Rashid Khosravi

Global estimates of gravity wave momentum flux from High Resolution Dynamics Limb Sounder observations

analyzed to derive global properties of gravity waves. We describe a wavelet analysis technique that determines covarying wave temperature amplitude in adjacent temperature profile pairs, the wave vertical wavelength as a function of height, and the horizontal wave number along the line joining each profile pair. The analysis allows a local estimate of the magnitude of gravity wave momentum flux as a function of geographic location and height on a daily basis. We examine global distributions of these gravity wave properties in the monthly mean and on an individual day, and we also show sample instantaneous wave events observed by HIRDLS. The results are discussed in terms of previous satellite and radiosonde observational analyses and middle atmosphere general circulation model studies that parameterize gravity wave effects on the mean flow. The high vertical and horizontal resolution afforded by the HIRDLS measurements allows the analysis of a wider range of wave vertical and horizontal wavelengths than previous studies and begins to show individual wave events associated with mountains and convection in high detail. Mountain wave observations show clear propagation to altitudes in the mesosphere.

Initial validation of ozone measurements from the High Resolution Dynamics Limb Sounder

Comparisons of the latest High Resolution Dynamics Limb Sounder (HIRDLS) ozone retrievals (v2.04.09) are made with ozonesondes, ground-based lidars, airborne lidar measurements made during the Intercontinental Chemical Transport Experiment–B, and satellite observations. A large visual obstruction blocking over 80% of the HIRDLS field of view presents significant challenges to the data analysis methods and implementation, to the extent that the radiative properties of the obstruction must be accurately characterized in order to adequately correct measured radiances. The radiance correction algorithms updated as of August 2007 are used in the HIRDLS v2.04.09 data presented here. Comparisons indicate that HIRDLS ozone is recoverable between 1 and 100 hPa at middle and high latitudes and between 1 and 50 hPa at low latitudes. Accuracy of better than 10% is indicated between 1 and 30 hPa (HIRDLS generally low) by the majority of the comparisons with coincident measurements, and 5% is indicated between 2 and 10 hPa when compared with some lidars. Between 50 and 100 hPa, at middle and high latitudes, accuracy is 10–20%. The ozone precision is estimated to be generally 5–10% between 1 and 50 hPa. Comparisons with ozonesondes and lidars give strong indication that HIRDLS is capable of resolving fine vertical ozone features (1–2 km) in the region between 1 and 50 hPa. Development is continuing on the radiance correction and the cloud detection and filtering algorithms, and it is hoped that it will be possible to achieve a further reduction in the systematic bias and an increase in the measurement range downward to lower heights (at pressures greater than 50–100 hPa).

Stratospheric CH3CN from the UARS microwave limb sounder

CH3CN in the stratosphere has been measured by the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS), providing the first global CH3CN dataset. The MLS observations are in broad agreement with past high and midlatitude observations of CH3CN, although concentrations are a little larger than previously observed. In the tropics, where CH3CN has not up to now been measured, a persistent ‘peak’ in the profiles is seen around 22 hPa, which may be evidence of a tropical stratospheric CH3CN source. Comparisons are made with the NCAR SOCRATES model, including runs having an artificial tropical stratospheric CH3CN source.

Overview and characterization of retrievals of temperature, pressure, and atmospheric constituents from the High Resolution Dynamics Limb Sounder (HIRDLS) measurements

Received 18 February 2009; revised 22 April 2009; accepted 26 June 2009; published 23 October 2009. [1] The retrieval algorithm for the High Resolution Dynamics Limb Sounder (HIRDLS) instrument onboard NASA’s Earth Observing System (EOS) Aura satellite is presented. The algorithm is based on optimal estimation theory, using a modified Levenberg-Marquardt approach for the iterative solution. Overview of the retrieval scheme, convergence criteria, and the forward models is given. Treatments of clouds and aerosols as well as line-of-sight gradients in temperature are described. The retrievals are characterized by high vertical resolution of 1 km and negligible a priori contribution for all products in regions of high signal-to-noise ratio (SNR) (most of the retrieval ranges). It is shown that these characteristics hold for all latitudes along a HIRDLS orbit. The weighting functions are narrow and show good sensitivity to temperature or gas perturbations in regions of high SNR. The retrieval error predicted by the algorithm consists of radiometric noise, pointing jitter error, smoothing error, and forward model error. For temperature, these components are shown for a midlatitude profile as well as for a full orbit. The predicted temperature error varies from 0.5 K to 0.8 K from the upper troposphere to the stratopause region, consistent with the empirical estimates given by Gille et al. (2008). For O3 and HNO3, the predicted errors and their useful pressure ranges are, respectively, 10–5% from 50 to 1 hPa and 5–10% from 100 to 10 hPa. These results are based on version V004 of the retrieved data, released in August 2008 to the Goddard Earth Sciences Data and Information Services Center (http://daac.gsfc.nasa.gov).

Significant reduction in the stratospheric ozone deficit using a three-dimensional model constrained with UARS data

We present a near-global analysis of the ozone deficit problem by constraining a fully diurnal, three-dimensional, chemical, radiative, transport model of the middle atmosphere with colocated UARS measurements of ClO, NO x , H 2 O, and CH 4 . The domain of the study covers a wide range of altitudes (37.4-49.6 km) and latitudes (62.5°S-27.5°N), for the period of January-February 1992. In this domain, the baseline (no constraints with measurements) model temperatures are mostly warmer than U.K. Meteorological Office (UKMO) observations (by up to 5 K), and the baseline O 3 mixing ratios are underestimated by 10 to 25% relative to HALOE measurements. Also, in this domain the model/data discrepancies in concentrations of the ozone-relevant species are as follows: [H 2 O] and [NO x ] are mostly in good agreement, [CH 4 ] is underestimated by 10-60%, and [ClO] is overestimated by 1.3 to 3 times. We find the following: (1) Constraining the model with UKMO temperatures eliminates about 3-10% of the deficit in the 40-48 km altitude range. (2) Constraining the model with observed NO x or H 2 O (in addition to temperature) has minimal effect on the ozone deficit in most parts of the domain. (3) When the model temperature and CIO profiles are constrained with observations, the deficit is reduced to about 5-15%, bringing the model ozone predictions in the 40 km region to within the uncertainties of HALOE ozone measurements. (4) A 40% reduction in the rate constant of HO 2 +O→ OH + O 2 , in addition to constraining T, NO x , and ClO, eliminates the deficit in portions of the 40 km region and in the upper stratosphere, but it results in 5-10% excess ozone near the equatorial stratopause. (5) When the model methane profile is constrained with HALOE observations and a 6% HCI + O 2 channel for the ClO + OH reaction is included in the chemistry, the model ClO abundance agrees well with MLS measurements in most parts of the domain. Further improvement in the ClO abundance can be obtained by decreasing [OH] through reducing the rate constant of the HO, + O → OH + O 2 reaction.

Final correction algorithms for HIRDLS version 7 data

The High Resolution Dynamics Limb Sounder (HIRDLS) instrument is a 21-channel limb scanning infrared radiometer, designed to make global measurements of temperature, ozone, water vapor, eight other gases and aerosols from 8 to as high as 80 km. with 1 km. vertical resolution. During launch on NASA’S Aura satellite a piece of interior lining material became lodged in the foreoptics, reducing the effective aperture by 80-95%, and inserting another signal into the system. The HIRDLS team has worked for several years to develop corrections for these effects, and recover as many as possible of the planned capabilities. This talk describes the last and probably final set of algorithms to recover the planned species. Early work developed corrections for channels with large radiances allowing temperature and ozone to be retrieved. Subsequent work has concentrated on refining these to allow species such as nitric acid, chlorofluorocarbons 11 & 12, nitrogen dioxide, N2O5, chlorine nitrate, nitrous oxide and water vapor to be recovered. Effort has gone into studying, then parameterizing in an adaptive way, the quasi-regular way the signal from the blockage varies with time during an orbit and during the mission. Several recent improvements are described. Results of these corrections show improvements in the retrieved products.