Correction
of humidity bias for Vaisala RS80-A sondes during AMMA 2006 Observing
Period
Nuret,
Mathieu (1), Jean-Philippe Lafore(1), Françoise Guichard(1),
Olivier Bock(2), Anna Agusti-Panareda(3), Jean-Blaise N'Gamini1(4)
and Jean-Luc Redelsperger(1)
J.
Atmos. Ocean. Tech., to appear (submitted
21 December 2007 , revised 30 April 2008)
1
: CNRM-GAME, Météo-France & CNRS, 42 avenue G.
Coriolis, F-31057 Toulouse
2
: LAREG/IGN, 6-8 avenue Blaise Pascal, F-77455 Marne La Vallée
3
: ECMWF, Shinfield Park, Reading, Berkshire, RG 29 AX, England
4
: ASECNA, Dakar, Sénégal
Abstract
During
the African Monsoon Multidisciplinary Analyses (AMMA) program whose
Special Observing Period took place over West Africa in 2006, a major
effort has been devoted to monitor the atmosphere and its water
cycle. The radiosounding network has been upgraded and enhanced, and
GPS receivers deployed. Among all sondes released in the atmosphere,
a significant part was Vaisala RS80-A sondes which revealed a
significant dry bias relative to Vaisala RS92 (a maximum of 14% in
the lower atmosphere reaching 20% in the upper levels). This paper
makes use of a simple but robust statistical approach to correct the
bias. Comparisons against independent GPS data show that the bias is
almost removed at night, whereas for daytime conditions, a weak dry
bias (5%) still remains. The correction enhances CAPE by a factor of
about four, it thus becomes much more in line with expected values
over the region.