Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: Daniel L. Cadet x
  • Refine by Access: All Content x
Clear All Modify Search
Sergio Reyes and Daniel L. Cadet

Abstract

Some meteorological features have been examined as part of a more extensive study on general circulation in the eastern Pacific and Central American region. The analysis is based on twice-daily data from May to August 1979. Different FGGE data sets (Level III-b, TIROS-N) were used to obtain fields of precipitable water (PW), 1000 mb wind, and surface water vapor fluxes. The results concerning precipitable water and wind are presented as monthly mean fields. The time and spatial evolution of three layers of PW (surface to 700 mb, 700–500 mb and 500–300 mb) show the synoptic characteristics prevailing during this period. The fields of PW reveal fluctuations that are associated with the number and trajectories of tropical perturbations observed over the Atlantic and Pacific Oceans. The time series of the 1000 mb water vapor flux for latitudinal and longitudinal segments around Mexico and the eastern equatorial Pacific 0cean were determined. The strongest horizontal mean flux takes place over the Gulf of Mexico and the eastern Pacific Ocean. Minimum intensity occurs during August, coincident with the month of observed fewer-than-normal tropical perturbations.

Full access
Daniel L. Cadet and Steve Greco

Abstract

Water vapor transport over the Indian Ocean during the 1979 summer monsoon is studied. The analysis is based on wind fields from the European Centre for Medium Range Weather Forecasts and humidity fields derived from a three-layer precipitable water dataset. Fields of zonal and meridional water vapor fluxes show significant variations over the north Indian Ocean in association with the different phases of the 1979 monsoon. Whereas after the onset, the cross-equatorial water vapor flux west of 50°E does not vary much; it undergoes significant fluctuations east of that longitude. The bulk of water vapor crossing the western coast of India comes from the Southern Hemisphere. The latitude band between 10° and 20°S appears as a major source of moisture during the northern summer. The major moisture supply for the western coast of Burma and Thailand is advected over the Bay from the Arabian Sea branch of the monsoon. The water vapor flux across the west coast of India undergoes large amplitude variations in relation with the active/break cycle of the 1979 monsoon (onset, active, break and revival periods). During active periods, the moist flow over the Arabian Sea strengthens and deepens. The water vapor flux across the west coast of India is well related to rainfall along the coast. Ale early retreat of the 1979 monsoon is associated with a decreasing trend in moisture transport over the Arabian Sea. In the Bay of Bengal, the cross-equatorial flux is not affected by the break/active cycle of the monsoon. There are strong surges of northward flux into the Bay. Some of them are related to the formation of Bay depressions.

Full access
Daniel L. Cadet and Steve Greco

Abstract

In this second part of the paper, moisture budgets over the Arabian Sea and the Bay of Bengal are investigated for the 1979 summer monsoon season.

Over the Arabian Sea the different terms of the moisture balance equation, except evaporation, strongly fluctuate depending on the activity of the monsoon. The relative contribution to the monsoon moisture supply by water vapor transport across the equator and Arabian Sea evaporation varies as the monsoon intensity changes from active through break and back to revival stages. However. it is shown that water vapor from the Southern Hemisphere is the major source of moisture for Indian rainfall. Total evaporation during the active period following the onset of the monsoon is found to be 30–40% of the total eastward flux across the west coast of India. This ratio increases to 40–45% during break condition but falls below 20% during a revival phase. These moisture budgets also show that convergence of water vapor flux is limited to the eastern part of the Arabian Sea whereas evaporation exceeds precipitation in the western Arabian Sea

Moisture budgets over the Bay of Bengal depend strongly on the monsoon intensity and the amount of moisture advected across the western coast of India and into the Bay of Bengal by the monsoon circulation. Moisture supply from the Southern Hemisphere via cross-equatorial flux at the longitude of the Bay of Bengal is very weak. Compared to weak monsoon periods a much larger percentage of the water vapor supplied by evaporation and boundary fluxes is transported towards Burma and Malaysia during active monsoon periods, fueling the heavy rainfall them.

Full access
Sergio Reyes and Daniel L. Cadet

Abstract

The physical characteristics of the southwest branch of the North American monsoon system during the summer of 1979 are studied with the FGGE dataset. The combined features such as the low pressure trough over northwestern Mexico, the penetration of the easterly flow from the Atlantic Ocean, and the intensification. of the anticyclonic gyre of the South Pacific, are responsible, during the summer, for a well established cross-equatorial surface air flow along the eastern tropical Pacific Ocean and western Mexico. Mean monthly maps of vertically integrated water-vapor flux show the development of a low-level jet favoring the penetration, into western Mexico, of a cross-equatorial moist flow which originates over the southern Pacific. It is shown that the South Pacific anticyclone gyre is an important feature which brings moist air along western Mexico. The mean monthly evolution of the net water-vapor flux divergence suggests a strong association with the precipitation pattern observed over Mexico.

Full access
Daniel L. Cadet and Bradley C. Diehl

Abstract

The interannual variability of surface meteorological fields over the Indian Ocean during the period 1954–76 is studied using 2 million ship reports obtained from different sources. Monthly mean fields of wind, pressure, air temperature, mixing ratio, cloud cover and sea surface temperature (SST) on a grid mesh of 2° have been determined by computing the monthly mean values of the data around each grid point. Because data coverage is poor over certain areas, an objective analysis based on the successive correction method was performed.

Seasonal anomaly fields are presented for the Northern Hemisphere summers of 1956 and 1972, with the two summers having opposite extreme features. During 1956 (1972), the intensity of the trade winds in the Southern Hemisphere and the summer cross-equatorial flow were above (below) normal. Sea surface temperature was below (above) normal over the entire Indian Ocean in 1956 (1972). Time series of the anomalies over different key areas show that weaker than normal trade winds persisted during a period extending from 1968–74. As a consequence, the summer cross-equatorial flow was reduced, mainly along the African coast, by about 20%. During the same period, SST and air temperatures were above normal (up to 2°C during the 1972 summer) presumably due to the decrease of evaporation and turbulent mixing of the surface layer by weaker winds. The fluctuations of the different surface parameter anomalies seem to be related to a similar variation of the activity of the summer monsoon: the end of the sixties and the beginning of the seventies correspond to dry monsoons. This is supported by fields of correlation coefficients between summer rainfall over India and different parameters over the Indian Ocean.

Full access