Abstract. Aerosol chemical, microphysical, and optical data collected from an island station and a ship during the first field phase of the Indian Ocean Experiment provided a unique opportunity to develop models for retrieving aerosol optical depth from the advanced very high resolution radiometer (AVHRR) onboard NOAA14 during JanuaryMarch 1998. Columnar aerosol optical depth (AOD) over Arabian Sea, Bay of Bengal, and Indian Ocean was derived for the 630 nm wavelength from the radiance in channel 1 (580-680 nm) of AVHRR. The satellite retrieval model for AOD accounts for several aerosol species (sulfates, nitrates, sea salt, soot, dust, and organics), the in situ measured value of single scattering albedo, and the wind speed dependence of sea surface albedo.

No abstract

No abstract

Tropospheric water-vapour and ozone measurements, using calibrated balloon-borne sensors, are reported from the Central Equatorial Pacific Experiment (CEPEX). The sensors were launched from the Research Vessel Vickers along 2"s latitude between 156"E (west of the international date line) and 155"W (east of the date line).These measurements are combined with those from water-vapour sondes launched over the western Pacific warm pool, during the Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE). Taking the two experiments CEPEX and TOGA-COARE together, the sensors included frost-point hygrometers, Humicap-A Viiisala sondes, Humicap-H Vaisala sondes and electrochemical ozone-sondes. Taken together, the CEPEX and TOGA-COARE data provide over 150 vertical profiles of water vapour within the troposphere in varied conditions of convective activity ranging from disturbed to suppressed. The primary motivation behind the present analyses is to understand the role of tropical deep convection in the vertical distribution of water-vapour. With this in mind, the profiles have been analysed in relation to occasions of recent deep convection and occasions when convection was suppressed.We employ three different criteria to identify the profiles influenced by deep convection: brightness temperature in the infrared-window channel of the Japanese Geostationary Meteorological Satellite (GMS); ozone as a quasi-conservative tracer for deep convection; and using water vapour itself, that is the wettest versus the driest soundings. Irrespective of the criteria used, we report here that the atmosphere, while under the influence of active deep convection, was found to have relative humidities in excess of 75% over most of the troposphere between the surface and about 14 km. The sondes were launched routinely over a period of 45 days (between CEPEX and TOGA-COARE), without biasing the sample towards convectively disturbed conditions. A feature of the convectively disturbed profile is a distinct minimum in relative humidity at about 700 hPa, where it was as low as 65%. The low relative humidity was accompanied by relatively high ozone mixing ratios, which raises the possibility of long-range transport of dry sub-tropical air into the warm, convectively disturbed, regions of the equatorial Pacific Ocean. Inspection of the analysed fields, and the wind fields from the sondes, supports this assertion.It then follows that the omnipresent minimum of moist static energy and minimum relative humidity at 700 hPa in the inner tropics may be the result of long-range, inclined, transport of dry air from non-convective regions. This detection suggests a linkage between the large-scale circulation, deep convection and the thermodynamic structure within the equatorial troposphere.The results presented here demonstrate the applicability of ozone as a quasi-conservative tracer of transport in the context of deep convection.The ozone-based criterion is used to diagnose recent deep convection, independent of the GMS satellite observations, and allows ...

Sensor synergy and close cooperation between experimentalists and modelers is required to gain more insight into complex cloud structures and processes. On a global scale, clouds have a strong cooling effect on our climate: more solar radiation is reflected back to space than thermal surface radiation is trapped in the atmosphere. However, because radiation reacts on the instantaneous cloudy atmosphere and not on some climatological mean, the physical processes leading to the overall radiative effect strongly depend on the spatial distribution and structure of clouds. AFFILIATIONS: CREWELL, LOHNERT, SIMMER, AND VENEMA-Meteorologi-