Sensitivity Study of Precipitation and T2m to Soil Moisture Using NCEP WRF Ensemble Jun Du and...

Sensitivity Study of Precipitation and T2m to Soil Moisture Using

NCEP WRF Ensemble

Jun Du and George Gayno

EMC/NCEP/NOAA

(The photo taken at NCEP in July 1994)

In Memory of Prof. Fred Sanders of MIT

outline

• Sensitivity study• Basic physical mechanism

understanding • Soil moisture perturbation design (on

going)• Ensemble system improvement (to be

done)• Summary

Motivation

Under dispersive issue in warm season precipitation and near-surface variables

such as T2m

Ensemble spread of 12h-apcp from NCEP 21-member SREF (Jun 2006)

Tal agrand Di stri buti on (2m temperature) averagefor 20060808-20060824

0. 00

0. 05

0. 10

0. 15

0. 20

0. 25

0. 30

0. 35

0. 40

0. 45

0. 50

1 2 3 4 5 6 7 8 9 10 11

NCEP 10 members at T12Z

Prob

abil

ity

18 hours

Tal agrand Di stri buti on (2m temperature)average for 20060808-20060824

0. 00

0. 05

0. 100. 15

0. 20

0. 25

0. 30

0. 35

0. 400. 45

0. 50

0. 55

0. 60

1 2 3 4 5 6 7 8 9

CAMS 8 members at T12Z

Probability

18 hours


0. 00

0. 05

0. 10

0. 15

0. 20

0. 25

0. 30

0. 35

0. 40

0. 45

0. 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

CMA 15 members at T12Z

Probability

18 hours


0. 000. 05

0. 100. 15

0. 200. 250. 30

0. 350. 40

0. 450. 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

MSC 16 members at T12Z

Prob

abil

ity

18 hours

( from NMC/CMA, Y. Li)

CMA 2M temperatureAverage for 22060808-20060814

0

1

2

3

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5

6 12 18 24 30 36

Forecast HoursRM

S er

ror

EPS meanSpread

CAMS 2M temperatureAverage for 22060808-20060814

0

1

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3

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6 12 18 24 30 36

Forecast Hours

RMS

erro

r

EPS meanSpread

J MA 2M temperatureAverage for 22060808-20060814

0

1

2

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6

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6 12 18 24 30 36

Forecast Hours

RMS

erro

r

EPS meanSpread

MSC 2m temperatureAverage for 22060808-20060814

0

1

2

3

4

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6 12 18 24 30 36

Forecast Hours

RMS

erro

r

EPS meanSpread

NCEP 2m temperatureAverage for 22060808-20060814

0

1

2

3

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6 12 18 24 30 36

Forecast Hours

RMS

erro

r

EPS meanSpread

(from NMC/CMA, Y. Li)

3 WRF_NMM (NCEP, 40km) and 3 WRF_ARW (NCAR, 45km)

Warm season case

0-10cm Soil moisture diff (nam-gfs)

Nam is wetter than gfs in general (except For SE US and Greenland)

NOAH

NOAH

Diff ~0.1

With NAM soil moisture

With GFS soil moisture

Diff between two NMM 3h-apcp forecasts

(WRF_NMM model)

With NAM soil moisture

With GFS soil moisture

Diff of two ARW 3h-apcp forecasts

(WRF_ARW model)

With nam soil moisture (NMM)

With gfs soil moisture (NMM)

T2m diff (namSM – gfsSM, NMM)

Within WRF_NMM model:Impact on T2m is significant!

With nam soil moisture (ARW)

With gfs soil moisture (ARW)

Within WRF_ARW model:Impact on T2m is significant.

T2m diff (namSM – gfsSM, ARW)

Impact comparison between “IC diff” and “soil moisture diff” within WRF_NMM

Difference caused by different ICs Difference caused by different soil moisture

Impact from diff soil moisture is comparable to that from diff ICs within NMM!

[note: (a) <0.1” contour not plotted, (b) it’s only 3h accumulation]

(3h-apcp)

Impact comparison between “IC diff” and “soil moisture diff” within WRF_ARW

Difference caused by different ICs Difference caused by different soil moisture

Impact from diff soil moisture is comparable to that from diff ICs within ARW!

(3h-apcp)

Impact from soil moisture diff is slightly less than but still comparable in some areas to that even from model diff (NMM vs. ARW)!

Impact comparison between “model difference” and “soil moisture difference”

Difference caused by different models Difference caused by soil moisture diff (nmm)

3h-apcp

Impact comparison between “model difference” and “soil moisture difference”

Difference caused by different models Difference caused by soil moisture diff (arw)

Impact from soil moisture diff is slightly less than but still comparable in some areas to that even from model diff (NMM vs. ARW)!

3h-apcp

different IC (NMM; namSM)

different models (nmm vs. arw; namSM)

Diff soil moisture (nam – gfs; NMM)

T2m -- impact comparison (NMM):Soil moisture impact on T2m is bigger Than that of IC and of model difference!

T2m -- impact comparison (ARW):Soil moisture impact on T2m is comparable To that of IC but smaller than model diff

Diff soil moisture (nam – gfs; ARW)

Different IC (ARW, namSM)

Diff models (nmm vs. arw; gfsSM)

Sensitivity/response of precip to soil moisture perturbation varies with model

In WRF_NMM (less sensitive) In WRF_ARW (more sensitive)

Sensitivity/response of T2m to soil moisture varies with model:

In WRF_NMM (more sensitive) In WRF_ARW (less sensitive)

Physical mechanism: soil moisture evapotranspiration

partitioning of net available surface thermal energy between latent heat and sensible heat flux

(temp and moisture) convection(a) dry case: increased sensible heat will have an earlier initiation of convection (e.g. afternoon thunderstorm);(b) wet case: in contrast to “dry case”, reduced sensible heat will delay initiation convection (e.g. late night thunderstorm);(c) perturb soil moisture local thermal gradient local circulation precipitation

0-10cm Soil moisture diff (max-min)

Wet ~0.5

Dry ~0.1

Diff ~0.3-0.4

T2m diff (wet – dry, NMM)

Local afternoon Local early morning

T2m diff (wet – dry, NMM)

With WRF_NMM model

With WRF_ARW model

T2m diff (wet – dry, ARW) T2m diff (wet – dry, ARW)

Local afternoon Local early morning

(Aligo, Gallus and Segal, 2006 WAF)

Afternoon (dry) Afternoon (wet)

Late night (dry) Late night (wet)

Wet soil moisture

Dry soil moisture

Diff (wet – dry) with ARW

Wet soil moisture more rainfallIn general especially in mid-high Latitudes than dry soil situation

Wet soil moisture

Dry soil moisture

Wet soil moisture more rainfallIn general especially in mid-high Latitudes than dry soil situation

Diff (wet – dry) with NMM

Local circulation/precipitation modification

Wet soil moisture condition Dry soil moisture condition

Response of 3h-apcp forecast to IC difference depends on soil moisture content:More sensitive in wet condition than in dry condition (WRF_NMM)


(WRF_NMM model)

T2m is more sensitive to IC in “dry soil” than in “wet soil” condition

Response of 3h-apcp forecast to IC difference depends on soil moisture content:More sensitive in wet condition than in dry condition (WRF_ARW)



T2m is similar maybe slightly more sensitive to IC in “dry soil” than in “wet soil”

(WRF_ARW model)

Response of 3h-apcp forecast to model difference depends on soil moisture content:More sensitive in wet condition than in dry condition



Similar sensitivity of T2m to model difference is observed under wet vs. dry tests

Sensitivity of T2m to model diff depends on which soil moisture initial states to use

With NAM soil moisture (wetter) With GFS soil moisture (dryer)

Cold season case

(Difference in 3h-apcp forecasts with WRF_NMM model)

Due to soil moisture difference Due to atmos IC difference (benchmark)

(Difference of 3h-apcp forecasts with WRF_ARW model)


Difference of T2m forecasts with WRF_NMM model


Difference of T2m forecasts with WRF_ARW model


Soil moisture perturbation design

Uniformly perturbed (0.05) Randomly perturbed (0.05)

Response of T2m sensitivity to soil moisture perturbation’s spatial structure (NMM)

Response of T2m sensitivity to soil moisture perturbation’s spatial structure (ARW)


Response of 3h-apcp sensitivity to soil moisture perturbation’s spatial structure (NMM)


Response of 3h-apcp sensitivity to soil moisture perturbation’s spatial structure (ARW)


Uniformly perturbed with 0.05 pert size Uniformly perturbed with 0.03 pert size

Response of T2m sensitivity to soil moisture perturbation size (NMM)

Response of T2m sensitivity to soil moisture perturbation size (ARW)

Uniformly perturbed with size of 0.05 Uniformly perturbed with size of 0.03

Response of 3h-apcp forecast to soil moisture perturbation size (NMM)

Uniformly perturbed with 0.05 pert size Uniformly perturbed with 0.03 pert size

Response of 3h-apcp sensitivity to soil moisture perturbation size (ARW)

Uniformly perturbed with size of 0.05 Uniformly perturbed with size of 0.03

f12h f24h

f36h f48h

Difference of T2m forecasts due to soil moisture difference with WRF_NMM

Difference of T2m forecasts due to atmos IC difference with WRF_NMM model

f12h f24h

f36h f48h

Difference of T2m forecasts due to soil moisture difference with WRF_ARW

f12h f24h

f36h f48h

Difference of T2m forecasts due to atmos IC difference with WRF_ARW model

f12h f24h

f36h f48h

Sensitivity of 3h-apcp to soil moisture with NMM model

f48 f60

f72 f84

Sensitivity of 3h-apcp to atmos IC with NMM model

f48 f60

f72

f48 f60

f72 f84

Sensitivity of 3h-apcp to soil moisture with ARW model

Sensitivity of 3h-apcp to atmos IC with ARW model

f48 f60

f72 f84

Next Step: to test a Breeding-like cycled approach to have land

surface initial states perturbation be consistent with atmospheric

variable’s perturbation.

Hopefully an Improved ensemble system after adding soil moisture

perturbations

Summary

• Impact on precipitation and T2m forecast caused by soil moisture uncertainty cannot be neglected. It could be comparable to that caused by atmospheric IC uncertainty. Therefore, soil moisture perturbation needs to be considered in mesoscale ensembling. The degree of such sensitivity varies with model used. Precipitation is less sensitive to soil moisture in cold season than that in warm season while T2m remains highly sensitive to soil moisture in both warm and cold seasons.

• In general, wet soil moisture produces more rainfall than dry soil moisture especially in high/mid-latitudes. [Others also showed that dry soil leads early afternoon thunderstorms while wet soil late night thunderstorms.] Precipitation becomes more sensitive to IC and model physics when soil moisture is wet than dry. (more evapotranspiration more moist air?)

Summary (con’t)

• Soil moisture directly impacts T2m by changing surface thermal energy balance. Perturbing soil moisture has larger impact on T2m than on precip. Sensitivity of T2m to soil moisture seems to favor certain geographical locations in a particular case. It’s also noticed that T2m is more sensitive to IC and model physics in “dry soil” than in “wet soil”. (more sensible heat?)

• Sensitivity of T2m and precipitation depends on soil moisture perturbation’s spatial structure and magnitude. It is not an easy task to design a realistic, simple and effective soil moisture perturbation scheme which also needs to be consistent with atmospheric model’s perturbation. A simple scheme is planned to be implemented in the NCEP regional ensemble system (SREF) in 2007.

SPC’s historical, first-ever Day-2 “High Risk” outlook for April 7, 2006’s “over 60 tornadoes” event (SREF played a

key role)

SPC’s Significant Tornado Probability forecast Derived from SREF (David Bright)

Subject: SREF and the sig tornado event last FridayFrom: David Bright [email protected]

Date: Mon, 10 Apr 2006 09:44:12 -0500To: Jun Du [email protected]

Hi Jun,I wanted to show you the image SREF attached. This is an experimental parameter one

of the forecasters is testing and it's definitely not ready for prime time (i.e., I'm not convinced its formulation is entirely defensible at this point, and its false alarm ratio has yet to be determined!). But, this F039 hour SREF forecast from last Thursday (09 UTC SREF 6 April 2006) shows the primary significant tornado threat centered over nrn AL,

nrn MS, and parts of TN (with SREF mean 850 mb height overlaid).The SREF played a large part in the first ever Day 2 "HIGH RISK" outlook ever issued by the SPC

(http://www.spc.noaa.gov/products/outlook/archive/2006/day2otlk_20060406_1730.html). Of course, other deterministic models, climatology, and forecaster experience were

involved in the decision process, but the SREF played a key role. Again, this product only in the evaluation stage, but I thought you'd be interested nonetheless.

David

Louis Uccellini wrote:Joe/Russ: Between this SREF result, the first time Day 2 High Risk and the 1.0 POD for over 60 tornadoes, I think it is time to celebrate in a big way. I recommend that you

guys need to put together a one pager and work with Dennis and Carmeyia to highlight this historic accomplishment(s).

Louis

mailto:[email protected]

mailto:[email protected]

Sensitivity Study of Precipitation and T2m to Soil Moisture Using NCEP WRF Ensemble Jun Du and...

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