17D.7
The Diurnal Cycle of Convection in NAME: Observations Versus Reanalysis
Paul E. Ciesielski, Colorado State University, Fort Collins, CO; and R. Johnson
Previous studies of the North American Monsoon (NAM) have been
hampered by the lack of observations, particularly over Mexico.
During the summer of 2004, the North American Monsoon Experiment
(NAME) established an enhanced observational network over Mexico
and the southwestern United States aimed at determining the sources
and limits of predictability of warm season precipitation associated
with the NAM. Nested within the larger NAME souding network,
an enhanced budget array with 4-6 daily sonde launches was
deployed over the southern Gulf of California extending eastward
into northwestern Mexico to study the diurnal cycle over the
core of the monsoon region. These sonde data, along with profiler and
pibal observations, were objectively analyzed at 4-h, 25 hPa, 1 degree
resolution over the core of the monsoon region. In addition,
observations from 157 surface sites in this region along with twice-daily
QuikSCAT oceanic winds were quality controlled and processed into a gridded
data set covering this domain at 1-h, 0.25 degree resolution.
Using these data sets, the mean, temporal variability, and diurnal
characteristics of the monsoon flow are documented with detail not
previously possible.
Independent of model data over land, these objectively analyzed
products are compared to similar analyses from a special North American
Regional Reanlysis (NARR) which was produced for the same period. This
comparison reveals the NARR's tendency to initiate the daily convective
cycle too early in the day despite the strong constraints placed on the
NARR by assimilating observed precipitation. General circulation models
over this region exhibit a similar behavior reaching their convective
maxima 2-3 hours earlier than observed. Using primarily objectively
analyzed surface data and observed surface fluxes, we explore
possible reasons for this erroreous behavior in the reanalyses and
models in this monsoon region.
Recorded presentationSession 17D, Monsoons I
Friday, 2 May 2008, 8:00 AM-9:45 AM, Palms I
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