Kinetic Energ...ammasun(2014)_Xin QUAN.pdf

Kinetic Energy Budgets during the Rapid Intensification ofTyphoon Rammasun(2014)Xin QUAN and Xiaofan LI*Key Laboratory of Geoscience Big Data and Deep Resource of Zhejiang Province,School of Earth Sciences,Zhejiang University,Hangzhou,Zhejiang 310027,China(Received 8 March 2022;revised 23 May 2022;accepted 30 May 2022)ABSTRACTIn this study,Typhoon Rammasun (2014)was simulated using the Weather Research and Forecasting model toexamine the kinetic energy during rapid intensification(RI).Budget analyses revealed that in the inner area of the typhoon,the conversion from symmetric divergent kinetic energy associated with the collocation of strong cyclonic circulation andinward flow led to an increase in the symmetric rotational kinetic energy in the lower troposphere.The increase in thesymmetric rotational kinetic energy in the mid and upper troposphere resulted from the upward transport of symmetricrotational kinetic energy from the lower troposphere.In the outer area,both typhoon and Earths rotation played equallyimportant roles in the conversion from symmetric divergent kinetic energy to symmetric rotational kinetic energy in thelower troposphere.The decrease in the symmetric rotational kinetic energy in the upper troposphere was caused by theconversion to asymmetric rotational kinetic energy through the collocation of symmetric tangential rotational winds and theradial advection of asymmetric tangential rotational winds by radial environmental winds.Key words:Typhoon Rammasun(2014),rapid intensification,kinetic energy budget,symmetric and asymmetric winds,divergent and rotational circulations,environmental flowsCitation:Quan,X.,and X.F.Li,2023:Kinetic energy budgets during the rapid intensification of Typhoon Rammasun(2014).Adv.Atmos.Sci.,40(1),7894,https:/doi.org/10.1007/s00376-022-2060-z.Article Highlights:The symmetric rotational kinetic energy in the troposphere increases during the rapid intensification of TyphoonRammasun.The increase in the lower troposphere results from the conversion of symmetric divergent kinetic energy via therotational-and divergent-flow interaction.The increase in the upper troposphere is due to transport of symmetric rotational kinetic energy from the lowertroposphere by strong upward motions.1.IntroductionTyphoons may experience a rapid intensification(RI)period before landfall,which often leads to large economiclosses and deaths in the coastal areas.For example,the maxi-mum wind speed in the super Typhoon Rammasun(2014),which is analyzed in this study,increased from 40 m s1 to60 m s1 within 24 h before landfall at Hainan,China on 18July2014,causing a huge economic loss of over 26 billionChinese Yuan and approximately 30 deaths.To effectivelyreduce the damage caused by typhoons,accurate typhoonforecasting is required to facilitate informed governmentaldecisions before landfall.When compared to the significantimprovement in the track forecasts of tropical cyclones(TC)in recent decades,improvement in TC intensity forecastshave shown relatively slower progress (Elsberry et al.,2007;Rappaport et al.,2009;DeMaria et al.,2014).The inten-sity forecasts mainly rely on numerical model guidance;how-ever,improvement of numerical predictions requires an in-depth understanding of the physical processes associatedwith the intensity change.Primary physical processes and fac-tors associated with TC intensity change include environmen-tal effects(DeMaria et al.,1993;Zeng et al.,2010;Feng etal.,2014),inner core dynamics(Montgomery and Kallen-bach,1997;Wang,2002;Miyamoto and Takemi,2015;Chen,2016;Chen et al.,2019),underlying surface forcing(Yang et al.,2008;Cheng et al.,2012;Cheng and Wu,*Corresponding author:Xiaofan LIEmail:xiaofanlizju.eduADVANCES IN ATMOSPHERIC SCIENCES,VOL.40,JANUARY 2023,7894 Original Paper Institute of Atmospheric Physics/Chinese Academy of Sciences,and Science Press and Springer-Verlag GmbH Germany,part of Springer Nature 20232020),and convection and latent heat release(Kanada andWada,2015;Li et al.,2016).Many studies have contributed to enhancing the under-standing of dynamic processes associated with the RI ofTCs.The RI of Hurricane Opal(1995)was caused by themean vertical advection and mean vorticity flux terms(Pers-ing et al.,2002).The RI of TC Dora(2007)was related tothe superposition of potential vorticity structure of thetrough with strong deformation(Leroux et al.,2013).TheRI of Typhoon Man-yi (2013)was associated with theenhanced mesovortex under the condition of reduced staticstability (Wada,2015).The RI of Typhoon Megi (2010)resulted from strengthened rotational circulations in the midand upper troposphere through the transport of vorticity(Chang and Wu,2017).The RI of Typhoon Vicente(2012)was largely affected by an upper-tropospheric “inverted”trough(Shieh et al.,2013).The analysis of the asymmetricimpacts at multiple scales during RI found that the changesin asymmetric circulations were associated with the baroclinicconversion from available potential to kinetic energies,andthe conversion between asymmetric kinetic energies(Pras-anth et al.,2020).Budgets of tangential wind,vorticity,and kineticenergy have been analyzed to examine dynamic processesassociated with the RI in previous studies.The RI ofVicente was related to mean radial flux of absolute mean verti-cal vorticity and vertical advection of the azimuthal mean tan-gential wind by the azimuthal mean vertical motion in theazimuthal mean tangential wind budget(Chen et al.,2017),and to tilting of the horizontal vorticity and upward vorticityadvection in the mean vorticity budget of circular area(Chen et al.,2018).The positive tendency of the TC kineticenergy associated with the RI of Typhoon Hato (2017)resulted mainly from the conversion of kinetic energy oflarge-scale circulations in the barotropic eddy kineticenergy equation(Zhang et al.,2019).Previous studies have focused on the analyses of RImechanisms using analyses that have been carried out in theinner core of the tropical cyclone where maximum windsare located.In the current case study of Typhoon Rammasun(2014),kinetic energy budgets in outer area during RI arealso examined in addition to the analyses in the inner region.The questions that are discussed in this study are:How dokinetic energies during RI change vertically and horizon-tally?What dynamic processes control the kinetic energychanges in inner and outer areas and in the lower,middle,and upper troposphere during RI?The paper is organized as follows.An overview ofsuper Typhoon Rammasun(2014)is presented,the modelsimulation design is introduced,and a comparison betweenobservations and simulations is presented in section 2.Thevertical structures of kinetic energy budgets are analyzed insection 3,and the dominant dynamic terms in kinetic energybudgets are discussed in-depth through partitioned analysisin section 4.Lastly,a summary is given in section 5.2.Overview of Typhoon Rammasun (2014),model design,and kinetic energy budgetsTyphoon Rammasun(2014)originated in the northwestPacific Ocean at 1400 Local Standard Time(LST;LST=UTC+8)on 12 July 2014 and moved westward,developinginto a severe typhoon.The first landfall was made on thesouthern Luzon Island of the Philippines at 1700 LST on 15July.Rammasun(2014)weakened to a typhoon followinglanding,continued to move northwestward after 1400 LSTon 17 July,and subsequently began to strengthen rapidly.Itdeveloped into a super typhoon at 1000 LST on 18 July andlanded at Wenchang,Hainan,China at 1400 LST.Duringlanding,the central pressure dropped to 918 hPa and the maxi-mum wind speed increased to 72 m s1,making it thestrongest typhoon among those that made landfall in Chinasince 1973.Kaplan and Demaria(2003)defined RI when change inthe maximum wind speed of the typhoon in 24 h is morethan 15 m s1.This definition has been adopted by previousstudies(Yamada et al.,2010;Leroux et al.,2016).Based onthis definition of RI,the 13-h period from 0200 LST to1400 LST on 18 July was considered as the RI of Rammasun(2014)in this study.Version 4 of the Weather Research and Forecasting(WRF)Model was used to simulate Typhoon Rammasun(2014),and Global Forecast System analysis data (GFS;0.5 0.5)were used to construct the initial and lateralboundary conditions.The model used two-way nesting andthree nested domains(Fig.1)with horizontal grid spacingsof 18,6,and 2 km and domain sizes of 299(lon.)235(lat.),634(lon.)538(lat.),and 1015(lon.)904(lat.)grid points,respectively.The model had 50 vertical layers,with the top at 10 hPa.The model physics packagesincluded the WRF single-moment 6-class cloud microphysicsscheme(WSM6;Hong and Lim,2006),BouLac planetaryboundary layer (Bougeault and Lacarrere,1989),KainFritsch cumulus parameterization scheme (Kain,2004),which was only used in the outermost domain,longwave radi-ation parameterization scheme(Mlawer et al.,1997),short-wave radiation parameterization scheme (Dudhia,1989),Monin-Obukhov surface layer model(Moon et al.,2007),and Noah Land surface model(Ek et al.,2003).The modelwas integrated from 1400 LST on 16 July to 1400 LST on19 July,which covered the 13-h RI period of Rammasun(2014)in the South China Sea.An average of the 13-h simula-tion data was used to conduct the following analysis of thekinetic energy budget.Comparing the simulation of Rammasun(2014)withthe Joint Typhoon Warning Center best track data(Fig.2),it can be seen that the simulated maximum wind speed ofRammasun(2014)is consistent with the observation,andthe difference in peak intensity between the simulation andobservation only was 0.74 m s1 at 1400 LST on 18 July.The simulated minimum sea-level pressure generally fol-lowed observations and the simulated typhoon track wasJANUARY 2023QUAN AND LI79slightly north of the observed track.The largest differencebetween the simulated and observed centers was less than90 km at 1400 LST on 17 July.Thus,the simulation reason-ably reproduced the intensity and track of Rammasun(2014).The change in TC intensity is accompanied by complexenergy conversion processes,including the conversionbetween the kinetic energies of the TC and the energy conver-sion between the large-scale environmental and TC compo-nents,as well as the conversion between the potential andkinetic energies.When a cylindrical coordinate system isestablished at the center of the typhoon and moves with thetyphoon,the kinetic energy associated with typhoon circula-tion can be decomposed into four components:symmetricrotational,symmetric divergent,asymmetric rotational,andasymmetric divergent components.The associated fourkinetic energy budgets can then be derived accordingly(Li,1993;Wang et al.,2016).The derivation of the four kineticenergy equations is provided in the appendix.Note that thetendencies of kinetic energy at a given time were calculatedtaking the differences in kinetic energy between the simula-tion data a time step ahead and a time step behind to guaranteethe accuracy of kinetic energy budgets.The conversion between the environmental kineticenergy and TC kinetic energy in Eq.(A3)can be used tostudy the impacts of environmental wind,particularly environ-mental wind shear,on the change in typhoon intensity.Weseparated environmental and typhoon circulations using Kuri-haras filtering method(Kurihara et al.,1993,1995),multi-scale window transform(Liang and Anderson,2007),and aFig.1.Map of the three nested model domains.The color bar indicates the height(m)of thetopography.80706050403020Vmax(m s-1)MSLP(hPa)14/16 02/17 14/17 02/18 14/18 02/19 14/191000980960940920900880(a)(b)Fig.2.(a)Maximum wind speed(solid,m s1)and minimumsea level pressure (dashed,hPa)and (b)track of TyphoonRammasun (2014)from simulation (blue)and observation(orange).Time is in LST.80KINETIC ENERGY BUDGETS OF TYPHOON RAMMASUN(2014)VOLUME 40combination of these two methods,respectively.We foundthat the combination of these two methods resulted in the bet-ter separation than the individual methods as shown in astudy by Zhao et al.(2015).Therefore,a combination ofthese two methods was used in this study.3.Analysis of area-averaged kinetic energybudgetsSince winds in the inner area of the typhoon are consider-ably larger than those in the outer area,the kinetic energy bud-gets in the inner area may be different from those in theouter area during RI.Thus,kinetic energy budgets were calcu-lated in a circular area with a radius of 200 km(inner area)and annular areas with radii of 200400 km and 400600 km(outer area),respectively.Because the maximumwind of a typhoon is mainly tangential rotational wind,wefirst analyzed the symmetric rotational kinetic energy budget(Fig.3).Analysis of symmetric rotational kinetic energy bud-(Ks,Ks)0(FKs 0)(Ka,Ks)0(FKs 0)get averaged over a circular area with a radius of 200 kmshowed that the symmetric rotational kinetic energyincreased in the troposphere;however,the physical processesthat were responsible for the increase varied with increasingheight(Fig.3a).Below 800 hPa,the increase in the symmetricrotational kinetic energy resulted from the conversion fromsymmetric divergent kinetic energy to symmetric rotationalkinetic energy.From 800 hPa to 600 hPa,the increase in symmetric rotational kinetic energy wasequally contributed from the convergence of the flux of thesymmetric rotational kinetic energy and geopotential and the conversion from asymmetric rotationalkinetic energy to symmetric rotational kinetic energy.Above 600 hPa,the increase in symmetricrotational kinetic energy originated from the convergence ofthe flux of the symmetric rotational kinetic energy and geopo-tential.Near 300 hPa,the conversion from environ-mental kinetic energy to symmetric kinetic energyFig.3.Vertical profiles of symmetric rotational kinetic energy budgets(m2 s3)averaged in(a)the circular area with a radius of 200 km and the annular area with radii of(b)200400 km and(c)400600 km,respectively.JANUARY 2023QUAN AND LI81(Ke,Ks)0FKs and contributed equally to the increasein the symmetric rotational kinetic energy.Similarly,the analysis of symmetric rotational kineticenergy budget averaged over the annular area with a radiusof 200400 km revealed an increase in the symmetric rota-tional kinetic energy in the troposphere(Fig.3b).However,the increase only appeared below 350 hPa in the calculationof the symmetric rotational kinetic energy budget averagedin the annular area with a radius of 400600 km(Fig.3c).The magnitude of the increase in symmetric rotationalkinetic energy and the associated conversion from symmetricdivergent kinetic energy to symmetric rotational kineticenergy significantly decreased as the radius increased(Fig.3).The conversion from symmetric divergent kineticenergy to symmetric rotational kinetic energy made a domi-nant contribution to the increase in the symmetric rotationalkinetic energy below 800 hPa within a radius of less than200 km(Fig.3a)and below 550 hPa within a radius of 200-(Ke,Ks)FKs(Ka,Ks)0600 km(Figs.3b and 3c).Unlike the analysis of the 200 kmcircular area a