, the solar backscatter ultraviolet (SBUV), space shuttle experiments (CRISTA), and ground‐based measurements.

Seasonal–latitudinal variations of PMC particle size from SME measurements for the northern 1983 season and SNOE measurements for the northern 2000 and southern 2000/2001 seasons

The ultraviolet spectrometers (UVS) on the solar mesosphere explorer (SME) and student nitric oxide explorer (SNOE) measured scattered limb radiance at small and large scattering angles from polar mesospheric clouds (PMCs). The SME data are for the northern summer hemisphere (NH) in 1983 and 1984. The SNOE measurements are for the NH in 2000 and for the southern hemisphere (SH) in the 2000/2001 season. From this database, we deduce the modal particle size from the measured scattering angle asymmetry in radiance. This quantity is determined as a function of time within the PMC season, and latitude, assuming several scattering models depending on the adopted size distribution and particle shape. For assumed spherical particles with a Gaussian distribution of width of 14 nm, the results for SME show mode particle sizes that vary from about 35 to 60 nm throughout the season. The results for SNOE under the same assumption show that for high latitudes in the NH the particle size grows systematically from the seasonal onset, from about 25 nm to a maximum of about 45 nm at 30 days after solstice. Lower latitudes show a similar time dependence, but with smaller particle sizes. SH PMC particle sizes display a more complicated seasonal variability. Generally, variability in measured cloud height is anti-correlated with particle size for the seasons analyzed here. Particle sizes in the SH are generally smaller than those in the NH, consistent with the northern bias in PMC brightness, and with previous satellite studies. These results are interpreted in terms of our understanding of PMC microphysics and inter-hemispheric differences in temperature and dynamics. Our quantitative results for mode radius depend on the assumption of a constant distribution width. If the width varies with latitude or time, our calculated gradients of mode radius would be different.

Properties of polar mesospheric clouds measured by Odin/OSIRIS in the northern hemisphere in 2002–2005

Interseasonal variations in the properties of Polar Mesospheric Clouds (PMC) measured by the Optical Spectrograph and InfraRed Imager System (OSIRIS) on the Odin satellite during the northern hemisphere (NH) summers of 2002–2005 are described in this work. The lowest PMC latitudes were about 50°N for every season with the number of detections smallest in 2002 and largest in 2004. In 2004 and 2005, the detection of PMCs at lower latitudes was asymmetric with the larger number of clouds observed during the first half and fewer at during the second half of the season. PMC occurrence frequency in 2002 was 25–30% lower than in 2003–2005, and the season duration was shortest in 2002 and longest in 2004. For all NH seasons except 2002, PMC occurrence frequency was systematically 20–50% higher than the Solar Mesosphere Explorer climatology. Similar to PMC occurrence frequency, cloud brightness was lowest in 2002 and highest in 2004 at all latitudes. The daily mean brightness maximum at 50°–60°N was less than 8% of that at highest latitudes. This contrasts with the maximum PMC occurrence frequency that reached nearly 30% at these latitudes in 2004 and 2005. PMC brightness showed no apparent seasonal asymmetry at lower latitudes in 2004 and 2005 that was seen in the occurrence frequency. Significant, by about a factor of 2, oscillations observed in the daily mean cloud brightness at high latitudes were also not seen in the corresponding occurrence frequency. These results suggest that the occurrence frequency alone does not provide detailed information on the cloud population and ice mass in the mesosphere. There is no significant interannual variability in the seasonal mean OSIRIS PMC altitude. Its value was very close to 8350 km for all seasons except 2004 when it was 83.42 km. The mean PMC altitudes for each season increased by 0.3–0.6 when the minimum altitude in the database was increased from 80 to 82 km. PACS Nos.: 92.05.Fg, 92.60.hc, 92.60.Jq, 92.60.Mt, 92.60.Nv, 92.60.Vb

A simple but accurate ultraviolet limb-scan spherically-layered radiative-transfer-model based on single-scattering physics

Here we present a study focusing on atmospheric limb-scattered radiative characteristics in the ultraviolet band by using a limb-scan spherically-layered radiative-transfer-model based on the single-scattering approximation, which was developed by the present authors. We have applied an accurate numerical integration technique involving an auto-adaptive modified-space step, which assured high accuracy and simplification. Comparisons were made to the newly released spherical radiative transfer model, SCIATRAN2.0, which was developed by Institute of Remote Sensing/Institute of Environmental Physics (IUP/IFE) at University of Bremen and to measurements collected via an ultraviolet spectrometer on the Solar Mesospheric Explorer (SME) satellite, which was launched in October, 1981. Preliminary results indicate that the present model provides a good interpretation of the earth-limb scattered ultraviolet radiance, and thus, is suitable for the study of the ultraviolet-limb radiative-transfer problem with high accuracy.

Observations of polar mesospheric clouds by the Student Nitric Oxide Explorer

Polar Mesospheric Clouds (PMCs) were observed by a limb‐scanning ultraviolet spectrometer on the Student Nitric Oxide Explorer (SNOE). Radiance profiles at 215 and 237 nm are analyzed to determine the presence of clouds. Once detected, the altitude and brightness of a cloud relative to the background atmosphere is determined. SNOE observations provide the frequency of occurrence of PMC as a function of location and time for the years 1998 through 2003. The observations show at high latitudes a general rise in frequency of occurrence beginning approximately 3 weeks before summer solstice in both hemispheres and lasting for approximately 1 week. These rises are followed by approximately 60 days of relatively high but variable occurrence frequencies. The declines in frequency of occurrence at the ends of the seasons are generally slower and more structured then the beginning of the seasons. One of the major results from the SNOE observations is that significantly more PMCs are observed in the Northern Hemisphere than in the south, leading us to conclude that the southern polar mesosphere must be on average less saturated than the northern polar mesosphere. The SNOE observations also suggest that the frequency of occurrence of PMCs is strongly modulated by local dynamical influences. The SNOE results are in general agreement with results from the Solar Mesosphere Explorer which observed PMC with similar instrumentation in the years 1981 through 1986.

Global variability of mesospheric temperature: Mean temperature field

Daytime zonally (longitudinally) averaged temperatures from the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS) and nightly temperatures from various ground‐based hydroxyl airglow observations are employed in the study of the global and seasonal variability of the upper mesospheric temperature field. The study examines the latitudinal variability of the annual cycle of mesospheric temperature at 75, 82, and 87 km employing 7 years (1991–1997) of WINDII mesospheric temperature data at latitudes from 20°S to 65°N at 75 km, 35°S to 65°N at 82 km, and from 45°S to 65°N at 87 km height. Particular attention is given to the latitude region of ±40° around the equator. Harmonic analysis of the 7‐year temperature time series reveals the presence of a dominant annual, ∼90‐ and 60‐day oscillations at high northern latitudes and a strong semiannual oscillation (SAO) at equatorial and tropical latitudes. A quasi‐biennial oscillation (QBO) is also identified extending from 45°S to 65°N. At 75 km the SAO is manifested as minima in the temperature composites at spring and fall equinox and maxima at winter and summer solstice; at 87 km the SAO is out of phase with respect to the 75‐km SAO, with maxima at equinox and minima around the solstice periods. The phase reversal takes place around 82 km and is associated with a mesospheric temperature inversion between 77 and 86 km height. Accounting for tidal contribution by adopting tidal predictions by the Extended Canadian Middle Atmosphere Model (CMAM) shows that a strong temperature decrease (∼35 K) seen during the 1993 March equinox at equatorial and tropical latitudes is not associated with solar migrating tides. WINDII global climatology derived at 75, 82, and 87 km revealed mesospheric SAO asymmetry with a stronger September equinox and interhemispheric asymmetry with a quieter and colder southern hemisphere. Comparisons with independent ground‐based observations and the Solar Mesospheric Explorer (SME) satellite data are also presented showing good to excellent agreement in the derived annual and SAO parameters. The results presented provide the first high‐vertical‐and‐temporal resolution global daytime temperature climatology in the upper mesosphere and in the vicinity of the mesopause.

Recent observations of mesospheric temperature inversions over a tropical station (13.5°N,79.2°E)

Present study mainly deals with recent observations of mesospheric temperature inversions (MTI) over Gadanki (13.5° N, 79.2° E) , a tropical station in India using for about 40 months of Nd:YAG lidar data. Long-term measurements of halogen occultation experiment, high resolution Doppler imager on board upper atmospheric research satellite and solar mesospheric explorer have been used to compare the characteristics (amplitude, height and percentage of occurrences) of the inversions observed with ground-based lidar measurements for the first time. In general, the height and percentage occurrence of the inversions are matching well between ground and satellite based measurements most of the time and there exists a large discrepancy in the amplitudes of MTI measured by these instruments as expected. The height occurrence of these inversions is at ∼76 km and for about 60% of the time, strong inversions can be seen at this tropical latitude. The height occurrence of the inversions shows annual oscillation with peak during summer and minimum in winter. The percentage occurrences of these inversions are showing semi-annual oscillation with peak during equinoxes and minimum during solstice. The possible causative mechanism for the frequent occurrence of these inversions over this tropical latitude are explained in light of current understanding of the gravity wave activity and also with the chemical heating/cooling taking place at these heights.

Three‐satellite comparison of polar mesospheric clouds: Evidence for long‐term change

Measurements of polar mesospheric clouds (PMCs) from three different satellite instruments are compared. These instruments are the Solar Mesospheric Explorer (SME), the Wind Imaging Interferometer (WINDII), and the Polar Ozone and Aerosol Measurement (POAM II). These measurements have been put on a common basis, correcting for differences in the wavelengths and measurement techniques used. This common basis is the probability distribution of the excess extinction ratio (EER) at a standard wavelength of 265 nm, where the EER is the ratio of the PMC extinction coefficient to the background molecular Rayleigh scattering coefficient. The results indicate that the POAM and WINDII measurements in the Southern Hemisphere had a higher probability of observing bright PMCs during the 1993–1996 time period than SME did a decade earlier in 1983–1986. Local time variations identified in WINDII data are interpreted in terms of a diurnal and semidiurnal component of average EER. These results are qualitatively similar to those found from lidar soundings of noctilucent cloud at sites in Norway and at the South Pole. Differences in interannual variability, local time of the measurements, assumed particle size distributions, and solar cycle effects are ruled out as possible explanations of the differences.

Validating the solar EUV Proxy, E10.7

A demonstration of the improvement in thermospheric densities using the daily E10.7 proxy compared to F10.7 is shown. The daily altitude decay for the Solar Mesosphere Explorer (SME) satellite from April 1, 1982 through August 9, 1983, using both proxies and the actual altitude data, are compared. The F10.7 case finished 2 km lower than each of the E10.7 and actual altitude cases which were nearly identical. During active solar conditions, daily F10.7 can overestimate the EUV energy input into the atmosphere by up to 60% and also underestimate it by as much as 50%. Progress is shown towards validating E10.7 as a more accurate proxy compared to F10.7 for use in atmospheric density calculations that are applicable to satellite drag problems. In support of the validation of the E10.7 proxy, an operational prototype hardware/software platform for visualizing of the near‐Earth space environment was created. This platform uses a data‐driven, data visualization environment. Platform development continues so as to accommodate not only historical data but also nowcast and forecast data streams. Upgrades to the SOLAR2000 Research Grade model are continuing in order to improve the correlation coefficients from multiple linear regressions in several wavelength regions. E10.7 is used in applications that incorporate F10.7, including empirical thermospheric models, ionospheric models, and general representations of solar activity ranging from climate research to engineering applications.

Spectral solar UV irradiance data for cycle 21

The Nimbus 7 Solar Backscatter Ultraviolet (SBUV) instrument, which began taking data in November 1978, was the first instrument to make solar UV irradiance measurements covering both the minimum and maximum activity levels of a solar cycle. The currently archived irradiance data set was processed with an instrument characterization which fails to completely account for sensor degradation in the later part of the data record, thus limiting the accuracy of estimated long‐term solar activity variations and the scientific value of the data. In this paper, we describe an improved Nimbus 7 SBUV spectral irradiance data set, which utilizes a more accurate model for instrument sensitivity and treats other time‐dependent problems in the archived data. Estimated long‐term irradiance changes during solar cycle 21 are 8.3(±2.6)% at 205 nm, and 4.9(±1.8)% at 240 nm. The revised Nimbus 7 SBUV irradiance data are in good agreement with predictions of solar cycle variations from the Mg II index proxy model. These solar irradiance changes are also consistent with overlapping irradiance data from the declining phase of solar cycle 21 measured by the Solar Mesosphere Explorer (SME). The Nimbus 7 SBUV irradiance data represent the earliest component of a 20+ year continuous record of solar spectral UV activity.

Improved solar Lyman α irradiance modeling from 1947 through 1999 based on UARS observations

The solar Lyman α radiation is the brightest solar vacuum ultraviolet (VUV: λ < 200 nm) emission, and this radiation is deposited in Earth's atmosphere above 70 km. The Lyman α irradiance and its variability are therefore important for many studies of the Earth's upper atmosphere. A long‐term data set of the solar Lyman α irradiance from 1947 through 1999 is constructed using the measurements from the Atmospheric Explorer E (AE‐E), the Solar Mesospheric Explorer (SME), and the Upper Atmosphere Research Satellite (UARS) along with predictions from proxy models to fill in data gaps and to extrapolate back to 1947. The UARS measurement is used as the reference, and the AE‐E and SME measurements and the proxy models are adjusted to agree with the UARS values. The estimated 1‐σ uncertainty for this long‐term Lyman α time series is 10%. The average solar rotation (27‐day) variability in Lyman α is 9% from this composite times series, and the solar rotation variability averaged over 2 years at solar minimum and maximum conditions is 5 and 11%, respectively. The average solar cycle (11‐year) variability is a factor of 1.5 when the data are smoothed over 2 years, and the extreme Lyman α variability is a factor of 2.1. The Lyman α irradiances averaged over 2 years during solar minimum and maximum conditions are 3.7 and 5.6 × 1011 photons s−1 cm−2, respectively. The proxy models include three components to better fit the UARS measurements; nonetheless, there remain differences between the proxy models and the observed Lyman α irradiance, which are related to the source of the Lyman α radiation being different than that for the proxies. The available proxies are primarily chromospheric and coronal emissions, whereas the Lyman α variability is manifested more in the transition region. It is shown that emissions throughout the chromosphere, transition region, and corona vary differently mainly because their contrasts for active network and plage components are different. A transition region proxy is needed to improve the empirical proxy models of solar irradiance, and this composite Lyman α time series could serve as a proxy for other transition region emissions.

Ground-based millimeter-wave observations of ozone in the upper stratosphere and mesosphere over Tsukuba

We present ground-based millimeter-wave observations of the upper stratospheric and mesospheric ozone, conducted at the National Institute for Environmental Studies (NIES) in Tsukuba, Japan (36°N, 140°E). The measurements were started in October 1995. The millimeter-wave radiometer used for the present study is equipped with the superconductor-insulator-superconductor (SIS) mixer receiver and the acousto-optical spectrometer (AOS). Vertical profiles of ozone mixing ratio from 20 to 80 km were retrieved from the observed ozone spectra for 23 months from October 1996 to August 1998 by using the weighted-damped least squares algorithm adopted for differential emission. Vertical resolution is estimated to be 14 km from the averaging kernels. The total random error on the retrieval is estimated to range from 3 to 13% in summer, and from 2 to 9% in winter, respectively, between 38 and 76 km in altitude. The ozone number density at 38 km with the radiometer which was convolved with the vertical resolution of the lidar agrees well with that of the lidar within a systematic difference of 1%, indicating that the millimeter-wave data at 38 km are validated by the lidar measurements. Annual and semi-annual variations are clearly seen at 50 and 76 km, respectively, in the time series of the ozone mixing ratio observed during 23 months. The annual variation at 50 km is consistent with that in the climatological models. The semi-annual variation at 76 km observed in this work is similar to that of the Solar Mesospheric Explorer (SME) data, except that the ozone mixing ratio in spring measured with SME is about 1.7 times larger than that in autumn while those with the radiometer are almost same.

Lower thermospheric nitric oxide concentrations derived from WINDII observations of the green nightglow continuum at 553.1 nm

Abstract. Vertical profiles of nitric oxide in the altitude range 90 to 105 km are derived from 553 nm nightglow continuum measurements made with the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS). The profiles are derived under the assumption that the continuum emission is due entirely to the NO+O air afterglow reaction. Vertical profiles of the atomic oxygen density, which are required to determine the nitric oxide concentrations, are derived from coordinated WINDII measurements of the atomic oxygen OI 557.7 nm nightglow emission. Data coverage for local solar times ranging from 20 h to 04 h, and latitudes ranging from 42°S to 42°N, is achieved by zonally averaging and binning data obtained on 18 nights during a two-month period extending from mid-November 1992 until mid-January 1993. The derived nitric oxide concentrations are significantly smaller than those obtained from rocket measurements of the airglow continuum but they do compare well with model expectations and nitric oxide densities measured using the resonance fluorescence technique on the Solar Mesosphere Explorer satellite. The near-global coverage of the WINDII observations and the similarities to the nitric oxide global morphology established from other satellite measurements strongly suggests that the NO+O reaction is the major source of the continuum near 553 nm and that there is no compelling reason to invoke additional sources of continuum emission in this immediate spectral region.Key words. Atmospheric composition and structure (airglow and aurora; thermosphere – composition and chemistry; instruments and techniques)

Rayleigh lidar observations of temperature over Tsukuba: winter thermal structure and comparison studies

Routine lidar observations are in progress at the National Institute for Environmental Studies (NIES), Tsukuba, Japan (36°N, 140°E), providing vertical profiles of ozone and temperature in the stratosphere and lower mesosphere. The present study focuses the winter thermal structure over Tsukuba and validation/comparison of the lidar derived temperature profiles. Atmospheric temperatures for the altitude region 30–75 km are determined from the neutral density profiles. 33 temperature observations recorded during the winter months of 1995 and 1996 are used in the study. Winter thermal structure is characterized with its variability with an observed stratopause temperature of about 260 K. Although evidence of minor stratospheric warming is seen on some days, there appears to be no direct linkage with major mid winter warmings at the poles. Temperature profiles show evidence of mesospheric temperature inversion layers. For the purpose of validation/comparison of the lidar temperature profiles, other datasets based on rocketsondes, National Meteorological Center (NMC) analyses, Solar Mesosphere Explorer (SME) spacecraft measurements, and CIRA 86 have been used. Encouraging agreements between the lidar and rocket profiles are evident, which confirms the potential of lidar technique for deriving the absolute temperatures in the atmosphere. Climatological comparisons also reveal satisfactory agreement between the lidar and other datasets.

Ozone concentration at meteor heights determined from forward-scatter radar echoes

The ozone concentration has been measured in the meteor zone using a method of radar echo duration distribution suggested by Jones and Šimek (1995). Data obtained by the forward-scatter system during the Lyrid meteor shower period in five consecutive years 1992–1996 agree with the Solar Mesosphere Explorer results for the same heights of 95 km. The mean value of the ozone concentration [O 3]=(1.56±0.05)×10 14 m −3 has been derived from a total of 6596 radar meteor echoes with duration ≥1 s. The results for individual years indicating a possible decrease in [O 3] are discussed.

Interplanetary Lyman α observations from Pioneer Venus over a solar cycle from 1978 to 1992

The Pioneer Venus Orbiter ultraviolet spectrometer (PVOUVS) routinely obtained interplanetary hydrogen Lyman α data while viewing ecliptic latitudes near 30°S from 1978 to 1992 (during solar cycles 21 and 22). We describe “hot” models for this interplanetary Lyman α data that include the solar cycle variation of (1) the solar flux, as a function of latitude and longitude; (2) the radiation pressure on hydrogen atoms; (3) the solar wind flux; (4) the solar EUV flux; and (5) the multiple scattering correction to an optically thin radiative transfer model. These models make use of solar radiation flux parameters (solar wind, solar EUV, and solar Lyman α) from spacecraft and ground‐based solar proxy observations. Comparison of the upwind data and model indicates that the ratio of the solar Lyman α line center flux (responsible for the interplanetary signal) to the observed solar Lyman α integrated flux is constant to within ∼20%, with an effective line width near 1.1 Å. Averaging the solar radiation pressure and hydrogen atom lifetime over 1 year before the observation reproduces the upwind intensity time variation but not the downwind. A better fit to the downwind time series is found using the 1 year average appropriate for the time that the atoms passed closest to the sun. Solar Lyman α measurements from two satellites are used in our models. Upper Atmosphere Research Satellite (UARS) solar Lyman α measurements are systematically higher than Solar Mesosphere Explorer (SME) values and have a larger solar maximum to solar minimum ratio. UARS‐based models work better than SME‐based models in fitting the PVOUVS downwind time series Lyman α data.