Search Results

You are looking at 1 - 3 of 3 items for

  • Author or Editor: Joseph S. Griffin x
  • Refine by Access: Content accessible to me x
Clear All Modify Search
Joseph S. Griffin, Robert W. Burpee, Frank D. Marks Jr., and James L. Franklin

Abstract

The Hurricane Research Division has developed a technique for real-time airborne analysis of aircraft data from reconnaissance and research flights in tropical cyclones. The technique uses an onboard workstation that analyzes flight-level observations, radar reflectivity patterns, radial Doppler velocities, and vertical soundings from Omega dropwindsondes (ODWs).

Many of the workstation analyses are in storm-relative coordinates that depend upon interactive identification of the cyclone center from the radar reflectivity data. Displays of the lower fuselage radar reflectivity, composited for 1–2 h, provide an overall perspective of the horizontal patterns of precipitation and a framework for interpretation of thermodynamic and kinematic observations. The workstation runs algorithms for estimation of the horizontal wind field in the hurricane core using radial velocities measured by the airborne Doppler radar during one or more penetrations of the storm center. Interactive software also supports real-time processing of ODW wind and thermodynamic data, objective editing of bad data, and automatic dissemination of mandatory and significant-level data in the standard dropwindsonde code. Similarly processed ODWs have been consistently shown to reduce forecast errors of hurricane track in several objective models used by the forecasters at NHC.

Plans for the 1992 hurricane season include the transmission of subsets of the data to the National Hurricane Center (NHC) through the Geostationary Operational Environmental Satellite (GOES) communications system and the display of the aircraft analyses for the forecasters at NHC. With the implementation of these plans, NHC will receive two-dimensional analyses of the mesoscale precipitation and wind structure of the storm core and more frequent estimates of the location and recent motion of tropical cyclones. The information will enable forecasters to take advantage of recent advances in the understanding of hurricane-intensity change.

Full access
William L. Woodley, Cecilia G. Griffith, Joseph S. Griffin, and Scott C. Stromatt

Abstract

Quantitative precipitation estimates have been made for the GARP (Global Atmospheric Research Program) Atlantic Tropical Experiment (GATE) from geosynchronous, infrared satellite imagery and a computer-automated technique that is described in this paper. Volumetric rain estimates were made for the GATE A scale (1.43 × 107 km2) and for a 3° square (1.10 × 105 km2) that enclosed the B scale for time frames ranging from all of GATE (27 June—20 September 1974) down to 6 h segments. The estimates for the square are compared with independent rain measurements made by four C-band digital radars that were complemented by shipboard raingages. The A-scale estimates are compared to rainfall estimates generated by NASA using Nimbus 5 microwave imagery. Other analyses presented include: 1) comparisons of the satellite rain estimates over Africa with raingage measurements, 2) maps of satellite-inferred locations and frequencies of new cumulonimbus cloud formation, mergers and dissipations, 3) latitudinal precipitation cross sections along several longitudes and 4) diurnal rainfall patterns.

The satellite-generated B-scale rainfall patterning is similar to, and the rain volumes are within a factor of 1.10, of those provided by radar for phases 1 and 3. The isohyetal patterns are similar in phase 2, but the satellite estimates are low, relative to the radar, by a factor of 1.73. The B-scale disparity in phase 2 is probably due to the existence of rather shallow but rain-productive convective clouds in the B scale. This disparity apparently does not carry over to the A scale in phase 2. Comparison of NASA Electronically Scanning Microwave Radiometer (ESMR) rain estimates with ours for several areas within the A scale for all GATE suggests that the former is low relative to the latter by a factor of 1.50. The satellite estimates of rainfall in Africa are similar to measurements by raingages in all phases of GATE up to 11°N and progressively greater than the gage measurements north of this latitude toward the Sahara desert.

The diurnal rainfall studies suggest a midday (about 1200 GMT) maximum of rainfall over the water areas and a late evening maximum (about 0000 GMT) over Africa and the northern part of South America. The latitudinal cross sections along several longitudes of phase rainfall clearly show the west-southwest/east-northeast orientation of the Intertropical Convergence Zone (ITCZ), the diminution of the rainfall west-southwestward from Africa into the Atlantic, and the northward progression of the ITCZ from phase 1 into phases 2 and 3. The center of action for cloud formation, merger and dissipation, and the area of maximum rainfall (>1600 mm for all of GATE) occur along the southwest African coast near 11°N. This agrees with past climatologies for this region. Superposition of the satellite-generated rainfall maps and sea surface temperature maps by phase suggests a strong relationship between the two. Almost all of the rainfall occurs within 26°C sea surface temperature envelope. The mean daily coverage of rainfall and the mean rainfall in the raining areas for the A scale for all GATE are 20% and 14.1 mm day−1, respectively. These and other results are discussed.

Full access
Robert W. Burpee, Sim D. Aberson, Peter G. Black, Mark DeMaria, James L. Franklin, Joseph S. Griffin, Samuel H. Houston, John Kaplan, Stephen J. Lord, Frank D. Marks Jr., Mark D. Powell, and Hugh E. Willoughby

The Hurricane Research Division (HRD) is NOAA's primary component for research on tropical cyclones. In accomplishing research goals, many staff members have developed analysis procedures and forecast models that not only help improve the understanding of hurricane structure, motion, and intensity change, but also provide operational support for forecasters at the National Hurricane Center (NHC). During the 1993 hurricane season, HRD demonstrated three important real-time capabilities for the first time. These achievements included the successful transmission of a series of color radar reflectivity images from the NOAA research aircraft to NHC, the operational availability of objective mesoscale streamline and isotach analyses of a hurricane surface wind field, and the transition of the experimental dropwindsonde program on the periphery of hurricanes to a technology capable of supporting operational requirements. Examples of these and other real-time capabilities are presented for Hurricane Emily.

Full access