In order to understand the atmospheric branch of the earth's
hydrologic cycle on the global scale, an atmospheric moisture balance
is diagnostically analyzed from the January and July data of the OSU
atmospheric general circulation model, which has been integrated for
thirty-nine months of simulation with seasonally-varying sea-surface
temperature and solar insolation. The model hydrologic processes
analyzed for the balance include the surface evaporation, the precipitation
by large-scale and cumulus condensation, the vertical transport
by large-scale and cumulus mass fluxes, and the horizontal transport
of water vapor. The large-scale transports include the contributions
from the standing and transient components of motion. Also
analyzed are the potential and stream functions of horizontal transport,
and the statistics of seasonal and interannual variabilities
of the global and hemispheric effects of the hydrologic processes.
As a result of these analyses, the hydrologic cycle is constructed
and understood for both January and July of the model. Large-scale
vertical transport moistens the upper layer; the standing and transient
motions contribute mostly in the tropics and higher latitudes, respectively.
Large-scale horizontal transport moistens the continental atmosphere
except for the relatively small transport from the continents to
the oceans by the standing motion in the upper layer; the runoff occurs
in the model to balance the marine transport but seasonal trends exist
such that snow assumulates during January and melts during July on the
global average. Cumulus convection drys not only the lower layer but
also the upper layer of the model, and the penetrating cumuli are a
major mechanism of maritime precipitation, whereas the large-scale condensation
and penetrating cumuli have the dominating effect on the continental
precipitation during January and July, respectively. The seasonal
precipitation over the Northern Hemisphere continents concurs with
strong surface evaporation in summer and also with strong cyclonic activity
in winter.
Comparison with other models and observational data indicates that
the model reproduced some basic features of the atmospheric branch of
the hydrologic cycle and its seasonal variation. The intense evaporation
(≥ 5 mm day⁻¹) over the Pacific and Atlantic oceans and the rain
belts in the tropics are well simulated for both January and July. The
poleward transport in the northern middle and high latitudes is in good
agreement with observations. The maximum toward-thermal-equator transport
in the tropics occurs, however, at the geographic equator for both
January and July, indicating that these maxima are about 5 degrees of
latitude closer to the seasonal thermal equator than the observed maxima.
Nevertheless the global statistics of the model atmosphere are not
significantly different from that of the real atmosphere.
Among others, we mention the following common features of the
January and July moisture balances in the present model. Most precipitation
of penetrating convection occurs in regions of strong surface
evaporation even though some occurs in the moisture convergence zones
where most of heavy mid-level convection is located. In the regions
of intense penetrating convection, however, the standing part of surface
evaporation is much larger in magnitude than the negative transient
part which is essentially due to the positive correlation between
the turbulence intensity and surface humidity over wet surfaces.
Moreover, the horizontal structure of the standing part conforms to
that of the standing vapor pressure difference between the air and the
underlying surface. A strategy for further studies is recommended on
the basis of our understanding of these features. / Graduation date: 1982
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28980 |
| Date | 15 June 1981 |
| Creators | Chang, Jy-tai |
| Contributors | Kim, Jeong-Woo |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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