P2.15 INVESTIGATION INTO ENVIRONMENTAL CONDITIONS FOR STORM INITIATION OVER THE OCEAN USING SATELLITE DATA Huaqing Cai*, Cathy Kessinger, Nancy Rehak and Daniel Megenhardt Natinal Center fr Atmspheric Research, P.O. Bx 3, Bulder, CO 1. INTRODUCTION The imprtance f shrt term strm initiatin frecasts has been recgnized by the aviatin cmmunity fr a lng time; hwever, the skill t crrectly frecast strm initiatin remains pr, even ver land where dense, surface-based bservatinal netwrks are available. Over the cean, strm initiatin frecasts becme even mre challenging, wing t the lack f surface-based bservatinal netwrks such as surface mesnets r the WSR-88D radar netwrk. Recgnizing the difficulty that the lack f surfacebased bservatins causes, this study strives t utilize satellite-derived envirnmental parameters t identify favrable cnditins fr ceanic strm initiatin. The envirnmental fields being evaluated include: 1) Advanced Micrwave Scanning Radimeter (AMSR-E) sea surface temperature (SST), 2) cnvergence/divergence derived frm QuikSCAT nearsurface winds, 3) Cnvective Available Ptential Energy (CAPE), Cnvectin Inhibitin (CIN) and the atmspheric relative humidity as derived frm ceanic sundings determined frm vertical prfiles taken by the Atmspheric Infrared Sunder (AIRS) in cmbinatin with the Advanced Micrwave Sunding Unit (AMSU) as well as frm the Natinal Center fr Envirnmental Predictin (NCEP) Glbal Frecasting System (GFS) numerical mdel analysis. Creating ceanic cnvectin initiatin nwcasts in cnjunctin with extraplatin f existing strms gives the ceanic aviatin cmmunity, dispatchers and frecasters valued infrmatin fr enrute planning and strategic avidance f ptentially hazardus cnvectin. * Crrespnding authr address: Huaqing Cai, Natinal Center fr Atmspheric Research, Bulder, CO 837; e-mail: caihq@ucar.edu A simple scatter plt apprach is emplyed in this preliminary study t investigate the envirnmental cnditins favrable fr cnvectin initiatin (CI) ver the cean. A brief descriptin f varius datasets and the methdlgy fr data analysis are given in sectin 2. Sectin 3 discusses the implicatins f varius scatter plt results. A summary and future wrk utline is given in sectin 4. 2. DATASETS AND METHODOLOGY The dmain fr this study is the Gulf f Mexic (see Fig.1 fr dmain size). The time perid spans Aug 12 23, 27. During this time perid, cnvective activity was abundant thrugh bth initiatin f new strms and thrugh the advectin f existing strms. A brief descriptin f each dataset used in this study is as fllws. (a) Cnvective Diagnsis Oceanic and Cnvective Nwcasting Oceanic The Cnvective Diagnsis Oceanic () prduct is derived frm a fuzzy lgic, data fusin technique and is used t detect the presence f mature cnvectin in cean/remte regins using satellite imagery (Kessinger et al. 26). T accmplish this, utputs frm three independent, satellite-based cnvectin detectin algrithms are cmbined using a fuzzy lgic algrithm t create the utput field. The interest values range frm zer (n cnvectin) t fur (cnvectin) with a typical threshld f abut 2. used t define cnvective activity. Next, the Cnvective Nwcasting Oceanic (CNO) system extraplates the field using an bject-tracking methdlgy (Dixn and Wiener, 1993) t prduce 1-hr and 2-hr nwcasts f cnvectin lcatin. Fr details f and the CNO system, the reader is referred t Kessinger et al. (28). An example f cmpared with the clud tp height prduct is shwn in Fig. 1, where Hurricane Dean was at the middle f ur analysis dmain; the hurricane was well-captured by the field. (b) AMSR-E Sea Surface Temperature (SST) The AMSR-E sea surface temperature (SST) cvering the Gulf f Mexic is prvided by Naval Research Labratry (NRL) and has been qualitycntrlled by remving precipitatin and land mass cntaminatin. This dataset culd be used t verify
(a) Clud Tp Height (b) Hurricane Dean Hurricane Dean Fig. 1. An example f a) culd tp height, and b) at 215 UTC n 18 August 27 shwing the Gulf f Mexic dmain used in this study. Hurricane Dean is right at the middle f the dmain. a well-knwn fact that trpical deep cnvectin tends t frm ver warmer water wing t the abundance f misture in that regin. (c) QuikSCAT Near-surface Winds The QuikSCAT near-surface winds, as prvided by NRL, cntain invaluable infrmatin abut the nature f the near-surface wind field ver the cean. N ther instruments can prvide this infrmatin at such a high spatial reslutin. The QuikSCAT winds have been quality-cntrlled by utilizing the rain flag fr remval f precipitatin cntaminated winds. Derived fields such as divergence and vertical vrticity are calculated and smthed fr the purpse f this study. (d) Temperature and Misture Sundings frm AIRS/ AMSU Atmspheric Infrared Sunder (AIRS) and Advanced Micrwave Sunding Unit (AMSU) can prvide temperature/misture vertical prfiles when the sunder is nt blcked by deep cluds. Varius cnvective parameters such as Cnvective Available Ptential Energy (CAPE) and Cnvective Inhibitin (CIN) are derived frm these data fr varius sunding levels. The CAPE/CIN frm 925 mb is used in this study. (e) Glbal Frecasting System (GFS) Mdel Analysis In additin t varius satellite-based bservatinal datasets described abve, the GFS mdel analysis is als used t identify favrable envirnmental cnditins fr CI ver the cean. Since mdel analysis data prvides a self-cnsistent frame wrk fr varius cnvective indicatrs, it will be interesting t cmpare the same parameters derived frm GFS versus that frm satellite-based bservatinal data. Cnsidering GFS already assimilates many f the satellite datasets, cnsistency between the tw shuld be expected. An interest field derived frm GFS data which will be used in this study is the frntal likelihd field. The frntal likelihd field is utilized as a tl t indicate where frnts are lcated. Details f hw the frntal likelihd field is derived can be fund in Megenhardt et al. (24) and in Kessinger et al. (28). (f) Methdlgy The purpse f this study is t identify the favrable envirnmental cnditins fr cnvectin initiatin (CI) ver the cean. T achieve this gal, a simple scatter plt apprach is emplyed, t determine if the cnvective parameters under investigatin serve as a gd precursr f CI. Namely, we are pltting new cnvective strms, which are represented by their values ver 2., against varius cnvective parameters such as the AIRS/AMSU CAPE field. The cnvective parameters are straight-frward t cmpute, as described in the earlier part f this sectin; defining when new strms have frmed is the mre tricky part. Frtunately, within the Cnvective Nwcasting Oceanic (CNO; Kessinger et al. 28) system, the Thunderstrm Identificatin, Tracking and Nwcasting (TITAN; Dixn and Wiener 1993) algrithm is used t extraplate/frecast the strm plygns. During the prcess f tracking the strm plygns, TITAN can identify new strms by
SST ( C) 4 38 36 34 32 3 28 26 24 22 SST versus mean = 29.5 std= 1.7 2 Fig. 2. Scatter plt f AMSR-E SST versus assciated with new strms fr the Gulf f Mexic dmain frm Aug 12-23, 27. Ave RH (%) 1 9 8 7 6 5 4 3 versus Averaged Relative Humidity mean = 83. std= 1.1 Fig. 4. Scatter plt f averaged relative humidity versus assciated with new strms fr the Gulf f Mexic dmain frm Aug 12-23, 27. DIV ( x 1 s ) -5-1 1 8 6 4 2-2 -4-6 -8-1 DIV versus mean = -.6 std= 4.3 Fig. 3. Scatter plt f QuikSCAT near-surface divergence versus assciated with new strms fr the Gulf f Mexic dmain frm Aug 12-23, 27. their first ccurrence. Using these TITAN-identified new strm plygns, the field can be threshlded t remve all strms except fr the new nes. Then, scatter plts f new strm versus varius envirnmental cnvective parameters can be easily created, as shwn in the next sectin. 3. Analyses f Varius Scatter Plts (a) AMSR-E SST Althugh it is a well-knw fact that new strms tend t frm ver warm water in the cean, it wuld be interesting t verify it and knw the distributin f SST fr newly initiated strms in the Gulf f Mexic. Figure 2 shws a scatter plt f SST versus assciated with new strms fr the Gulf f Mexic dmain during August 12-23, 27. Ntice that mst new strms frmed where SST is greater than 26. C. The apprximate nrmal distributin f SST has a mean f 29.5 C and a standard deviatin f 1.7 C. Since summer and warm SST cnditins are prevalent during the perid f interest, the high SST average values assciated with new strms is an expected result. (b) QuikSCAT Near-surface Divergence Surface cnvergence assciated with surface bundaries has lng been recgnized as a precursr f CI ver the land. Over the cean, surface-based CI studies have been lagging due t lack f bservatinal data. Thanks t QuikSCAT near surface wind measurements, the relatin between surface cnvergence and CI ver the cean can be studied. A scatter plt f QuikSCAT-derived near-surface divergence versus f newly initiated strms is shwn in Fig. 3. It was fund that new strms were assciated with bth near-surface cnvergence and divergence, with a slight bias tward cnvergence, as indicated by the mean divergence assciated with all the new strms being -.6 x 1-5 s -1. (c) Averaged Relative Humidity Misture cntent in the atmsphere is ne f the mst crucial ingredients fr CI, as demnstrated by numerus bservatinal and numerical mdeling studies. Figure 4 shws a scatter plt f averaged
CAPE (J/kg) (a) AIRS CAPE versus 2 18 16 14 12 1 8 6 4 2 mean = 773.2 std= 736.1 (b) GFS Surface CAPE versus 2 18 16 14 12 1 8 6 4 2 mean = 99.7 std= 627.2 Fig. 5. Scatter plt f a) AIRS/AMSU CAPE fr 925 mb, and b) GFS surface CAPE versus assciated with new strms fr the Gulf f Mexic dmain frm Aug 12-23, 27. CAPE (J/kg) CIN (J/kg) (a) AIRS CIN versus 1 9 8 7 6 5 4 3 2 1 mean = 52.2 std= 75.1 CIN (J/kg) (b) GFS Surface CIN versus 1 9 8 7 6 5 4 3 2 1 mean = 9.1 std= 28.2 Fig. 6. Scatter plt f a) AIRS/AMSU CIN fr 925 mb, and b) GFS surface CIN versus assciated with new strms fr the Gulf f Mexic dmain frm Aug 12-23, 27. relative humidity abve the tp f bundary layer frm GFS analysis versus s f new strms. Clearly Fig. 4 illustrated that new strms tends t frm in an envirnment rich in misture; and rarely new strms can frm when averaged relative humidity was less than 5%. The mean f all averaged relative humidity assciated with CI is ~83%, with a standard deviatin f ~1%. (d) AIRS/AMSU and GFS CAPE/CIN AIRS/AMSU prvides vertical prfile f atmspheric temperature and humidity, that can be used t calculate standard cnvective parameters such as CAPE/CIN. Fr cmparisn, GFS surfaced-based CAPE and CIN fields are als btained. The CAPE/ CIN versus scatter plts frm bth AIRS/AMSU and GFS are shwn in Figs. 5 and 6, respectively. It is nt surprising that bth CAPE fields frm AIRS/ AMSU and GFS demnstrate n clustering in their distributins, which is reinfrced by the large standard deviatin in Fig. 5 a and b. This results suggests that new strm frmatin can ccur ver a wide range f psitive CAPE values. Cnsidering the AIRS/ AMSU CAPE is fr air parcels at 925 mb while the GFS CAPE is surface-based, the mean value f CAPE frm AIRS/AMSU and GFS are fairly similar. CIN fields frm bth AIRS/AMSU and GFS shw clear trends that new strms tend t frm in lw/zer CIN regins, althugh high CIN values d nt exclude CI. Cnvectin initiatin is the tug f war be-
Frntal Likelihd 1.9.8.7.6.5.4.3.2.1 Fig. 7. Scatter plt GFS-derived frntal likelihd interest field versus assciated with new strms fr the Gulf f Mexic dmain frm Aug 12-23, 27. tween tw ppsite frces, ne is the upward frcing, and the ther is the cap which needs t be penetrated befre new strms can frm. When frcing is strng, large CIN can still be destryed. (e) Frntal Likelihd Field Frntal Likelihd versus One methd t find ut if frntal frcing plays an imprtant rle in strm initiatin is t lk at the scatter plt f frntal likelihd field versus f new strms. Frntal likelihd field is an interest field derived frm GFS mdel data and is designed t indicate the psitin f frnts. High frntal likelihd interest values crrespnd t frnt lcatins (Megenhardt et al. 24). A scatter plt f frntal likelihd interests versus f new strms is shwn in Fig. 7. It was fund that there was n clear trend f frntal likelihd versus. This result suggests that frntal frcing might nt be the sle imprtant frcing mechanism in new strm frmatin ver the Gulf f Mexic in August 27. 4. Summary and Future wrk mean =.2 std=.1 In this preliminary study, a simple scatter plt apprach is emplyed t study the relatin between varius envirnmental cnditins and new strm frmatin ver the Gulf f Mexic dmain fr a relatively shrt perid in August 27. Varius satellitebased cnvective parameters were derived, which include 1) AMSR-E SST, 2) QuikSCAT divergence, 3) AIRS/AMSU CAPE/CIN, 4) GFS surface CAPE/ CIN, and 5) GFS-derived averaged relative humidity and frntal likelihd field. It was fund that CIN and averaged relative humidity were ptentially gd discriminatrs f atmspheric cnditins needed fr cnvectin initiatin t ccur, while CAPE and frntal likelihd field might nt be gd discrminatrs. Future wrk will expand this wrk t ther envirnmental parameters and ther dmains and ver lnger time perids, and hpefully, cnsistent results with this paper will be btained. REFERENCES Dixn, M., and G. Wiener, 1993: TITAN: Thunderstrm Identificatin, tracking, Analysis and Nwcasting - A radar-based methdlgy. J. Atms. Oceanic Technl., 1, 785-797. Kessinger, C., C. Mueller, H. Cai, G. Blackburn, N. Rehak, K. Levesque, b. Hendricksn, S. Carsn and D. Megenhardt, 26: Oceanic Cnvectin Diagnsis and Nwcasting. 5th Internatinal Cnference n Messcale Meterlgy and Typhn, East Asia Weather Research Assciatin, Bulder, CO, 31 Oct- 3 Nv 26. http://www.el.ucar.edu/icmcs/ prgram.html (Tuesday sessin) Kessinger, C. K., H. Cai, N. Rehak, D. Megenhardt, J. Hawkins, R. Bankert and E. Williams: Oceanic Cnvectin Diagnsis and Nwcasting. 13th cnference n Aviatin, Range and Aerspace Meterlgy, American Meterlgical Sciety, New Orleans, LA, 21-24 January 28. Megenhardt, D., C. Mueller, S. Trier, D. Ahijevych, and N. Rehak, 24:NCWF-2 Prbabilistic Nwcasts. Preprints, 11th Aviatin, Range and Aerspace Meterlgy Cnference, American Meterlgical Sciety, Hyannis, MA, 4-8 Octber 24. ACKNOWLEDGMENTS The authrs wuld like t thank Jeff Hawkins and Rich Bankert at NRL fr prviding all the satellite datasets and many insightful discussins related t the prper usage f the data. This wrk is supprted by NASA grants NASA CAN-NNH4ZYO1C and NASA ROSES 25-NNH5ZDA1N-DECISION.