Retrieval of upper tropospheric water vapor and upper tropospheric humidity from AMSU radiances

International audienceA regression method was developed to retrieve upper tropospheric water vapor (UTWV in kg/m2) and upper tropospheric humidity (UTH in % RH) from radiances measured by the Advanced Microwave Sounding Unit (AMSU). In contrast to other UTH retrieval methods, UTH is defined as the average relative humidity between 500 and 200hPa, not as a Jacobian weighted average, which has the advantage that the UTH altitude does not depend on the atmospheric conditions. The method uses AMSU channels 6-10, 18, and 19, and should achieve an accuracy of 0.48 kg/m2 for UTWV and 6.3% RH for UTH, according to a test against an independent synthetic data set. This performance was confirmed for northern mid-latitudes by a comparison against radiosonde data from station Lindenberg in Germany, which yielded errors of 0.23 kg/m2 for UTWV and 6.1% RH for UTH

Notes on Decoherence at Absolute Zero

The problem of electron decoherence at low temperature is analyzed from the perspective of recent experiments on decoherence rate measurement and on related localization phenomena in low-dimensional systems. Importance of decoherence at zero temperature, perhaps induced by quantum fluctuations, is put in a broader context.Comment: 7 pages in PRB format, 1 figur

Geometry dependent dephasing in small metallic wires

Temperature dependent weak localization is measured in metallic nanowires in a previously unexplored size regime down to width $w=5$ nm. The dephasing time, $\tau_{\phi}$, shows a low temperature $T$ dependence close to quasi-1D theoretical expectations ($\tau_{\phi} \sim T^{-2/3}$) in the narrowest wires, but exhibits a relative saturation as $T \to 0$ for wide samples of the same material, as observed previously. As only sample geometry is varied to exhibit both suppression and divergence of $\tau_{\phi}$, this finding provides a new constraint on models of dephasing phenomena.Comment: 6 pages, 3 figure

Retrieval of upper tropospheric water Retrieval of upper tropospheric water Retrieval of upper tropospheric water

International audienceA regression method was developed to retrieve upper tropospheric water vapor (UTWV in kg/m2) and upper tropospheric humidity (UTH in %RH) from radiances measured by the Advanced Microwave Sounding Unit (AMSU). In contrast to other UTH retrieval methods, UTH is defined as the average relative humidity between 500 and 200 hPa, not as a Jacobian weighted average, which has the advantage that the UTH altitude does not depend on the atmospheric conditions. The method uses AMSU channels 6?10, 18, and 19, and should achieve an accuracy of 0.48 kg/m2 for UTWV and 6.3%RH for UTH, according to a test against an independent synthetic data set. This performance was confirmed for northern mid-latitudes by a comparison against radiosonde data from station Lindenberg in Germany, which yielded errors of 0.23 kg/m2 for UTWV and 6.1%RH for UTH

Expected improvements in the atmospheric humidity profile retrieval using the Megha-Tropiques microwave payload

International audienceThe microwave payload of the Megha-Tropiques mission is explored to quantify the expected improvements in the retrieval of relative humidity profiles. Estimations of the profiles are performed using a generalized additive model that uses cubic smoothing splines to address the nonlinear dependencies between the brightness temperatures (TB) in the 183.31 GHz band and the relative humidity of specified tropospheric layers. Under clear-sky and oceanic situations, the six-channel configuration of the SAPHIR radiometer clearly improves the retrieval and reduces by a factor of two the variance of the residuals with respect to the current space-borne humidity sounders that have three channels in this band (AMSU-B, MHS). Additional information from the MADRAS radiometer (at 23.8 and 157 GHz) further improves the restitution with correlation coefficient higher than 0.89 throughout the troposphere