Engineering topics

Rodgers, E.

Publications and source records attributed to Rodgers, E..

12 records

NASA NTRS1999

The Impact of TRMM on Mesoscale Model Simulation of Super Typhoon Paka

Tropical cyclone Paka formed during the first week of December 1997 and underwent three periods of rapid intensification over the following two weeks. During one of these periods, which initiated early on December 10, Paka's Dvorak-measured windspeed increased from 23 to 60 m/s over a 48-hr period. On December 18, during the last rapid deepening episode, Paka became a supertyphoon with a maximum wind speed of about 80 m/s. In this study, the Penn State/NCAR Mesoscale Model (MM5) with improved physics (i.e., cloud microphysics, radiation, land-soil-vegetation-surface processes, and TOGA COARE flux scheme) and a multiple level nesting technique (135, 45 and 15 km horizontal resolution) will be used to simulate supertyphoon Paka. We performed two runs initialized with Goddard Earth Observing System (GEOS) data sets. The first GEOS data set does not incorporate either TRMM (tropical rainfall measuring mission satellite) or SSM/I (sensor microwave imager) observed rainfall fields into the GEOS's assimilation system while the second one does. Preliminary results show that the MM5 simulated surface pressure deepened by more than 25 mb (45 km resolution domain) in the run initialized with the GEOS data set incorporating TRMM and SSM/I derived rainfall, compared to the one initialized without. However, the track and precipitation patterns are quite similar between the runs. In our presentation, we will show the impact of TRMM rainfall upon the MM5 simulation of Paka at various horizontal resolutions. We will also examine the physical processes associated with initial explosive development by comparing MM5 simulated rainfall and latent heat release. In addition, budget (vorticity, PV, momentum and heat) calculations and sensitivity tests will be performed to examine the upper-tropospheric and SST mechanisms responsible for the explosive development of Paka.

Tao, W.-K.↗

NASA NTRS1992

Effects of a lightning discharge detected by the DE 2 satellite over Hurricane Debbie

The satellite observation of a large, about 40-mV/m, transient electric field disturbance over Hurricane Debbie in September 1982 is reported. The electric field event is viewed as a spheric disturbance from a lightning discharge in the active weather system located beneath the satellite. To elucidate this observation of upward moving electrons in the ionosphere associated with a lightning event, several mechanisms for electron acceleration by electric field with components, E(parallel), along the magnetic field are compared. 'Runaway' electrons were accelerated in about 1 ms by a downward directed E(parallel) pulse of about 1 V/m magnitude. Such fields can result from rapidly exposed, negative space charges near the tops of clouds during positive cloud-to-ground discharges. HF frequency Fourier components of the E(parallel) pulse must propagate through the low-conducting nighttime atmosphere to the ionosphere with little dissipation.

Burke, William J.↗

NASA NTRS1983

The utilization of Nimbus-7 SMMR measurements to delineate rainfall over land

Approaches for developing an improved passive microwave technique to delineate rain from wet land surfaces are considered, and an investigation is conducted with the objective to study the application of these ideas with empirical data. The investigation includes a statistical analysis of Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) 37.0, 18.0, and 10.7 GHz data. The possibility was assessed to make use of the 18.0 and 10.7 GHz channels in order to reduce the ambiguities found in the 37.0 GHz radiometer data for differentiating rainfall areas from wet land surfaces. It was found, however, that none of the SMMR channels could differentiate rain from wet or dry land when surface temperatures were less than 15 C. It appears that an improved rainfall-over-land detection technique could be developed by two different methods, utilizing both satellite infrared and multifrequency dual polarized passive microwave data.

Rodgers, E.↗

NASA NTRS1983

Monitoring tropical-cyclone intensity using environmental wind fields derived from short-interval satellite images

The feasibility of predicting changes in tropical storm intensity based on satellite observations of the dynamical relationships between the large-scale upper and lower tropospheric circulations surrounding the cyclone and the characteristics of the storm's inner core is studied. Rapid-scan visible images from the SMS-1 and GOES-1 satellites were used to examine the local change in relative angular momentum (RAM), the lower and upper tropospheric environmental areal mean relative vorticity and transverse circulation on three consecutive days for tropical storms Caroline (August, 1975), Anita (August and September, 1977) and Ella (September, 1978). The three case studies suggest that storm intensification may be predicted from the storm's local change of net RAM, with this quantity best correlated with storm intensification after a time lag of 6 hours. Intensification is also found to be related to the environmental lower and upper tropospheric areal-mean relative vorticity, and to the upper tropospheric environmental circulation, which acts either to hinder or to enhance the storm's anticyclonic outflow channels.

Rodgers, E.↗

NASA NTRS1980

Predicting tropical cyclone intensity using satellite-measured equivalent blackbody temperatures of cloud tops

A relationship between maximum winds and satellite-measured equivalent blackbody temperatures near tropical cyclones is investigated with data from both the Atlantic and western North Pacific areas. This investigation revealed not only a significant correlation between satellite-derived equivalent blackbody temperatures and maximum winds but also a strong lag relationship between these temperatures and maximum winds. From this latter relationship a regression technique was developed to forecast 24-h changes of the maximum winds for weak (maximum winds less than or equal to 65 kt) and strong (maximum winds greater than 65 kt) tropical cyclones by utilizing the equivalent blackbody temperatures around the storm alone, together with changes in maximum winds during the preceding 24 h and the current maximum winds. Testing of these equations with independent data showed that the mean errors of forecasts made by the equations are lower than the errors in forecasts made by persistence techniques.

Gentry, R. C.↗

NASA NTRS1979

A statistical technique for determining rainfall over land employing Nimbus 6 ESMR measurements

Statistical analysis of the Nimbus 6 ESMR measurements for remote monitoring of active rainfall data over land is presented. Horizontally and vertically polarized brightness temperature pairs from ESMR 6 were sampled for areas of rainfall over land as determined from the rain recording stations and the WSR 57 radar, and wet and dry ground over the southeastern U.S. These three categories of brightness temperatures were significantly different so that the possibilities of the mean vectors of any two populations coinciding were less than 1 in 100, so that classification algorithms were then developed. The Fisher linear classifier, the Bayesian quadratic classifier, and a non-parametric linear classifier were examined, and the Bayesian algorithm performed best. It was concluded that a rainfall area delineated by the Bayesian classifier coincided well with the synoptic-scale rainfall area mapped by ground recording rain data and radar echoes.

Rodgers, E.↗

NASA NTRS1979

The benefits of using short-interval satellite images to derive winds for tropical cyclones

During the 1975, 1976 and 1977 North Atlantic hurricane seasons, NOAA/NESS and NASA/GSFC conducted a cooperative program to determine the best resolution and frequency now available from satellite images for deriving winds to study and forecast tropical cyclones. High spatial and temporal resolution satellite imagery made it feasible to provide a large number of lower and upper tropospheric winds which can be obtained by tracking clouds within 650 km of tropical cyclone centers. Up to 10 (5) times as many low-level winds were derived from images spaced at 3 or 7.5 min intervals as from those at 30 min (15 min) intervals. Rapid-scan full-resolution IR and visible images minimized the 'erroneous' winds derived by tracking cloud elements that propagate by growing on one side and dissipating on the other and by tracking repetitive patterns that provided ambiguous indications of direction of movement.

Rodgers, E.↗

NASA NTRS1978

Predicting tropical cyclone intensity using satellite measured equivalent blackbody temperatures of cloud tops

A regression technique was developed to forecast 24 hour changes of the maximum winds for weak (maximum winds less than or equal to 65 Kt) and strong (maximum winds greater than 65 Kt) tropical cyclones by utilizing satellite measured equivalent blackbody temperatures around the storm alone and together with the changes in maximum winds during the preceding 24 hours and the current maximum winds. Independent testing of these regression equations shows that the mean errors made by the equations are lower than the errors in forecasts made by the peristence techniques.

Gentry, R. C.↗

NASA NTRS1978

A statistical technique for determining rainfall over land employing Nimbus-6 ESMR measurements

At 37 GHz, the frequency at which the Nimbus 6 Electrically Scanning Microwave Radiometer (ESMR 6) measures upwelling radiance, it was shown theoretically that the atmospheric scattering and the relative independence on electromagnetic polarization of the radiances emerging from hydrometers make it possible to monitor remotely active rainfall over land. In order to verify experimentally these theoretical findings and to develop an algorithm to monitor rainfall over land, the digitized ESMR 6 measurements were examined statistically. Horizontally and vertically polarized brightness temperature pairs (TH, TV) from ESMR 6 were sampled for areas of rainfall over land as determined from the rain recording stations and the WSR 57 radar, and areas of wet and dry ground (whose thermodynamic temperatures were greater than 5 C) over the Southeastern United States. These three categories of brightness temperatures were found to be significantly different in the sense that the chances that the mean vectors of any two populations coincided were less than 1 in 100.

Rodgers, E.↗

NASA NTRS1978

The benefits of using short interval satellite images to derive winds for tropical cyclones

During the 1975, 1976, and 1977, NOAA's National Environmental Satellite Service and NASA's Goddard Space Flight Center conducted a cooperative program to determine the optimum resolution and frequency of satellite images for deriving winds to study and forecast tropical cyclones. Rapid scan images were obtained at 7.5 minute interval from SMS-2 for hurricane Eloise and cyclone Caroline, and at 3 minute intervals from GOES-1 for tropical storms Belle, Holly, and Anita. Cloud motions were derived from these images using the Atmospheric and Oceanographic Information Processing System. Winds that were derived from the movement of upper and lower tropospheric level clouds using rapid scan data were compared with the 15 and 30 minute interval data. Greater than 10 (5) times as many clouds could be tracked to obtain winds using 3 and 7.5 minute rapid scan images as when using 15 or 30 minute interval images. A few bright areas within the central dense overcast which appeared to be moving with the winds at low levels were tracked.

Rodgers, E.↗

NASA NTRS1978

A statistical technique for determining rainfall over land employing Nimbus-6 ESMR measurements

Statistical analysis is performed by first sampling three categories of Nimbus 6 ESMR brightness temperatures (representing rain over land, wet land surfaces without rain, and dry land surfaces), then testing these populations for uniqueness. A classification algorithm to delineate rain over land is developed. It is found that synoptic-scale rainfall over land, where surface thermodynamic temperatures are greater than 5 C and the vegetation is bereft of dew, can indeed be delineated despite the large ESMR-6 instantaneous field of view. However, some ambiguity exists in distinguishing between rainfall areas and wet land surfaces.

Rodgers, E.↗

NASA NTRS1977

Deriving winds for hurricanes using short interval satellite imagery

Results are presented for a study program designed to develop a better means of obtaining wind data needed by hurricane forecasters and to determine the optimum space and time resolution of satellite data used to obtain such winds. The discussion covers cloud tracking with an image display and manipulation system and analysis of IR imagery of Hurricane Eloise. It is shown that greater resolution in time and space of satellite imagery made it possible to derive up to six times as many low-level winds in a hurricane case, to eliminate 'bad winds' caused by mistaking cloud growth for cloud motion, and to remove ambiguities that would have caused difficulty in tracking clouds using only the imagery taken at 30-min intervals. It is suggested to use short-interval imagery (less than 10 min) for wind determination for future research in areas of tropical cyclones.

Gentry, R. C.↗