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N. Wolfson, Y. Mekler, and J. H. Joseph

Abstract

A new way to assess the resolution of inversion methods is defined. The dependence of resolution on accuracy is broken into three parts, each of which has a distinct practical significance. Representatives of four commonly used inversion techniques are evaluated in this context.

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N. Wolfson, J. H. Joseph, and Y. Mekler

Abstract

Four commonly used families of inversion techniques have been investigated. The accuracy and stability of the Chahine, Twomey–Phillips, Backus–Gilbert and non-linear regression techniques have been evaluated and compared. Practical and empirical rules for efficient use have been obtained.

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N. Wolfson, R. Atlas, and Y. C. Sud

Abstract

A series of numerical forecast experiments has been conducted with the Goddard Laboratory for Atmospheres (GLA) fourth-order general circulation model in order to study the role of (i) sea-surface temperature (SST) anomalies in the North Pacific, (ii) soil moisture anomalies over the continental United States, as derived from observations of precipitation and surface temperature, and (iii) solar radiational forcing in the maintenance and breakdown of the severe heat wave over the United States in the summer of 1980.

Results from these experiments show opposite effects of the SST and soil moisture anomalies on the model's medium-range (ten-day) simulations of the maintenance of the heat wave. The lower than normal soil moisture over the United States during the summer of 1980 resulted in reduced surface evaporation, higher ground temperature, increased sensible heat flux from ground to air, higher surface temperature, lower sea-level pressure and higher 500 mb height over much of the Great Plains in the model forecasts. In contrast, the SST anomalies in the North Pacific during the same period resulted in an enhanced northerly flow of cooler and dryer air, increased evaporation, decreased ground and air temperature and reduced 500-mb heights over the Great Plains. These results suggest that once established, soil moisture deficits contribute to maintaining warm, dry conditions. Although long-term effects of North Pacific SST anomalies may be to create or enhance the heat wave, ten-day simulations showed that such anomalies contributed to lower temperatures over shorter time scales.

A limited number of experiments, with modified solar radiational forcing, showed a dramatic weakening of the heat wave pattern in the model forecasts and indicated that the interaction of changing solar declination with the prevailing synoptic situation was probably responsible for the breakdown of the heat wave in September 1980.

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R. Atlas, N. Wolfson, and J. Terry

Abstract

A series of simulations of the late spring and early summer of 1988 were conducted in order to study the relative importance of different boundary forcings to the Goddard Laboratory for Atmospheres model's simulation of the heat wave and drought over the Great Plains of the United States during this time period. Separate 60- day simulations were generated from 10, 20, and 30 May 1988 with a variety of boundary condition datasets. For the control experiment, climatological boundary conditions were used. This was followed by experiments in which either the observed 1988 sea surface temperatures (SST) or derived 1988 soil moisture values, or both, were used in place of the climatological fields. Additional experiments were conducted in which only tropical or midlatitude SST anomalies were used.

The impact of the different boundary forcings was evaluated relative to the control simulations of the precipitation and surface air temperature over the Great Plains. It was found that the tropical SST anomalies had a significant effect in reducing precipitation in this area, while the midlatitude anomalies did not. Due to the prescribed climatological soil moistures for the SST experiments, a significant increase in surface temperature did not occur in these simulations. In contrast, the simulations with the anomalous 1988 soil moistures produced both a larger reduction of precipitation and a significant increase in surface temperature over the Great Plains. The simulations with both anomalous SST and soil moisture showed only a slight augmentation of the heat wave and drought relative to the experiments with anomalous soil moisture alone.

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A. Thomasell Jr., A. Gruber, H. Brodrick, N. Wolfson, and Z. Alperson

Abstract

Experiments with the numerical models of the Israel Meteorological Service show that the impact of satellite soundings can be substantial but depends on how the soundings are used by the models. The quasi-optimum use of satellite data in defining a first guess for the hemispheric analyses results in average reductions of error of up to 20% for 48-h predictions of sea level pressure and 10% for 500 mb height. The greatest average impact occurs at low levels in the atmosphere over the ocean near where the satellite data are introduced. Impact for individual cases tends to be large and concentrated near important synoptic features such as lows, but small elsewhere.

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