R. T. Pierrehumbert Department of Geophysical Sciences University of Chicago
It is hypothesized that the subtropical water vapor distribution results from the interplay of three simple factors: subsidence, which brings down dry air from aloft; lateral mixing, which brings in moistened air from the convective region at various rates; and drying by processing of air through the cold extratropics. A simplified Lagrangian model is formulated, and used to study how this process works during the CEPEX period (March, 1993). A key result is that the Northern subtropics should be viewed as a general background of dry air with mass mixing ratio of 10-4 or less on the 330K surface, interrupted by a few coherent moist plumes with mixing ratios on the order of 10-3. It is suggested that the Lagrangian model would also be useful in interpreting satellite water vapor data, and in diagnosing water vapor transport errors in general circulation models.
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