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by: Demarcus Schaden V
Demarcus Schaden V
Texas A&M
GPA 3.65

Craig Epifanio

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About this Document

Craig Epifanio
Class Notes
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This 16 page Class Notes was uploaded by Demarcus Schaden V on Wednesday October 21, 2015. The Class Notes belongs to ATMO 435 at Texas A&M University taught by Craig Epifanio in Fall. Since its upload, it has received 20 views. For similar materials see /class/225942/atmo-435-texas-a-m-university in Atmospheric Sciences (ATM S) at Texas A&M University.

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Popular in Atmospheric Sciences (ATM S)


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Date Created: 10/21/15
PRESSURE mb ICC 200 A O O 600 800 K l000 20 0 TEMPERATURE C 9e 4209 4076 3947 3322 370 I 3584 347 l 34 I l 3382 3353 3326 330 I 3278 3253 3242 323 l 3225 3227 3236 3256 3288 3335 3382 3358 Physical Processes Controlling Storm Structure Thermodynamic processes Lowlevel moisture content and moisture pro le Available potential energy LNB CAPE 9 dz LFC Physical Processes Controlling Storm Structure Gust front processes Strength and depth of cold pool Balance between vorticity generated at front and lowlevel wind shear Physical Processes Controlling Storm Structure Dynamic processes Formation of rotational updraft Vortex stretching tilting and associated dynamic pressure gradient Interaction with midtoIower tropospheric shear uv STORM MOTION Types of Storm Structure Singlecell storms Shortlived storms life cycles of 3060 min Potentially several updraft cores but one rainshaft Propagate with mean wind HEIGHT HEM FEET a KlLOMETERs L 39 k armn 94 l IMu 311 TOWERlNG CUMULUS STAGE MATURE STAGE DISSIPATING STAGE Types of Storm Structure Multicell storms Collections of singlecell storms Individual cells move with mean wind Movement of group depends on new cell fomation Figure 86 THE HAVMER HAlLSTORM 9 JULY 1973 STORM 2 s A 6 A RCRAFTYRACK HElGHT Km MSL lOU 100 F50 quotmmquot m SURFACE RAINFALL RATE R mmmr so 415 4 6 4394 4392 40 re 76 ii 32 b 2 4 6 DlSTANCE AHEAD OF OUTFLOW BOUNDARY km l Figure 87 a 0 Wl d t V iowleveis D 2 Vs New mil New all quot4 Wlnd ai low eve s V gt gt V6 V P VS Types of Storm Structure Supercells Longlived life cycles often exceeding 2 hours Characterized by rotational updraft Continuous motion to the right occasionally left of mean wind Often associated with tornados and large hail Observed Structure of Supercells Radar echos seen at am various heights above ground Roughly NS crosssection from A to B HEIGHT krn Roughly EW crosssection from C to D HEIGHTikm BWER Bounded Weak Echo Region Region of weak radar retuns where updraft speeds are too fast to support precipitation growth squot MAXIMUM UPDRAFT m 00 IO I5 20 25 30 35 4O 45 u m squot 50 I I I I I I 40 l 30 film quot3935 I 39v s I I c 2 H quotvhl n n 39 l 39 I 25 20 l f 45 O I x 39 Io 395 A O I I I I I I 20 40 60 80 lOO I20 Time min Wind speed pro les corresponding to updraft strengths below Dependence of Storm Structure on Shear No shear singlecell storm that grows and dies over 40 min Weak shear multicell storm with repeated growth and decay of cells Strong shear longlived supercells with one continuous updraft Maximum updraft strength as a function of time for shear pro les given above Moisture CAPE Moisture CAPE Moisture CAPE a INITIAL STORM MAXIMUM w m squot I l l l l I l l i 4000 e 5049 4a 454237343333 47 464540302928 3000 4293 3 28 26 35 33 3 30 28 264204 Mo 23 22 2l 2l 0000 l N 2000 l 25 2L 8 O lOOO l I4 I l5 20 25 30 35 4045 U5msl o o o I I I O 5 IO b SECONDARY STORM MAXIMUM W m squot l l j l l l l I if r 4ooo 0l232728293017FOO iwAQ 3 o o 3000 2I 22 24 23 o o o 2ooo o o o o o 0 o o o o o o o o 0 IOOO I I I I I I I I I I O 5 IO l5 20 25 30 35 4O 45 Us m s39l c SPLIT STORM MAXIMUM w m squot I I f F I I I l I I 4000 o 0 I7 32 3I 3395 39 32 o o 21 253 353634 3000 l 00232832323025 o o W l 2000 o o o o o o 1000 o o o o o o o o I L I I I I I I I I O 5 IO 15 20 25 3O 35 4O 45 US m squot i l l 000 0002 0004 0006 0007 m 5quot Shear Strength magma 2 3 ewla Max strength of initial updraft all storm types Max strength of secondary updraft indicates multicell Max strength of split sustained updraft indicates supercell Dependence of Storm Structure on Shear In all cases updraft strength increases with CAPE Weak shears result in cyclic multicell structure Strong shears result in sustained supercell structure Question Why are supercells so dependent on shear Dynamic Characteristics of Supercells Decompose pressure into ordinary cell 39Supercell dynamic and buoyant parts ldefl2 lwl2 V213 D 2 2 8b V2P B 82 with Dw 8PD b 8P3 Dt 82 592 dynamic accleration net buoyant acceleration Results o In ordinary cell buoyant l w m S effects dominate B Contribution from net buoyancy term 39 In SUPerce dynamic term D Contribution from dynamic term dominates W Net updraft strength Weak shear multicell Strong shear supercell 535 515ms 1 31 535 u535m5 l X gt gt Time 8 h h h h h h F H a e k k V ar40min 39 251 r leap Hr i r vwki gh TIme 2 7 39 8 Cf kkeee 39 WAFW P 1 l6 7 y I39 h h 1 k F gg w 39 39 k F k 9 h v hquot A A2471 quot39II E E I Vkr k 39 y k e k F k k e 5 g k e k k g k F H k e k F F k 5 39 39 80 min A in 180 min a kkkkkkkkkkk 5 32 a a a c k k h a h a a Time3 Mecca s hacked a a a a a c Re 8 IG r a a r r if f f r K 24r r 32 y w zr lTk VHFquot Flanrp 317 Figure 818 Vectors lowlevel winds gust front Shaded lowtomid updraft strength Contours midlevel vorticity Note symmetric simulation with southern half shown only Mirror image occurs in northern half Dynamic Characteristics of Supercells Multicell o Gust front spreads ahead of updraft and cuts off supply of warm air 0 Old cells decay and new cells form at gust front edge Supercell 0 Updraft splits with half propagating southward and half northward 0 Vorticity maxima lead the updrafts on each side 0 Updraft stays phaselocked with gust front continuous supply of warm air Elk lt gt 396 Supercell Dynamics the Mid level Rotational Pump Background shear has inherent ycomponent vorticity 81L 8w 8U 77 82 81 82 Updraft tilts and extends vortex lines causing enhanced vorticity on both sides of storm Ly Enhanced vorticity implies reduced pressure at mid levels further implying upward dynamic PGF 2 v2PD N 2 Updraft follows the enhanced PGF north and south sustaining the updraft and causing it to split Typical Shear Pro les for Supercell Formation Vortexline tilting and stretching explains both the splitting and long time duration of supercell updrafts but one question remains Why do most supercells rotate cyclonically rather than anticyclonically Answer most supercells form in environments with curved shear pro les COMPOSITE HODOGRAPH 24 MAY I973 I400 CST I6 krn IO 4 30 40 OR 14 I 5 3 I0 12 Mean wmd sounding in m s for 62 tornado outbreak cases l0 FIG ll Proximity hodograph for the OKC 900314 00 UTC FORECAST Union City Oklahoma splitting storm STORMS OF 3 APRIL l964 139o J 1390 2390 3390 4390 5390 6390 7390 8390 939016011390 I I l I l I I 500 5 l0 I5 20 25 30 35ms Fig 2A Hodograph of Oklahoma City forecast wmds for Mar 14 1990 at 00 UT C As in Fig 1 except winds are in knots Examples showing environmental shear pro les for various supercell events Supercell Splitting in Straight vs Curved Shear Pro les Straight Hodograph Straightline shear no turning of wind with height Curved Hodograph V Curved shear wind rotates anti cyclonically with height x 40 min In typical environments where the wind turns anticyclonically with height the rightwardmoving cyclonic storm is favored The UpdraftShear Feedback Intuitive Version Suppose we start with a shear pro le gt gt gt shear vector 82 82 Pressure increased on upshear side of updraft def2 2 VQPD N and then superimpose a enhanced shear deformation ce i 82 830 i quot a4 t gt V Xl l V localized updraft gt i L enhanced vorticity i871 8w Ufa E Pressure decreased on downshear side of updraft 2 w The UpdraftShear Feedback and Cyclonic Enhancement straightline shear pro le Straightline shear pro le 0 Updraftshear feedback results in low pressure in front of storm and high pressure behind 0 Neither side cyclonic or anticyclonic of split storm favored Curved shear pro le 0 Updraftshear feedback at low levels results in high pressure on S side and low pressure on N side curved shear pro le 0 Shear in midlevels opposite that at m39d39leve39 low levels resulting in low pressure Shear VeCtor on S side and high on N 0 Dynamic PGF strengthens updraft on S side but not on N side updraft Result cyclonic side of storm dynamically lowlevel favored induced PGF shear vector


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