Search Results

You are looking at 1 - 10 of 25 items for

  • Author or Editor: Edward Rodgers x
  • Refine by Access: All Content x
Clear All Modify Search
Edward Rodgers and Honnappa Siddalingaiah

Abstract

In light of previous theoretical calculations, an empirical-statistical analysis using satellite multifrequency dual polarized passive microwave data to detect rainfall areas over land was performed. The addition of information from a lower frequency channel (18.0 or 10.7 GHz) was shown to improve the discrimination of rain from wet ground achieved by using a single frequency dual polarized (37 GHz) channel alone.

The algorithm was developed and independently tested using data from the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR). Horizontally and vertically polarized brightness temperature pairs (TH, TV) at 37, 18, 10.7 GHz were sampled for rain areas over land (determined from ground-based radar), wet ground areas (adjacent and upwind from rain areas determined from radar), and dry land regions (areas where rain had not fallen during a previous 24 h period) over the central and eastern United States. Surface thermodynamic temperatures were both above and below 15°C. An examination of the data from each separate channel indicated that the probability (using the F test) for the mean vectors of any two populations being identical is less than 0.01 for classes sampled with surface thermodynamic temperatures ⩾15°C except for the rain over land and wet ground classes observed with the SMMR 37 GHz channel. For the classes sampled with surface thermodynamic temperatures <15°C, none of the classes were significantly different.

Since most of the categories were significantly different for the warmer (≥15°C) land surface cases, a Fisher linear discriminant classifier was then developed for each channel and independently tested. The results from one test case showed that for areas of large-scale heavy rainfall, the lower frequency SMMR channels were better able to delineate rain from wet ground than the 37 GHz channel. However, in areas of light rain and/or where the rain area did not fill the lower frequency instantaneous field of view these channels were not able to differentiate, rain from wet ground.

Full access
John Stout and Edward B. Rodgers

Abstract

The Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) was used to map the distribution of total ozone around western North Pacific tropical cyclones from 1979 to 1982. The strong correlation between total ozone distribution and tropopause height found in the subtropical and midlatitudes made it possible for TOMS to monitor the propagation of upper-tropospheric waves and the mutual adjustment between these waves and tropical cyclones during their interaction. Changes in these total ozone patterns reflect the three-dimensional upper-tropospheric transport processes that are involved in tropical cyclone intensity and intensity and motion changes. The total ozone distributions indicate that 1) the mean upper-tropospheric circulations associated with western North Pacific and Atlantic tropical cyclones are similar; 2) more intense tropical cyclones have higher tropopauses around their centers; 3) more intense tropical cyclones have higher tropopauses on the anticyclonic-shear side of their outflow jets, which indicate that the more intense tropical cyclones have stronger outflow channels than less intense systems; 4) tropical cyclones that intensify (do not intensify) are within 10° (15°) latitude of weak (strong) upper-tropospheric troughs that are moderately rich (very rich) in total ozone; and 5) tropical cyclones turn to the left (right) when they move within approximately 15° latitude downstream of an ozone-poor (ozone-rich) upper-tropospheric ridge (trough).

Full access
Edward Rodgers and R. Cecil Gentry

Abstract

Rapid-scan visible images from the Visible Infrared Spin Scan Radiometer (VISSR) sensor on board SMS-2 and GOES-1 have been used to derive high-resolution upper and lower tropospheric environmental wind fields around three western Atlantic tropical cyclones (Caroline, August 1975; Anita, August and September 1977; and Ella, September 1978). These wind fields were used to derive the local change of the net relative angular momentum (RAM), upper and lower tropospheric areal mean relative vorticity and their difference, and the storm's transverse circulation. The local change of the storm's net RAM was investigated for the purpose of predicting future storm intensification while the areal mean relative vorticity and transverse circulation were investigated to better understand how the storm's environmental circulation was affecting its intensification.

The three cases studied suggested that storm intensification could be predicted from the analyses of the storm's local change of net RAM and that there is an ∼6 h lag between the local change in the net RAM and storm intensification. In addition, it was found that changes in the local change of net RAM wore being affected primarily by the net horizontal transport of relative angular momentum caused either by the convergence of cyclonic vorticity in the lower troposphere or by the divergence of anticyclonic vorticity in the upper troposphere. For the three cases studied, the upper tropospheric environmental circulation helped to influence the local change of net RAM and, therefore, changes of storm intensity by hindering or enhancing the storm's outflow and by weakening or strengthening the environmental anticyclonic circulation.

Full access
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
Edward B. Rodgers and Harold F. Pierce

Abstract

The distribution and intensity of tropical cyclone precipitation has been known to have a large influence on the intensification and maintenance of the system. Therefore, monitoring the tropical cyclone convective rainband cycle and the large-scale environmental forcing mechanisms that initiate and maintain the tropical cyclone convective rainbands may aid in better understanding and predicting tropical cyclone intensification.

To demonstrate how the evolution of the tropical cyclone precipitation can be monitored, the frequent Special Sensor Microwave/Imager (SSM/I) observations of precipitation from Typhoon Bobbie (June 1992) were used to help better delineate Bobbie's convective rainband cycle. Bobbie's SSM/I-observed convective rainband cycle was then related to the tropical cyclone's intensity change. To obtain a better understanding of how Bobbie's convective rainbands were initiated and maintained, total precipitable water (TPW) over the ocean regions, mean monthly sea surface temperatures (SSTs), and analyses from the European Centre for Medium-Range Weather Forecasts(ECMWF) model were examined. The SSM/I TPW helped to substantiate the ECMWF-analyzed regions of dry and moist air that were interacting with the system's circulation, while the mean monthly SSTs were used to determine whether the western North Pacific, where Bobbie traversed, was warm enough to allow for sufficient energy flux to support convection. The ECMWF model was employed to examine the environmental forcing mechanisms that may have initiated and maintained Bobbie's convective rainbands, such as mean vertical wind shear, environmental tropospheric water vapor flux and divergence, and upper-tropospheric eddy relative angular momentum flux convergence.

Results from the analyses of Typhoon Bobbie suggested the following: 1) The SSM/I observations of Bobbie's precipitation were able to detect and monitor convective rainband cycles that were similar to those observed with land-based and aircraft radar, in situ measurements, and SSM/I observations of western North Atlantic tropical cyclones. 2) The evolution of Bobbie's intensity coincided with the SSM/I-observed convective rainband cycles. 3) The SSM/I observations of the TPW over nonraining ocean regions were able to substantiate the ECMWF-analyzed moist and dry regions that were interacting with Bobbie's circulation. 4) In regions of warm SSTs and weak vertical wind shear, the enhancement of the precipitation in Bobbie's inner-core convective rainbands coincided with the inward convergence of upper-tropospheric eddy relative angular momentum, while the initialization of Bobbie's outer-core convective rainbands appeared to coincide with the large horizontal convergence of moisture. 5) The dissipation of rain in the inner-core convective rainbands appeared to be associated with inward propagation of newly formed outer convective rainbands, strong vertical wind shear (above 10 m s−1), and cool SSTs (below 26°C).

Full access
Edward B. Rodgers and Harold F. Pierce

Abstract

Special Sensor Microwave/Imager (SSM/I) observations were used to examine spatial and temporal changes in the precipitation characteristics for western North Pacific tropical cyclones that reached storm stage or greater during 1987-92. The second version of the Goddard scattering algorithm, that employed the 85-GHz brightness temperatures to measure rain rate, provided an analysis of the tropical cyclone precipitation distribution in greater detail, while the numerous SSM/I observations helped to better define the relationship between the tropical cyclones’ spatial and temporal distribution of precipitation and the systems intensity, intensity change, radiational forcing, and mean monthly sea surface temperatures (SSTs). The two SSM/Is flown since 1992 also helped to provide a more detailed analysis of the evolution of the tropical cyclone inner-core diabatic heating.

Similar to the SSM/I-observed 1987–89 western North Atlantic tropical cyclones, the SSM/I observations of the western North Pacific tropical cyclones revealed that the more intense systems had higher rain rates and greater areal distribution of rain. In addition, the heaviest rain rates were found nearer to the center of all the tropical cyclones. However, western North Pacific typhoons were found to have heavier azimuthally averaged rain rates and a greater contribution from the heavier rain within the inner core (i.e., within 111 km of the center) than the western North Atlantic hurricanes.

The SSM/I observations of the western North Pacific tropical cyclones also suggested the following: 1) there appears to be a diurnal variation in the tropical cyclone precipitation (i.e., morning maximum and an evening minimum) except in the inner-core regions of systems that are at storm stage and greater; 2) the maximum rain rate that a tropical cyclone can produce in the inner-core region is dictated by SSTs with maximum rain rates occurring at SSTs greater than 29°C; 3) the large changes in the tropical cyclone inner-core rain rate (latent heat release) help to initiate and maintain periods of tropical cyclone intensification; and 4) the intensity of these tropical cyclones become more responsive to rain-rate changes as the tropical cyclones become more intense.

Full access
Robert F. Adler and Edward B. Rodgers

Abstract

Data from the Nimbus 5 Electrically Scanning Microwave Radiometer (ESMR) are used to make calculations of the latent heat release (LHR) and the distribution of rainfall rate in a case study of a tropical cyclone as it grows from a tropical disturbance to a typhoon. The results indicate that the latent heat release characteristics of tropical cyclones can be determined from the microwave data and that such observations are potentially useful in the monitoring of such storms. The LHR (calculated over a circular area of 4° latitude radius) increases during the development and intensification of the storm from a magnitude of 2.7 × 1014 W (in the disturbance stage) to 8.8 × 1014 W (typhoon stage). The later value corresponds to a mean rainfall rate of 2.0 mm h−1. Even during the disturbance stage, the LHR increases significantly. It is also shown that the more intense the cyclone and the greater the LHR, the greater the percentage contribution of the larger rainfall rates to the LHR. In the disturbance stage the percentage contribution of rainfall rates ⩾ 6 mm h−1 is typically 8%; for the typhoon stage, the value is 38%. The distribution of rainfall rate as a function of radial distance from the center indicates that as the cyclone intensifies, the higher rainfall rates tend to concentrate toward the center of the circulation.

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
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
Edward Rodgers, John Stout, Joseph Steranka, and Simon Chang

Abstract

No abstract available.

Full access