M icrowave-TC intensity estimation Ryo Oyama M eteorological - - PowerPoint PPT Presentation

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

• n 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.

Use applications:

• Early analysis
• Best track analysis
• Creation of TC bogus

vortex for NWP initial analysis TC intensity analysis (MSLP , MSW) In situ observations : Low spatial resolution Satellite observations: Wide coverage, high temporal resolution (for MTSAT)

3

Dvorak technique

(based on Infrared image from geostationary satellite) :A primary method based on satellite observation

Brightness temperature (TB) of M TSAT infrared channel for TC Songda (1102)

：

Cloud top temperature Dvorak technique requires analysis skills based on enough experience ! Curved band pattern Eye pattern Shear pattern

00UTC 23 May 2011 20UTC 26 May 2011 23UTC 28 May 2011

CDG CM G W B LG M G DG OW WM G

Cold Warm

4

However, Dvorak technique has some weak points.

Jun.22 11UTC (CB cluster) Jun.23 20UTC (CB cluster) Jun.24 10UTC (Curved band) Jun.26 06UTC (Shear/LCV)

970 975 980 985 990 995 1000 1005 1010 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 MSLP (hPa) Month/Day and Time (UTC) Dvorak MSLP Best track MSLP

6/21 6/22 6/23 6/24 6/25 6/26 6/27

TC Meari (1105)

in situ observation at M iyako-jima: 982 hPa

5

Satellite microwave sensor can observe TC internal structure !

Warm core

M W radiation from cloud/ rain :ice/ liquid water 55 GHz M W radiation from the atmosphere : temperature IR radiation from cloud top : cloud top temperature

gray : clouds, white: ice cloud/ rain, light blue : liquid rain Eye wall Spiral rain band

10-19 GHz M W radiation from sea surface : sea foams induced by surface winds

Sea surface with sea foams induced by winds Scattering by ice particles MTSAT NOAA/AMSU TRMM/ TMI

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

Pressure level (hPa)

Inner core (radius < 100～200 km) Convergence near the surface increases due to increase of inflow with tangential wind intensified, Cloud and rain water increases as eye walls and rain bands are formed. Radial cross section through an idealized, axially symmetric hurricane in TC inner core (Wallace and Hobbs 2006)

8

T R M M / T M I

• 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

85GHz

TM I can obtain information on ice/ liquid rain and sea surface.

10GHz 19GHz 37GHz

TM I TB images for TC Francisco (1327) at 1759UTC on 20 Oct 2013

R=200km

Emission from liquid cloud/rain and water vapor Scattering by ice Emission from sea surface with foams induced by winds

V-Pol V-Pol V-Pol V-Pol H-Pol H-Pol H-Pol 21GHz V-Pol H-Pol

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

Domains for computing TB parameters

about 200km

2.0° 1.5° 1.0° 0.5°

0.25°

TC M oving

(Step 1) TB parameters (max, average, min etc. in the defined domains) for TM I channels are computed. (Step 3) M SW is estimated by using a multiple- regression equation for each TB image pattern. (Step 2) TB image pattern of TC inner core (radius < 2 degrees) was determined (out of 10 patterns) using TB parameters. Regression equation for M SW estimation: M SW = A0 + Σ {A(n) x TBparam(n)} TBparam(n): TB parameters highly correlated to M S W n = 1 to 7

12

85GHz TB

Validation of M SW estimates by TM I technique with reference to the best-track data

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 estimation during TC formation stage (ii) Determination error of TC center position Best track MSW (m/s) MSW estimate by TMI technique (m/s)

13

TC Soulik (1307)

13 18(m/s) 33.4 51.5 46.3 41.2 30.9 /July

MSW

in situ

• bservation at

Y

• naguni-jima

14

10 15 20 25 30 35 40 45 50 55 60 00 12 00 12 00 12 00 12 00 12 00 12 00 12 00 MSW （ m/s） （ UTC）

TM I M SW Dvorak M SW JM A best track

7/7 7/8 7/9 7/10 7/11 7/12 7/13

TC Soulik (1307)

85GHz (PCT) 10GHz (H)

① ② ③ ④ ① ② ③ ④ in situ observation at Y

• naguni-jima:

44 m/s (10-min ave.)

ice cloud/ rain 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.

Warm air Low surface pressure Large (small) warm core Large (small) TC size

TC Bolaven (1215) M SLP=940 hPa, M S W=41 m/ s, R30 = 555km Temperature anomaly by AM SU-A for TC Danas (1324) M SLP=975 hPa, M S W=31 m/ s, Shortest radius of 30knot winds (R30)= 222km Anomaly～5K at 200 hPa Anomaly～11K at 200 hPa TB attenuation

• f microwave

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).
• bserves twice per day at maximum (5 satellites available)
• consists of twelve channels (Ch3 - Ch14) for atmospheric temperature

sounding.

atmosphere AMSU-A 55-GHz band channels observe radiation from oxygen in the atmosphere. width of scan line: about 2000 km NOAA

19

Weighting functions of AM SU-A channels (Kidder et al. 2000)

troposphere

Field of View (FOV) of AM SU-A channels (open ellipses) (kidder et al. 2000)

AM SU-A FOV size: 48km - 150 km

20

• 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.

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

with RSM C T

• kyo – Typhoon Center in 2011-2012.
• 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

M SLP Environmental surface pressure Surface pressure decrease equivalent to temperature anomaly at TC center

≅ －

Tenv Teye

Height Top of the atmosphere (ZT

• p)

Surface (Z=Z0)

P0

env

P0

eye

Hydrostatic equilibrium theory ：

550 km～600 km (Default value) Warm core

MSLP

22

Warm core intensity used for M SLP estimation

Max TB anomaly Max TB anomaly Max TB anomaly TB anomaly for Ch6 (～400 hPa level) TB anomaly for Ch7 (～250 hPa level) TB anomaly for Ch8 (～180 hPa level)

M aximum (defined as warm core intensity)

23

y = 0.0235x - 0.0965 Number = 102

• 4
• 3
• 2
• 1

1 2 3 4

• 4 0
• 3 0
• 2 0
• 1 0

1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 AMAX_DIFF (K) SIWAMAX

(c) Ch8

Correction of warm core intensity retrieval errors and M SLP estimation

Error due to low spatial resolution (48

～150 km) of AMSU-A observation

Scattering Index over Water (SIW) underestimation of warm core intensity (K)

M SLP estimation equation derived using AM SU-A observations with reference to JM A best track data for TCs in 2008 :

MSLP = SLOPE× (warm core intensity) + OFF FFSET

TB attenuation error due to ice particles These warm core intensity retrieval errors are corrected by developed schemes. Ch8

24

Validation of AM SU M SLPs to JM A best-track data for TCs during 2009-2011

y = 0.878 x + 120.99 R = 0.89 RMSE =10.1 hPa BIAS = 0.3 hPa 880 900 920 940 960 980 1000 1020 8 8 0 9 0 0 9 2 0 9 4 0 9 6 0 9 8 0 1 0 0 0 1 0 2 0 Estimation (hPa) Best track MSLP (hPa)

2009 - 2011

Number of observations: 1029 RMSE : 10.1 hPa BIAS: 0.3 hPa Statistical validation revealed several characteristics of AMSU MSLPs: 1. Better quality of AMSU MSLPs for large TCs than compact TCs, suggesting a difficulty of observing small warm core. 2. Quality degrading of AMSU MSLPs due to too large microwave scattering near TC center. 3. Superiority of AMSU MSLPs to Dvorak MSLPs when TC is not compact and TC cloud pattern is

“Curved band” or “Shear/ LCV”.

25

Characteristics of M SLP estimates by AM SU technique

• Characteristics of M SLP estimates by AM SU technique (AM SU

M SLP) are shown in comparison with JM A best track data and M SLP estimates by Dvorak technique (Dvorak M SLP) for three typical cases of TCs during 2009-2011.

• For TCs during 2009-2011, JM A best track data depends on Dvorak

M SLP , while it does not depend on AM SU M SLP .

• Shortest radius of 30 knot winds (R30) from best track data is used

as TC size related to warm core size. Average R30 value between 2000-2011 for each M SLP is also used as the criterion.

26

TC M eari (1105)

970 975 980 985 990 995 1000 1005 1010 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 MSLP (hPa) Month/Day and Time (UTC) Dvorak MSLP AMSU MSLP Best track MSLP

6/21 6/22 6/23 6/24 6/25 6/26 6/27

average R30 (261 km) < R30 of Meari (370 km) for MSLP of 975 hPa

AM SU-A TB anomaly (Ch6): ～400 hPa M W scattering (SIW) IR TB; Shear pattern

27

TC Noru (1113)

980 985 990 995 1000 1005 1010 1 2 0 0 1 2 0 0 1 2 0 0 1 2 0 0 1 2 0 0 1 2 0 0 MSLP (hPa) Month/Day and Time (UTC) Dvorak MSLP AMSU MSLP Best track MSLP

9/2 9/3 9/4 9/5 9/6

average R30 (197 km) < R30 of Noru (370 km) for MSLP of 990 hPa

AM SU-A TB anomaly (Ch6): ～400 hPa M W scattering (SIW) IR TB; Shear/ LCV

28

TC M irinae (0921)

950 960 970 980 990 1000 1010 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 1 2 0 0 1 2 0 0 MSLP (hPa) Month/Day and Time (UTC) Dvorak MSLP AMSU MSLP Best track MSLP 10/25 10/26 10/27 10/28 10/29 10/30 10/31 11/1 11/2

average R30 (354 km) > R30 of Mirinae (148 km) for MSLP of 960 hPa

AM SU-A TB anomaly (Ch6): ～400 hPa M W scattering (SIW) IR TB

29

Summary and conclusion on M SLP estimation by AM SU technique

• AM SU technique estimates M SLP using TC warm core

intensity as observed by AM SU-A.

• M SLP estimates by AM SU technique tended to be better than

those by Dvorak technique for incompact TCs with specific TC cloud patterns (Curved band or Shear/ LCV).

• AM SU M SLP is expected to support operational M SLP analysis

when in situ data is not available and the estimation accuracy

• f Dvorak technique is low.

30

Future plan for M icrowave-TC intensity estimation

RSM C T

• kyo – Typhoon center began to use TC intensity

estimates by AM SU and TM I techniques as references for the

• perational TC intensity analysis in 2013.

Future works for further contribution of the estimation to

• perational TC intensity analysis are:
• Improvements to the current algorithms
• Use of satellite observations other than AM SU-A and TM I for

TC intensity estimation SS MIS microwave imager/ sounder (DMS P) AMS R2 microwave imager (GCOM-W1) ATMS microwave sounder (NPP)

31

Thank you

32