Abstract
[1] CloudSat observations have indicated that multiple scattering affects 94 GHz spaceborne radar observations. The ESA EarthCARE explorer mission scheduled to launch in 2015 features also a spaceborne 94-GHz radar with Doppler capability for providing a global data set of convective motions and particle sedimentation rates. Vertical velocity measurements will be collected in all cloud conditions, including deep convection where multiple-scattering is expected to contaminate the signal. Thus, before the spaceborne Doppler radars are used for science application, it is imperative to develop a method to identify radar range gates contaminated by multiple scattering contributions. Based on simulations, a criterion to identify the onset of multiple scattering is presented in this paper; the cumulative integrated reflectivity from the top of the atmosphere is a proxy of the multiple scattering enhancement and can be confidently used to detect the onset of multiple scattering. Analysis of a limited (two months) CloudSat data set reveals that, for deep tropical convective cores, the onset of significant multiple scattering typically occurs in the region between 9–10 km and more than 35% of the range bins above the freezing level height and with reflectivity above −20 dBZ are not affected by multiple scattering. This assessment offers a conservative upper limit for EarthCARE 94-GHz radar multiple scattering effects due to the narrower field of view of the Doppler radar compared to CloudSat's radar. Identification of multiple scattering contamination in the CloudSat and EarthCARE radar observations facilitates the following objectives: (1) to constrain the region of validity of currently developed CloudSat products based on single scattering theory (e.g. 2B-CWC-RO, 2B-CWC-RVOD) and (2) to filter out multiple scattering affected range bins in any analysis aimed at the assessment of the feasibility and of the accuracy of the EarthCARE Doppler estimates within deep convective cores.
Highlights
[2] Deep convection plays a key role in the exchange between the upper troposphere and the lower stratosphere with important consequences for the energy and heat budget [Tian and Ramanathan, 2002; Kuang and Bretherton, 2004] and moisture distribution [e.g., Sohn and Schmetz, 2004]
The top left panel shows the precipitating hydrometeor content taken from the Weather Research and Forecasting Model (WRF) model while on the right panel the mean Doppler velocity is plotted
Based on a simulation framework, a criterion to identify the MS onset in W‐band radar observations has been derived for two typical configurations
Summary
[2] Deep convection plays a key role in the exchange between the upper troposphere and the lower stratosphere with important consequences for the energy and heat budget [Tian and Ramanathan, 2002; Kuang and Bretherton, 2004] and moisture distribution [e.g., Sohn and Schmetz, 2004]. [14] The goal of this study is to narrow down to what altitude the SS approximation remains valid, i.e. to identify criteria based on the reflectivity profile alone for flagging MS‐contaminated radar‐ranges This is a timely effort both for the evaluation and further development of CloudSat products (e.g. estimates of ice water content in mesoscale convective systems) and in preparation of the EarthCARE mission (e.g. characterization of the accuracy in mean Doppler velocities). The forward unit computes the cross and co‐polar reflectivities including all scattering order contributions and the ideal radar Doppler spectra (sampled at very high PRF, a multiple of the real PRF) as measured by a spaceborne radar flying over 3D highly resolved scenes produced via Weather Research and Forecasting Model (WRF) simulations [Skamarock et al, 2005] In this context, “ideal” means that no Doppler aliasing or second trip echoes affect the signal. The signal processing component is better described in a future paper
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