M icrowave-TC intensity estimation Ryo Oyama M eteorological Research Institute Japan M eteorological Agency
Contents 1. Introduction 2. Estimation of TC M aximum Sustained Wind (M SW) using TRM M M icrowave Imager (TM I) data 3. Estimation of TC M inimum Sea Level Pressure (M SLP) based on warm core intensity observed by Advanced M icrowave Sounding Unit-A (AM SU-A) 4. Future plan for M icrowave-TC intensity estimation 2
Introduction Satellite observations are essential for analysis of tropical cyclone (TC) intensity, such as M inimum Sea Level Pressure (M SLP) and M aximum Sustained Wind (M SW), particularly where in situ observations are sparse. In situ observations : Low spatial resolution TC intensity analysis (MSLP , MSW) Satellite observations: Wide coverage, high Use applications: temporal resolution (for MTSAT) • Early analysis • Best track analysis • Creation of TC bogus vortex for NWP initial analysis 3
Dvorak technique (based on Infrared image from geostationary satellite) : A primary method based on satellite observation Eye pattern Shear pattern Curved band pattern CDG Cold CM G W B LG M G DG OW 23UTC 28 May 2011 20UTC 26 May 2011 00UTC 23 May 2011 Warm WM G Brightness temperature (TB) of M TSAT infrared channel for TC Songda (1102) ： Cloud top temperature Dvorak technique requires analysis skills based on enough experience ! 4
However, Dvorak technique has some weak points. TC Meari (1105) Dvorak MSLP Best track MSLP 1010 1005 Jun.22 11UTC Jun.26 06UTC 1000 MSLP (hPa) (CB cluster) (Shear/LCV) 995 990 985 980 975 970 0 0 1 2 0 0 1 2 0 0 1 2 0 0 1 2 0 0 1 2 0 0 1 2 0 0 1 2 0 0 6/21 6/22 6/23 6/24 6/25 6/26 6/27 Month/Day and Time (UTC) Jun.23 20UTC Jun.24 10UTC (CB cluster) (Curved band) in situ observation at M iyako-jima: 982 hPa 5
Satellite microwave sensor can observe TC internal structure ! NOAA/AMSU MTSAT TRMM/ TMI 55 GHz M W radiation M W radiation from 10-19 GHz M W radiation cloud/ rain from the atmosphere from sea surface IR radiation from cloud top :ice/ liquid water : temperature : sea foams induced by : cloud top temperature surface winds Scattering by ice particles Warm core Spiral rain band Eye wall Sea surface with sea foams induced by winds gray : clouds, white: ice cloud/ rain, light blue : liquid rain 6
Estimation of TC maximum sustained wind (M SW) using TRM M M icrowave Imager (TM I) data 7
Basic TC structure seen in rain and wind distributions Radial cross section through an idealized, axially symmetric hurricane in TC inner core (Wallace and Hobbs 2006) Pressure level (hPa) Inner core (radius < 100 ～ 200 km) Convergence near the surface Cloud and rain water increases as increases due to increase of inflow eye walls and rain bands are with tangential wind intensified, formed. 8
T R M M / T M I o b s e rv a tio n TM I microwave imager (November 1997 ～ ) • Onboard TRM M for observing rain and sea surface over the tropical region. • Channel frequencies (GHz) : 10.7(V/ H), 19.35(V/ H), 21.3(V), 37(V/ H) and 85.5(V/ H). Spatial resolution of data is 38.3 km (10.7GHz) ～ 4.4 km (85.5GHz). • • 3 observations per day at maximum available (depending on TC location) TRMM 9
TM I can obtain information on ice/ liquid rain and sea surface. Emission from sea surface Emission from liquid cloud/rain with foams induced by winds Scattering by ice and water vapor 19GHz 37GHz 85GHz 10GHz H-Pol H-Pol H-Pol H-Pol R=200km 21GHz V-Pol V-Pol V-Pol V-Pol V-Pol TM I TB images for TC Francisco (1327) at 1759UTC on 20 Oct 2013 10
TC maximum sustained wind estimation (M SW) method using TM I observation (TM I technique) • TM I technique had been developed by M RI/JM A in 2004-2011 and has been validated in 2012-2013. • TM I technique estimates M SW using information on ice/ liquid rain distribution and sea foams induced by surface winds in TC inner core (radius < 2 degrees) obtained from TM I observation. • M SW is estimated by using a multiple-regression equation where TB parameters computed using TM I TBs are used as the input variables. The TB parameters are also used for recognition of TB image pattern. • The multiple-regression equations for M SW estimation were derived for respective TB image patterns from TM I observations in reference to JM A best-track data for TCs during 1998-2008. 11
Algorithm of TM I technique for M SW estimation (Step 1) TB parameters (max, average, min etc. 85GHz TB in the defined domains) for TM I channels are TC M oving computed. about 200km (Step 2) TB image pattern of TC inner core (radius < 2 degrees) was determined (out of 10 patterns) using TB parameters. 0.25 ° 0.5 ° 1.0 ° (Step 3) M SW is estimated by using a multiple- 1.5 ° regression equation for each TB image pattern. 2.0 ° Regression equation for M SW estimation: Domains for computing TB M SW = A0 + Σ {A(n) x TBparam(n)} parameters TBparam(n): TB parameters highly correlated to M S W n = 1 to 7 12
Validation of M SW estimates by TM I technique with reference to the best-track data MSW estimate by TMI technique (m/s) Black : Observations for TCs in 1998-2008 (used for deriving the estimation equation) Number = 749 Red : Observations for TCs in 2009-2012 (independent on the estimation equation) Number = 341 RMSE = 6.26 m/s BIAS = 0.99 m/s Relatively large estimation errors come from (i) Inadequate use of TB parameters for Best track MSW (m/s) estimation during TC formation stage (ii) Determination error of TC center position 13
TC Soulik (1307) in situ 30.9 observation at 13 41.2 46.3 Y onaguni-jima 51.5 MSW 33.4 18(m/s) /July 14
TC Soulik (1307) in situ observation at Y onaguni-jima: 60 44 m/s (10-min ave.) ② ④ 55 ③ m/s ） 50 45 TM I M SW MSW （ ① 40 35 Dvorak M SW 30 JM A best track 25 20 15 10 （ UTC ） 00 12 00 12 00 12 00 12 00 12 00 12 00 12 00 7/10 7/11 7/7 7/9 7/12 7/13 7/8 ③ ④ ② ① 85GHz (PCT) ice cloud/ rain 10GHz (H) liquid rain and sea foams 15
Summary and conclusion on M SW estimation by TM I technique • TM I technique estimates M SW based on TB parameters computed using TM I TBs in TC inner core. • Validation of the M SW estimates to best track data for TCs in 2009-2012 showed that RM SE is 6.26 m/s (comparable to Dvorak technique). • It is essential to find in which situation M SW estimate by TM I technique could support operational TC intensity analysis, in addition to improvements of the algorithm. 16
Estimation of TC M inimum Sea Level Pressure (M SLP) based on warm core intensity observed by Advanced M icrowave sounding Unit-A (AM SU-A) 17
What is warm core ? • Warm core is formed near TC center, with a positive temperature anomaly to the environment. • Warm core is a characteristic feature to identify TC intensity and TC size. Anomaly ～ 5K Anomaly ～ 11K at 200 hPa at 200 hPa TB attenuation of microwave Temperature anomaly by AM SU-A for TC Danas (1324) TC Bolaven (1215) M SLP=975 hPa, M S W=31 m/ s, M SLP=940 hPa, M S W=41 m/ s, Shortest radius of 30knot winds (R30)= 222km R30 = 555km Low surface pressure Warm air Large (small) TC size Large (small) warm core 18
Advanced M icrowave Sounding Unit-A (AM SU-A) AM SU-A - is onboard NOAA and M ETOP series polar orbital satellites. - has been operated since 1998 (NOAA-15 is the first satellite for AM SU). - observes twice per day at maximum (5 satellites available) - consists of twelve channels (Ch3 - Ch14) for atmospheric temperature sounding. NOAA AMSU-A 55-GHz band channels observe radiation from oxygen in the atmosphere. atmosphere width of scan line: about 2000 km 19
Field of View (FOV) of AM SU-A channels Weighting functions of AM SU-A (open ellipses) channels ( kidder et al. 2000 ) ( Kidder et al. 2000 ) troposphere AM SU-A FOV size: 48km - 150 km • AM SU-A channels for observing the troposphere are Ch4 (900 hPa level), Ch5 (600 hPa), Ch6 (400 hPa), Ch7 (250 hPa) and Ch8 (180 hPa). • TBs for Ch4 and Ch5 for observing the lower troposphere tend to be attenuated significantly by rain near TC center. 20
M SLP estimation method based on TC warm core intensity observed by AM SU-A (AM SU technique) • AM SU technique was developed by M RI/JM A in collaboration okyo – Typhoon Center in 2011-2012. with RSM C T • This technique estimates TC M inimum Sea Level Pressure (M SLP) using AM SU-A brightness temperature (TB) anomaly corresponding to TC warm core intensity. • A regression equation for M SLP estimation was derived using AM SU-A observations in reference to JM A best-track data for 22 TCs for 2008. 21
Basis of M SLP estimation from temperature anomaly corresponding to TC warm core Height Hydrostatic equilibrium theory ： Top of the atmosphere (Z T op ) T env Warm core T eye eye P 0 Surface (Z=Z 0 ) env P 0 550 km ～ 600 km (Default value) MSLP ≅ M SLP Environmental surface pressure Surface pressure decrease equivalent to temperature － anomaly at TC center 22
Warm core intensity used for M SLP estimation TB anomaly for TB anomaly for TB anomaly for Ch8 ( ～ 180 hPa level) Ch6 ( ～ 400 hPa level) Ch7 ( ～ 250 hPa level) Max TB anomaly Max TB anomaly Max TB anomaly M aximum (defined as warm core intensity) 23
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