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Warm Conveyor Belts in the NAWDEX campaign

by Marie Mazoyer and Philippe Arbogast

published in the Météo-France 2018 Research Report (ISSN : 2116-4541)


Warm Conveyor Belts (WCBs) are dynamically important airstreams in mid-latitude cyclones. They correspond to the ascent of warm and humid air masses from the lower atmospheric layers to the high troposphere.

WCBs represent the cloudy part of the depression. Heat release associated with the formation of cloud species could have a strong impact on the dynamics of these depressions. Representation of these badly known processes could constitute an important source of uncertainty for the prediction of these depressions.

The NAWDEX (North Atlantic Wave-guide Downstream and impact EXperiment) measurement campaign was aimed at improving knowledge about them. It occurred from 19th September 2016 to 16th October 2016 on the Iceland coast. Embedded instrumentation on Falcon et Gulfstream V planes (LIDAR : LIght Detection And Ranging, RADAR : RAdio Detection And Ranging, Drop-sonde) allowed the reconstitution of wind and reflectivity profiles of cloudy species in WCBs. These observations are compared to simulation results obtained with the Méso-NH model (atmospheric Mesoscale and Non-Hydrostatic model). Different parametrizations for the representation of cloud species are evaluated and confronted to measure made by the RASTA airborne radar (see figure).

A comparison of RADAR reflectivities as measured (top) in the case of a warm conveyor belt on 1st October 2016 and simulated by Méso-NH using either ICE3 (middle) for the cloud representation or LIMA (bottom).


This cloud system is overall well simulated by the two models used. However, a systematic study of different processes, and of their representation, associated with heat release during the given WCB case should allow the clarification of uncertainty sources and ways of improving parametrizations to be opened.