Anu Dudhia

Abstract:

The infrared emission limb sounder MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) will be operated as an ESA core instrument on the ENVISAT-1 satellite. Near real time retrieval of pressure, temperature (p,T) and volume mixing ratio (VMR) of five key species (O-3, H2O, N2O, CH4, and HNO3) from calibrated spectra will be performed in the Level 2 processor of the ENVISAT Payload Data Segment. In order to develop an optimized (with respect to speed and accuracy) retrieval algorithm suitable for the implementation in MIPAS Level 2 processor, an ESA supported study is being carried out. In the framework of this study, an optimized forward / retrieval code based on the global fit approach was implemented. In this approach all the spectra of a limb-scanning sequence are simultaneously fitted, so that error propagation in the altitude domain is avoided.The attained accuracy performances of the retrieval code are the following:Temperature error < 2 K at all the altitudes covered by the standard MIPAS scan (8-53 km)Tangent pressure error: < 3%Error on the retrieved VMR of the key species: < 5 % at most of the altitudes of scientific interest covered by the standard MIPAS scan.The run-time required to perform p,T and VMR retrieval of the five MIPAS target species from a limb-scanning sequence of 16 limb-views is less than 6 minutes on a SUN SPARCstation 20. The most effective code optimizations were implemented in the radiative transfer model and in the computation of the jacobian of the retrieval.

Abstract:

Atmospheric temperature measurements from the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS), determined from the observed Rayleigh scattering are presented. Infrared radiances predicted from these profiles are compared with measurements from the Improved Stratospheric and Mesospheric Sounder on UARS for nine cases of spatial and temporal coincidence with an effective difference of about 5-10 K in the height range 70-85 km. A comparison with monthly averaged SME results and Rayleigh lidar temperature observations at mid-latitudes taken 8 years earlier indicated that WINDII temperatures were cooler on average by 10 K; this is consistent with a temperature decrease of 1.5 K/year inferred from the SME and lidar results. At high latitudes the agreement between falling spheres and WINDII was found to be very good.

Abstract:

Data from the Stratospheric and Mesospheric Sounder (SAMS) on Nimbus 7 have been used as the basis for a model of the abundances of nitrous oxide and methane in the stratosphere. The model is presented in tabular form on seventeen pressure surfaces from 20 to 0.1-mb, in 10° latitude bins from 50°S to 70°N, and for each month of the year. Some details of the acquisition of the data which went into the model, its limitations, and the general behaviour of methane and nitrous oxide in the middle atmosphere are given. Formal errors in the data and other uncertainties, interannual variability, and systematic trends are discussed. As expected, no trends which exceed the estimated error in the data are found in either methane or nitrous oxide over the five-year period of SAMS observations.