John Stout

Rain Estimation from Geosynchronous Satellite Imagery—Visible and Infrared Studies

Abstract A diagnostic method to estimate rainfall over large space and time scales by the use of geosynchronous visible or infrared satellite imagery has been derived and tested. Based on the finding that arms of active convection and rainfall in the tropics are brighter or colder on the satellite visible or infrared photographs than inactive regions, ATS-3 and SMS/GOES images were calibrated with gage-adjusted 10 cm radar data over south Florida. The resulting empirical relationships require a time sequence of cloud area, measured from the satellite images at a specified threshold brightness or temperature to calculate rain volume over a given period. Satellite rain estimates were made for two areas in south Florida that differ in size by an order of magnitude (1.3×104km2 vs 1.1×105km2) and verified by a combined system of gages and radar. Contrary to our expectations, the rain estimates for the smaller area agreed better with the raingage-radar groundtruth than the satellite rain estimates for the large...

Do the Tallest Convective Cells over the Tropical Ocean Have Slow Updrafts

Far from continents, a few storms lift precipitation-size ice particles into the stratosphere, 17 to 18 km above the tropical ocean. This study is the first to examine the observed properties of a large sample of these extremely tall convective storm cells. The central questions in this study are whether the unusually tall ocean cells have the slow updrafts known to be typical of oceanic convection, and if so, how can these tall cells reach such extreme heights. The precipitation radar on the Tropical Rainfall Measuring Mission (TRMM) satellite observed 174 extremely tall oceanic cells from 1998 to 2007. Relative updraft intensity is inferred from 17-km-tall oceanic cells having, on average, a 7-km lower 40-dBZ radar reflectivity height and an order of magnitude less lightning than do equally tall cells over the Sahel region of Africa, a region known for vigorous convective updrafts. Despite some ambiguity, the potential temperature and lapse rate of the NCEP reanalysis suggest that the environment in which these oceanic cells form is conducive to modest updrafts reaching extreme heights. Extrapolating based on the limited coverage of the TRMM satellite radar, it is likely that such extremely tall cells occur more often than once each day somewhere over the tropical ocean.

Low-Level Monsoon Dynamics Derived from Satellite Winds

Abstract The dynamics of low-level summer monsoon flow near 900 mb is studied using daily MONEX (1979) satellite wind data to estimate mechanisms influencing the horizontal momentum. We present an improved estimate of the large-scale monsoon geopotential field near the level of maximum wind, and a more approximate field of friction as well. Average fields for the premonsoon and established monsoon periods of 1.5 months are shown. The evolution of forces and accelerations along different trajectories crossing the western Indian Ocean are compared. The net horizontal force, equal to the pressure gradient plus friction force, is obtained for the two periods by directly estimating the mean Coriolis and relative acceleration vectors. The contribution to mean acceleration by synoptic-scale transient eddies is significant only south of 30°S. Inertial acceleration by the mean flow produces a Rossby number in excess of 0.25 in an equatorial belt which expands to 10°N in the Somali Jet entrance. A method is devised...

The Goddard Profiling Algorithm (GPROF): Description and Current Applications

Atmospheric scientists use different methods for interpreting satellite data. In the early days of satellite meteorology, the analysis of cloud pictures from satellites was primarily subjective. As computer technology improved, satellite pictures could be processed digitally, and mathematical algorithms were developed and applied to the digital images in different wavelength bands to extract information about the atmosphere in an objective way. The kind of mathematical algorithm one applies to satellite data may depend on the complexity of the physical processes that lead to the observed image, and how much information is contained in the satellite images both spatially and at different wavelengths. Imagery from satellite-borne passive microwave radiometers has limited horizontal resolution, and the observed microwave radiances are the result of complex physical processes that are not easily modeled. For this reason, a type of algorithm called a Bayesian estimation method is utilized to interpret passive microwave imagery in an objective, yet computationally efficient manner.

Selected analyses of TRMM instantaneous rainfall data

Distributions of Tropical Rainfall Measuring Mission (TRMM) Version 5 (V5) and Version 6 (V6) data are presented. The fraction of pixels determined by the Precipitation Radar (PR) to be convective has increased by 5% from V5 to V6. In V6, PR contributes more rain in medium ( 4 to 20 mm/hr) but less in heavy ( >20 mm/hr) rainfall rates than the TRMM Microwave Imager (TMI). Joint probability distributions show the V6 TRMM Combined Instrument rainfall more strongly related to PR than to TMI.

Estimating TRMM spacecraft attitude errors using the precipitation radar

Results are presented from analysis of the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data for the purpose of estimating satellite attitude information. Deviations from nominal roll are detected using the surface echo distances measured by the PR. This technique has been used for continued monitoring of attitude anomalies that occurred shortly after the TRMM satellite altitude increase and for historical data.

A generalized logical format for inter-calibrated brightness temperatures for the global precipitation measurement mission

An important aspect of the GPM mission is the merging of precipitation data from multiple radiometers on different satellites. This requires that each radiometer be consistently calibrated and that each be intercalibrated with a mission reference standard. For GPM the reference standard is to be the core satellite carrying a dual frequency precipitation radar and a well calibrated conically scanning radiometer. This paper describes a common format for representing these intercalibrated brightness temperatures which will be used for all radiometer products from GPM partner satellites. The use of common formats ensures that users obtain all the required information and also facilitates the rain retrieval algorithm code preparation as it can always except to have the data that it needs for the retrieval.

Content-based browsing of data from the Tropical Rainfall Measuring Mission (TRMM)

Through content based browsing, the TSDIS Orbit Viewer can help scientists decide which files to order from the TRMM archive. The Orbit Viewers Mission Index can locate large-scale rain events in six terabytes of data. The Orbit Viewers TRMM Tracker can locate coincidences between the TRMM orbit and a user-defined surface track.

Tropical Rainfall Measuring Mission algorithm consistency studies

Results are presented from analysis of the Tropical Rainfall Measuring Mission (TRMM) data from two perspectives: instrument/algorithm consistency checks and comparisons of precipitation retrievals between instruments. The instruments specific to this study are the Precipitation Radar (PR) and the TRMM Microwave Imager (TMI).

Variations in the convective rain fraction observed by the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR)

Using a data clustering method, monthly statistics are calculated from rain rate estimates of the TRMM Precipitation Radar. The statistics show how the following variables change with the size of a rain event: convective rain rate, total rain rate, and convective rain fraction. On average, the convective rain fraction is found to be greatest for small mesoscale events covering 10/sup 3/ km/sup 2/, while rain rate increases monotonically with the size of the rain event.