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NASATechnical Memorandum 80591

A Comparison of GLAS SAT and NMCHigh Resolution NOSAT ForecastsFrom 19 and 11 February 1976

Robert Atlas

(NASA-TM-80591) A COMPARISON OF GL AS SATAND NHC HIGH RESOLUTION NOSAT PORECASTS PROM19 IWD 11 PEBRUART 1976 (NASA) 19 PHC A02/H! A01 CSCL 04B

1180-16678

UnclasG3/47 11668

I

NOVEMBER 1979

National Aeronautics andSpace Administration

Oaddwd Speoe F1Wd CenterGreenbelt, Maryland 20771

A Cogmrison of GLAS SAT and NKC High ResolutionNOSAT Forecasts Fran 19 and 11 February 1976

by

Robert Atlas

Laboratory for Atmospheric SciencesGoddard Space Flight Center

Greenbelt, MD 20771

A .

November 1979

CONTENTS

Lim-

11. Introduction r:

2. Forecasts from 0000 GIST February 19, 1976

3. Forecasts from 0000 GMT February 11, 1976

2

4

4. Summary & Acknowledgement

5

5. References

6

I v

1. Introduction

The evaluations of the impact of satellite sounding data on weather for caning,

for the Data Systems Tests (D6T), have led to substantially different eonclusiona

regarding the utility of satellite data. On the basis of the DS4-5 experiment,

Tracton and McPherson (1977) found the impact an the National Meteorological

•

Center's (NMC) analysis and forecast system to be slight, and speculated that

satellite sounding data would actually degrade higher resolution foarecasts. Ghil

et al. ( 1979a) found a modest but statistically significant beneficial impact of

DST-6 sounding data on coarse mesh ( 400 km resolution) GLAS model forecasts.

Desmaris et al. ( 1978), using the NMC 6-level model with a horizontal resolution

of 381 km, obtained a smaller beneficial influence of satellite sounding data with

the DST-6 sounding data. In their report, they argued that the difference between

the GLAS and NMC results might be due to the poorer forecast skill of the GLAS

model and analysis system, thereby allowing more room for the satellite data to

prWuoe a larger beneficial impact.

A repetition of the DST-6 forecast experiments with a higher ( 280 km) resolution

version of the GLAS model, has shown that the influence of satellite data on

numerical forecasts was actually enhanced by the increased resolution (Atlas et al.

1979, Ghil et al. 1979b). A subjective evaluation of the impact of satellite

data for eleven forecast cases (Atlas 1979), revealed no examples of significant

negative impact. Two cases of significant forecast improvements compared to either

A the GLAS high resolution NOSAT or the NMC 6-level model NOSAT were found: the 72

j hour forecasts from 0000 GMT 19 and 11 February 1976.1

k

^ J jt

i.

lAdditional experiments (not reported here) with the new fourth order coarse meshR GLAS model (Kalnay-Rivas 1979) agree well with the results obtained with the high

resolution, second order GLAS model.

1

ovrr the coarser mesh. -level model# and has been adopted by MIC-as theiV

apsntional forecasting mx*L Comparison VE -the OW BAT ftk*amb--V1 1the

NMC high resolution N0SAT forecasts should provide additional evidence concerning

the meteorological significance of the GIAS samding data impact results.

2. Forecasts fmm 0000 an, February 19, 1979

7hi initial analysis fc r this case showed a moderately intense low presst t

system, associated with an Q__ 11evkr short wave tragh, located off the nort1w st

coast of the U.S. As this system mated inland, a new low developed along an already

existing stationary front and became the dominant feature by 1200 GMT on 19 February.

During the next 24 hours, the cyclone moved southeastward and intensified, after which

time it recurved and then accelerated toward the northeast. 7he storm produced

heavy snow, blizzard, or near-blizzard conditions in Oolorado, Kansas, Nebraska,

Iowa, Michigan, and Wisconsin. Tornadoes or severe thunderstorms were reported in

Kansas, Oklahoma, Texas, Arkansas, Missouri, Illinois, Louisiana, and Mi"ippi.

The majority of the severe weather occurred toward the end of the forecast period !

after recurvature of the cyclone to the northeast. 3

Figures 1-6 depict the NMC 7-level NO6AT and GIAS SAT 72-hour sea level pressure

(solid lines) and 1000-500 mb thickness (dashed lines) forecasts and corresponding

verification at twelve tour intervals. Oonparison of the two forecasts reveals that

the GEM SAT prediction of the cyclone's 72-hair evolution is significantly better

than the NMC NOSAT prediction.

^ Ecy

3

At tPKV* ham Afti - , tie mac of thw CYCIOWG position it ry_.-

- ..'*gThz .' -.i#°4s .a 1&^:: s. ',' '';k "^ '*.+^, Rff^rlit _

sit and tl ^*i et'! U to by -*C ._.

1101R"s_ (!'ig. 2) t no i& evtw AA the WC

(frig. 3) 0 the differences between the two so level WSMUMfor t*: ^

However a mare intense cyclonic.. alacoulati.on la swedicto to t to GL W-i '

greater aaplitauds of the associated thidmess pattern in the SAT famoast Si VW

in better agreement with the analysis. At forty-eight hours (Fig. 41, just

prior to the out of severe 110 Mrstonar and -toam does, ala jor doss

between the GLAS SAT and NBlC NMT proghosis are evident. The structure,

intensity, and position of the SAT cyclone is substantially better than in the WE

NOSAT. The position error has been reduced by 841 the reduction of ventral

pressure error is 451. This trend continues to sixty hours (Fig. 5), where the

position error is reduced by 881 and the ventral pressure error by 461. At

72 hours (Fig. Or there is a 341 reduction in position error and a 751 reduction

in central pressure error.

To investigate the effect of these differences further, the Cm puterixed Severe

Storm Model (CSSM) developed by Atlas (1978) has been applied to both the GLAS

SAT and AMC NOSAT predictions. The CSSM consists of an objective procedure for

computing and combining specific measures of instability and destabilization to

yield a prediction of high, moderate, low, or neglible potential for severe local

stolen develoLa wt. The SAT prediction of high potential accounted for 701 of the

severe thunderstorm and tornado occurrences while the NMC NOSAT CSSM did not

predict any areas of high potential. The differences between the two CSE14

forecasts were due primarily to a substantially immproved prediction of differential

equivalent potential temperature advection and convective instability in the SAT

L4ystem.

4

3. Forecasts fran 0000 QIT, Februsty 11, 1976

In this case, a weak cyclone formed along a stationary front in southwest Canada # .

moved southeastward while intensifying during the first 40 h of the period, and

then recurved to the east-northeast.

Figures 7-9 depict the WC 7-level NOBAT and GLAS SAT 72-hour wa level pressure

(solid lines) and 1000-500 nb thickness (dashed lines) forecasts and corresponding

verification at twenty-four hour intervals. Oagarison of these charts reveals

the significant forecast inptvvements that have occurred in the GLAS SAT system

At bwenty-four hours (Fig. 7), there has been a 668 reduction of position error

and an 878 reduction of ventral pressure error of the cyclone located in southwest

Canada. Similarly at fc -ty-eight hours (Fig. 8), there has been a 768 reduction

of position error and a 258 reduction of ventral pressure error of this cyclone,now

cemered near the Great Lakes. The position and orientation of the pressure

trough extending southwestward from this cyclone, and the position of the anticyclone

located off the east coast of the U.S. are better forecast by the GLAS SAT. In

addition, a spurious cyclone, forecast by the NNC NOSAT to be over southwest Canada

and the northwestern U.S., does not appear in the GLAS We At 72 hours (Fig. 9),

the GLAS SAT is significantly better than the WC NOMT in its prediction of the

cyclonic circulation over southeastern Canada and the northeastern U.S., the anti-

cyclone over the midwest, the pressure trough extending southeastward fran south-

west Canada, and the shallow pressure troughing off the west coast of the U.S. The

MC NOSAT is slightly better in its prediction of the cyclone located off the northwest

coast of the U.S. and also has a 268 smaller position error of the cyclone now located

in eastern Canada. However the central pressure error of this cyclone has been

reduced by 53% in the GLAS SAT.

57777

TWOMM Where MC's oPereddhil model in had suriax xietgrfagWOUng for the United 4-ftifte-bow bon exminaL

forty obts in diiie cum nwlted from the use of the higher resolution VC-7-1ml

• mDftL Hmavers, the GLAS model, Mm utilLsint , initial candtiono which-16161id4Satellite sounding data, was still. Able IWPW" Wan the

operational modalS pied' two-, "do -WiggIM that

soundings have the potential to correct gross analysis errors, which infrequently

occur in the operational AMC system in Beta spwo vegiom

AcItnowledgment,

The author wishes to acknowledge Drs. J. Brown and J. Stackpole of the NNC

Development Division for providing copies of their 7-level model fixecut

for these can studies.

6

References

Atlas, R., 1978: Development of a computerized proosdure for the prediction of

severe local storm potential. Atmospheric and Oosanographic Research Review,

NASA Tich. Mem., 80253, 7-13.

1979: Cass studies of major DST-6 sounding impacts with the GUS model.

Proomlinas of the Fourth NASA Weather and Climate Program Scienoe Review, CP-2076,

147-151.

M. Hslem, and M. Ghil, 1979: Subjective evaluation of the combined

influence of satellite temperature sounding data and increased model resolution on

numerical weather forecasting. ProoeedinH of the Fourth Conferenoe an Numerical

Weather Prediction, 319-328.

Uesmaris, A. S. Tracton, R. McPherson, and R. Van Hum, 1978: 7he N C report on

the Data Systems Zest. NQAA ST 78-216, National Meteorological Center, NCAA,/National

Weather Servioe, 331 pp.

; Ghil, M., M. Halem, and R. Atlas, 1979x: Time-continuous assimilation of remote-

sounding data and its effect on w,'tather forecasting. Mon. Wea. Rev., 107, 140-171.

1979b: Effects of sounding temperature assimilation on weather fore-

casting: model dependence studies. Remote Sounding of the Atmosphere from Space,

H. J. Bolle, ed., Pentagon Press, Oxford and New York, 21-25.

Kalnay-Rivas, 1979: Personal communication.

Tracton, M. S. and R. D. McPherson, 1977: On the impact of radiometric sounding

data upon operational numerical weather prediction at NMC. Bull. Am. Meteorol.

Soc. , 58, 1201-1209.

a) 12 Ale. NC XNOW Pbrecast

C) Analysis

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b) 12 hr. CHAS

Sm Forecast

A,

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Fiq. 1. Sea level Mwaire/1000-S00 mb tie W.for 1200 cW 19 Feb. 1976.

- M•w •.M ,M •M •M

Fig. 2. Sea local pressure/1000-5W mb thickr e" mapsfor 0000 GM 20 Feb. 1976.

M

w•w

Y

w•w

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a) 24 hr. IvC 7L

pOBin' Forecast

b) 24 hr. QAS

W& Forsoaft

c) 1lnalytie

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Fig. 3. sea level promure/1000-500 rfi thickness ms sfor 1200 GMT 20 M. 1976.

b) 36 hr. GIMSin' Fbrecast

a

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c) Analysis

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a) 36 hr. IIC 7L

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c) Armaysis

A) 40 hr. NMC 7L

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F4. 4. Sss 16VOI vc+SPXO/1000-SW sb thickn s urpstar 0000 OC 21 lob. 1976.

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a) 60 hr. NW 7L

NOW Forecast

b) 60 hr. GAS

SAT Forecast

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701.0 -170 -100 -80 -60 {

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Fig. 5. Sea level pressure/1000-500 mb thickness mapsfor 1200 CM 21 Feb. 1976.

c) Analysis

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Fig. 6. Sea level pressare/1000-500 mb thickness napefor 0000 GC 22 Feb. 1976.

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c) Analysis

b) 72 hr. QLi.SSAL Forecast

a) 72 hr. WC 7L

NOSAT Fbreaest

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a) 24 hr. NC 7L

NOSAT Forecast

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c) Analysis

b) 24 hr. QASSAT Forecast

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Fig. 7. Sea level pressure/1for 0000 GV 12 Feb.

M

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a) 48 hr. NW 7L

NCCM Forecast

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SAT Forecast

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Fig. 8. Sea level pressure/1000-500 mb thickness mapsfor 0000 (M 13 Feb. 1976.

Ica'-°w -1}0

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M b) 72 hr. (V.S

SAT Forecast

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c) Analysis

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Fig. 9. Sea level pressure/1000-500 mb thickness mapsfor 0000 GMr 14 Feb. 1976.

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