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title: Report Series

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<h1>Report 12:&nbsp; Simulation of the Indian and East-Asian

Summer Monsoon in the ECMWF Model: Sensitivity to Horizontal Resolution</h1>

<ul><b>Sperber, </b>Kenneth R., Sultan Hameed, Gerald L. Potter and James

S. Boyle

<br>November 1993, 37 pp.&nbsp;

<hr>The ability of the ECMWF model (cycle 33) to simulate the Indian and

East Asian summer monsoon is evaluated at four different horizontal resolutions:

T21, T42, T63, and T106. Generally, with respect to the large scale features

of the circulation, the largest differences among the simulations occur

at T42 relative to T21. However, on regional scales, important differences

among the high frequency temporal variability serve as a further critical

test of the model's ability to simulate the monsoon. More generally, the

results indicate the importance of evaluating high frequency time scales

as a component of the climate sytem.

<p>T106 best captures both the spatial and temporal characteristics of

the Indian and East Asian Monsoon, while T42 fails to correctly simulate

the sequence and development of synoptic scale milestones that characterize

the monsoon flow. In particular, T106 is superior at simulating the development

and migration of the monsoon trough over the Bay of Bengal. In the T42

simulation, the development of the monsoon occurs one month earlier than

typically observed. At this time the trough is incorrectly located adjacent

to the east coast of India which results in an underestimate of precipitation

over the Burma/Thailand region. This early establishment of the monsoon

trough affects the evolution of the East-Asian monsoon and yields excessive

preseason rainfall over the Mei-yu region. EOF analysis of precipitation

over China indicates that T106 best simulates the Mei-yu mode of variability

associated with an oscillation of the rainband that gives rise to periods

of enhanced rainfall over the Yangtze River Valley. The coarse resolution

of T21 precludes simulation of the aforementioned regional scale monsoon

flows. <a href="pdf/rep12.pdf">(pdf file)</a>

<p><font size=-1>UCRL-MI-123395</font></p>