JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 91, NO. C2, PAGES 2321-2330, FEBRUARY 15, 1986 Mesoscale and Synoptic Scale Features of North Pacific Weather Systems Observed With the Scanning Multichannel Microwave Radiometer on Nimbus 7 KRISTINA B. KATSAROS AND ROBERT M. LEWIS Department of Atmospheric Sciences, University of Washin•7ton, Seattle Rain rates, wind speeds, and vertically integrated valuesof both atmospheric water vapor and cloud liquid water content were obtained from the brightness temperatures measuredby the ScanningMulti- channel Microwave Radiometer (SMMR) on the Nimbus 7 satellite during the winter of 1979. We examine their spatial relationshipto wintertime midlatitude cyclones and a shortwavetrough over the North Pacific Ocean as they approach the west coast of North America. Cold fronts are found to be located near the edge of the strongestgradient in integrated atmospheric water vapor. The rain rates exhibit patterns that bear a strong relationship both to the shortwave trough and to the cold fronts. Mesoscale features such as frontal undulations and rain cells are indicated in the rain rate data, even though the sensor resolution is marginal for such features. Rain rates are in reasonably good agreement with rain gage measurements on the coast. Furthermore, the onset of rain on the coast agrees with the timing found by simple advection of the SMMR observed rain areas, suggesting their possiblefuture use in forecasting the timing of coastal rain events. Wind speedsranging from 5 to 15 m/s in a region surrounding a cold front agree with surface observations.Cloud liquid water content exhibits patterns that are consistent with the frontal cloud patternsand with the analysis of the shortwave position. INTRODUCTION In this study, we examine integrated water vapor, cloud liquid water, and rain rate in weather systems employing the Scanning Multichannel Microwave Radiometer (SMMR)on the Nimbus 7 satellite. For one case the surface wind speed derived from SMMR is also presented.The SMMR measures brightness temperaturesof the earth and its atmosphereat five microwave frequencies in both vertical and horizontal polar- izat•on. These 10 s•gnals are used singly or in combination to infer the values of many geophysically important parameters: sea surfacetemperature, near surfacewind speeds over the oceans, sea ice concentrationand age, snow cover over land, atmospheric water vapor, cloud liquid water, and rain rate over the oceans and intense rain over land [Gloersen et al., 1984; Car, alieri et al., 1984; Prabhakara et al., 1982, 1983; Spencer et al., 1983a, b; Wilheit et al., 1983]. The Nimbus 7 satellite was launched in October 1978, and the SMMR in- strument has been collectingdata sincethe launch up to the present(November 1985). Such long, continuous time series are valuablein geophysical work, eventhough degradation of the sensors with time requires careful calibrations after col- lection to obtain absolute values. The SMMR instrument flown on Nimbus 7 and its sister instrument on the Seasat satellite (also launched in 1978 but only lasting 3 months) were designed primarily for sea surface observations: sea sur- face temperature, near-surface winds over the ocean,and sea ice. The channels sensitive to the atmospheric water in its vapor and liquid forms were mainly included to aid in evalu- ating the correctionsto be applied for the atmosphericab- sorption,which occurs at the radiometer frequencies usedfor the sea surface parameters and also at frequencies employed by two of the instruments aboardSeasat (scatterometer and altimeter). These channels, however, can also be used to pro- vide valuable and unique information about atmospheric water content over the data-sparse world ocean.Because alter- native methods for measuringthe atmosphericcloud liquid Copyright 1986 by the American GeophysicalUnion. Paper number 5C0664. 0148-0227/86/005C-0664505.00 water and rain rates over the oceans are inadequate,we have only limited comparison data sets for evaluatingthe quality of these products from SMMR. We must therefore begin by using these parameters in a qualitative sense, doing the ver- ification as the opportunity arises, and using our existing knowledgeand insights to build confidence in the accuracyof our algorithmsor to correct them as needed. For this reason we have chosen a study area and a time frame for which high quality in situ data are available from the Cyclonic Extratrop- ical Storms (CYCLES) Project, carried out by the University of Washington (Seattle) Cloud Physics Group. The present study is part of the Nimbus 7 SMMR experiment team's effort to verify the geophysicalparameters which can be calculated from SMMR brightnesstemperatures.In this report we only present data from the first year's record, which has now been archived at the National Space ScienceData Center (Code 601, NASA, Goddard Space Flight Center, Greenbelt, MD 20771). A strong motivation for attempting to obtain information on the distribution of the water vapor, cloud liquid water, and rain drop-sized particlesin stormsover the ocean is that the weather systems over the oceansevolve in a manner more dependenton their own dynamicsthan on the variations of the underlying boundary. Even though an ocean surfacehas substantial variability, it is more uniform than a land surface. The advantageof studyingcyclonicstorms over the ocean has been recognized [e.g., Browning,1971], but because of the difficulty in making measurements at sea, Browning et al. [1973] and Hobbs and Persson [1982] used shore-based radars for this purpose. With the microwave instrumentation on satellites, we are now able to map many of the important variablesin these stormson scales which are approximating the scales of their variability. Microwave data on atmospheric water parameters from the Seasatsatellite were related to the radiosondeand surfaceobservations obtained from ships in the Joint Air Sea Interaction {JASIN) Experiment [Katsaros et al., 1981' Taylor et al., 1983] and in the Gulf of Alaska Experiment (GOASEX) [McMurdie and Katsaros, 1985]. In the latter article, one late summer cyclonicstorm was followed in its course across the North Pacific. 2321