[1] Large fine mode-dominated aerosols (submicron radius) in size distributions retrieved from the Aerosol Robotic Network (AERONET) have been observed after fog or low-altitude cloud dissipation events. These column-integrated size distributions have been obtained at several sites in many regions of the world, typically after evaporation of low-altitude cloud such as stratocumulus or fog. Retrievals with cloud-processed aerosol are sometimes bimodal in the accumulation mode with the larger-size mode often $0.4-0.5 mm radius (volume distribution); the smaller mode, typically $0.12 to $0.20 mm, may be interstitial aerosol that were not modified by incorporation in droplets and/or aerosol that are less hygroscopic in nature. Bimodal accumulation mode size distributions have often been observed from in situ measurements of aerosols that have interacted with clouds, and AERONET size distribution retrievals made after dissipation of cloud or fog are in good agreement with particle sizes measured by in situ techniques for cloud-processed aerosols. Aerosols of this type and large size range (in lower concentrations) may also be formed by cloud processing in partly cloudy conditions and may contribute to the "shoulder" of larger-size particles in the accumulation mode retrievals, especially in regions where sulfate and other soluble aerosol are a significant component of the total aerosol composition. Observed trends of increasing aerosol optical depth (AOD) as fine mode radius increased suggests higher AOD in the near-cloud environment and higher overall AOD than typically obtained from remote sensing owing to bias toward sampling at low cloud fraction.

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[1] To investigate the probable mixing state of aerosols in the Indo-Gangetic Basin, six different mixing cases, viz. external mixing, internal mixing, and four combinations of core-shell type mixing (black carbon, BC over dust, watersoluble over dust, BC over water-soluble and water-soluble over BC) have been considered. Composite single scattering albedo (SSA) have been computed for six cases for postmonsoon, winter and pre-monsoon seasons and are compared with the Aerosol Robotic Network (AERONET) retrieved SSA values. The most probable mixing state in the post-monsoon season seems either to be external mixing or water-soluble coating over dust and in the winter season, the external mixing seems to be the probable mixing state. However, in the pre-monsoon season, BC coating over dust seems to be the most probable mixing state. This type of mixing leads to enhanced absorption and needs future attention to better understand the aerosol radiative effect in this region.

The assessment of direct radiative forcing (DRF) of aerosol is uncertain, particularly where the natural dust particles mix with the anthropogenic components. One of the sources of such uncertainty is the assumption of morphology (size and shape) and composition of pure dust particles. Recently Mishra and Tripathi [2008] have computationally assessed the effect of particle morphology on optical properties over the Great Indian Desert. As a continuation of the previous study, in this paper, we have further examined the effects on dust radiative properties. Non‐spherical pure dust particles show large variations in the optical and radiative properties from spherical pure dust particles, however, particle composition is found to have greater influence than particle shape on the radiative properties. Among the various shapes, sharp‐edged particles show larger difference than smooth‐shaped particles. Although the overall atmospheric absorption monotonically increases with increase in hematite content, maximum effect of particle non‐sphericity at 4% hematite content implies that non‐sphericity should be considered to minimize the uncertainty of regional estimates of aerosol DRF, as most of the global dusts contain that much hematite. However the difference in radiative properties for two different background dust cases due to particle morphology is low. Our results show that ignoring non‐sphericity will lead to under‐estimation of the regional warming and dust‐absorption efficiency.

EddyPro checks for signal quality and gas analyzer signal strength (which depends on the cleanliness of sensor optical windows and/or presence or absence of rain drops/fog in the measuring volume). A missing samples allowance of 10% was set for the raw data in the flux averaging intervals and linear interpolation of the data is done by Eddy pro within this limit. The effect of wind blowing normal to the sonic path on the speed of sound (sonic temperature) is corrected for in the CSAT3 firmware(CSAT3 3-D Sonic Anemometer Instruction Manual). Other corrections are as follows.