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David W. Martin and Barry B. Hinton

Abstract

Rainfall is analyzed for the Indian and west Pacific Oceans. The analysis uses a multichannel scheme to retrieve open-ocean rain rate from brightness temperatures measured between 1979 and 1986 by the Nimbus-7 Scanning Multichannel Microwave Radiometer. Rain rates were averaged over calendar months for 1° boxes. These rain rates were checked against two published climatologies. They were analyzed in light of historical climatologies of rainfall over the Indian and west Pacific Oceans.

Except for the Somali jet, the scheme adequately represented ambient conditions over the Indian and west Pacific Oceans. Rain tended to fall in two bands paired across the equator. Over the Indian Ocean, the southern member consistently dominated the northern member. Over the west Pacific Ocean, at times through the course of the year, each member dominated the other. Close to the East Indies northern and southern members merged. Bands were modulated by a pair of wavelike conglomerates. Following the sun, each wave conglomerate strengthened on the poleward legs of its track and weakened on the equatorward legs. One wave conglomerate appeared to follow a clockwise loop connecting waters near Madagascar with the Arabian Sea, India, and the Bay of Bengal. The other appeared to follow a counterclockwise loop connecting Austral–Melanesian waters with the Philippine Sea, the South China Sea, and the Bay of Bengal. Converging in boreal spring on northbound legs, the wave conglomerates appeared to merge over South Asia.

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Donald Wylie, Barry B. Hinton, and Kevin Kloesel

Abstract

We have studied the changes in marine stratocumulus cloud cover observed during the FIRF, Program and how cloud cover related to synoptic conditions. Statistical analyses of the 21 day FIRE period show that marine stratocumulus cloud cover over the eastern Pacific ocean was related to wind direction and temperature advection. Good coorelations were found between the cloud cover fraction observed on satellite imagery and the NMC Global Spectral Model analyses of surface winds and temperature advection. This comparison was made in even locations in the Eastern Pacific. Regional differences were found between the area of FIRE operations several hundred kilometers west of San Diego and the other oceanic areas studied.

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Donald P. Wylie and Barry B. Hinton

Abstract

A detailed analysis of the wind stress patterns over the Indian Ocean was made from 1 May to 31 July 1979. A combination of cloud motion and ship data obtained once per day was used to diagnose the surface-wind patterns to a degree of detail not possible in the past for an individual season. These data show the monsoon development and the fluctuations of the Somali Jet and the Southern Hemispheric tradewinds. Wind stress patterns produced by two traveling tropical storms are discussed. These combined to exert an unusually high westerly wind stress on the equator before the monsoon developed.

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Donald P. Wylie and Barry B. Hinton

Abstract

Cloud motions over the Indian Ocean for May–July 1979 were used to obtain spatial auto correlations of the deviations of the wind components from local means. Best correlations were associated with u′, low altitude clouds and alongwind displacements. Worst correlations arose from v′, high clouds and crosswind displacements. The crosswind anisotropy was ∼15%. All correlations were 0.49 or greater at 5° separation or less.

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David Suchman, Brian Auvine, and Barry Hinton

To examine whether the addition of satellite data to forecasting procedures helps forecasters make better forecasts, we studied a meteorological consulting firm and its clients before and after satellite data were used in the preparation of weather forecasts, and whether the clients benefited from this new data source. We found that the satellite data were most valuable when they could be looped to show evolving cloud patterns and enhanced to show brightness differences. The satellite data would have been even more useful if the dissemination system were more flexible and the images were not pregridded.

Our main conclusions are:

  1. Satellite data are most useful to forecasters in data-poor areas and also help to fine-tune forecasts in data-rich areas. Because even slight improvements in forecast accuracy can result in sizable savings for clients, the use of satellite data can produce a significant economic benefit.
  2. Working with satellite data is a valuable educational experience for forecasters and undoubtedly improves their forecasting skills.
  3. Any future satellite data delivery system should take into account the needs and facilities of the user community.

Finally, we have shown that it is possible, using real data in actual situations, to help determine some of the economic effects of a new tool and the ways it can be used to bring about greater public benefits.

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Barry B. Hinton and Donald P. Wylie

Abstract

The errors in ship wind reports of light winds tend to significantly bias their mean. This occurs because wind speed is a scalar quantity that is constrained to zero or positive values. Therefore, observations tend to overestimate the light winds because of the one-sided distribution of errors, but the bias disappears under stronger winds. A method for removing this bias from ship data is presented. In particular, the method is applied to interpreting the ratios of wind speeds observed by ships to those obtained from tracking low level clouds. Contracted ratios allow low cloud speeds to serve as proxy data for surface based observations.

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Donald P. Wylie, Barry B. Hinton, and Kellie M. Millett

Abstract

The feasibility of using satellites for providing surface winds or wind stress data was explored. Three popular methods were compared using nearly colocated data to assess the accuracies of each and the coverage that each could provide. The three methods tested were 1) the use of the sun glitter reflection seen on visible images of the ocean surface; 2) the use of active microwave sensors (flown on SEASAT) which reflect microwaves off the ocean surface; and 3) the use of cloud motions as indicators of the surface winds.

Close agreement in wind speed estimates was found among the three methods. The biases were <0.6 m s−1 for comparisons between comparable methods of estimating surface winds (1 and 2). Cloud motion comparisons to the other methods exhibited biases of <3.0 m s−1. Individual point-by-point comparisons between wind measurements had an average scatter of 2.0 m s−1 (rms) or less after the mean biases were removed. Atmospheric variability caused as many of the differences as the instrumental errors indicating that meaningful wind information could be obtained from all three methods.

Very detailed spacial coverage was obtained with the sun-glitter method for wind speeds. However, the coverage was restricted to a narrow band 5° of latitude wide in the tropics. SEASAT also provided good coverage for two swaths (4° longitude wide) on each side of the satellite's orbit. Gaps between the swaths and orbits (polar non-synchronous orbits) were left unsampled. Both methods required external data on the wind directions which were obtained from cloud motions. The cloud motions provided coverage over larger areas than the other two methods because of the abundance of low-level cumuli.

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Carl C. Norton, Frederick R. Mosher, and Barry Hinton

Abstract

Applications Technology Satellite (ATS) 3 green sensor data are used to measure surface reflectance variations in the Sahara/Sahel during the recent drought period 1967–74. The magnitude of the seasonal reflectance change is shown to be as much as 80% for years of normal precipitation and less than 50% for drought years. Year-to-year comparisons during both wet and dry seasons reveal the existence of a surface reflectance cycle coincident with the drought intensity. The relationship between the green reflectance and solar albedo is examined and estimated to be about 0.6 times the reflectance change observed by the green channel.

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David Suchman, Brian A. Auvine, and Barry H. Hinton

The clients of a meteorological consulting firm were studied to determine the effects of weather forecasts on their operations. We determined what weather conditions triggered certain operational decisions in three groups of clients—governmental bodies, gas utilities, and electric utilities. Then, using actual forecasts over a 2-year period, we calculated the monetary losses incurred as a result of incorrect forecasts. The results generally show losses in the thousands of dollars for each erroneous forecast. Thus, if the weather service is able to prevent even one set of poor decisions based on a forecast, the cost of the service would be returned and in many cases greatly exceeded. Other effects of the clients' use of the forecast are discussed qualitatively. These include nonmonetary gains to the clients and their customers through increased convenience, easier planning, and fewer breakdowns in service. At least some clients fail to realize these advantages through inefficient use of the forecast.

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Roy W. Spencer, Barry B. Hinton, and William S. Olson

Abstract

In a comparison between 37 GHz brightness temperatures from the Nimbus 7 Scanning Multichannel Microwave Radiometer and rain rates derived from the WSR-57 radars at Galveston, Texas and Apalachicola, Florida, it was found that the brightness temperatures explained 72% of the variance of the rain rates. The functional form relating these two types of data was significantly different from that predicted by models of radiative transfer through plane-parallel clouds. Most of the difference can be explained in terms of the partial coverage of footprints by convective showers. Because residual polarization is always present, even for large obscuring storms over land and water, it is hypothesized that emission by nonspherical hydrometeors is at least partly responsible for the observed polarization.

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