Comparison of Lidar Backscatter with Particle Distribution and GOES-7 Data in Hurricane Juliette

Maurice A. Jarzembski, I Vandana Srlvastava," Eugene W. McCaul, Jr., 2 Gary J. Jedlovec,1Robert J. Atkinson, 3 Rudolf F. Pueschel, 4 and Dean R. Cutten 5Abstract. Measurements of calibrated backscatter, using twocontinuous wave Doppler lidars operating at wavelengths 9. I and10.6p.m were obtained along with cloud particle size distributionsin Hurricane Juliette on 21 September 1995 at altitude -11.7 km.Agreement between backscatter from the two lidars and with thecloud particle size distribution is excellent. Features inbackscatter and particle number density compare well withconcurrent GOES-7 infrared images•IntroductionLidars can be used to measure backscatter of atmosphericaerosols and clouds [Menzies and Trait, 1994], where thebackscatter magnitude is in part indicative of particle numberdensity. Their high resolution capability provides a uniquemethod of measuring fine-scale atmospheric variations[Srivastava et al., 1995]. Recently, two National Aeronauticsand Space Administration (NASA)/Marshall Space Flight Center(MSFC) continuous wave (CW) focused Doppler lidars obtainedin-situ high resolution calibrated backscatter measurements inHurricane Juliette as part of the 1995 NASA/MulticenterAirborne Coherent Atmospheric Wind Sensor (MACAWS)mission on board NASA's DC8 aircraft. Two traverses ofJuliette's eye were made off the west coast of Mexico at altitude11.7 km on 21 September 1995. The two independent lidar datasets offered an opportunity for intercomparison and validation ofthe calibrated backscatter results. These were also intercomparedwith in-situ cloud particle size distributions obtained fromNASA/Ames Research Center's forward scattering spectrometerprobe (FSSP), the DC8 aircraft infrared (IR) surface temperatureradiometer data, and the Geostationary OperationalEnvironmental Satellites (GOES-7) l 11am IR emission imageswith their corresponding estimates of cloud top temperature andheight. At the time of the DC8 flight through Juliette, GOES-7was in geosynchronous orbit over the equator and 135 ° Wlongitude and provided superior viewing geometry of the easternPacific ocean region• GOES-7 IR data for the 12-h periodbeginning at t600 UTC and spanning the DC8 flight, were usedto monitor the cloud development and structure of Juliette.Meteorology, Flight, and GOES-7 DataJuliette developed off the west coast of Mexico on 16September 1995. It moved slowly west-northwestward andgradually intensified, reaching hurricane strength by 18i NASA/Marshall Space Flight Center, Huntsville, AL2 I.Tniversities Space Research Association, Huntsville, AL3 Lockheed Martin Corp., Huntsville, AL4NASA/Ames Research Center, Moffett Field, CA5 University of Alabama in Huntsville, Huntsville, ALCopyright 1997 by the American Geophysical Union.Paper number 97GL00832.0094-8534/97/97GL-0083250500September. Juliette reached its maximum strength at 2100 UTCon 20 September, with peak winds of 64 m s-_ (125 kt) andminimum central pressure of 925 hPa. At this time, eyewalldecay-replacement cycles were occurring, with the old eyewallcontracting and dissipating while a new, larger annular eyewallformed outside [Willoughby et al., 1982]. Late stages of thiscycle were observed at the time of the DC8 traversal of Juliette'score on 21 September. As the storm moved over cooler water itgradually lost strength, ultimately dissipating on 26 September.During the DC8 flight around and through Juliette, the stormdisplayed a nearly symmetrical, rapidly expanding cirrus outflowshield, according to concurrent GOES-7 imagery. The storm'srainfall pattern, however, exhibited considerable azimuthalasymmetry, with heaviest precipitation located in the storm'score and in strong rainband convection along the storm's southernperiphery, as diagnosed from the 85 GHz channel of the SpecialSounder Microwave/Imager (SSM/I) at 1756 UTC on 21September. Outer rainbands were absent on the storm's northernflanks, perhaps because of the presence of cooler ocean water anddrier midtropospheric air. The small, old eyewall, still evidentwithin the center of the new, larger annular eye, remainedconnected to the new eyewall by a vestigial spiral band structurein the storm's north quadrant, with a veil of thin cirrus coveringthe developing new large eye.Flight through Juliette lasted -2.5-h, during which twotraverses of the eye were made separated by -1.6-h. A GOES-7IR image of Juliette at 2100 UTC (-21 rain. after the first eyepenetration) is shown in Fig.1. Flight track from 2010 to 2250Figure 1. GOES-7 IR image of Hurricane Juliette on 21September 1995 at 2100 UTC. The co-located position of theNASA DC8 flight track is shown from 2010 to 2250 UTC.1063