Search Results

You are looking at 1 - 8 of 8 items for

  • Author or Editor: E. B. Rodgers x
  • Refine by Access: All Content x
Clear All Modify Search
William E. Shenk and Edward B. Rodgers

Abstract

Three periods within the life cycle of Hurricane Camille (1969) are examined with radiometric and camera measurements from Nimbus 3 and camera information from ATS 3 in conjunction with conventional information. These periods are the deepening phase, the interaction of Camille with mid-latitude westerlies, and the excessive rain-producing period when the cyclone was over the central Appalachians.

Just prior to significant deepening, the Nimbus 3 Medium Resolution Infrared Radiometer (MRIR) window and water vapor channels showed a band of developing convection that extended to the cirrus level in the southeastern quadrant of the storm which originated from the ITCZ. Low-level wind fields were derived from conventional sources as well as from cumulus clouds tracked from a series of ATS 3 images. Within this band were low-level 30 kt winds that supplied Camille with strong inflow where the air passed over sea surface temperatures that were 1–3 standard deviations above normal.

At the beginning of the rapid deepening the MRIR radiometer measurements indicated a rapid contraction of the central dense overcast and then an expansion as the maximum deepening rate occurred. Simultaneously, the increase in the MRIR equivalent blackbody temperatures (TBB) indicated the development of large-scale subsidence throughout the troposphere northwest of the center. When Camille weakened as it moved over the lower Mississippi Valley, the cyclone acted as a partial obstruction to the synoptic-scale flow and increased the subsidence west and north of the cyclone center as indicated by the increase in water vapor TBB and verified by three-dimensional trajectories. Increased cloud-top elevations, approaching the levels reached when Camille was an intense cyclone over the Gulf of Mexico, were estimated from the Nimbus 3 High Resolution Infrared Radiometer (HRIR) measurements on 20 August 1969, when Camille produced rains of major flood proportions near the east slopes of the Appalachians in central Virginia.

Full access
E. B. Rodgers and R. F. Adler

Abstract

Data from the Nimbus-5 F-Electrically Scanning Microwave Radiometer (ESMR-5) have been used to calculate latent heat release (LHR) and other rainfall parameters for over 70 satelite observations of 21 tropical cyclones during 1973, 1974 and 1975 in the tropical North Pacific Ocean. The results indicate that the ESMR-5 measurements can be useful in determining the rainfall characteristics of these storms and appear to be potentially useful in monitoring as well as predicting their intensity. The ESMR-5 derived total tropical cyclone rainfall estimates agree favorably with previous estimates for both the disturbance and typhoon stages. The mean typhoon rainfall rate (1.9 mm h−1) is approximately twice that of disturbances (1.1 mm h−1).

Case studies suggest that tropical cyclone intensification is indicated by the increase in the ESMR-5 derived LHR, the increase in the relative contribution of the heavier rain rates (≥5 mm h−1) to the total storm rainfall, and the decrease in the radius of maximum rain rate from the cyclone center. It also appears evident from these case studies that by monitoring the trend of increasing LHR the first indication of tropical cyclone intensification may be obtained 1–2 days prior to the tropical cyclone reaching storm stage and often prior to the first reconnaissance aircraft observation. Further, the time of the maximum intensity of the tropical cyclone lags by 1–2 days the time of maximum LHR. The statistics of the western Pacific tropical cyclones confirm the case study results in that tropical cyclone intensity can be monitored from ESMR-5 derived rainfall parameters. As the mean tropical cyclone intensifies from disturbance to typhoon stage the average LHR increases steadily. The mean relative contribution of the heavier rate (≥5 mm−1) to the total storm rainfall increased from 0.24 at depression stage to 0.33 at storm stage and finally to 0.39 at typhoon stage. The radial distance of the maximum rain rate from the center decreases with intensification while the azimuthal distribution indicates a slight preference for maximum rain rate in the right half of the composite storm at all stages. The study also indicates that eastern Pacific hurricanes have less LHR, are more compact, and have less intense rainfall than western Pacific typhoons.

Full access
Herbert E. Hunter, Edward B. Rodgers, and William E. Shenk

Abstract

An empirical analysis program, based on finding an optimal representation of the data, has been applied to 120 observations of twenty nine 1973 and 1974 North Pacific tropical cyclones. Each observation consists of a field of Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR-5) radiation measurements at 267 grid points covering and surrounding the tropical cyclone plus nine other non-satellite derived descriptors. Forecast algorithms to estimate the maximum wind speed at 12, 24, 48 and 72 h after each observation were developed using three bases: the non-satellite-derived descriptors, the ESMR-5 radiation measurements, and the combination of the two data bases. Independent testing of these algorithms showed that the average error made by algorithms developed from all three bases was less than the average error made by the persistence 24, 48 and 72 h maximum wind speed forecast and less than the average errors made operationally by the Joint Typhoon Warning Center (JTWC) 48 and 72 h maximum wind speed forecasts. The algorithms developed from the ESMR-5 base alone outperformed the JTWC operational forecast for the 48 and 72 h maximum wind speed. Also, the ESMR-5 data base, when combined with the non-satellite base, produced algorithms that improved the 24 and 48 h maximum wind-speed forecast by as much as 10% and the 72 h maximum wind forecast by approximately 16% as compared to the forecast obtained from the algorithms developed from the non-satellite data base alone.

Full access
Herbert E. Hunter, Edward B. Rodgers, and William E. Shenk

Abstract

A statistical method has been developed using satellite, climatological, and persistence data to predict tropical cyclone position 12, 24, 48 and 72 h after initial observation. The satellite measurements were infrared window channel (11.0 μm) equivalent blackbody temperatures (TBB), which gave representations (through the cloud and surface temperature fields) of the structure of the cyclones and the circulation features surrounding them. There were 197 individual measurements of TBB for each cyclone observation. Algorithms have been prepared using digital data from a single satellite image, 14 climatological and persistence type variables, and a combination of these data sources. The algorithms were developed using a unique statistical procedure based on an eigenvector preprocessing and the use of independent tests for screening decisions.

Independent testing of these algorithms showed that the average error made by the algorithms developed from the single satellite observation were comparable to the 48 h Joint Typhoon Warning Center (JTWC) forecast and were approximately 10% better for 72 h forecasts. Forecasts using only the climatological and persistence variables were about 20% worse than JTWC for 24 h forecasts and 10% worse for 48 and 72 h forecasts. When both satellite and nonsatellite variables were included, the performance was comparable to JTWC's for the 24 and 48 h forecasts and approximately 25% better than JTWC's for the 72 h forecasts.

The performance of the objective algorithms for various partitions was analyzed. It is shown that both the satellite and nonsatellite variables make significant and unique contributions.

Full access
E. B. Rodgers, R. Mack, and A. F. Hasler

Abstract

Observations of the mean cloud top temperature and height of the eye wall of two tropical cyclones, using GOES infrared and stereoscopic measurements, presented an opportunity to estimate the storm's eye wall tropopause temperature and height. If it is assumed that for a mature tropical cyclone there is little dilution by outside air at the highest eye wall clouds so that the mean-equivalent potential temperature is constant with height from the surface to the cloud top (tropopause), then the mean equivalent potential temperature can be determined knowing the eye wall cloud top temperature and height. With knowledge of the storm's environmental equivalent potential temperature, using either climatological data or rawinsonde measurements together with the satellite derived eye wall equivalent potential temperature, estimation of either the storm's central pressure from the hydrostatic relationship or maximum winds from a cyclostrophic thermal wind relationship becomes possible.

The technique was tested first on Hurricanes Frederic (between 1645 to 2115 GMT 12 September 1979) and Allen (at 2245 GMT on 8 August 1980). Hurricane Frederic's maximum surface wind and central pressure were estimated to be ∼63 m s−1 and 945 mb, which compares well with reconnaissance aircraft measurements (58 m s−1/948 mb) near the time of the GOES observations. Allen's satellite derived maximum wind and central pressure were 78 m s−1 and 915 mb, which again compares favorably with aircraft measurements (73 m s−1/915 mb).

Full access
T. T. Wilheit, J. S. Theon, W. E. Shenk, L. J. Allison, and E. B. Rodgers

Abstract

The Electrically Scanned Microwave Radiometer (ESMR) on the Nimbus 5 satellite measures the microwave radiation emitted by the earth and the atmosphere in a wavelength band centered at 1.55 cm. The ESMR scans perpendicularly to the spacecraft suborbital track from 50° left to 50° right in 78 steps every 4 s, producing an image which has a spatial resolution of 25 km at nadir.

At these wavelengths, the emissivity of the earth and atmosphere varies considerably more than at infrared wavelengths. Thus the contrast in radiance between land surfaces, which have high emissivities, and ocean surfaces, which have low emissivities, makes continents and islands readily distinguishable. There is a minimum of interference from clouds since most non-raining clouds are virtually transparent at these wavelengths. However, atmospheric moisture does modify the radiation emitted by the surface and when cloud droplets reach precipitable size, they enhance the radiation considerably over surfaces of low emissivity (e.g., over oceans), making it possible to map areas of rainfall as well as regions of heavy cloudiness.

In this application the ESMR images are meteorologically useful in determining the extent, structure and, qualitatively, the intensity of rainfall. It is then possible, over oceans, to determine the location of frontal rain, rain/snow boundaries, and the structure of tropical storms. Because of the generally high emissivities of land surfaces and the wide range of values they assume, interpretation of atmospheric parameters over land is not possible at present.

Full access
T. T. Wilheit, A. T. C. Chang, M. S. V. Rao, E. B. Rodgers, and J. S. Theon

Abstract

A theoretical model for calculating microwave radiative transfer in raining atmospheres is developed. These calculations are compared with microwave brightness temperatures at a wavelength of 1.55 cm measured by the Electrically Scanning Microwave Radiometer (ESMR) on the Nimbus 5 satellite and rain rates derived from WSR-57 meteorological radar measurements. A specially designed ground-based verification experiment was also performed, wherein upward viewing microwave brightness temperature measurements at wavelengths of 1.55 and 0.81 cm were compared with directly measured rain rates. It is shown that over ocean areas, brightness temperature measurements from ESMR may be interpreted in terms of rain rate with about an accuracy of a factor of 2 over the range 1–25 mm h−1 rain rate.

Full access
T. T. Wilheit, A. T. C. Chang, J. L. King, E. B. Rodgers, R. A. Nieman, B. M. Krupp, A. S. Milman, J. S. Stratigos, and H. Siddalingaiah

Abstract

Observations of rain cells in the remains of a decaying tropical storm were made by Airborne Microwave Radiometers at 19.35 and 92 GHz and three frequencies near 183 GHz. Extremely low brightness temperatures, as low as 140 K, were noted in the 92 and 183 GHz observations. These can be accounted for by the ice often associated with raindrop formation. Further, the 183 GHz observations can be interpreted in terms of the height of the ice. The brightness temperatures observed suggest the presence of precipitationsized ice as high as 9 km or more.

Full access