Energetics of super cyclone ‘GONU’ and very severe cyclonic storm ‘SIDR’

This paper discusses the energetics aspects of two tropical cyclones formed over the north Indian Ocean during 2007, viz., the Super Cyclonic Storm (GONU) and the Very Severe Cyclonic Storm (SIDR). From the analysis of various energetics terms such as the Eddy Available Potential Energy (AE), Zonal Available Potential Energy (AZ), Zonal Kinetic Energy (KZ), Eddy Kinetic Energy (KE) and their generation and inter-conversions i.e., G(AE), G(AZ), C(AE, KE), C(AZ, KZ), C(KZ, KE) and C(AZ, AE) have been computed on day to day basis during the periods of their intensifications over the domain 5° N to 25° N, 55° E to 75° E in respect of ‘GONU’ and 5° N to 25° N, 77° E to 97° E for ‘SIDR’. Besides the above, the area averaged value of s (Sigma), the vertically averaged Moist Static Energy (MSE), has also been computed on each day. Day-to-day evolution of these parameters is mapped and described. Some of the distinguishing features in the energetic of these two intense vortices which formed in entirely different climatological settings have been brought out. It is noticed that in the case of ‘GONU’, though both barotropic and baroclinic energy conversions have taken place during the life cycle, the intensification phase is characterized by an enhancement in AE, KE and vertically integrated Moist Static Energy. Enhancement in AE can be attributed to the generation of AE, which may again be attributed to the asymmetric latent heat of condensation associated with the asymmetric rainfall in the cyclone field. Enhancement in KE may be attributed to the enhancement in both barotropic and baroclinic conversion into KE. Though most of these observations made for ‘GONU’ are found to be attributable to ‘SIDR’ as well, the intensification of ‘SIDR’ appears to have more similarity to that of a typical growing mid-latitude baroclinic wave. In this case, the enhancement in AE, could also be attributed to positive C(AZ,AE), which is mainly due to interaction with mid-latitude baroclinic westerly wave. The energetics analysis also indicates that GONU had helped in the enhancement of seasonal mean meridional circulation where as the SIDR had inhibited the enhancement of seasonal mean meridional circulation.

Role of Hamiltonian energy in thunderstorms

In the present study, we propose a hypothesis that “Hamiltonian energy of thunder storm is contributing towards the energy that overcomes convective inhibition energy to lift the parcel to the level of free convection and releases convective available potential energy in the environment”. We attempt to substantiate the hypothesis. We have applied Hamiltonian structure to a thundercloud which has occurred vertically above the meteorological observatory station. Further, a total of 62 cases of thunderstorms are selected for both stations Palam and Dumdum. Hamiltonian energy is computed and investigated the cases having significant large convective inhibition energy as compared to that of convective available potential energy. We attempt to show that Hamiltonian is the energy that overcomes convective inhibition energy to lift the parcel to the level of free convection and plays a major role in thunderstorms for giving rain. Results reveal that Hamiltonian energy is seen to be maximum at the surface and contributes to both convective inhibition energy and convective available potential energy. At the lower troposphere, it overcomes the convective inhibition energy and provides necessary trigger for air mass to move from surface to the level of free convection. While in the upper troposphere, it is contributing to the convective available potential energy such that the part of potential energy converted into kinetic energy & warm and moist air mass (unstable) acceleration is enhanced by pressure energy. Further, in all the six special cases stability indices had indicated possibility of thunderstorm. In addition, synoptic conditions were also favorable for the same.

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.

Role of CAPE and CINE in modulating the convective activities during April over India

During the month of April, except over northwest India, where rain is normally associated with the intrusion of midlatitudinal westerly systems in the form of western disturbances, other parts of the country receive rain due to enhancement of convective activities in the form of thundershowers, occurring over many parts of the country. The role of Convective Available Potential Energy (CAPE) and Convective Inhibition Energy (CINE) were studied for the occurrence of more convective activities in the month of April 1997 compared to other years. The results reveal that larger values of CAPE and smaller values of CINE in April 1997 over various parts of India compared to other years were responsible for more convective activities and consequently appreciable fall in temperature in April 1997.

Should Reversible Convective Inhibition be Used when Determining the Inflow Layer of a Convective Storm?

Convective inhibition (CIN) is one of the parameters used by forecasters to determine the inflow layer of a convective storm, but little work has examined the best way to compute CIN. One decision that must be made is whether to lift parcels following a pseudoadiabat (removing hydrometeors as the parcel ascends) or reversible moist adiabat (retaining hydrometeors). To determine which option is best, idealized simulations of ordinary convection are examined using a variety of base states with different reversible CIN values for parcels originating in the lowest 500 m. Parcel trajectories suggest that ascent over the lowest few kilometers, where CIN is typically accumulated, is best conceptualized as a reversible moist adiabatic process instead of a pseudoadiabatic process. Most inflow layers do not contain parcels with substantial reversible CIN, despite these parcels possessing ample convective available potential energy and minimal pseudoadiabatic CIN. If a stronger initiation method is used, or hydrometeor loading is ignored, simulations can ingest more parcels with large amounts of reversible CIN. These results suggest that reversible CIN, not pseudoadiabatic CIN, is the physically relevant way to compute CIN and that forecasters may benefit from examining reversible CIN instead of pseudoadiabatic CIN when determining the inflow layer.

Assessing Atmospheric Instability over the Bay of Bengal during October and November Months between 2007 – 2018

An attempt has been made in this research to delineate a pattern for atmospheric instability during the months of October and November from 2007 to 2018. The results show an alarming trend of increasing instability throughout the study period. The average temperature at 2-meters height around the Bay of Bengal has changed significantly over time. Most notably, the gap between monthly average highest and monthly average lowest temperatures (at 2-meters height) is more or less increasing from 2007 to 2018 – ranging from 3.0 degrees to 11.0 degrees Celsius. Similar tendencies are observed for CAPE (Convective Available Potential Energy) as well – with the highest value of more than 3000 J/Kg. The findings of this research will help in understanding the prevailing conditions over the Bay, and also enable better preparedness for any potential severe convective activities. The Dhaka University Journal of Earth and Environmental Sciences, Vol. 9(2), 2020, P 45-54