Upper Atmosphere Research Satellite Research Articles

Middle atmospheric thermal structure over sub-tropical and tropical Indian locations using Rayleigh lidar

Earth's middle atmospheric thermal structure is unique, and having imprints of various physical and chemical processes taking place in the Earth's atmosphere. Nd-YAG laser based Rayleigh lidars are operational at Mt. Abu (24.5°N, 72.7°E) and at Gadanki (13.5°N, 79.2°E) to study the middle atmospheric temperature structure in the altitude region of 30–75km. Temperature profiles are derived using Rayleigh lidar measured neutral density profiles. Nightly mean temperature profiles, during 1997–2001, are utilized to obtain average temperature profile for each month over Mt. Abu. Lidar observed temperatures are compared with the temperatures observed by Halogen Occultation Experiment (HALOE), on-board Upper Atmospheric Research Satellite (UARS), the CIRA-86 and MSISE-90. Observed temperature profiles are in qualitative agreement with CIRA-86 and MSISE-90 model below 50km, and the agreement is better during winter months. Quantitatively there are significant differences noted, up to 10K, above 50km. The temperature profiles are also compared with the equatorial model for the Indian region, based on rocket and balloon measurements. Significant day to day variability is found, which is as high as ±10K at ∼70km. The mean values of the stratopause height and temperature are found to be 48km and 271K, respectively. Seasonal variation shows equinoctial and summer maxima below 55km, whereas above 70km winter maximum with equinoctial minima are present. Comparative study of thermal structure with Gadanki, a tropical station, revealed significant differences in the thermal structure over tropical and sub-tropical locations.

UV solar irradiance low during recent solar minimum

Solar irradiance, which varies with the 11‐year solar cycle and on longer time scales, can affect temperatures and winds in the atmosphere, influencing Earth's climate. As the Sun currently wakes up from a period of low sunspot activity, researchers want to know how irradiance during the recent solar minimum compares to historical levels. In addition to understanding the total received power, it is important to know how various spectral bands behave, in particular, the ultraviolet, which causes heating and winds in the stratosphere. Lockwood analyzed solar ultraviolet spectral irradiance data from May 2003 to August 2005 from both the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) instrument on board the Upper Atmosphere Research Satellite (UARS) and the Solar Stellar Irradiance Comparison Experiment (SOLSTICE) instrument on the Solar Radiation and Climate Experiment (SORCE) satellite. Using several different methods to intercalibrate the data, he developed a data composite that can be used to determine differences between the recent solar minimum and previous minima. The author found that solar irradiance during the recent sunspot minimum has been especially low. (Journal of Geophysical Research‐Atmospheres, doi:10.1029/2010JD014746, 2011)

Was UV spectral solar irradiance lower during the recent low sunspot minimum?

[1] A detailed analysis is presented of solar UV spectral irradiance for the period between May 2003 and August 2005, when data are available from both the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) instrument (on board the Upper Atmosphere Research Satellite (UARS) spacecraft) and the Solar Stellar Irradiance Comparison Experiment (SOLSTICE) instrument (on board the Solar Radiation and Climate Experiment (SORCE) satellite). The ultimate aim is to develop a data composite that can be used to accurately determine any differences between the “exceptional” solar minimum at the end of solar cycle 23 and the previous minimum at the end of solar cycle 22 without having to rely on proxy data to set the long-term change. SUSIM data are studied because they are the only data available in the “SOLSTICE gap” between the end of available UARS SOLSTICE data and the start of the SORCE data. At any one wavelength the two data sets are considered too dissimilar to be combined into a meaningful composite if any one of three correlations does not exceed a threshold of 0.8. This criterion removes all wavelengths except those in a small range between 156 nm and 208 nm, the longer wavelengths of which influence ozone production and heating in the lower stratosphere. Eight different methods are employed to intercalibrate the two data sequences. All methods give smaller changes between the minima than are seen when the data are not adjusted; however, correcting the SUSIM data to allow for an exponentially decaying offset drift gives a composite that is largely consistent with the unadjusted data from the SOLSTICE instruments on both UARS and SORCE and in which the recent minimum is consistently lower in the wave band studied.

Latitudinal variation of trends in ClO in the vertical structure of the tropical–subtropical stratosphere

Trends in chlorine monoxide (ClO) over the tropical–subtropical stratosphere (40° S–40° N) have been studied by analysing data from the Microwave Limb Sounder (MLS) onboard the Upper Atmospheric Research Satellite (UARS) for the period 1991–1999 using the multifunctional regression model. Trends in ClO show latitudinal variation and they are almost symmetrical around the equator. Trend profiles reveal negative trends in the middle stratosphere (46–30 mb), no trends near 20 mb and then positive trends in the upper stratosphere. A negative maximum near 46 mb and a positive maximum near 6.8–4.6 mb level is observed over the tropical and subtropical belts.

Coherence of long-term stratospheric ozone vertical distribution time series used for the study of ozone recovery at a northern mid-latitude station

Abstract. The coherence of stratospheric ozone time series retrieved from various observational records is investigated at Haute-Provence Observatory (OHP–43.93° N, 5.71° E). The analysis is accomplished through the intercomparison of collocated ozone measurements of Light Detection and Ranging (lidar) with Solar Backscatter UltraViolet(/2) (SBUV(/2)), Stratospheric Aerosol and Gas Experiment II (SAGE~II), Halogen Occultation Experiment (HALOE), Microwave Limb Sounder (MLS) on Upper Atmosphere Research Satellite (UARS) and Aura and Global Ozone Monitoring by Occultation of Stars (GOMOS) satellite observations as well as with in situ ozonesondes and ground-based Umkehr measurements performed at OHP. A detailed statistical study of the relative differences of ozone observations over the whole stratosphere is performed to detect any specific drift in the data. On average, all instruments show their best agreement with lidar at 20–40 km, where deviations are within ±5 %. Discrepancies are somewhat higher below 20 and above 40 km. The agreement with SAGE II data is remarkable since average differences are within ±1 % at 17–41 km. In contrast, Umkehr data underestimate systematically the lidar measurements in the whole stratosphere with a near zero bias at 16–8 hPa (~30 km). Drifts are estimated using simple linear regression for the data sets analysed in this study, from the monthly averaged difference time series. The derived values are less than ±0.5 % yr−1 in the 20–40 km altitude range and most drifts are not significant at the 2σ level. We also discuss the possibilities of extending the SAGE II and HALOE data with the GOMOS and Aura MLS data in consideration with relative offsets and drifts since the combination of such data sets are likely to be used for the study of stratospheric ozone recovery in the future.

The Solar Ultraviolet Spectrum Estimated Using the Mg ii Index and Ca ii K Disk Activity

As part of a program to estimate the solar spectrum back to the early twentieth century, we have generated fits to UV spectral irradiance measurements from 1 – 410 nm. The longer wavelength spectra (150 – 410 nm) were fit as a function of two solar activity proxies, the Mg ii core-to-wing ratio, or Mg ii index, and the total Ca ii K disk activity derived from ground based observations. Irradiance spectra at shorter wavelengths (1 – 150 nm) where used to generate fits to the Mg ii core-to-wing ratio alone. Two sets of spectra were used in these fitting procedures. The fits at longer wavelengths (150 to 410 nm) were derived from the high-resolution spectra taken by the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) on the Upper Atmospheric Research Satellite (UARS). Spectra measured by the Solar EUV Experiment (SEE) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite were used for the fits at wavelengths from 1 to 150 nm. To generate fits between solar irradiance and solar proxies, this study uses the above irradiance data, the NOAA composite Mg ii index, and daily Ca ii K disk activity determined from images measured by Big Bear Solar Observatory (BBSO). In addition to the fitting coefficients between irradiance and solar proxies, other results from this study include an estimated relationship between the fraction of the disk with enhanced Ca ii K activity and the Mg ii index, an upper bound of the average solar UV spectral irradiance during periods where the solar disk contains only regions of the quiet Sun, as was believed to be present during the Maunder Minimum, as well as results indicating that slightly more than 60% of the total solar irradiance (TSI) variability occurs between 150 and 400 nm.

Ground-based measurements of ClO from Mauna Kea and intercomparisons with Aura and UARS MLS

[1] The ground-based measurements of upper stratospheric ClO, made with a ground-based millimeter wave instrument at Mauna Kea, Hawaii (19.8°N, 204.5°E) starting in 1992, are compared with UARS (Upper Atmosphere Research Satellite) MLS ClO measurements (1991–1998) and the Aura MLS ClO measurements (2004–2009). The ground-based measurements are made as part of the Network for the Detection of Atmospheric Composition Change (NDACC). Intercomparisons between the ground-based measurements and the Aura MLS measurements show that both instruments retrieve similar seasonal variations over Mauna Kea. The seasonal variation in ClO is also compared with measurements of variations in stratospheric CH4, which affects the partitioning of total inorganic chlorine. Using the ground-based instruments as a transfer standard, we find that the agreement between UARS and Aura MLS ClO measurements near the peak of the mixing ratio profile is within ∼1%. Combining the uncertainties in the biases calculated from the coincident ground-based and satellite measurements, we find that using the ground-based data as a transfer standard allows us to provide a 2σ limit to the bias between the UARS and Aura measurements of 3%–4% near the peak of the ClO profile. Given agreement between UARS and Aura MLS of ∼1% ± 4%, there is no reason to apply any bias correction in order to use the UARS and Aura MLS ClO measurements as a single data set.

Decadal solar signal in ozone and temperature through the mesosphere of Northern tropics

To investigate the effects of decadal solar variability on ozone and temperature in the mesosphere of the Northern tropics, data obtained from the Halogen Occultation Experiment (HALOE) aboard Upper Atmospheric Research Satellite (UARS) during the period 1992–2005 are analyzed using a multifunctional regression model. The inferred annual-mean solar signal in ozone is found to be insignificant in the lower mesosphere whereas it is of the order of 5%/100sfu in the upper mesosphere. Seasonal variation of ozone response to solar variability indicates a strong positive response (22–30%/100sfu) during summer and autumn between 5E-3 and 0.01mb pressure levels (∼80–85km). The annual mean temperature response is found to be of the order of 0.5–1K/100sfu. Significant positive temperature response is observed during winter and autumn in the lower mesosphere and during summer and spring in the upper mesosphere. Results obtained in the present study are also compared with the results obtained by other workers.

Solar spectral irradiance variability in the ultraviolet from SORCE and UARS SOLSTICE

The SOLar-STellar Irradiance Comparison Experiment (SOLSTICE) on the SOlar Radiation and Climate Experiment (SORCE) has been measuring the solar spectral irradiance on a daily basis since early 2003. This time period includes near-solar maximum conditions, the Halloween storms of 2003, and solar minimum conditions. These results can be compared to observations from the SOLSTICE I experiment that flew on the Upper Atmosphere Research Satellite (UARS) during the decline of the previous solar cycle as well as with currently operating missions. We will discuss similarities and differences between the two solar cycles in the long-term ultraviolet irradiance record.

Solar cycle variability in middle atmospheric ozone over tropics

To investigate the effects of decadal solar variability in ozone, data obtained from the Halogen Occultation Experiment (HALOE) onboard Upper Atmospheric Research Satellite (UARS) during the period 1992–2004 have been analysed using a multifunctional regression model. Solar effects on ozone are analysed over the 0–30˚ N and 0–30˚ S belts. The solar effect on ozone is found to be significant in most of the stratosphere (2 ± 1.1 to 4 ± 1.6%/100 sfu). It is negligible in the lower mesosphere whereas it is of the order of 5%/100 sfu in the upper mesosphere. These observed results are in reasonable agreement with model simulations. Results indicate a hemispheric symmetry in the tropics. Results obtained in the present study are also compared with the results obtained by other workers.

Direct observations of nonmigrating diurnal tides in the equatorial thermosphere

We present direct observations of nonmigrating diurnal tides in the 90–270 km range inferred from the Upper Atmosphere Research Satellite (UARS) wind imaging interferometer (WINDII). A prominent zonal wavenumber 4 appears in daytime zonal winds, extending to 180 km. We interpret this signature as an eastward‐propagating diurnal wavenumber 3 (DE3) viewed from the satellite perspective. This evidence of the extended upward propagation of DE3 demonstrates that it acts as a direct coupling agent between the troposphere and the thermosphere (and F‐region), in addition to its role in the E‐region dynamo.

Validation of the Harvard Lyman‐α in situ water vapor instrument: Implications for the mechanisms that control stratospheric water vapor

Building on previously published details of the laboratory calibrations of the Harvard Lyman‐α photofragment fluorescence hygrometer (HWV) on the NASA ER‐2 and WB‐57 aircraft, we describe here the validation process for HWV, which includes laboratory calibrations and intercomparisons with other Harvard water vapor instruments at water vapor mixing ratios from 0 to 10 ppmv, followed by in‐flight intercomparisons with the same Harvard hygrometers. The observed agreement exhibited in the laboratory and during intercomparisons helps corroborate the accuracy of HWV. In light of the validated accuracy of HWV, we present and evaluate a series of intercomparisons with satellite and balloon borne water vapor instruments made from the upper troposphere to the lower stratosphere in the tropics and midlatitudes. Whether on the NASA ER‐2 or WB‐57 aircraft, HWV has consistently measured about 1–1.5 ppmv higher than the balloon‐borne NOAA/ESRL/GMD frost point hygrometer (CMDL), the NOAA Cryogenic Frost point Hygrometer (CFH), and the Microwave Limb Sounder (MLS) on the Aura satellite in regions of the atmosphere where water vapor is <10 ppmv. Comparisons in the tropics with the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite show large variable differences near the tropopause that converge to ∼10% above 460 K, with HWV higher. Results we show from the Aqua Validation and Intercomparison Experiment (AquaVIT) at the AIDA chamber in Karlsruhe do not reflect the observed in‐flight differences. We illustrate that the interpretation of the results of comparisons between modeled and measured representations of the seasonal cycle of water entering the lower tropical stratosphere is dictated by which data set is used.

Search for periodicities of the Solar Irradiance Data from Earth Radiation Budget Satellite (ERBS) using Rayleigh Power Spectrum Analysis

The solar irradiance data plays a very important role for understanding of Solar internal Structure and the solar terrestrial relationships. The Total Solar Irradiance (TSI) is integrated solar energy flux over the entire spectrum which arrives at the top of the atmosphere at the mean sun earth distance. TSI has been monitored from several satellites, e.g. Nimbus 7, Solar Maximum Mission (SMM), The NASA, Earth Radiation Budget Satellite (ERBS), NOAA9, NOAA10, Eureca and the Upper Atmospheric Research Satellite (UARS) etc. From these observations it reveals that the total solar irradiance varies about a small fraction of 0.1 over solar cycle being higher during maximum solar activity condition. In the present paper we have analysed the solar irradiance data from ERBS during the time period from October 15, 1984 to October 15, 2003. First filtering the data by Simple Exponential Smoothing we have applied the Rayleigh Power Spectrum Analysis on the processed data in order to search for its time variation. Study exhibits multi-periodicities on these data around 7, 11, 42, 80, 104, 130, 160, 254, 536, 752, 1142, 1388, 2474 and 4951 days with very high confidence levels (more than 95%). Apart from these strong periods there are some other weak periods around 22, 47, 53, 67, 69, 149, 167, 365, 489 and 683 days. These periods are significantly similar with the periods of other solar activities which may suggest that solar irradiance may be associated with other solar activities.

Gravity wave temperature variance calculated using the ray‐based spectral parameterization of convective gravity waves and its comparison with Microwave Limb Sounder observations

The ray‐based spectral parameterization of convective gravity wave drag, which explicitly calculates the gravity wave propagation properties, is validated against the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS). Offline calculations of the ray‐based parameterization are performed using global reanalysis data and gravity wave temperature variances calculated from the parameterization are compared with those measured from the MLS. The parameterized temperature variances are calculated from gravity wave packets that are visible from the MLS to allow for comparison. The MLS visibility is analytically obtained using the three‐dimensional MLS filter function. Comparisons between the parameterization calculations and MLS measurements show that both the magnitude and spatial distribution of the MLS‐filtered temperature variances in the ray‐based parameterization are in good agreement with observations. However, the MLS‐filtered temperature variances are found to be sensitive to the source‐level wave propagation direction, which, until now, has been regarded as a free parameter in the ray‐based parameterization. This result indicates that the wave propagation direction can be crucial for more realistic parameterization of gravity wave (GW) effects and thus needs to be reasonably determined. Comparisons between the ray‐based parameterization and columnar parameterization, which considers the gravity wave propagation only in the vertical direction, are also made in terms of temperature variance, and both results, after filtered, are similar to MLS observations. However, the magnitude of the unfiltered temperature variance in the equatorial regions with weak MLS visibility is smaller in the ray‐based parameterization than in the columnar parameterization.

Global Gravity Wave Variances from Aura MLS: Characteristics and Interpretation

Abstract The gravity wave (GW)–resolving capabilities of 118-GHz saturated thermal radiances acquired throughout the stratosphere by the Microwave Limb Sounder (MLS) on the Aura satellite are investigated and initial results presented. Because the saturated (optically thick) radiances resolve GW perturbations from a given altitude at different horizontal locations, variances are evaluated at 12 pressure altitudes between ∼21 and 51 km using the 40 saturated radiances found at the bottom of each limb scan. Forward modeling simulations show that these variances are controlled mostly by GWs with vertical wavelengths λz > 5 km and horizontal along-track wavelengths of λy ∼ 100–200 km. The tilted cigar-shaped three-dimensional weighting functions yield highly selective responses to GWs of high intrinsic frequency that propagate toward the instrument. The latter property is used to infer the net meridional component of GW propagation by differencing the variances acquired from ascending (A) and descending (D) orbits. Because of improved vertical resolution and sensitivity, Aura MLS GW variances are ∼5–8 times larger than those from the Upper Atmosphere Research Satellite (UARS) MLS. Like UARS MLS variances, monthly-mean Aura MLS variances in January and July 2005 are enhanced when local background wind speeds are large, due largely to GW visibility effects. Zonal asymmetries in variance maps reveal enhanced GW activity at high latitudes due to forcing by flow over major mountain ranges and at tropical and subtropical latitudes due to enhanced deep convective generation as inferred from contemporaneous MLS cloud-ice data. At 21–28-km altitude (heights not measured by the UARS MLS), GW variance in the tropics is systematically enhanced and shows clear variations with the phase of the quasi-biennial oscillation, in general agreement with GW temperature variances derived from radiosonde, rocketsonde, and limb-scan vertical profiles. GW-induced temperature variances at ∼44-km altitude derived from operational global analysis fields of the ECMWF Integrated Forecast System in August 2006 reveal latitudinal bands of enhanced GW variance and preferred GW meridional propagation directions that are similar to those inferred from the MLS variances, highlighting the potential of MLS GW data for validating the stratospheric GWs simulated and/or parameterized in global models.

On the response of Halogen Occultation Experiment (HALOE) stratospheric ozone and temperature to the 11‐year solar cycle forcing

Results are presented on responses in 14‐year (1991–2005) time series of stratospheric ozone and temperature from the Halogen Occultation Experiment (HALOE) of the Upper Atmosphere Research Satellite (UARS) to a solar cycle (SC‐like) variation. The ozone time series are for ten, 20‐degree‐wide, latitude bins from 45°S to 45°N and for thirteen “half‐Umkehr” layers of about 2.5 km thickness and extending from 63 hPa to 0.7 hPa. The temperature time series analyses were restricted to pressure levels in the range of 2 hPa to 0.7 hPa. Multiple linear regression (MLR) techniques were applied to each of the 130 time series of bin‐averaged, sunrise plus sunset ozone points over that latitude/pressure domain. A simple, 11‐year periodic term and a linear trend term were added to the final MLR models after their seasonal and interannual terms had been determined. Where the amplitudes of the 11‐year terms are significant, they are in phase with those of the more standard proxies for the solar UV flux. The maximum minus minimum response for ozone is on the order of 2 to 3% from about 2 to 5 hPa and for the latitudes of 45°S to 45°N. There is also a significant maximum minus minimum response on the order of 1 K for temperature between 15°S and 15°N and from 2 to 0.7 hPa. The associated linear trends for ozone are near zero in the upper stratosphere. It is noted, however, that effects of the changes in total chlorine during this 14‐year period were not accounted for explicitly and that their omission can be a confounding effect for both the analyzed solar cycle responses and the linear terms, especially for tropical upper stratospheric ozone. It is concluded that the solar occultation technique of HALOE provided adequate sampling and sufficient vertical resolution for obtaining the solar cycle response in stratospheric ozone.

Spatiotemporal variation of the ozone QBO in MLS data by wavelet analysis

Abstract. Spatiotemporal characteristics of the ozone quasi-biennial oscillation (QBO) over the tropical-subtropical stratosphere (40° S–40° N) have been examined by analyzing data from the Microwave Limb Sounder (MLS) aboard Upper Atmospheric Research Satellite (UARS) for the period 1992–1999. A combination of regression analysis and wavelet analysis combines to act as an accurate QBO filter. Wavelet analysis provides inter-annual variability of amplitude and phase of the ozone QBO in the vertical structure of tropical-subtropical stratosphere. It gives minute details of phase propagation and descend rates, which can be used as input to models. Latitude-height structure shows evidence of a secondary meridional circulation induced by the QBO as double peak structure at the equator with maximum amplitude at two pressure levels 30 hPa and 9 hPa and a node at 14 hPa. The equatorial maxima are out of phase with each other. The maximum amplitude (~1.4 ppmv) of the ozone QBO was observed near the equator at 10 hPa. Descent rate of the easterly phase is greater than westerly. The lag correlation of the ozone QBO with circulation and variation of descent rates in the vertical structure of the stratosphere are examined in detail. In the equatorial upper stratosphere ozone anomalies descent with the rate ~1.5 km/month but in tropics and subtropics (above 2 hPa) they propagate upward.

DWM07 global empirical model of upper thermospheric storm‐induced disturbance winds

We present a global empirical disturbance wind model (DWM07) that represents average geospace‐storm‐induced perturbations of upper thermospheric (200–600 km altitude) neutral winds. DWM07 depends on the following three parameters: magnetic latitude, magnetic local time, and the 3‐h Kp geomagnetic activity index. The latitude and local time dependences are represented by vector spherical harmonic functions (up to degree 10 in latitude and order 3 in local time), and the Kp dependence is represented by quadratic B‐splines. DWM07 is the storm time thermospheric component of the new Horizontal Wind Model (HWM07), which is described in a companion paper. DWM07 is based on data from the Wind Imaging Interferometer on board the Upper Atmosphere Research Satellite, the Wind and Temperature Spectrometer on board Dynamics Explorer 2, and seven ground‐based Fabry‐Perot interferometers. The perturbation winds derived from the three data sets are in good mutual agreement under most conditions, and the model captures most of the climatological variations evident in the data.

Extreme longitudinal disturbances in the mesosphere and thermosphere observed with the Wind Imaging Interferometer on UARS

[1] Extreme longitudinal disturbances in the O(1S) emission rate and horizontal winds in the mesosphere and thermosphere (90–180 km) are identified on three March days in 1994, 1996, and 1997 in the database of the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS). This type of disturbance has a wave structure with apparent zonal wavenumber 1 and a very long vertical wavelength. It generates longitudinal amplitudes of 70 photons cm−3 s−1 and 120 ms−1 in the O(1S) volume emission rate and winds, respectively, and is strong enough to break the structures of migrating tides in the E-region. In the same longitudinal zone for day and night the zonal wind driven by this disturbance has the same phase, suggesting a wave with s = −1 and a very long period, but the meridional wind has opposite phases, suggesting a standing non-migrating diurnal tide. This super disturbance has not been observed before, and fundamental questions about it await future investigation.

First UV satellite observations of mesospheric water vapor

We report the first UV satellite observations of mesospheric water vapor. The measurements are of nonthermal OH prompt emission between 300–330 nm produced directly from the photodissociation of water vapor by H Lyman‐α. This technique is most sensitive to water vapor concentrations between 70–90 km altitude. We present OH data from two limb scanning experiments: the Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) and the Optical Spectrograph and Infra‐Red Imager System (OSIRIS). Interpretation of the lower resolution (∼1 nm) OSIRIS spectra requires the rotational emission rate factors for OH(1,1) solar fluorescence between 313–318 nm, which we present for the first time herein. Comparison of water vapor concentration profiles with the most coincident profiles from the Halogen Occultation Experiment on the Upper Atmosphere Research Satellite shows agreement to within 30% between 75–80 km for both MAHRSI and OSIRIS. We discuss the benefits of this promising new approach to measuring upper mesospheric water vapor and the need for new laboratory measurements to improve the analysis.