Earth Observation Data Group

Abstract:

Gas-phase photochemical models do not account for the formation of a secondary altitude HNO3 maximum in the upper stratosphere at high latitudes during winter, suggesting that some processes are missing in the currently accepted chemistry of reactive nitrogen species [Kawa et al., 1995]. Heterogeneous chemistry on aerosol particles had been discounted as the cause because the aerosol surface area is expected to be very low at these altitudes. We have coupled a sulphate aerosol microphysical model to a chemical transport model to investigate this model deficiency in the Arctic during January 1992. The aerosol model predicts the formation of small sulphate particles at 1100 K. Comparisons with cryogenic limb array etalon spectrometer (CLAES) HNO3 and improved stratospheric and mesospheric sounder (ISAMS) N2O5 observations show that the heterogeneous conversion of N2O5 to HNO3 on the modeled small sulphate particles can account for some of the unexpected features seen in Upper Atmosphere Research Satellite (UARS) observations.

Abstract:

Gas-phase photochemical models do not account for the formation of a secondary altitude HNO3 maximum in the upper stratosphere at high latitudes during winter, suggesting that some processes are missing in the currently accepted chemistry of reactive nitrogen species [Kawa et al., 1995]. Heterogeneous chemistry on aerosol particles had been discounted as the cause because the aerosol surface area is expected to be very low at these altitudes. We have coupled a sulphate aerosol microphysical model to a chemical transport model to investigate this model deficiency in the Arctic during January 1992. The aerosol model predicts the formation of small sulphate particles at 1100 K. Comparisons with cryogenic limb array etalon spectrometer (CLAES) HNO3 and improved stratospheric and mesospheric sounder (ISAMS) N2O5 observations show that the heterogeneous conversion of N2O5 to HNO3 on the modeled small sulphate particles can account for some of the unexpected features seen in Upper Atmosphere Research Satellite (UARS) observations.

Abstract:

Simultaneous observations of Polar Stratospheric Cloud (PSC) aerosol extinction and HNO3 mixing ratios over Scandinavia are examined for January 9-10, 1992. Data measured by the Microwave Limb Sounder(MLS), Cryogenic Limb Array Etalon Spectrometer (CLAES), and Improved Stratospheric and Mesospheric Sounder (ISAMS) experiments on the Upper Atmosphere Research Satellite (UARS) are examined at locations adjacent to parcel trajectory positions. Regression coefficients, obtained from Mie calculations, are used to transform aerosol extinctions into aerosol volume densities. Graphs of volume density versus temperature, and importantly, HNO3 mixing ratio versus temperature, show volume increases and simultaneous loss of HNO3 as temperatures decrease. The data is consistent with initial PSC growth processes which transform sulfate droplets into ternary droplets or nitric acid dihydrate (NAD) particles.

Abstract:

The cryogenic limb array etalon spectrometer (CLAES) and the improved stratospheric and mesospheric sounder (ISAMS) instruments on board the Upper Atmosphere Research Satellite (UARS) have been used to produce global information on the Mt. Pinatubo volcanic aerosol for the period from October 1991 to April 1993, The Satellite infrared extinction measurements near 12 mu m are converted into the aerosol-related parameters necessary for modelling the effects of the volcanic aerosol on the aeronomy of the stratosphere and are presented as zonal mean distributions for 80 degrees S to 80 degrees N averaged over similar to 35-day periods. The aerosol composition is derived from the CLAES and ISAMS temperature measurements and the water vapour abundances are obtained from the microwave limb sounder (MLS). The aerosol volume density is obtained from the extinction measurements from which the Surface area density and the effective particle radius are estimated. The maximum aerosol surface area density has a value of about 50 mu m(2) cm(-3) at a height of 24 km at the equator in October 1991, before decaying exponentially with a time constant of 443 +/- 10 days. The surface area density remained well above preeruption values in April 1993. The effective particle radius in the tropics decays monotonically from 0.65 mu m in October 1991 to 0.4 mu m in April 1993. The global aerosol sulphate mass loading is 19.5 Mt in October 1991 and decays exponentially with a time constant of 342 +/- 8 days to a value of 4.3 Mt by April 1993. Four months after the eruption the calculated optical thickness at 1.02 mu m was similar to 0.25 in the tropics. Rate constants are derived for the heterogeneous reactions of N2O5 and ClONO2 on the sulphate aerosols. The application of the aerosol parameters to the investigation of tracer transport, heterogeneous chemistry, and radiative transfer is discussed.

Abstract:

Simultaneous observations of Polar Stratospheric Cloud (PSC) aerosol extinction and HNO3 mixing ratios over Scandinavia are examined for January 9-10, 1992. Data measured by the Microwave Limb Sounder (MLS), Cryogenic Limb Array Etalon Spectrometer (CLAES), and Improved Stratospheric and Mesospheric Sounder (ISAMS) experiments on the Upper Atmosphere Research Satellite (UARS) are examined at locations adjacent to parcel trajectory positions. Regression coefficients, obtained from Mie calculations, are used to transform aerosol extinctions into aerosol volume densities. Graphs of volume density versus temperature, and importantly, HNO3 mixing ratio versus temperature, show volume increases and simultaneous loss of HNO3 as temperatures decrease. The data is consistent with initial PSC growth processes which transform sulfate droplets into ternary droplets or nitric acid dihydrate (NAD) particles.