Barry B. Hinton

Nimbus-7 37 GHz Radiances Correlated with Radar Rain Rates over the Gulf of Mexico

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.

Removal of Ambiguous Wind Directions for a Ku-Band Wind Scatterometer Using Three Different Azimuth Angles

The Seasat-A satellite scatterometer (SASS) sensor demonstrated very successfully that Ku-band scatterometers can make accurate synoptic measurements of surface wind speed over the ocean. Because SASS provided normalized radar cross section (NRCS) measurements from only two azimuths, however, the harmonic relationship of NRCS with azimuth results in up to four ambiguous wind directions. The primary improvement to be incorporated in a next-generation scatterometer design such as Navy Remote Ocean Sensing System (NROSS) is the addition of a third azimuth look at each sampled cell. With this and other instrument improvements, preliminary studies indicate that wind-direction ambiguities (aliases) could successfully be removed in at least 80 percent of the cases. Furthermore, these studies show that in over 90 percent of the wind solutions, the two most probable solutions correctly identify the wind streamlines. Methods were studied which could examine typical streamline patterns derived from scatterometers using continuity or pattern-recognition techniques to determine which of the possible two wind directions was correct. In addition, unambiguous solutions were sought for cases where streamlines were not correctly defined. This paper describes several approaches for such alias-removal algorithms. These algorithms were developed with the aid of simulated three-beam scatterometer ambiguous wind-solution data (based on NOSS conditions) over a known windfield. The resulting algorithms were evaluated using a different set of simulated orbital data, but withholding the true winds.

A Passive Microwave Algorithm for Tropical Oceanic Rainfall

Abstract This study discusses a rainfall algorithm utilizing six channels of microwave radiance data from the Nimbus-7 Scanning Multifrequency Microwave Radiometer. The algorithm is intended for short-term climate studies over the ocean at low latitudes. To find a set of functional relationships, rain ratios are regressed on brightness temperatures for each channel. Next, these functions are integrated over a class of rain-rate distributions to find relations between mean brightness temperatures and mean rain rates. This step accounts for beam filling. Finally, weights are obtained for combining the rain rates from the individual channels. The weights vary with the rain rates, so that the optimum combination of channels is always used. Results are stored in a database grid 1° latitude × 1° longitude by one month. To test the algorithm, three years (1979–81) of data from the Indian Ocean are processed. These show spatial patterns very similar to previous climatological studies and to expected seasonal vari...

A Comparison of Three Satellite-Based Methods for Estimating Surface Winds over Oceans

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 instrume...

Autocorrelation of wind observations

Abstract Autocorrelation and variance statistics were calculated for seven types of wind data in the western hemispheric tropics. Most of these data came from the Global Weather Experiment (GWE) in January 1979. They were: 1) cloud motion measurements from four different sources, 2) rawinsonde wind reports, 3) synoptic land station reports, 4) marine ship reports, 5) aircraft pilot reports, 6) automatic aircraft reports for the GWE, and 7) Seasat scatterometer winds from September 1978. Winds were analyzed within a target area from 30°N to 30°S latitude and 0° to 180°W longitude. The Seasat scatterometer data had the highest autocorrelations and lowest standard deviations over short distances (<500 km). Cloud motions and rawinsondes had lower autocorrelations than Seasat, while synoptic land stations, ship reports, and aircraft pilot reports had the poorest autocorrelations. These correlations imply that synoptic land stations, ship reports, and aircraft reports were either more sensitive to small‐scale f...

The Wind Stress Patterns over the Indian Ocean During the Summer Monsoon of 1979

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.

Three years of rainfall over the Indian Ocean

Abstract Monthly rain failing on the Indian Ocean is mapped for the period 1979 through 1981 by means of observations of the Nimbus-7 Scanning Multichannel Microwave Radiometer. Both stationary and mobile parts were found in the pattern of rain. The stationary part consisted of three zonal and two meridional bands. Only one, the band along and south of the equator, maintained a strong presence through all seasons. A north equatorial counterpart to this south equatorial band also was persistent, but weak. The mobile part of the pattern look the form of a wave. The locus of this wave was an eastward-tilted figure eight, which straddled the equator. The wave moved clockwise along the north loop of the figure eight, counter-clockwise along the south loop. The crest of the wave crossed the equator from south to north in May or June and crossed the equator from north to south between August and October. Along its path the equatorial bands were alternately amplified and damped, and the transient bands were activ...

A comparison of cloud motion and ship wind observations over the Indian Ocean for the year of FGGE

Cloud motions over the Indian Ocean were compared to ship observations for the FGGE year. The statistics of this comparison show seasonal changes in the cloud-ship relationship as well as geographical and wind-pattern-dependent fetch history changes. Most of these changes follow simple boundary-layer relationships governed by friction and temperature advection. The most significant result is the improvement of the cloud-ship directional shear with wind speed. The mean veering angle between cloud and ship measurements decreased at higher wind speeds along with scatter of the shearing angle. This implies that the ability of cloud motion measurements to indicate the wind stress on the ocean improves for the important situations when the winds are strong.

The feasibility of estimating large-scale surface wind fields for the summer MONEX using cloud motion and ship data

Cloud motion data were compared to ship observations over the Indian Ocean during the summer monsoon, 1 May to 31 July 1979, with the objective of using the cloud data for estimating surface wind and ultimately the wind stress on the ocean. The cloud-ship comparison indicated that the cloud motions could be used to estimate surface winds within reasonable accuracy bounds, 2.6 m s-1 r.m.s. speeds and 22° to 44° r.m.s. directions (22° r.m.s. for winds < 10 m s-1). A body of statistics is presented which can be used to construct an empirical boundary layer with the eventual goal of producing a stress analysis for the summer MONEX from cloud motion data.

The Relationship of Marine Stratus Clouds to Wind and Temperature Advection

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.