Barotropic energetics analysis of tropical cyclone Khai Muk

bl 'kks/k i= esa 11&14 uoEcj 2008 ds nkSjku caxky dh [kkM+h esa cuus vkSj mlds vkxs c<+us okys m".kdfVca/kh; pØokr dSeqd dh xfrdh; fLFkfr;ksa ds fo’kys"k.k ij fopkj&foe’kZ fd;k x;k tks fupys Lrj ij ifjofrZr ok;qnkc&m".kdfVca/k ¼csjksVªkfid½ mtkZ ij dsfUnzr FkkA bl nkSjku ;g ik;k x;k fd if’peh iz’kkar egklkxj ls miks".kh; iwohZ gok;sa e/; caxky dh [kkM+h ds mRrj rd c<+h vkSj Åij m)`r vof/k esa Hkwe/;js[kh; if’peh gok;sa ¼iNok¡½ vkbZ-Vh-lh-tsM+- ds nf{k.k rd c<+h ftlds dkj.k {kSfrt; vi:i.k izokg vR;kf/kd ek=k esa cukA blls pØokrh vi:i.k Hkzfeyrk mRiUu gqbZ vkSj fo{kksHk cuk] tks ckn esa m".kdfVca/kh; pØokr dSeqd esa fodflr gks x;kA fupys {kksHkeaM+y esa ewyHkwr {ks=h; izokg ok;qnkcm".kdfVca/k :i ls vfLFkj Fkk ftls fujis{k Hkzfeyrk ds ;kE;ksrjh forj.k ds y{k.k ds ifjorZu }kjk crk;k x;k gS ftlls coaMj ds cuus esa xfrdh; ÅtkZ feyhA bl nkSjku fujis{k Hkzfeyrk ds ek/; {ks=h; izokg vkSj ;kE;ksrjh izo.krk ds chp ldkjkRed lglaca/k Fkk ftlls ok;qnkcm".kdfVca/k }kjk coaMj ek/; izokg dh vUrjfØ;kvksa ds }kjk coaM+j dh xfrdh; ÅtkZ esa o`f) gqbZA ÅtZLoh fo’ys"k.k ls irk pyk gS fd coaM+j okyh xfrdh; ÅtkZ ds ldkjkRed ifjorZu ds mPp nj ds {ks= ifjorhZ ok;qnkc m".kdfVca/k ds ldkjkRed {ks=ksa ls esy [kkrs gSa vkSj ifjorhZ m".kdfVca/k ds ifjek.k Hkzfey mRifRr okys {ks= ds vkl&ikl coaM+j okyh xfrdh; ÅtkZ ds ifjorZu ds LFkkuh; le; ds lkFk esy [kkrs gaSA ewyHkwr {ks=h; izokg ds ;kE;ksrjh vi:i.k }kjk ifjofrZr ok;qnkc m".kdfVca/k ÅtkZ m".kdfVca/kh; pØokr dSeqd ds cuus vkSj mlds vkxs c<+us okys ,d egRoiw.kZ ÅtkZ L=ksr FkkA Analysis of dynamical conditions in respect of formation and growth of tropical cyclone Khai Muk over the Bay of Bengal during 11-14 November 2008 is discussed with focus on barotropic energy conversion at lower level. It is observed that the extension of subtropical easterlies from the Western Pacific in to central Bay of Bengal to the north and equatorial westerlies to the south of ITCZ during the above period constituted a large scale horizontal shear flow. This led to generation of cyclonic shear vorticity and initiation of disturbance which later developed in to tropical cyclone Khai Muk. The basic zonal flow in the lower troposphere was barotropically unstable as depicted by change of sign of meridional distribution of absolute vorticity which provided the kinetic energy for the growth of eddy. There existed positive correlation between mean zonal flow and the meridional gradient of absolute vorticity which favoured increase of eddy kinetic energy through barotropic eddy-mean flow interactions. Energetic analysis indicated that areas of high rate of positive change of eddy kinetic energy coincided with positive areas of barotropic conversion and the magnitude of barotropic conversion matched with local rate of change of eddy kinetic energy around the area of vortex generation. Barotropic energy conversion by meridional shear of basic zonal flow was an important energy source for the formation and initial growth of tropical cyclone Khai Muk.

A diagnostic study on the energetics aspects of hiatus in the advance of southwest monsoon

Advance of southwest monsoon, after its onset, often gets stalled for a week or more causing concern to the farmers and other community whose activities are weather dependent. The present study on the energetics aspect of hiatus in the advance of southwest monsoon over India aims at understanding the dynamical reasons for this. Nine cases of hiatus of duration more than 10 days during 1982-2006 have been selected. For each hiatus case, different energy terms, their generation and conversion among different terms have been computed during the hiatus period and also during the pre-hiatus pentad over a limited region between 65° E to 90° E, 5° N to 30° N. These computations are based on NCEP 2.5° × 2.5° re-analysed daily composite data during different hiatus period and during corresponding pre-hiatus pentad. From this study it is found that : (i) In most of the cases there is a reduction in the generation of zonal available potential energy [G(AZ)] during hiatus period compared to pre-hiatus pentad. (ii) Drop in the conversion from zonal available potential energy to zonal kinetic energy [C(AZ, KZ)] during hiatus period has been observed in most of the cases. (iii) In most of the cases there is a reduction in zonal kinetic energy (KZ) and in eddy kinetic energy (KE) during hiatus period compared to pre-hiatus pentad.

Transient eddy kinetic energetics on Mars in three reanalysis datasets

The ability of Martian reanalysis datasets to represent the growth and decay of short-period (1.5 < P < 8 sol) transient eddies is compared across the Mars Analysis Correction Data Assimilation (MACDA), Open access to Mars Assimilated Remote Soundings (OpenMARS), and Ensemble Mars Reanalysis System (EMARS). Short-period eddies are predominantly surface-based, have the largest amplitudes in the northern hemisphere, and are found, in order of decreasing eddy kinetic energy amplitude, in Utopia, Acidalia, and Arcadia Planitae in the northern hemisphere, and south of the Tharsis Plateau and between Argyre and Hellas Basins in the southern hemisphere. Short-period eddies grow on the upstream (western) sides of basins via baroclinic energy conversion and by extracting energy from the mean flow and long-period (P > 8 sol) eddies when interacting with high relief. Overall, the combined impact of barotropic energy conversion is a net loss of eddy kinetic energy, which rectifies previous conflicting results. When Thermal Emission Spectrometer observations are assimilated (Mars years 24–27), all three reanalyses agree on eddy amplitude and timing, but during the Mars Climate Sounder (MCS) observational era (Mars years 28–33), eddies are less constrained. The EMARS ensemble member has considerably higher eddy generation than the ensemble mean, and bulk eddy amplitudes in the deterministic OpenMARS reanalysis agree with the EMARS ensemble rather than the EMARS member. Thus, analysis of individual eddies during the MCS era should only be performed when eddy amplitudes are large and when there is agreement across reanalyses.

A Contrast of Recent Changing Tendencies in Genesis Productivity of Tropical Cloud Clusters over the Western North Pacific in May and October

Tropical cloud clusters (TCCs) are embryos of tropical cyclones (TCs) and may have the potential to develop into TCs. The genesis productivity (GP) of TCCs is used to quantify the proportion of TCCs that can evolve into TCs. Recent studies have revealed a decrease in GP of western North Pacific (WNP) TCCs during the extended boreal summer (July–October) since 1998. Here, we show that the changing tendencies in GP of WNP TCCs have obvious seasonality. Although most months could see recent decreases in GP of WNP TCCs, with October experiencing the strongest decreasing trend, May is the only month with a significant recent increasing trend. The opposite changing tendencies in May and October could be attributed to different changes in low-level atmospheric circulation anomalies triggered by different sea surface temperature (SST) configurations across the tropical oceans. In May, stronger SST warming in the tropical western Pacific could prompt increased anomalous westerlies associated with anomalous cyclonic circulation, accompanied by the weakening of the WNP subtropical high and the strengthening of the WNP monsoon. Such changes in background atmospheric circulations could favor the enhancement of atmospheric eddy kinetic energy and barotropic energy conversions, resulting in a recent intensified GP of WNP TCCs in May. In October, stronger SST warming in the tropical Atlantic and Indian Oceans contributed to anomalous easterlies over the tropical WNP associated with anomalous anticyclonic circulation, giving rise to the suppressed atmospheric eddy kinetic energy and recent weakened GP of WNP TCCs. These results highlight the seasonality in recent changing tendencies in the GP of WNP TCCs and associated large-scale atmospheric-oceanic conditions.

Eddy-induced Heat Transport in the South China Sea

Eddy-induced heat transport (EHT) in the South China Sea (SCS) is important for the heat budget. However, knowledge of its variability is limited owing to discrepancies arising from the limitation of the down-gradient method and uncertainties arising from numerical models. Herein, we investigated the spatiotemporal variability and dynamics of EHT using a well-validated assimilated model. In particular, to the southeast of Vietnam (SEV) and west of Luzon Strait (WLS), significant values of annual mean EHT are observed and most EHT is confined in the upper 400 m. EHT also exhibits significant seasonality, and the largest EHT amplitude in autumn at SEV is mainly driven by the wind stress curl, while that in winter at WLS is mainly related to the Kuroshio intrusion. Energy budget analysis reveals that both the barotropic and baroclinic instabilities increase the eddy kinetic energy in autumn at SEV, whereas only the barotropic instability contributes to the eddy kinetic energy at WLS in winter. Specially, an up-gradient EHT is observed at WLS in all four seasons, characterized by the same directions between EHT and mean temperature gradient. The up-gradient EHT at WLS is induced by the baroclinic instability through an inverse energy transfer, which is generated by the interaction between the Kuroshio intrusion and topography below the surface layer. Moreover, the most significant up-gradient EHT in winter shows a wave-like southwestward propagating pattern in the subsurface layer.

Understanding the variability of the Eddy Kinetic Energy in the Arctic Ocean.

&lt;p&gt;Mesoscale activity in the Arctic Ocean remains largely unexplored, owing primarily to the challenges of i) observing eddies in this ice-covered region and ii) modelling at such small deformation radius. In this talk, we will use results from a simulation performed with a high-resolution, eddy resolving model to investigate the spatial and temporal variations of the eddy kinetic energy (EKE) in the Arctic Basin. On average and in contrast to the typical open ocean conditions, the levels of mean and eddy kinetic energy are of the same order of magnitude, and EKE is intensified along the boundary and in the subsurface. On long time scales (interannual to decadal), EKE levels do not respond as expected to changes in the large scale circulation. This can be exemplified when looking at the spin up of the gyre that occurred in response to a strong surface input of momentum in 2007-2008. On seasonal time scales, the estimation of a Lorenz energy cycle allows us to investigate the drivers behind the peculiarities of the EKE field, and to understand the relative roles played by the atmospheric forcing for them.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;