J.-P. Pinty

Development of precipitation retrievals at millimeter and sub‐millimeter wavelengths for geostationary satellites

Received 19 March 2007; revised 19 September 2007; accepted 14 December 2007; published 23 April 2008. [1] We study the potential of millimeter and sub-millimeter wavelengths for precipitation retrieval from geostationary sensors based on mesoscale cloud modeling and radiative transfer computation. Hydrometeor profiles simulated with the Meso-NH cloud resolving model for five European midlatitude situations are used to compute the brightness temperatures at frequencies from 23.8 to 875 GHz with the Atmospheric Transmission at Microwaves (ATM). Performances of both rain detection and rain rate retrieval are analyzed for different frequency sets, over ocean and land separately, and compared to the user requirements. The performances of a frequency set such as that already planned for geostationary satellites (with channels in the O2 lines at 50, 118, and 424 GHz, and in the H2O lines at 183, 325, 380 GHz) satisfy the requirements for Numerical Weather Prediction and NoWCasting in terms of rain detection as well as for rain rate retrieval above 1 mm/h. Suppressing the 50 GHz O2 channels does not seriously degrade the performances, except for rain rate below 1 mm/h, and, in addition, limits the spatial resolution problem from a geostationary orbit. Adding the thermal infrared observations has a limited impact. The retrieval of other hydrometeor quantities (cloud, ice) is also tested as well as the possibility to retrieve rain and the other hydrometeor profiles. These theoretical results are evaluated at close-to-millimeter wavelengths with coincident AMSU-B and radar observations (BALTEX and CAMRa). The results are degraded with respect to the theory, as expected, but are consistent with the observations.

Lightning-produced NOx in an explicit electrical scheme tested in a Stratosphere-Troposphere Experiment : Radiation, Aerosols, and Ozone case study.

[1] An explicit lightning-produced nitrogen oxide (LNO x ) scheme has been implemented in a 3-D mesoscale model. The scheme is based on the simulation of the electrical state of the cloud and provides a prediction of the temporal and spatial distribution of the lightning flashes. The frequency and the 3-D morphology of the lightning flashes are captured realistically so fresh nitrogen oxide molecules can be added along the complex flash path as a function of the pressure, as suggested by results from laboratory experiments. The scheme is tested on the 10 July 1996 Stratosphere-Troposphere Experiment: Radiation, Aerosols, and Ozone (STERAO) storm. The model reproduces many features of the observed increase of electrical activity and LNO x flux density between the multicell and supercell stages. LNO x dominates the NO x budget in the upper part of the cells with instantaneous peak concentrations exceeding 4 ppbv, as observed. The computed flux of NO x across the anvil shows a mean value of 6 mol m -2 s -1 during the last 90 min of the simulation. This value is remarkably stable and compares favorably with the observations.