1 Satellite Applications in Tropical Weather Forecasting Mark DeMaria Regional and Mesoscale Meteorology Team NESDIS/CIRA Colorado State University, Ft. Collins CO Satmet 99-2 Tuesday, 27 April 1999

2 Acknowledgments RAMMT –Roger Phillips, Ray Zehr, Jack Dostalek, John Knaff, Bernadette Connell, Stan Kidder TPC –Jiann-Gwo Jiing (SOO), Richard Pasch, Michelle Huber, Bill Frederick CIMSS –Chris Velden NESDIS ORA –Roger Weldon

3 Outline General Circulation in the Tropics –ITCZ –Subtropical Ridge –Tropical Upper Tropospheric Trough Synoptic-Scale Weather Systems –Upper-level lows –Tropical Waves Tropical Cyclones –Dvorak method –Environmental interactions –Measurements from Polar orbiting satellites

4 Terminology Channel 1 - Visible -.6  m ( ) Channel 2 - Shortwave IR  m ( ) Channel 3 - Water Vapor  m ( ) Channel 4 - Longwave IR  m ( ) Channel 5 - Split Window  m ( ) Microwave frequencies Ghz ( cm)

5 Hadley Cell Walker Cells P (mb) DJFJJA

January Average 200 mb Streamlines

July Average 200 mb Streamlines

January Average 850 mb Streamlines

July Average 850 mb Streamlines

10 GMS, GOES, METEOSAT IR Imagery Composite

11 GMS, GOES, METEOSAT IR Imagery Composite

12 Tropical Upper-Level Lows Typically form within TUTT Cold-core systems Shallower circulation than mid-latitude lows (little circulation below 500 mb) Often produce precipitation Can influence intensity and track of tropical cyclones Can be tracked using water vapor imagery

mb700 mb Cold-low in NCEP Analysis 8/19/ UTC

14 Perturbation Temperature Cross-Section from NCEP Analysis 8/26/ UTC

15 Schematic Representation of Cold Low Structure (from Whitfield and Lyons, WF, 1992)

16 Radiation Analysis of WV Imager Channel for Idealized Sounding

17 16-Frame Water Vapor Imagery Loop 7/26/98 02:45 to 7/29/98 20:45 Formation of a Cold-Low

18 TPC Tropical Analysis and Forecast Branch Cold-Low Study Period of Study: Aug. 12-Oct. 1, 1996 Domain: 0-35 N, N Cold-low centers tracked using GOES WV imagery 47 lows during 50 days Average Duration of 3 days, Max of 12 days Up to 8 lows in domain at once (average of 3) Vorticity center present in NCEP 200 mb analyses for nearly all cold lows identified by satellite observations –Average NECP analysis location error of 100 nm

19

20 NCEP Aviation Model Cold-Low Average Track Error Extrapolation Persistence Cold Lows 1996 Tropical Cyclones

21 Tropical Waves Formation near western Africa –Barotropic/baroclinic instability, PV gradient changes sign –Secondary instability region in Western Caribbean Maximum amplitude near 700 mb Period of 2-5 days, wavelength km, May-Dec Precipitation associated with waves About 2/3 of Atlantic TC genesis associated with waves Role in east Pacific tropical cyclogensis

22 Seasonal Mean PV at 750 mb (Molinari et al, 1997) Mean meridional wind from GATE wave composite (Reed et al, 1977)

23 TAFB Methods for Tracking Waves TAFB tropical surface analysis generated 4 times per day, includes surface wave positions Rawindsone time series Surface data when available Satellite analysis over west Africa –Animation of channels 1, 2 and 4 indicates rotation Hovmoller satellite diagrams for continuity across tropical Atlantic NCEP aviation model analyses and forecasts

24 Dakar Sounding (15 N, 18 W) Time Series August

25 20 W40 E20 W40 E 08/01/96 08/15/96 08/16/96 08/31/96 Tropical Strip Time Series 40 E-40 W 0 N-15 N

26 Tropical Cyclone Classification NHC has responsibility for Atlantic and east Pacific basins –Atlantic: 10 storms, 6 hurricanes –East Pacific: 16 storms, 10 hurricanes Aircraft recon available only for Atlantic west of 55 W Majority of center and intensity estimates from GOES satellite data TAFB, SAB, AFWA provide classifications

27 Overview of the Dvorak Technique Visible and Infrared Technique Simplified Visible Technique given here (See Technical Report for full details) Uses patterns and measurements as seen on satellite imagery to assign a number (T number) representative of the cyclone’s strength. The T number scale runs from 0 to 8 in increments of 0.5.

28 Overview of the Dvorak Technique Cont’d In the following examples, only the Data T Number (DT) will be calculated, the final (official) T number assigned to a tropical cyclone includes further considerations. DT computations familiarize one to various tropical cyclone patterns.

29 Four Basic Patterns Curved Band Pattern Shear Pattern Central Dense Overcast (CDO) Pattern Eye Pattern –Pattern is not always obvious –Pattern typically varies with time

30 Patterns and Associated T Numbers

31 Empirical relationship between T number and wind speed

32 Finding the Cloud System Center (CSC) First step in the Dvorak technique From Dvorak (1985): “The cloud system center is defined as the focal point of all the curved lines or bands of the cloud system. It can also be thought of as the point toward which the curved lines merge or spiral.” Center not always obvious, especially at night TPC technique combines channel 2 and 4

33 T.S. Lisa Channel 4

34 T.S. Lisa

35 Curved Band Pattern TS Ivan 9/23/98 11:15 UTC

36 Curved Band Pattern Cont’d DT Number

37 Shear Pattern Hurricane Bertha 7/11/ UTC

38 Shear Pattern DT Numbers 1° latitude = 60 nautical miles (nmi) = 111 km

39 Central Dense Overcast (CDO) Hurricane Georges 9/21/ UTC

40 CDO No eye DT number determined by CF+BF=DT –CF=CENTRAL FEATURE –BF=BANDING FEATURE –DT=DATA T NUMBER

41 CDO Central Feature (CF) Measure Diameter of CDO in degrees latitude For a well defined CDO –3/4 °CF=2 –1 1/4 °CF=3 –1 3/4 °CF=4 –>2 1/4 °CF=5 For an irregular CDO –1° to 1 1/2 °CF=2 –>1 1/2 °CF=3

42 CDO - Banding Feature (BF)

43 Eye Pattern Hurricane Georges 9/19/ UTC

44 Eye Pattern DT number determined by CF+BF=DT –CF=CENTRAL FEATURE –BF=BANDING FEATURE –DT=DATA T NUMBER

45 Banding Eye Hurricane Bonnie 8/25/ UTC

46 Infrared (IR) Technique Can be used during night as well as during day At times, more objective than visible technique Fully objective version developed at CIRA Updated objective technique from CIMSS

47 Example Digital IR: Hurricane Erika 1515 UTC 8 September 1997 Warmest eye pixel 16 °C Warmest pixel 30 nmi (55 km) from center -71 °C Nomogram gives Eye no. =7

48

49

50 Operational Dvorak Technique Verification for Atlantic Seasons

51 Input for NHC Track and Intensity Forecasts Track –70 % Numerical model guidance –15 % Synoptic reasoning –15 % Recent trends Intensity –50 % Recent trends –40 % Synoptic reasoning –10 % Numerical model guidance

52

53

54 Applications of Satellite Data to TC Forecasting Track –Inclusion of remotely sensed data in NWP models –Diagnosis of model initial state –Evaluation of synoptic situation Intensity –Evaluation of factors affecting intensity SST changes vertical shear (especially cloud track winds) trough interaction –Inclusion in NWP models

mb AVN Winds and WV Image 19 Sept 1998

56 NEW GOES WINDS PRODUCTS ARE BEING PRODUCED BY CIMSS/NESDIS: - HIGH - DENSITY WINDS DERIVED FROM IR AND HIGH-RESOLUTION VISIBLE CLOUD MOTIONS AS WELL AS WATER VAPOR MOTIONS, USING AUTOMATED ALGORITHMS - DISPLAYS OF THESE WINDS FOR UPPER- & LOWER-LEVEL LAYERS OVER THE TROPICS ARE ROUTINELY AVAILABLE VIA THE INTERNET -UWISC/CIMSS TC WEB SITE:

57

58 Vertical Wind Shear Analysis from GOES High Density Winds

59

60 Hurricane-Trough PV Interaction During Hurricane Elena 1985 (Molinari et al 1995)

61 8-Frame Water Vapor Imagery Loop 9/20/98 23:45 to 9/21/98 23:45 Hurricane/Trough Interaction

62 Storm-Scale Structure Convective transients, asymmetries –Velden and Olander (1998) technique IR BT usually warmer than WV Deep convection transport into stratosphere WV BT warmer than IR Concentric eye walls, eye wall cycles Mesovortices within the eye –High spatial and time resolution imagery (RSO, SRSO) –Extra-high density satellite winds

63 Channel 3, 4 Convective Parameter (CP) for Hurricane Opal 1995 (From Bosart, et al 1999) Min P P (mb) CP

64 GOES-East Scanning Strategies Routine Scanning –Conus hr+01,31 –Extended NH hr+15,45 –(2 or 4 per hr) Rapid Scan –Conus, NH 5-10 min –(8 per hr) Super Rapid Scan –Selected Sector 1-5 min –(22 per hr)

65 10-frame Rapid-Scan Visible Imagery Loop 9/21/98 19:02 to 20:10 Hurricane Georges Approaching Puerto Rico

66

67 Hurricane Luis 9/6/ UTC

68 TC Measurements from Microwave Frequencies Special Sensor Microwave Imager (SSM/I) –DMSP polar orbiting satellites –19, 22, 37, 85 GHz, 25 km resolution Advanced Microwave Sounding Unit (AMSU) –NOAA polar orbiting satellites (NOAA 15 +) –15 channels GHz, 50 km resolution Can see “through” clouds Depicts rainband, eye structure Rainfall and surface wind algorithms AMSU temperature retrievals

69 Hurricane Jeanne 9/23/ UTC From NRL web site

70

71 AMSU Retrieved Temperature Anomaly and Gradient Wind for Hurricane Bonnie 8/25/ UTC

72 AMSU Retrieved Temperature Anomaly and Gradient Wind for Hurricane Bonnie 8/25/ UTC (Adjusted to remove low-level cold anomaly)

73 AMSU and Aircraft Reconnaissance 700 mb Tangential Winds

74 IR Imagery from Bonnie 8/25/ UTC (Blue Rings at 100 and 350 km Radius)

75 IR Imagery March 1, 1999 AMSU Tempertature Retrieval (570 mb)

76 Summary Multispectral GOES imagery provides synoptic overview –ITCZ, Subtropical Ridges, TUTT and cold lows, waves, TCs WV Imagery is especially useful for tracking cold lows Continuity in imagery is primary tool for tropical waves Dvorak method provides quantitative intensity estimates –Also provides framework for operational forecasting –Shortwave IR aids center location, especially at night Sat. winds: environmental interactions, model intialization WV- IR difference isolates tropical deep convection Rapid-scan imagery: storm-scale fluctuations Microwave imagery is useful for low-level storm structure New AMSU data shows promise for hurricane analysis