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					 National Aeronautics and Space Administration
                                                                                            Observations of Tropical Cyclones
                                                                                               with Microwave Sounders
                                                                                                                                          Bjorn Lambrigtsen, Shannon Brown
                                                                                                 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109
The High Altitude MMIC Sounding Radiometer (HAMSR) is an atmospheric sounder intended for aircraft deployment. It was designed and built                                                              (NAMMA) field campaign in Cape Verde – this time using the NASA DC-8. Excellent results were obtained in all three campaigns, and the anal-
at the Jet Propulsion Laboratory under the NASA Instrument Incubator Program and uses advanced technology to achieve excellent                                                                        ysis of the data is proceeding. The primary data products generated with HAMSR consist of calibrated brightness temperatures in two tempera-
performance in a small package. It was first deployed in the field in the 2001 Fourth Convection and Moisture Experiment (CAMEX-4) – a                                                                ture sounding bands and one water vapor sounding bands. Derived products include vertical temperature profiles and water vapor and liquid
hurricane field campaign organized jointly by NASA and the Hurricane Research Division (HRD) of NOAA in Florida. HAMSR also participated                                                              water profiles from the ground to the flight altitude, and experimental products include estimates of precipitation, ice water path and distribution
in the Tropical Cloud Systems and Processes (TCSP) hurricane field campaign in Costa Rica in 2005. In both campaigns HAMSR flew as a                                                                  in clouds and above convective cells, and convective intensity. HAMSR provides observations similar to those obtained with microwave
payload on the NASA high-altitude ER-2 aircraft. It was also one of the payloads in the 2006 NASA African Monsoon Multidisciplinary Activities                                                        sounders currently operating on NASA, NOAA and ESA spacecraft, and this offers an opportunity for valuable comparative analyses.


                                             The High Altitude MMIC Sounding Radiometer - HAMSR - was developed in 2001 under the NASA Instrument Incubator Program

                                                                            HAMSR                          Chan
                                                                                                            #

                                                                                                           I-1
                                                                                                                   Center
                                                                                                                    freq.
                                                                                                                   [GHz]
                                                                                                                   118.75
                                                                                                                               Offset
                                                                                                                               [GHz]

                                                                                                                               -5.500
                                                                                                                                          Bandwidth
                                                                                                                                           [MHz]

                                                                                                                                             1500
                                                                                                                                                          Wt-func. Peak
                                                                                                                                                          [mb or mm]

                                                                                                                                                           Sfc/[30 mm]
                                                                                                                                                                                                                          HAMSR Absolute Calibration
                                                                              summary                      I-2
                                                                                                           I-3
                                                                                                                      “
                                                                                                                      “
                                                                                                                               -3.500
                                                                                                                               -2.550
                                                                                                                                             1000
                                                                                                                                             500
                                                                                                                                                              Surface
                                                                                                                                                              Surface
                                                                                                                                                                                The absolute calibration of the HAMSR TBs is assessed from TCSP data using the measurements taken during the accent after take-off and the descent
                                                                                                           I-4        “        -2.050        500             1000 mb            before landing. For the channels near the absorption line, the surface will be obscured and the measured brightness temperature as a function of height will
                                                                                                           I-5        “        -1.600        400             750 mb
                                                                                                           I-6        “        -1.200        400             400 mb
                                                                                                                                                                                trace out a smoothed version of the temperature profile allowing one to assess gain and offset errors. During the TCSP flights, radiosondes (RaObs) were
                                                                                                           I-7        “        ±0.800       2x400            250 mb             launched from the originating airport every six hours. A radiative transfer model is used, with the upper-air data from the RaObs, to model the HAMSR TBs as
                                                                                                           I-8        “        ±0.450       2x300            150 mb
                                                                                                           I-9        “        ±0.235       2x130              80 mb            a function of altitude during take-off and landing. Because the land emissivity is not known exactly, only the opaque channels are compared to the model.
                                                                                                           I-10       “        ±0.120       2x100              40 mb
                                                                                                           II-1    50.30          0          180          Sfc/[100 mm]
                                                                                                                                                                                The Rosencrantz 1998 and the Liebe 1993 models are used to determine the atmospheric absorption coefficient profile and a clear atmosphere is assumed.
                                                                                                           II-2    51.76          0          400              Surface
                                                                                                           II-3    52.80          0          400             1000 mb
                                                                                                           II-4    53.596      ±0.115       2x170            750 mb                                                                                                               HAMSR comparison to model - July 5,6,9,15,16,17,23,25,27 and 28
                                                                                                           II-5    54.40          0          400             400 mb                                                                                                                Chan     Center    Offset    Avg Model      Std Model –     Avg Model –     Std Model –
                                                       Band III                                            II-6    54.94          0          400             250 mb                                                                                                                 #        freq.    [GHz]     – Measured      Measured        Measured        Measured
                                                       Band I
                                                                                                           II-7    55.50          0          330             150 mb                                                                                                                         [GHz]               Rosencrantz    Rosencrantz     Liebe (1993)    Liebe (1993)
                                             Band II                                                       II-8    56.02          0          270               90 mb
                                                                                                                                                                                                                                                                                                                (1998) [K]     (1998) [K]          [K]             [K]
                                                                                                                   56.67                     330
                                                                                                           III-1   183.31       -17.0        4000             [11 mm]                                                                                                              I-8      118.75    ±0.450         1.1           1.2             0.82            1.2
                                                                                                           III-2      "         ±10.0       2x3000            [6.8 mm]                                                                                                             I-9        “       ±0.235        0.83           1.2             0.26            1.2
                                                                                                           III-3      "         ±7.0        2x2000            [4.2 mm]                                                                                                             I-10       “       ±0.120         1.2           1.2             0.47            1.3
                                                                                                           III-4      "         ±4.5        2x2000            [2.4 mm]               54.4,54.94,55.5,                                 117.95,118.3,118.515,                        II-5     54.40       0          -0.20           0.75           -0.17            0.74
                                                                                                           III-5      "         ±3.0        2x1000            [1.2 mm]
                                                                                                           III-6      "         ±1.8        2x1000            [0.6 mm]               56.02 GHz                                        118.63 GHz                                   II-6     54.94       0           0.19           0.62            0.17            0.62
                                                                                                           III-7      "         ±1.0        2x500             [0.3 mm]                                                                                                             II-7     55.50       0           0.03           0.83           -0.01            0.83
                                                                                                                                                                                                                                                                                   II-8     56.02       0           -1.4           1.0             -1.4            1.1
                                                                                                                                                                                                                                                                                              &
                                                                                                                                                                                                                                                                                            56.67
                                                                                                                                            Scan
                                                                                                                                          direction
                                                                                                                                                                                                                                                                                   III-5    183.31     ±3.0         0.50           2.4              0.06            2.4
                                                                                                                                                                                                                                                                                   III-6      "        ±1.8        -0.19           2.3             -0.43            2.3
                                                                                                                                                                                                                                                                                   III-7      "        ±1.0         0.20           2.4              0.13            2.3
                                                                                                                             Flight                                                                                                                                               There is good agreement between the model and the measurements for the opaque
                                                                                                                            direction
                                                                                                                                                                                   Comparison of HAMSR to the modeled upwelling brightness temperature (black line) as a          HAMSR channels. The measurements agree to better than 1 K, with the exception of
                                                                                                                                                                                   function of altitude for July 28th. HAMSR data is shown during ascent (red) and descent        channel II-8. A good assumption is that most potential calibration errors, such as
                                                                                                                                                                                   (blue) and is at the sensor resolution (25 ms).                                                calibration target temperature knowledge, will be common within each frequency band.




                                         CAMEX-4 campaign (2001, Florida)                                                                                                 TCSP campaign (2005, Costa Rica)                                                                 NAMMA campaign (2006, Cape Verde)
                                                                Hurricane Erin 09/10/2001                                                                                             Hurricane Emily 07/17/2005                                                                           Saharan Air Layer (SAL) 08/25/2006
 Hurricane Erin, which developed from tropical wave off the coast of Africa, reached tropical storm status on September                 HAMSR observed Hurricane Emily from the ER-2 on July 17, 2005. Emily became a tropical depression on July 10 and               In the NAMMA field campaign HAMSR was mounted in the cargo bay of the NASA DC-8. The purpose
 2nd, 2001 and reached hurricane status on September 8th. It reached peak intensity on September 8th and was                            reached Category 5 status briefly around 0 UTC on July 17th before weakening to Category 4 status on July 18th. It is          of this campaign was to observe the early stages of transitions from African Easterly Waves to tropical
 weakening when it was observed by the ER-2 on September 10th between 16-20 UTC. At the time of the overflights, it                     estimated that the surface pressure and maximum sustained winds at the time of the ER-2 overflights (7-12 UTC) were 940        cyclone and the influence of the SAL on this process.
 is estimated that the central pressure was 970 mb and the maximum sustained winds were 90 kts (NHC Tropical Cycle                      mb and 135 kts, respectively (NHC Tropical Cycle Report). A direct fly over of the eye allowed HAMSR to retrieve the warm
                                                                                                                                        core anomaly, which is shown along track below. The warm core anomaly is computed by subtracting the temperature profile       During the August 25 flight (as well as in several others) HAMSR measured the dry air associated with
 Report). The warm core temperature anomaly was imaged along track on the east-west flight track. It was computed
                                                                                                                                        retrieved in the eye, to an environmental profiled retrieved on the approach to the storm, > 600 km from the eye. The          the SAL. The figures below show observations from a segment of this flight (the initial north-easterly leg
 by differencing the temperature profiles retrieved in the eye to those retrieved greater than 600 km from the eye, on the
                                                                                                                                        maximum magnitude of the warm anomaly peaks near 11-12 oC between 150-250 mb. A second peak near 8oC is observed               from Cape Verde towards the African mainland), while there was a SAL outbreak in the region.
 approach to the storm. The maximum magnitude of the warm anomaly is observed to be near 11-12oC and occurs
 between 400-600 mb. The HAMSR retrieved warm core image in the eye is very similar to that reconstructed from a                        around 500 mb.
 number of dropsondes released from the ER-2 and DC-8 (Halverson et al., 2006; J.Atm. Sci.), including a dropsonde                      HAMSR “cloud slices” reveal intense convection in the eyewall region, with storm tops reaching above 15 km on North-West
 which was released into the eye. A comparison of the retrieved temperature profile in the eye from HASMR and the                       side of the eyewall. Two transits across the eye wall are shown, the first in a N-W heading and the second in a N-E heading.
 dropsonde released into the eye is shown. The differences are generally less than 2oC.                                                 The 5 HAMSR cloud slicing levels are shown with the nadir ER-2 Doppler Radar (EDOP) X-band reflectivity profile in the
                                                                                                                                        background. It is evident that HAMSR is able to assess the three-dimensional structure of the storm.

                                                                                                                                                                                                                     Hurricane Emily Warm Core Anomaly

                                                                                                                                                                                     Pass 1: SENW
                                                                                                                                                                      5
                                                                                                                                                                  4
                                                                                                                                                              3

                                                                                                                                                          2
                                                                                                                                                          1



  E                                                      W
                                                                                                                                                                                                                   SE                                 NW


                                                                                                                                                                                                                                                                                           SAL

                                                                                                                                                                                     Pass 2: SWNE


                                                                                                                                                                  5
                                                                                                                                                          4
                                                                                                                                                      3
                                                                                                                                                      2
                                                                                                                                                      1




                                                                                                                             Radar-like observations with a microwave sounder

                                                                                              Scattering index - HAMSR water vapor channels                                                                                  Nadir along-track view                                                                  Scan swath view

                                   0.6
                                                                                                                                                                                                                                                                                                                                                                          10 km


                                                                                                                                                                                                       Hurricane Emily, 17 July 2005
                                                                                                                                                                                                                                                                                                                                                                          9 km
        Fractional Tb depression




                                   0.4
                                                         HAMSR

                                                                                                                                                                                                                                                      167: 3-4k m
                                                                                                                                                                                                                                                      183±3: 8k m
                                                                                                                                                                                                                                                      183±1:10k m
                                                                                                                                                                                                                                                                                                                                                                          8 km
                                   0.2



                                                                                                                                                                                                                                                              7 water vapor
                                                                                                                                                                                                                                                                sounding                                                                                                  7 km
                                   0.0
                                         0                             50               100                             150                                                  200                          250                           300
                                                                                                                                                                                                                                                                channels
                                                                                                                    Dis ta nc e             [k m ]

       MW sounder                                                                                                                                                                                                                                              gives slices
       Is equivalent                                                                                                                                                                                                                                           at 7 heights
          to radar!                                                                                                                                                                                                                                                                                                                                                       6 km




                                                                                                                                                                                                                                                                                                                                                                          5 km

                                                            EDOP




                                                                                                                                                                                                                                                                                                                                                                          4 km




                                The strong correlation between the microwave sounder observations and the radar can be used to derive equivalent radar reflectivity from the brightness temperatures
        Algorithm development is under way - preliminary results are very encouraging (to be published). This is a powerful new way of analyzing tropical cyclones. The large number of satellite based microwave sounders
      currently in operation and the 3-D nature of the observations will greatly expand available radar-like data sets, which will be used to derive vertically resolved precipitation rates as well as microphysical properties such
      as ice particle density and size distribution. A geostationary microwave sounder, such as GeoSTAR, will make such measurements available continuously with no coverage gaps as occur with low-earth-orbiting sensors
                                                                                                                                                                           This is a breakthrough development

                                                                                                                                                                                                                                                                                                                                          Jet Propulsion Laboratory
                                                                                                                                                                                                                                                                                                                                          California Institute of Technology
 This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration                                                                                                                                                                   Pasadena, California

				
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