Circulation mechanisms related to northeast Brazil rainfall anomalies

Journal Article · Sat Mar 20 04:00:00 EST 1993 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/92JD02646· OSTI ID:6617037

Hastenrath, S; Greischar, L ^[1]

---

1. Univ. of Wisconsin, Madison (United States)

This study explores the role of the upper ocean for circulation anomalies in the overlying atmosphere, with focus on the late boreal winter and extreme climatic events in northeast Brazil. Data sources comprise rainfall records in the Nordeste, surface ship observations of the sea surface temperature (SST), pressure, and wind fields (COADS, period 1948-1990), satellite observations of tropical convection (HRC, 1971-1988), and upper air analyses of the European Centre for Medium Range Weather Forecasts (ECMWF, 1980-1991), all for the tropical Atlantic sector. Enhanced northward temperature increase in the tropical Atlantic is accompanied by steeper meridional pressure gradient and accelerated southerly wind component, which is representative of a northward displaced Intertropical Convergence Zone (ITCZ), with the latter in turn leading to drought in northeast Brazil. Interhemispheric contrasts in the 850/1000 mbar layer mean temperature are similar to those of SST and account for most of the meridional surface pressure gradient. During wet as compared to dry years in northeast Brazil, the tropical North Atlantic is cooler and the South Atlantic warmer, and accordingly the lower tropospheric thickness is reduced to the north but inflated to the south of the equator, resulting in increased/reduced surface pressure over the North/South Atlantic, as well as reduced southerly surface wind, stronger subsidence over the outer tropics of the northern hemisphere and intensified ascending motion and convective activity over the Nordeste, related to a southward displaced near-equatorial convection belt. The surface and upper air evidence thus indicates the ways in which the interhemispheric SST gradients exert a hydrostatic control on the lower tropospheric thickness pattern, and thus force the south-north surface pressure gradients and the surface meridional wind component, and hence modulate the latitude position of the ITCZ and Nordeste rainfall. 23 refs., 8 figs., 4 tabs.

• OSTI ID: 6617037
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 98:D3; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540110*
540210 -- Environment
Terrestrial-- Basic Studies-- (1990-)
540310 -- Environment
Aquatic-- Basic Studies-- (1990-)
58 GEOSCIENCES
580000 -- Geosciences
AIR
AMBIENT TEMPERATURE
ATLANTIC OCEAN
ATMOSPHERIC CIRCULATION
ATMOSPHERIC PRECIPITATIONS
BRAZIL
CLIMATES
COMPARATIVE EVALUATIONS
CONTROL
CONVECTION
CONVERGENCE
DEVELOPING COUNTRIES
DIMENSIONS
EARTH PLANET
ENERGY TRANSFER
EQUATOR
EVALUATION
FLUIDS
GASES
HEAT TRANSFER
LATIN AMERICA
MASS TRANSFER
MOTION
NORTHERN HEMISPHERE
PLANETS
PRECIPITATION
PRESSURE GRADIENTS
RAIN
RANGE
SATELLITES
SEAS
SEPARATION PROCESSES
SOUTH AMERICA
SURFACE WATERS
THICKNESS
TROPICAL REGIONS
WEATHER
WIND