A STUDY OF THE HYDROLOGY OF EASTERN NORTH AMERICA USING ATMOSPHERIC VAPOR FLUX DATA

EUGENE M. RASMUSSON Geophysical Fluid Dynamics Laboratory, ESSA, Princeton, N.J.

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Abstract

The atmospheric water vapor flux divergence and certain aspects of the water balance of Eastern North America are investigated, using data from the period May 1, 1958, to Apr. 30, 1963.

Mean monthly values of evapotranspiration and storage change are computed as residuals, using measured values of vapor flux divergence, precipitation, and streamflow. Computations are performed for regions varying in size from 42 × 105 km2 to approximately 5 × 105 km2. The results for the smaller areas, which are the least reliable, are critically examined.

Computed values of evapotranspiration and storage change are compared with the climatological estimates Thornthwaite Associates and Budyko. The Thomthwaite climatic water balance data appear to overestimate , the difference between precipitation and evapotranspiration, during winter and underestimate it during summer. Budyko's values of evapotranspiration generally show a slightly smaller seasonal variation and appear to lead the values obtained from the atmospheric budget computations by around 0.5 to 1 mo.

Flux divergence computations are made for the Gulf of Mexico and Caribbean Sea, and the results are compared with values obtained by Hastenrath and with estimates of by Wüst and Budyko.

Interannual variations in storage over the Eastern Region of North America are examined and are found to be comparable with the seasonal changes. The onset of the drought of the early and mid-1960s is clearly reflected in the computed storage values.

It is found that variations in mean monthly precipitation during winter are positively correlated with the strength of the northward flow of moisture across the Gulf Coast, but little or no relationship between these quantities appears to exist during summer.

Now affiliated with the BOMAP Office, NOAA, Rockville, Md.

Abstract

The atmospheric water vapor flux divergence and certain aspects of the water balance of Eastern North America are investigated, using data from the period May 1, 1958, to Apr. 30, 1963.

Mean monthly values of evapotranspiration and storage change are computed as residuals, using measured values of vapor flux divergence, precipitation, and streamflow. Computations are performed for regions varying in size from 42 × 105 km2 to approximately 5 × 105 km2. The results for the smaller areas, which are the least reliable, are critically examined.

Computed values of evapotranspiration and storage change are compared with the climatological estimates Thornthwaite Associates and Budyko. The Thomthwaite climatic water balance data appear to overestimate , the difference between precipitation and evapotranspiration, during winter and underestimate it during summer. Budyko's values of evapotranspiration generally show a slightly smaller seasonal variation and appear to lead the values obtained from the atmospheric budget computations by around 0.5 to 1 mo.

Flux divergence computations are made for the Gulf of Mexico and Caribbean Sea, and the results are compared with values obtained by Hastenrath and with estimates of by Wüst and Budyko.

Interannual variations in storage over the Eastern Region of North America are examined and are found to be comparable with the seasonal changes. The onset of the drought of the early and mid-1960s is clearly reflected in the computed storage values.

It is found that variations in mean monthly precipitation during winter are positively correlated with the strength of the northward flow of moisture across the Gulf Coast, but little or no relationship between these quantities appears to exist during summer.

Now affiliated with the BOMAP Office, NOAA, Rockville, Md.

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