Multiscale analysis of precipitable water vapor over Africa from GPS data and ECMWF analyses
Bock1, O., F. Guichard2, S. Janicot3, J.-P. Lafore2, M.-N. Bouin4 and B. Sultan3
2007
Geophys. Res. Lett., 34, L09705
doi:10.1029/2006GL028039
(1) Institute Pierre-Simon Laplace, Service Aeronomie du CNRS, Université Paris VI, Paris, France
(2) CNRM-GAME, CNRS & Météo-France, Toulouse, France
(3) Institute
Pierre-Simon Laplace, Laboratoire d'Océanographie et du Climat,
Université Paris VI, Paris, France
(4) Laboratoire de Recherches en Géodésie, Institut Géographique National, Marine la Vallee, France
Abstract
This
is the first climatological analysis of precipitable water vapor (PWV)
from GPS data over Africa. The data reveal significant modulations and
variability in PWV over a broad range of temporal scales. GPS PWV
estimates are compared to ECMWF reanalysis ERA40. Both datasets show
good agreement at the larger scales (seasonal cycle and inter-annual
variability), driven by large scale moisture transport.
At intra-seasonal (15–40 days) and synoptic (3–10
days) scales, strong PWV modulations are observed from GPS,
consistently with ECMWF analysis. They are shown to be correlated
with convection and the passage of equatorial waves and African
Easterly waves. The high-frequency GPS observations also reveal a
significant diurnal cycle in PWV, which magnitude and spectral content
depends strongly on geographic location and shows a seasonal
modulation. The diurnal cycle of PWV is poorly represented in ERA40
reflecting weaknesses in the water cycle of global circulation
models at this timescale.