Asymmetric Vortex Initialization and GOES 13/15 Imager Radiance Assimilation for Improved

Tropical Storm Prediction Using HWRF �

1

X. Zou1 , F. Weng2 and Z. Qin3

1Earth System Science Interdisciplinary Center University of Maryland, USA 2NOAA’s Center for Satellite Applications and Research, USA 3Nanjing University of Information & Science Technology, Nanjing, China

Outline

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§  Introduction to HWRF System

§  HWRF Vortex Initialization

§  Impacts of GOES-13/15 Imager Radiance Assimilation on Track and Intensity Forecasts of Tropical Storm

§  Summary and Conclusions

J(x) = 12(x − xb )

TB−1(x − xb )+12(H (x)− yobs )T (O+ F)−1(H (x)− yobs )

x − analysis variablexa − final analysisxb − backgroundB − background error covariance

J(xa ) = min

xJ(x) ∀x near xb

Cost Function that is minimized in DA

yobs − observationsO − observation error covarianceH − observation operatorF − forward model error covariance

•  NCEP GSI 3D-Var Data Assimilation System •  Hurricane Weather Research Forecast (HWRF) System

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Hurricane Forecast Improvement Program （HFIP）

HFIP provides the basis for NOAA and other agencies to coordinate hurricane research needed to significantly improve guidance for hurricane track, intensity, and storm surge forecasts. It also engages and aligns the inter-agency and larger scientific community efforts towards addressing the challenges posed to improve hurricane forecasts.

NOAA 10-Year Program （2008－2018）

http://www.hfip.org

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NOAA HFIP Teams

§  Global Model/Physics §  Regional Model/Physics §  Ensembles §  Data Assimilation/Vortex Initialization §  Verification §  Applications Development and Diagnostics §  Hurricane Observations §  Coupled Air-Sea Interaction §  Socio-Economic

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Motivation for Vortex Initialization

•  Rain contamination for QuikSCAT surface wind •  Cloud contamination of infrared observations except for cirrus clouds •  Cloud contamination of microwave observations in heavy precipitation •  Inaccurate model simulation in cloudy radiance (bias, QC, …) •  Uncertainty in surface emissivity model over various land surface types

1.  Initial vortices in background fields are often too weak and misplaced.

2.  Observations within hurricanes are insufficient either in their spatial and/or temporal coverage, or in atmospheric state variables. Many observations are difficult to assimilate because of

Having an initial vortex at the right location and with realistic size and intensity is extremely important for both track and intensity forecasts of tropical cyclone.

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1.  The structure of the vortex should be dynamically and thermodynamically consistent.

Wind and mass fields in balance; Coherent moisture field

2.  Size and intensity of the real TC should be represented. A real storm evolving in its own environmental conditions possesses its unique size and intensity.

3. The vortex is compatible with the resolution and physics of the prediction model.

False spinup is prevented.

Guidelines for Vortex Specification

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(1)  Decompose the NCEP GFS fields at all model levels into basic field, non-hurricane perturbation, and hurricane component using the GFDL method.

Vortex Initialization in HWRF

hNCEP GFS

! = hBbasic field! + hN

non-hurricane disturbance! + hGFS-vortex

hurricane component"#$ %$

hD , disturbance field& '$$$$$ ($$$$$

(2) Determine the boundary (e.g., size) of the vortex based on the disturbance field (hD) at 850 hPa:

Ω850hPa

?

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Vortex Initialization in HWRF

(3) Remove the GFS hurricane component at different model levels within the 850-hPa vortex region to obtain the residual hurricane component

hGFS-vortexresidual =

hGFS-vortex , outside Ω850hPa 0, within Ω850hPa

"#$

%$

(4) Add one of the two symmetric HWRF vortices (1000 km radius) onto the sum of basic field, non-hurricane perturbation, and the residual hurricane component

h '

model initial condition! = hB + hN + hGFS-vortex

residual

residual hurricane component"#$ %$ + hV

HWRF vortex!

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500 hPa Temperature: Extracting Environmental Flow from GFS

GFS Basic Field

Hurricane Component Non-hurricane

Component

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Mixing Ratio at 500 hPa: Extracting Environmental Flow from GFS

GFS Basic Field

Hurricane Component Non-hurricane

Component

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HWRF Vortices

One for deep TCs One for shallow and medium depth TCs

(1)  The two-dimensional symmetric tangential wind, radial wind, temperature and mixing ratio were stored in data format for two

vortices:

(2) Tangential and radial winds are scaled based on radius of the maximum wind, radius of the outermost closed isobar and the maximum wind speed

(3) Surface pressure is derived from surface tangential wind based on gradient wind balance

(4) Temperatures at different levels are scaled by an empirical factor

(5) The mixing ratio is modified based on the scaled temperature under the constraint that relative humidity does not change

?

?

?

HWRF Stored Vortices

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Radial Distance (km) Radial Distance (km)

Pres

sure

(hPa

)

Pres

sure

(hPa

)

Pres

sure

(hPa

)

Radial Distance (km) Radial Distance (km)

Tangential Wind (u)

(m s-1)

(K)

Deep TC Shallow TC

Pres

sure

(hPa

) Temperature (T)

Pres

sure

(hPa

)

HWRF Stored Vortices

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Radial Distance (km) Radial Distance (km)

Pres

sure

(hPa

)

Pres

sure

(hPa

)

Pres

sure

(hPa

)

Radial Distance (km) Radial Distance (km)

Mixing Ratio (q)

(g kg-1)

Deep TC Shallow TC

(m s-1)

Radial Wind (v)

Tangential Winds before and after Scaling for Hurricane Sandy at 0000 UTC October 24, 2012

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Radial Distance (km) Radial Distance (km)

Pres

sure

(hPa

)

Pres

sure

(hPa

)

(m s-1)

Stored Shallow TC After Scaling

Vortex intensity correction:

�������� �� −�� �� = α���� −�� �� +

β����� −�� �� ��

�Vortex size correction:

�

corrected-vortex = γ���� −�����

corrected-vortex = γ���� −�����#$%

&%

Vortex Size and Intensity Corrections in HWRF

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Vortex intensity correction:

�������� �� −�� �� = α���� −�� �� +

β����� −�� �� ��

�

��

���

����� �� −�� �� ! ���

��

��

����� �� −�� �� ! ��

��

"#$

%$⇒ α�β

Vortex size correction:

�

corrected-vortex = γ���� −�����

corrected-vortex = γ���� −�����#$%

&%

��� ���corrected-vortex ! �

���

��� ⇒ γ

HWRF System and Its Required Improvements

•  In 2011 and 2012 version of HWRF system, most of satellite data are not assimilated in HWRF analysis process due to mixed impacts on hurricane track and intensity forecasts

•  Analyses show GSI quality controls for satellite water vapor sounding data are problematic (lots of bad data sneak into the analysis process) •  Bias correction schemes for satellite data developed for the global model applications have not been fully vetted for regional model applications

•  Cold start (background fields are not the HWRF 6-h forecasts

•  Model top in 2011-2013 versions of HWRF is too low for assimilation of upper-level channels

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Four Landfall Tropical Storms in 2012

Debby Beryl

Sandy

Isaac

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parent domain

ghost D2

middle nest

3X domain

inner nest

2012 HWRF Model Domains �

2012 HWRF DA Domains

Parent domain 27 km, 750x750

Middle Nest 9 km, 238x150

Background SLP 0000 UTC June 27, 2012

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Proposed and Completed Modifications to the HWRF System

1. Raise the model top from 50 hPa to 10 hPa

3. Remove the GFS hurricane component at different model levels within the the boundary (e.g., size) of the vortex based on the disturbance field (hD) at the same level instead of the disturbance at 850 hPa

4. Include the asymmetric component using the GFDL method, i.e., integration of a barotropic model

√

√

√

5. Add GOES-13 and -15 radiance assimilation

2. Change the cold start (GFS 6-h forecasts) to warm start (HWRF 6-h forecasts

√

√

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Model Top and Model Levels

ATMS Weighting Function

Pres

sure

(hPa

)

Layer Thickness (hPa)

ATMS Weighting Function

Pres

sure

(hPa

)

Layer Thickness (hPa)

43 levels 51 levels

pt=10 hPa

pt=50 hPa

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Boundaries ( ) Separating Sandy Vortex from Its Environmental Flow

0000 UTC October 24, 2012

0600 UTC October 25, 2012

100 hPa 200 hPa 500 hPa 850 hPa 900 hPa

§  Sandy vortex tilts northward with altitude at 0000UTC October 24, 2012

§  Sandy vortex size reduces with altitude at 0600UTC October 24, 2012

Ω850hPa

Ω500hPa

Ω200hPa

Ω100hPa

Ω850hPa

Relative Vorticity and Wind Fields of Symmetric and Asymmetric Vortices �

Streamfunction（unit: 106 m2/s)

Wind vector (unit: m/s)

Relative vorticity (unit: 1/s)

Symmetric Asymmetric

Differences

1800 UTC June 23, 2012

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Asymmetric Bogus Vortex �

1800 UTC June 23, 2012

Tangential Wind Radial wind

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Tangential Wind Radial wind Tangential Wind

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Symmetric and Asymmetric Bogus Vortex �

Symmetric Vortex Asymmetric Vortex

Tropical storm Debby at1800 UTC June 23, 2012

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Data Coverage of GOES-15 and GOES-13

GOES-13: May 24, 2006

GOES-15: March 14, 2010 Launch Time：

GOES-13/15 Imager Channel Characteristics

Channel  Central

Frequency (µm)

Band Width (µm)

Spatial Resolution (km)

Observation Error (K)

GOES-13 GOES-15 GOES-13 GOES-15

1 0.65 0.19 1.0 1.0 ±5% ±5%

2 3.90 0.34 4.0 4.0 0.051 0.063

3 6.55 1.50 4.0 4.0 0.140 0.170

4 10.7 1.00 4.0 4.0 0.053 0.059

6 13.35 0.70 8.0 4.0 0.061 0.130

•  GOES-13/15 have no channel 5 •  GOES channel 5 (12.0 µm) had been changed to

channel 6 (13.35 µm) since the launch of GOES-12 27

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GOES-13/15 Weighting Functions

Weighting Function

Ch3

Ch2

Ch6

Ch4

Pres

sure（

hPa)

Near infrared channel 2： low cloud, fog and fire

Infrared channel 3： upper tropospheric water vapor

Infrared channel 4： surface and cloud-top temperature

Infrared channel 6： cloud

130W 110W 90W 70W 50W

50N

40N

30N

20N

10N

EQ130W 110W 90W 70W 50W

50N

40N

30N

20N

10N

EQ

130W 110W 90W 70W 50W

50N

40N

30N

20N

10N

EQ130W 110W 90W 70W 50W

50N

40N

30N

20N

10N

EQ

1800

UTC

, Jun

e 23

00

00 U

TC, J

une

24

GOES-15 GOES-13

Quality Control of GOES-13/15 Imager Channel 3 �

Pass QC

Surface type Observation error O-B

Removed by QC

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130W 110W 90W 70W 50W

50N

40N

30N

20N

10N

EQ130W 110W 90W 70W 50W

50N

40N

30N

20N

10N

EQ

130W 110W 90W 70W 50W

50N

40N

30N

20N

10N

EQ130W 110W 90W 70W 50W

50N

40N

30N

20N

10N

EQ18

00 U

TC, J

une

23

0000

UTC

, Jun

e 24

GOES-15 GOES-13

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Quality Control of GOES-13/15 Imager Channel 5 �

Pass QC

Surface type Observation error O-B

Removed by QC

Differences in Geopotential Analysis with and without Assimilating GOES-13/15 Data �

300 hPa

Pres

sure（

hPa)

Difference

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Symmetric Vortex Symmetric Vortex＋GOES

Asymmetric Vortex Asymmetric Vortex＋GOES

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Forecasts of Geopotential at 500 hPa at 1800 UTC June 24, 2012 with and

without Assimilating GOES-13/15 Data �

2324252627282930

Track Prediction �Asymmetric Vortex without GOES DA

Asymmetric Vortex with GOES-13/15 DA

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Statistical Results of Track Prediction (2012) �

Symmetric Vortex Asymmetric Vortex

Without GOES With GOES Standard Deviation 34

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Summary and Conclusions

A much larger positive impact of GOES imager radiance assimilation on hurricane track and intensity forecasts was achieved when an asymmetric vortex component

was added to the HWRF symmetric bogus vortex.

§  Asymmetric component was successfully added to the HWRF vortex initialization

§  GOES-13 and -15 imager radiance assimilation was successfully added to the HWRF/GSI system

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Future Plan

§  Putting things together

(i)  Axisymmetric model (Rotunno and Emanuel, 1987) (ii)  Dropsonde-derived composite structures (iii)  Radial profiles of different satellite retrieval products (SST, SSW, TPW, T)

§  Axisymmetric part

§  Asymmetric part

(i)  Barotropic model + specified vertical structure function (ii)  Asymmetric satellite derived 3D fields (T, LWP, LWP, IWP) (iii)  Baroclinic model (assimilating satellite derived products)

More details for this talk can be found in： �

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Zou, X., Z. Qin and Y. Zheng, 2014: Improved tropical storm forecasts with GOES-13/15 imager radiance assimilation and asymmetric vortex initialization in HWRF. Mon. Wea. Rev., (accepted)