Variability in radiative properties of major aerosol types: a year-long study over Delhi--an urban station in Indo-Gangetic Basin.

Aerosol measurements over an urban site at Delhi in the western Ganga basin, northern India, were carried out during 2009 using a ground-based automatic sun/sky radiometer to identify their different types and to understand their possible radiative implications. Differentiation of aerosol types over the station was made using the appropriate thresholds for size-distribution of aerosols (i.e. fine-mode fraction, FMF at 500 nm) and radiation absorptivity (i.e. single scattering albedo, SSA at 440 nm). Four different aerosol types were identified, viz., polluted dust (PD), polluted continent (PC), mostly black carbon (MBC) and mostly organic carbon (MOC), which contributed ~48%, 32%, 11% and 9%, respectively to the total aerosols. Interestingly, the optical properties for these aerosol types differed considerably, which were further used, for the first time, to quantify their radiative implications over this station. The highest atmospheric forcing was observed for PC aerosol type (about +40 W m(-2), along with the corresponding atmospheric heating rate of 1.10 K day(-1)); whereas the lowest was for MBC aerosol type (about +25 W m(-2), along with the corresponding atmospheric heating rate of 0.69 K day(-1)).

Analysis of the spectral and angular response of the vegetated surface polarization for the purpose of aerosol remote sensing over land.

A precise estimate of the polarization induced by the surface in reflected radiation is crucial for remote sensing applications dedicated to monitoring the atmosphere. Here we present airborne observations acquired during a field campaign in the North of France over vegetated surfaces. Polarized reflectances were measured in four spectral bands in the range between 0.67 and 2.2 µm and for scattering angles between 75° and 145°. Our results confirm that the polarization generated by the reflection of vegetated surfaces can be understood as being primarily a specular reflection process. It is not possible from our measurements to see any spectral dependence of the surface polarization in the given spectral channels. The surface polarization is well fitted by existing surface models which have two degrees of freedom that allow the magnitude and angular behavior of the surface-polarized reflectance to be adjusted.

An instrumented station for the survey of ozone and climate change in the southern tropics.

The assessment of changes induced by human activities on Earth atmospheric composition and thus on global climate requires a long-term and regular survey of the stratospheric and tropospheric atmospheric layers. The objective of this paper is to describe the atmospheric observations performed continuously at Reunion Island (55.5 degrees east, 20.8 degrees south) for 15 years. The various instruments contributing to the systematic observations are described as well as the measured parameters, the accuracy and the database. The LiDAR systems give profiles of temperature, aerosols and ozone in the troposphere and stratosphere, probes give profiles of temperature, ozone and relative humidity, radiometers and spectrometers give stratospheric and tropospheric integrated columns of a variety of atmospheric trace gases. Data are included in international networks, and used for satellite validation. Moreover, some scientific activities for which this station offers exceptional opportunities are highlighted, especially air mass exchanges nearby dynamical barriers: (1) On the vertical scale through the tropical tropopause layer (stratosphere-troposphere exchange). (2) On the quasi-horizontal scale across the southern subtropical barrier separating the tropical stratospheric reservoir from mid- and high latitudes.