Simulation of Severe Thunderstorms in Conjugation of Westerly and Easterly on 31 March 2019 in Bangladesh

The diagnostic and prognostic studies of thunderstorms/squalls are very important to save live and loss of properties. The present study aims at diagnose the different tropospheric parameters, instability and synoptic conditions associated the severe thunderstorms with squalls, which occurred at different places in Bangladesh on 31 March 2019. For prognostic purposes, the severe thunderstorms occurred on 31 March 2019 have been numerically simulated. In this regard, the Weather Research and Forecasting (WRF) model is used to predict different atmospheric conditions associated with the severe storms. The study domain is selected for 9 km horizontal resolution, which almost covers the south Asian region. Numerical experiments have been conducted with the combination of WRF single-moment 6 class (WSM6) microphysics scheme with Yonsei University (YSU) PBL scheme in simulation of the squall events. Model simulated results are compared with the available observations. The observed values of CAPE at Kolkata both at 0000 and 1200 UTC were 2680.4 and 3039.9 J kg-1 respectively on 31 March 2019 and are found to be comparable with the simulated values. The area averaged actual rainfall for 24 hrs is found is 22.4 mm, which complies with the simulated rainfall of 20-25 mm for 24 hrs. Journal of Engineering Science 12(3), 2021, 29-43

Estimation of divergent wind from OLR data for use in objective analysis over the Indian region

A scheme is formulated for the use of OLR data in the estimation of vertical velocity; divergence and then the divergent part of the wind over Indian region. In this scheme, ascending motion over cloudy region is estimated from an empirical relation between the cloud top temperature and descending motion over cloud-free region is estimated from the thermodynamic energy equation and both are blended. From this blended vertical velocity field, aivergence, velocity potential and divergent winds at all standard levels from 4 to 8 July 1979 at 00 UTC are computed. These fields are compared with satellite cloud pictures, rainfall etc and they are found to be realistic in depicting the synoptic conditions. Total wind is computed as the sum of the estimated divergent component and rotational component computed from observed wind field. For assessment of the scheme, this total wind field at 850 hPa is used as initial. guess field in univariate optimum interpolation scheme and analyses were made for the period 4 to 8 July 1979. Results show that scheme is able to produce realistic analyses which included divergent part of the wind.

Assessing the role of compound drought and heatwave events on unprecedented 2020 wildfires in the Pantanal

The year 2020 had the most catastrophic fire season over the last two decades in the Pantanal, which led to outstanding environmental impacts. Indeed, much of the Pantanal has been affected by severe dry conditions since 2019, with evidence of the 2020’s drought being the most extreme and widespread ever recorded in the last 70 years. Although it is unquestionable that this mega-drought contributed significantly to the increase of fire risk, so far, the 2020’s fire season has been analyzed at the univariate level of a single climate event, not considering the co-occurrence of extreme and persistent temperatures with soil dryness conditions. Here, we show that similarly to other areas of the globe, the influence of land-atmosphere feedbacks contributed decisively to the simultaneous occurrence of dry and hot spells (HPs), exacerbating fire risk. The ideal synoptic conditions for strong atmospheric heating and large evaporation rates were present, in particular during the HPs, when the maximum temperature was, on average, 6 ºC above the normal. The short span of the period during those compound drought-heatwave (CDHW) events accounted for 55% of the burned area of 2020. The vulnerability in the northern forested areas was higher than in the other areas, revealing a synergistic effect between fuel availability and weather-hydrological conditions. Accordingly, where fuel is not a limiting factor, fire activity tends to be more modelled by CDHW events. Our work advances beyond an isolated event-level basis towards a compound and cascading natural hazards approach, simultaneously estimating the contribution of drought and heatwaves to fuelling extreme fire outbreaks in the Pantanal such as those in 2020. Thus, these findings are relevant within a broader context, as the driving mechanisms apply across other ecosystems, implying higher flammability conditions and further efforts for monitoring and predicting such extreme events.

The influence of shallow cloud populations on transitions to deep convection in the Amazon

In this study, a pair of convection-permitting (2-km grid spacing), month-long, wet season Weather Research and Forecasting (WRF) simulations with and without the Eddy-Diffusivity Mass-Flux (EDMF) scheme are performed for a portion of the Green Ocean Amazon (GoAmazon) 2014/5 field campaign period. EDMF produces an ensemble of subgrid-scale convective plumes that evolve in response to the boundary layer meteorology and can develop into shallow clouds. The objective of this study is to determine how different treatments of shallow cumulus clouds (i.e., with and without EDMF) impact the total cloud population and precipitation across the Amazonian rainforest, with emphasis on impacts on the likelihood of shallow-to-deep convection transitions. Results indicate that the large-scale synoptic conditions in the EDMF and control simulations are nearly identical, however, on the local scale their rainfall patterns diverge drastically and the biases decrease in EDMF. The EDMF scheme significantly increases the frequency of shallow clouds, but the frequencies of deep clouds are similar between the simulations. Deep convective clouds (DCC) are tracked using a cloud tracking algorithm to examine the impact of shallow cumulus on the surrounding ambient environment where deep convective clouds initiate. Results suggest that a rapid increase of low-level cloudiness acts to cool and moisten the low-to-mid troposphere during the day, favoring the transition to deep convection.

Unusual weather over northwest & west India during November, 2010

lkekU;r% uoEcj dk eghuk /kwi ds fnuksa o fcuk ckfj'k okyk eghuk dgykrk gS vkSj uoEcj eghus ds chrus ds lkFk-lkFk mRrj if'peh Hkkjr ds eSnkuh Hkkxksa esa lqcg dh gYdh BaMd fy, ekSle lqgkouk jgrk gS fdUrq uoEcj 2010 ds nkSjku mRrj if'peh vkSj if'pe Hkkjr esa o"kkZ dh ckSNkjksa ds lkFk yEcs le; rd yxkrkj ckny Nk, jgs ftlds dkj.k ekSle vlkekU; jgkA bl vlkekU; ekSle ds fy, mRrjnk;h HkkSfrd izfØ;kvksa dk irk yxkus ds fy, bl 'kks/k i= esa bl ekg esa cuh flukfIVd fLFkfr;ksa dk foLr`r fo'ys"k.k fd;k x;k gSA bl v/;;u ls ;g irk pyk gS fd vjc lkxj esa xgu fuEu vonkc iz.kkyh dh mifLFkfr vkSj fupys Lrjksa esa if'peh gokvksa esa e/; {kksHkeaMyh; nzksf.k;ksa ds lkFk&lkFk iwohZ gokvksa esa mPp vk;keh nzksf.k;ksa dh ijLij fØ;kvksa ds dkj.k uoEcj ekg esa ekSle vlkekU; jgkA Generally, November is the dry month with sunny days and pleasant weather for plains of northwest & west India with a bit of early morning chill as the month progresses. But during November, 2010, there was unusual weather in the form of prolonged and persistent cloudy conditions with wet spell over northwest & west India. To find out the physical processes leading to this unusual weather, detailed analysis of synoptic conditions during the month has been carried out in this paper. This study reveals that the unusual weather that occurred in association with presence of an intense low pressure system in the Arabian Sea and interaction of high-amplitude troughs in easterlies in the lower levels with mid-tropospheric troughs in the westerlies.

Synoptic study of extremely heavy rainfall events over lower Yamuna catchment : Some cases

vR;f/kd o"kkZ gksus ds dkj.k HkwL[kyu gksrk gS vDlekr ck<+ vk tkrh gS vkSj Qly dks {kfr igq¡prh gSA lekt] vFkZO;oLFkk vkSj i;kZoj.k ij bldk cgqr nq"izHkko iM+rk gSA i;kZoj.kh; vkSj flukWfIVd fLFkfr;ksa ds mRiUu gksus ls vR;f/kd vFkok cgqr Hkkjh o"kkZ gksus ds dkj.k Hkkjr esa nf{k.k if’peh ekulwu _rq ds nkSjku vf/kdk¡’kr% ck<+ vkrh gSA bl 'kks/k i= esa izeq[k flukWfIVd dkj.kksa dk irk yxkus dk iz;kl fd;k x;k gS tks y?kq vof/k iwokZuqeku ds {ks= esa fodflr iwokZuqeku rduhd vkSj vk/kqfud izs{k.kkRed izkS|ksfxdh ij vk/kkfjr o"kZ 1998&2010 dh vof/k dh bl o"kkZ vkSj ok;qeaMyh; iz.kkfy;ksa ds e/; laca/kksa ds fo’ys"k.k ds ek/;e ls ;equk ds fupys tyxzg.k {ks= ¼,y-okbZ-lh-½ esa vR;f/kd Hkkjh o"kkZ dh ?kVukvksa ds fy, mRrjnk;h gSA bl v/;;u ls ;g irk pyk gS fd bl {ks= esa caxky dh [kkM+h esa fuEu nkc iz.kkfy;ksa dk cuuk izeq[k dkjd gS fuLlansg ;fn LFkkuh; fLFkfr;k¡ izHkkoh gks tSlsa fd xehZ dk c<+uk rks ogk¡ ij Hkkjh o"kkZ gksrh gSA lkekU;r% caxky dh [kkM+h esa fuEu vcnkc iz.kkfy;k¡ ¼pØokr] vonkc] fuEu vonkc {ks= vkfn tSls ¼,y-ih-,l-½ fodflr gqbZ tks if’pe ls mRrjh if’peh fn’kk dh vksj c<+h rFkk ;equk ds fupys tyxzg.k ¼,y-okbZ-lh-½ {ks= esa igq¡phA ,slh ?kVukvksa ds fy, mRrjnk;h mifjru ok;q pØokrh ifjlapj.k ¼lkblj½ ds izHkko ls ogha ij ,y- ih- ,l- Hkh cu ldrk gSA ,slh iz.kkyh ls bDds&nwDds LFkkuksa ij vR;f/kd Hkkjh o"kkZ dh ?kVuk,¡ ¼lkekU;r% iz.kkyh ds nf{k.k if’pe {ks= esa½ vkSj dqN LFkkuksa ij Hkkjh ls cgqr Hkkjh o"kkZ gqbZ ftlds dkj.k ck<+ vkbZA ;fn ;equk ds fupys tyxzg.k ¼,y-okbZ-lh-½ {ks= esa ,y-ih-,l- fuf"Ø; ;k /khek iM+ tkrk gS rks bl izdkj dh o"kkZ dh ?kVukvksa dh laHkkouk c<+ ldrh gSA ,y-ih-,l- ds vkxs c<+us dk lgh iwokZuqeku nsus ds fy, vkj-,l-,e-lh- ¼Hkkjr ekSle foKku foHkkx½ ubZ fnYYkh ds iwoZuqeku :i js[kk ds ,u-MCY;w-ih- mRikn@72] 48 vkSj 24 ?kaVksa ds iou pkVZ lgh lk/ku ik, x, gSaA vR;f/kd o"kkZ dh ?kVukvksa ds iwokZuqeku esa bl izdkj dh lwpuk nsus ls iwokZuqekudrkvksa dks fuf’pr :i ls lgh iwokZuqeku feysxk rkfd ftyk izkf/kdkjh le; jgrs vkink dh rS;kjh ds fy, vko’;d ewyHkwr lqfo/kk,¡ miyC/k djk ldsaA Extreme rainfall results in landslides, flash flood and crop damage that have major impact on society, the economy and the environment. During southwest monsoon season, flood mostly occurs in India due to extremely or very heavy rain that originates from environmental and synoptic conditions. An attempt has been made to identify the main synoptic reasons, which are responsible for extremely heavy rainfall events over Lower Yamuna catchment (LYC) through the analysis of the relationship between this rainfall and atmospheric systems for the period 1998-2010 based on modern observational technology and developed forecasting technique in the field of short range prediction. The finding of this study show that the major factor have is the arrival of Bay of Bengal low pressure systems in this region, of course if the ascent local conditions such as heat occur, causing the heaviest rains there. The low pressure systems (LPS like, Cyclone, depression, low pressure area etc.) developed generally over Bay of Bengal moved in west to north-westwards direction and reached over the LYC region. Also LPS may be formed in situ under the influence of upper air cyclonic circulation (cycir) responsible for such events. Such system yield extremely heavy rainfall events (generally in the south-west sector of the system) at isolated places and heavy to very heavy rainfall at a few places and there by caused flood situation. The possibility of occurrence of such type of rainfall would be higher if the LPS is either stagnate or slow over LYC region. The NWP products of RSMC (IMD) New Delhi forecast contours / wind charts for 72, 48 & 24 hrs were found good tool for accurate forecast position of the movement of the LPS. Such information certainly facilitate to forecaster in prediction of extreme rainfall events more accurately so that district authorities may set up necessary infrastructures for disaster preparedness in time.

Evaluation of surface processes in the PALM model system 6.0 for a real urban environment: a case study in Dejvice, Prague

&lt;p&gt;In recent years, the the Large-eddy simulation (LES) model PALM has been rapidly developed its capability to simulate physical processes within urban environments. For example, this includes energy-balance solvers for building and land surfaces, a radiative transfer model to account for multiple reflections and shading, a plant-canopy model to consider the effects of plants on flow (thermo-)dynamics, and a chemistry transport model, as well as nesting capabilities that enable &amp;#8220;hot-spot&amp;#8221; analysis, to name a few.&lt;/p&gt; &lt;p&gt;This contribution provides an evaluation of modeled meteorological as well as ground and wall-surface quantities against dedicated in-situ measurements taken in an urban environment in Dejvice, Prague. Measurements included monitoring of surface temperature and wall heat fluxes. Simulations were performed for multiple days during several summer and winter episodes, characterized by different atmospheric conditions. To consider time-evolving synoptic conditions, boundary conditions were obtained from mesoscale WRF simulations.&lt;/p&gt; &lt;p&gt;For the simulated episodes, the resulting temperature and wind speed within street canyons show a realistic representation of the observed state, except that the LES did not adequately capture night-time cooling near the surface in some scenarios. At most of the evaluation points, the simulated surface temperature reproduces the observed surface temperature reasonably well, for both, absolute and daily amplitude values. However, especially for the winter episodes and for modern buildings with multi-layer wall structure, the heat transfer through the walls is not well captured in some cases, leading to discrepancies between the modeled and observed wall-surface temperature. Moreover, we also show that the model performance with respect to the observations strongly depends on the accuracy of the input data. To name a few, this includes e.g. the prescribed initial soil moisture, the given leaf-area densities to account for correct shading, or if a facade is insulated or not. Additionally, we will point out current model limitations, particularly implications accompanied by the step-like topography on the Cartesian grid, or wide glass facades that are not fully represented in terms of radiative processes.&lt;/p&gt; &lt;p&gt;With our findings we are able to evaluate the representation of physical processes in PALM, while also pointing out specific shortcomings.&lt;/p&gt;

Formation conditions of an ice storm in Vladivostok in November 2020

Synoptic conditions for the formation of an unprecedented ice storm with the generation of long-lived high-intensity glaze ice on the vast territory in Primorsky Krai are investigated. The leading role of the strong extension of the layer with positive temperature towards the cold air mass and the existence of two-way temperature advection in the lower troposphere are shown. It is shown that the long-term preservation of glaze ice on the territory of the region was associated with the movement of the southern cyclone to the east and the arrival of cold air masses from the continent. Experiments were implemented to simulate freezing precipitation using the WRF-ARW mesoscale model. The simulation results made it possible to obtain more detailed data on the vertical structure of the atmosphere during the formation of freezing precipitation and to fill in the missing data for analysis. Keywords: severe weather events, ice accretion, glaze ice, freezing rain, ice pellets, numerical weather prediction, WRF-ARW

Quasi-idealized numerical simulations of processes involved in orogenic convection initiation over the Sierras de Córdoba mountains

The Sierras de Córdoba (SDC) mountain range in Argentina is a hotspot of deep moist convection initiation (CI). Radar climatology indicates that 44% of daytime CI events that occur near the SDC in spring and summer seasons and that are not associated with the passage of a cold front or an outflow boundary involve a northerly LLJ, and these events tend to preferentially occur over the southeast quadrant of the main ridge of the SDC. To investigate the physical mechanisms acting to cause CI, idealized convection-permitting numerical simulations with a horizontal grid spacing of 1 km were conducted using CM1. The sounding used for initializing the model featured a strong northerly LLJ, with synoptic conditions resembling those in a previously postulated conceptual model of CI over the region, making it a canonical case study. Differential heating of the mountain caused by solar insolation in conjunction with the low-level northerly flow sets up a convergence line on the eastern slopes of the SDC. The southern portion of this line experiences significant reduction in convective inhibition, and CI occurs over the SDC southeast quadrant. Thesimulated storm soon acquires supercellular characteristics, as observed. Additional simulations with varying LLJ strength also show CI over the southeast quadrant. A simulation without background flow generated convergence over the ridgeline, with widespread CI across the entire ridgeline. A simulation with mid- and upper-tropospheric westerlies removed indicates that CI is minimally influenced by gravity waves. We conclude that the low-level jet is sufficient to focus convection initiation over the southeast quadrant of the ridge.