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Communication Dans Un Congrès Année : 2019

Observation and forecast verification of cloud fraction over Reunion Island (21°S, 55.5°E) using a 95 GHz cloud radar

Résumé

In order to validate and improve the representation of low and high level tropical clouds in NWP systems, a 95 GHz Doppler cloud radar (BASTA) was deployed in Reunion Island (SW Indian Ocean, 21°S; 55.5E) in November 2016. The benefit of cloud radars over satellite observations lies in their ability to characterize cloud properties at very high resolution. With this respect BASTA allows for several operation modes characterized by vertical resolutions of 12.5m (fog and low clouds), 25m (midlevel clouds), and 100m (cirrus and high clouds). Cloud radar observations are first compared against lidar and satellite measurements to evaluate the radar capability to sample clouds up to the tropopause level (20 km). Then a 2-year analysis of the vertical distribution of clouds over Saint-Denis (Réunion Island) is performed from 12s resolution radar observations. Radar data show an abnormal vertical distribution of the cloud fraction during winter 2017 with much higher cloud occurence than usual. A close examination of operational radiosoundings indicate that this unusual situation was due to the presence of a positive moisture anomaly resulting from warmer than usual sea surface temperatures in the Mascarene Archipelago. Cloud fraction observations are then compared against high resolution (2.5 km) AROME-Indian Ocean NWP forecasts over the same period. Results indicate that the model tends to underestimate (resp. overestimate) cloud cover at low (resp. high) levels. Differences appear related to both an improper representation of orography at low levels and looser vertical resolution of the model at higher levels.

Domaines

Météorologie
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Dates et versions

insu-04449973 , version 1 (09-02-2024)

Identifiants

Citer

J. Durand, O. Bousquet, Julien Delanoë, S. Bielli. Observation and forecast verification of cloud fraction over Reunion Island (21°S, 55.5°E) using a 95 GHz cloud radar. American Geophysical Union, Fall Meeting 2019, Dec 2019, San Francisco, United States. pp.abstract #A53L-3078. ⟨insu-04449973⟩
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