Wednesday, 16 January 2002
Moisture advection and fresh water flux over oceans
Under stationary conditions, ocean surface fresh water flux,
which is the difference between precipitaiton (P) and
evaporation (E), is balanced by the divergence of
column-integrated moisture tansport (IMT) in the atmosphere.
The balance affects the global hydrologic balance and governs
the thermohaline circulation in the oceans. The computation
of the IMT requires vertcial profiles of wind vector and
specific humidity, which traditionally come from rawindsondes.
Over the ocean, rawindsondes are sparse. Spacebased scatterometer
can measure wind vectors at the surface of the ocean (SWV) and
the microwave radiometers can measure the column-integrated
water vapor (IWV). This study is intended to demonstrate that
the two spacebased measurements can contribute to estimation
of IMT and, therefore, the monitoring and study of the variability
of global hydrologic balance and P-E.
IMT can be written as the product of IWV and an equivalent
velocity (EV). EV is the depth-averaged wind velocity weighted
by humidity. One year of wind and humidity profile from the
reanalysis of the European Center for Medium Weather Forecast
are used to compute EV. The EV computed exhibit close relation
to SWV. Both statistical and physical model relating EV to SWV
are being developed and tested. Maps of P-E over tropical oceans
computed for scatterometer and radiometer data using the models
are found to be in agreement with P-E climatologies compiled
from ship reports and directly estimated from spacebased data.