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12-1-2017

Climatology of an Explosive Cyclone: Revival of aMid-Latitude Explosive CycloneCalvin A. ChaffinIowa State University

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Recommended CitationChaffin, Calvin A., "Climatology of an Explosive Cyclone: Revival of a Mid-Latitude Explosive Cyclone" (2017). Meteorology SeniorTheses. 22.https://lib.dr.iastate.edu/mteor_stheses/22

Climatology of an Explosive Cyclone: Revival of a Mid-Latitude ExplosiveCyclone

Calvin A. Chaffin

Department of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa

Dr. Mike Chen – Mentor

Professor of Geological and Atmospheric Sciences, Dynamic Meteorology

Amanda Black – Co-mentor

Department of Geological and Atmospheric Sciences, Iowa State University, Ames, Iowa

Abstract

In 1980, Frederick Sanders and John Gyakum classified the maritime cold season rapidly deepening low pressure system as an explosive cyclone due in part to its intense “bombing” nature. Ever since this phenomenon has been discovered, there have been many, papers, books, and lectures covering the mysterious anomaly. Many scientists attribute the behavior of this weather anomaly to baroclinicity. Baroclinicity is most often conjuncted with vertical shear caused by horizontal temperature gradient leading to the thermal wind in the mean flow. Baroclinicity, coupled with the upper level trough will leadto cyclonic circulation, leading to further amplification of the aloft disturbance, which leads to further intensification. However, not all researchers agree with this theory and suggest that other mechanisms arethe cause of this phenomenon. By manually tracking explosively developing low pressure systems through means of NCEP surface analysis charts and OPC products, we are able to determine the forcings behind the low. A key identifier in determining these forcings is whether or not they re-intensify after the initial cyclone decays, leaving behind a residual low that continues to propagate until it redevelops or dissipates entirely. This tells us that baroclinic instability is not involved here and that other forcings are the cause of this intensification. In this study 33 cases of explosive cyclogenesis were collected and analyzed, coming up with 2 cases of reintensification. A revival case and a dissipation case were compared in order to determine what exactly caused on case to dissipate and another to reintensify so long into its life.

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1. Introduction & Background

In 1980, two researchers, FrederickSanders and John R. Gyakum, defined arapidly deepening cyclone that dropped 24mb over 24 hours (or an average rate of 1Bergeron) as an explosive cyclone. The rateat which this explosive deepening is defined

varies at latitudes between 12 mb/day at thelowest, towards the equator, and up to 28mb/day at the highest around the North Pole(Sanders and Gyakum 1980). Due to thebehavior of this rapidly deepening lowpressure system, the phenomenon wasproperly named the meteorological “bomb”due to its sudden, explosive nature.

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Seasonally, explosive cyclones are aprimarily winter occurrence, however, thereare other cases of explosive cyclogenesisoccurring during other periods.Additionally, this phenomena is an almostexclusively maritime event, being found inmany places around the globe at mid-latitudes including the Northern PacificOcean (NPO), Northern Atlantic Ocean(NAO), and the Norwegian Sea, just toname a few. Many researchers havecontributed this to baroclinicity, otherwiseknown as baroclinic instability(Wang andRogers 2000). Baroclinic waves are causedby a balance of static stability and tropicaleffect stability along with vertical windshear. Regions of baroclinicity are definedby polar jets, frontal boundaries indicatingtemperature advections, and densitygradients increasing with height(Pierrehumbert 1984). In order to look atthis we must first track an explosivelyconvective cyclone as it propagates off ofthe Northern Pacific Ocean and reaches itsdissipation stage defined by Cyclolysis.Cyclolysis is a process of decay that occurswhen the cold air coming from behind acyclone has overtaken the inflow of warm,moist air, leading it to deteriorate. Theprocess of cyclolysis is most often ignoredin most research regarding explosivecyclones, however it has become an area ofinterest to some researchers (Grauman et al.2001).

Formation

If we take a look over the Atlantic,we see that the likelihood of an explosivelydeepening event increases with the presenceof pre-storm destabilization. Pre-stormdestabilization is when low level

baroclinicty near the coast of the Atlantic isnear the Gulf Stream. Sea leveltemperatures were observed, measured, andcompared to the colder air temperaturescoming off the coast. These measurementswere taken between 15 and 38 degreeslatitude, which is around the Eastern UnitedStates coast (Broccoli and Manabe 1992).The results of this study revealed to us thatthe pre-storm baroclinic disturbance waslinked to the formation of cyclones just offthe coast of North Carolina and Virginia.This relationship doesnt mean that anycyclones formed will be stronger (Cione etal. 1998).

Baroclinicity does not just here areother factors that lead to explosivecyclonegenesis. Fu et al. (2014) suggeststhat Latent Heat Release (LHR) played animportant role in a case involving two stageexplosive cyclonegenesis development.During the first stage LHR acted against theintensification of the low pressure system,along with the characteristics ofprecipitation such as the intensity, precipcenter, etc. During the second stagedevelopment, upper level potential vorticityforcings were found to play an importantrole in the development of the explosivecyclone. Similarly, in a separate studyconducted by Kuwano-Yushida and Asuma(2008), found that latent heat release playedan important role in the formation ofcyclones as they affect upper level jets. Thiswas done by studying a control case thenremoving any latent heat release in theatmosphere via a “dry run”, results showeda significant decrease in the disturbance ofupper level jets which led to a decrease inthe likelihood of formation. A study

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conducted by Riviere and Joly (2005) setout to explore the effect Low FrequencyDeformation field has on explosivecyclones. Their study concluded that underspecific spatial restraints, convergence canbe effected by deformation when upper leveljets exist over baroclinic regions. When thisoccurs the surface cyclone can intenselyinteract with the upper level disturbancesleading to an explosive growth in thecyclone.

Hypothesis and Research Question

Despite the abundance of cases overthe many years of research, the mechanismsthat contributed to explosive deepening ofmid-latitude cyclones are still very muchdisputed today. Many researchers believethat regions of baroclinicity wereresponsible for the rapid deepening,however, not all cases could be explained bythis. Other explanations for this rapiddeepening have been proposed, includingthe location of upper and lower level jetscoordinating with one another to createcyclonic circulation. (Fu et al. (2014),Kuwano and Yashida (2008)). Then, ifbaroclinic environments only account for aminority of the explosive cyclonesdeveloped, then there must be other forcingsresponsible for this. In this research paperwe will be looking to see if baroclinicinstability is the primary mechanism behindthe genesis of explosive cyclones. To lookinto this we will be tracking, observing, andinterpreting different cases that exhibit allthe characteristics of an explosive mid-latitude cyclone. We will then look beyondthe decayed cyclone and track the residuallow in order to observe its behavior. For thehypothesis of this research thesis, we will be

attempting to track the residual low of analready explosively deepened mid-latitudecyclone to see if it re-intensifies after it hasdecayed. If it does re-develop then we willanalyze it to determine whether or notbaroclinic instability is the primarymechanism.

2.Data

Region

For the focus of this research thesis,the regions that will be focused on will bethe North Pacific Ocean (NPO), theContiguous United States (CONUS), and theNorth Atlantic Ocean (NAO). These regionshave been chosen for the frequent amount ofcyclones and explosive cyclones theyproduce. The NPO was selected for themain region of focus due to its frequentoutput of explosive cyclones, therefore, weused it as the origin for our cases we found.This is because the Taiwanese lowspropagating out of the South China sea areable to create these explosive lows that formover the NPO. Additionally, the interannualvariability of El Nino events, warm wateranomalies propogated up into the NPOwhere the colder Sea Surface Temperatures(SST) resided and led to explosive cyclonegenesis during the cold season. The naturaloscillation of El Nino events over this regionhas led to the increased frequency of theseevents (Chen et al. 1991). Some importantregions where cyclone genesis occurs arefrom the east side of Japan, to just south ofAlaska, however, explosive cyclone genesisoccurs primarily south of 50 degrees Northover the NPO (Gyakum et al. 1988).

Selection Criteria

In this study, the criteria we used fordefining explosive cyclones at mid-latitudeswas finding a drop of 24 millibars (orhectapascals) over the duration of 24 hours.Since the purpose of this study was to

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observe and track the revival of a mid-latitude explosive cyclone, all cases musthave originated in the NPO between thelatitudes of 25 degrees North and 50 degreesNorth to classify as mid-latitude. The timeperiod this data was taken from fell between2010-2013. Additionally, the temporaldistribution covered the “cold Season”,which for our purposes were between themonths of November through Februarysince the explosive cyclogenesis is mostfrequent during this season (Gulev et al.2001).

Data & Method Analysis

A total of 33 cases were collected foranalysis in this thesis. For the methodology of this study, manual tracking via the National Weather Services (NWS) Weather Prediction Center (WPC) surface analysis map archive were utilized to observe the CONUS/North American regions. The WPC surface analysis maps have a temporalresolution of 3 hour intervals from 00Z to 24Z. The WPC doesnt cover the NPO and NAO entirely so in order to manually track and observe data over maritime regions, the NWS’s Ocean Prediction Center’s (OPC) archived surface maps were utilized for this purpose. The OPC’s surface products temporal resolution has a 6 hour interval for both the NPO and NAO regions, however, for the analysis of upper air data at 500mb height/vorticity, temperature, etc. charts NOAA’s archived analysis charts had a temporal resolution of 12hrs. For consistency in the data time intervals of 6 hours were used for data gathering.

This is how data was collected. Anycases that fit the criteria were flagged andadded to a list of cases to track its life cyclelater. To achieve this we utilized mid-upperlevel 500mb height charts to find anytroughs or perturbations aloft. This is

because the cyclones will form on the leeside or east side of the trough since PositiveVorticity Advections exist ahead of thetrough. After we noticed any perturbationsaloftwe used the OPC surface analysis chartsin order to find a closed pressure low. If alow was found, it was tracked in order toobserve whether or not it explosivelydeveloped. After all cases were gathered,they were tracked throughout their life cycleto determine if they decayed or re-intensified. Each case was tracked as thecyclone propagated across the CONUS untilthe decay stage. After the decay stage hasoccurred, the low pressure that remains mustbe tracked to observe the lows revival ordissipation. After determining if the low hasdissipated or re-intensified (revived), it iscontinually tracked until it has dissipatedcompletely or until it moved out of ourregions of interest. After the data has beencollected, the cases that exhibited explosivecyclogenesis were compared with the mid-upper 500mb heights/vorticity, temperature,etc. plots in order to determine if baroclinicinstability is responsible for the formation.After having reviewed all the cases, they arethen determined to be revivals or dissipated.Then a case comparison was used todemonstrate the behavioral differences in acyclone that re-intensified and another casethat decayed.

3. Results and Conclusions

Results

This study examined the surfaceanalysis data during 3 winter seasonsbetween 2010 and 2013 looking forexplosive cyclogenesis caused by baroclinicwaves over the NPO. Later in the cycloneslife cycle a revival was sought out in orderto answer our hypothesis question. As aresult of the data, methods and selectioncriteria, we found a total of 33 explosivecyclone cases, and of those 33 cases 2 werefound to show re-intensification (revival)

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later in its life cycle. Of the 33 cases alldisplayed that baroclinicity was themechanism behind the initial explosivedeepening of each case. A table compilingall the cases dates and dissipation/revivalwas inserted in the appendix of thispaper(see Table 1). For our examples andconclusions we chose one of the two casesthat re-intensified and compared its behaviorwith a case that dissipated withoutreintensifying.

Case Comparison

For this case comparison wecompared both cases as through the genesisand decay stages of their duration todetermine what set them apart from eachother. Determining what made these casesso different helped us in our conclusion anddiscussion for this research. The case weused for our dissipation example occurredDecember 30th, 2012, at 00 UTC, thebeginning of the explosive development.This cyclone case started its explosivedevelopment at its physical location of172W Longitude and 38N Latitude. We havecalled this cyclone “Case A”. The case wehave used for our revival case occurredNovember 17th, 2010 at 00 UTC, also thebeginning of the explosive development.The cyclone for this case started itsdevelopment at 139W Longitude and 49NLatitude. We have called this cyclone “CaseB”. We have compared both cases to eachother and broken them down through eachstage of the typical Norwegian cyclonemodel.

Fig. 1 (Top Right) Surface analysis chart forCase B at the beginning of its explosivedevelopment 00 UTC 17 November, 2010. Thecentral pressure low starts at 1005mb at 138W

Longitude and 38N Latitude. (Source: NCEPOPC Surface analysis chart archive)Fig. 2 (bottom) Surface analysis chart for CaseB 12 hours into its explosive deepening at 12UTC 17 November, 2010. The central pressurelow tracked N. Eastward at 132W longitude and52N latitude.

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Looking at the initiation phase of each case,we found that both cases are caused due tobaroclinic instability. Since baroclinicitymost often depends on temperature gradientscaused by vertical shear and stability factorsfrom both the static short wave stability andtropical effect we looked at NH verticalwind shear charts to determine areas of windshear were in fact baroclinic. Initially, welooked for perturbations at 500mb heightsover the NPO in order to find potentialcases. We were able to look for that bylooking at the surface height analysis andthe 500mb height/vorticity charts. What wefound was a westward tilt in the troughsbetween the surface and 500mb, somethingmost often found in mid-latitudedisturbances caused by baroclinic instability.

Fig. 3 Map outlining vertical wind shear againstsurface pressure low. Blue lines indicatepressure contours while dotted lines indicatevertical wind shear contours with yellow colorsindicating westward shear and purple colorsindicating eastward shear. (Source: NCEPNorthern Hemisphere Pressure/Vertical Windshear chart)

Looking at the development stage, thecyclones we observed displayed differentpressure value drops during their deepening.Over the course of 24 hours each caseexhibited a different drop in pressure. CaseA dropped a total of 24mb from 994mb to968mb. Case B dropped a total of 27mbfrom 1005mb to 978mb at its deepest centralpressure low. Unlike Case A, Case Bdeveloped the most in the first 12 hours ofits central pressure deepening. If a cyclonedevelops more than 16 mb in the first 12hours of its development, it is classified as astrong cyclone. Therefore, Case B was astrong cyclone, having dropped a total of27mb in the first 12 hours, while Case A wasnot with a total of . The mature phase ofeach cyclone was fairly similar, the lows atsurface and upper 500mb levels havebecome overlapped with one another atsimilar positions as the warm air that has fedinto the system has been cut off from thelow, so it is no longer intensifying. It was atthis time the central pressure low for eachrespective case was at its deepest, for CaseB in particular this was at 12 UTC on the 17November, 2010. Each cyclone soon begandissipating not long after Moving onto thedissipation stage, each case starts todissipate and rise in pressure as the heightsaloft start to fall. At its highest, Case Abecomes 979mb before it is absorbed intoanother developing system off the southwestcoast of Alaska. Case B shows behavior ofthe decay stage, however, it doesn’t dissipateright away. Instead, the low propagatesalong the west coast until it travels inland ofthe CONUS and re-intensifies, unlike CaseA. A cyclones reintensification isnt anofficial stage in a cyclones lifecycle,however, we have treated it like such. Post

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decay stage, Case B has left behind aresidual low. After propagating Inland ofthe CONUS, the residual low re-intensifiedinto another system. However, theredevelopment doesnt share the samecharacteristics for baroclinic instability.While the low had frontal boundariesformed around it, this doesnt mean that theinstability present is baroclinic, instead itappears to have been frontal disturbance.

Fig. 4 The residual low was over E Iowa at 18Z22 November, 2010 1003 on this surface analysischart as it began to re-intensify. (Source: NWSSurface Analysis Archive)

The main difference between these two isthat baroclinic instability is geostrophic,meaning the coriolis and pressure gradientforces are in balance of one another leadingto the geostrophic wind component to beincredibly similar with the real wind.However, disturbances amplified by frontalinstability is very ageostrophic, which worksagainst the geostrophic component. This isdue to forces such as friction and the coriolisforce working against the balance of the

pressure gradient force causing thegeostrophic winds to intersect with theheight and pressure contours.

Fig. 5 Northern Hemisphere verticalshear/pressure chart outlining the vertical shearover CONUS. This was taken at 12 UTC 22November, 2012. The purple represents windshear towards the east and areas of yellowindicate westward vertical shear with the bluelines indicating pressure contours and thedotted lines indicating the vertical wind shearcontours.

Further analysis shows that there is verylittle wind shear associated with the verticalpressure heights during this development,concluding that baroclinic instability is notthe cause for re-intensification. Anotherkey difference in the analysis of these twocases were the tracks that each explosivecyclone followed along the duration of theirlife cycles. Both cases underwent explosivedeepening in the East NPO, however, thesimilarities end here. After Case A hadintensified, the explosive cyclone trackedeast towards the west coast of the CONUS,then started heading north steered by thewinds at 500mb height. The explosivecyclone tracks just south of Alaska until it

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slowly propagates back west, decaying to apressure low of 979mb before beingabsorbed by deeper developing low system.Case B on the other hand explosivelydeepened closer to CONUS than Case A, asit moved NW just off the coast of Canada.After the cyclone matured, it started todecay leaving a residual low that propagatedsouthward along the coast moving intowarmer waters keeping the low alive duringits travel. The residual low steered inlandtowards the Rockies Region as it trackedacross California and into NE Utah. Thelow then moves over the Rocky Mountainregion and into SE Colorado where the lowis 996mb, indicating down slope pressurefall. The residual low tracks East over East-central Kansas where a warm front boundaryalong the low has formed. At 18 UTCNovember 22, 2010 the low re-develops as itpropagates NE over the great lakes wherewarm water allows for the re-developing

Fig 5. (Top) Track taken by Case A outlines theposition the central pressure low is every 6hours. The red X marks the beginning of theexplosive development and the red circle marksthe dissipation of the central pressure low. Thepurple lines indicate latitude and longitudegiven that they are horizontal and verticalrespectively. Fig 6. (Bottom) is a figure of the track taken byCase B. Each dot is the position of the explosivecyclone taken every 6 hours. The red X marksthe start of the explosive low pressure systemand the circle marks the dissipation of the lowsystem.

low to intensify once again. The newlyrevived low then propagates North intoCanada, reaching a central pressure low of989mb SW of Hudson. The low persistsuntil it rapidly decays and completelydissipates North of the Hudson Bay at 12UTC November 24, 2010.

Conclusion & Discussion

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According to the results, the revivalof an explosive low is possible under thecorrect circumstances. What stood out mostwas the track that Case B took after itdecayed, crossing over the Rocky MountainRange and into the lee side trough caused bydown slope motion as it follows a path thatmost storms that cross the midwest wouldhave followed. Although the low didn’t re-develop into an explosive cyclone, under theright circumstances a new explosivelydeepening redevelopment could occur. Forthis to occur the proper baroclinic conditionsmust be met, however, that may not be thecase for all occurrences. It seems thatwhether or not baroclinicity was theprimary, the key point to the lows revivalwas the path that it took. If any otherrevival cases were to occur, the most logicalway that would happen is if any future casesfollowed the same tracking behaviordisplayed in Case B.

In the event of future work done overthe topic, here are some key points forfurther discussion. Although the revivalcases displayed mechanisms other thanbaroclinicity, this only occurred within 2 ofthe 33 cases found during this researchpaper. While this does suggest that cyclonicforcings other than baroclinicity are thecause for reintensification, the fact remainsthat it did not explosively develop. Thismay be the fact that although the residuallow did not reach high enough latitudes inorder to rapidly reintensify since the primaryarea for explosive cyclones at mid-latitudesover the NAO originate around Nova Scotia.In the future perhaps finding explosivecyclones that originate over the NAO then

manually tracking backwards in time couldresult in proving this theory.

References

Wang, C. and J.C. Rogers, 2001: A Composite Study of Explosive Cyclogenesis in Different Sectors of the North Atlantic. Part

I: Cyclone Structure and Evolution. Mon.

Wea. Rev., 129, 1481–1499,

Rivière, G. and A. Joly,2006:Role of the Low-Frequency Deformation Field on the Explosive Growth of Extratropical Cyclones at the Jet Exit. Part II: Baroclinic Critical Region.J. Atmos. Sci.,63,1982–1995,

Pierrehumbert, R.T.,1984:Local and Global Baroclinic Instability of Zonally Varying Flow.J. Atmos. Sci.,41,2141–2162,

Broccoli, A.J. and S. Manabe, 1992: The Effects of Orography on Midlatitude NorthernHemisphere Dry Climates. J. Climate, 5 , 1181–1201

Cione, J.J., S. Raman, and L.J. Pietrafesa, 1993: The Effect of Gulf Stream-induced Baroclinicity on U.S. East Coast Winter Cyclones. Mon. Wea. Rev., 121 , 421–430,

Kuwano-Yoshida, A. and Y. Asuma, 2008: Numerical Study of Explosively Developing Extratropical Cyclones in the Northwestern Pacific Region. Mon. Wea. Rev., 136 ,712–740

Fu, S. F., Sun, J., & Sun, J. (2014). Accelerating two-stage explosive development of an extratropical cyclone over the northwestern Pacific Ocean: a piecewise potential vorticity

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diagnosis. Tellus A: Dynamic Meteorology and Oceanography , 66 (1).

Sanders, F. and J.R. Gyakum, 1980: Synoptic-Dynamic Climatology of the “Bomb”. Mon. Wea. Rev., 108 , 1589–1606

Martin, J.E., R.D. Grauman, and N. Marsili, 2001: Surface Cyclolysis in the NorthPacific Ocean. Part I: A Synoptic Climatology. Mon. Wea. Rev., 129, 748–765

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Gyakum, J.R., J.R. Anderson, R.H. Grumm,and E.L. Gruner, 1989: North Pacific Cold-Season Surface Cyclone Activity: 1975–

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Appendix

Fig. 7

Surface analysis chart taken at 12UTCDecember 30, 2012, the beginning of theexplosive cyclonegenesis for Case A.

(Source: NCEP OPC Surface AnalysisChart)

Fig. 8

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Surface analysis chart taken at 12 UTCDecember 31, 2012 for Case A.

(Source: NCEP OPC Surface AnalysisChart Archive)

Fig. 9

(Source: NCEP Northern Hemisphere500mb Height/Vorticity chart)

Table 1

Date Revival/Dissipation

11/07/2010 12 UTC Dissipation

11/17/2010 00 UTC Revival

11/02/2010 06 UTC Dissipation

11/09/2010 18 UTC Revival

12/05/2010 00 UTC Dissipation

01/05/2011 12 UTC Dissipation

01/15/2011 12 UTC Dissipation

01/26/2011 00 UTC Dissipation

02/18/2012 00 UTC Dissipation

11/01/2012 00 UTC Dissipation

11/17/2012 12 UTC Dissipation

11/21/2012 12 UTC Dissipation

12/01/2012 00 UTC Dissipation

12/07/2012 12 UTC Dissipation

12/22/2012 12 UTC Dissipation

12/30/2012 12 UTC Dissipation

12/29/2012 00 UTC Dissipation

11/01/2011 00 UTC Dissipation

11/07/2011 12 UTC Dissipation

11/11/2011 00 UTC Dissipation

11/28/2011 00 UTC Dissipation

12/02/2011 12 UTC Dissipation

12/08/2011 00 UTC Dissipation

12/10/2011 12 UTC Dissipation

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12/13/2011 00 UTC Dissipation

12/21/2011 00 UTC Dissipation

12/25/2011 00 UTC Dissipation

01/14/2013 00 UTC Dissipation

01/20/2013 00 UTC Dissipation

02/04/2013 12 UTC Dissipation

02/07/2013 12 UTC Dissipation

02/11/2013 12 UTC Dissipation

02/12/2013 18 UTC Dissipation

Table 1 table outlining each cases date in the left column listing date and time the explosive deepening started. The right hand column indicates whether or not the case dissipated completely or had a revival during its duration.

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