scholarly journals A diagnostic study of some flood producing rainfall events in Bangladesh with a limited area analysis-forecast system

MAUSAM ◽  
2021 ◽  
Vol 57 (3) ◽  
pp. 475-488
Author(s):  
K. PRASAD ◽  
ROMEE AFROZ ◽  
M. A. SARKER ◽  
MIZANUR RAHMAN
Keyword(s):  
Heavy Rainfall ◽  
Large Scale ◽  
Forecast Model ◽  
Southwest Monsoon ◽  
Reanalysis Data ◽  
Limited Area ◽  
Synoptic Situation ◽  
Data Sets ◽  
Diagnostic Study ◽  
Monsoon Period

Lkkj & bl ’kks/k&Ik= esa nf{k.kh if’peh ekulwu dh vof/k ds nkSjku caxykns’k esa Hkkjh o"kkZ ds dkj.k vkus okyh ck<+ dk uSnkfud v/;;u fd;k x;k gSA bl v/;;u dk eq[; mn~ns’; caxykns’k ds unh csfluksa ds m/oZ izokg okys Hkkxksa esa yxkrkj gksus okyh Hkkjh o"kkZ dh flukWfIVd fLFkfr;ksa dk irk yxkuk gS A o"kZ 1987 vkSj 1998 ds nkSjku gqbZ lcls vf/kd o"kkZ vkSj lcls vf/kd ck<+ okys nks o"kksZa dk Hkkjh o"kkZ okys rwQku ds laca/k esa v/;;u fd;k x;k gSA bZ- lh- ,e- MCY;w- ,Q-  bZ- vkj- ,-&40 ls muds fQi lkbV ls MkmuyksM fd, x, uSnkfud fo’ys"k.k ds fy, ekSle laca/kh ekufp= rS;kj fd, x, gSaA y?kq vof/k esa o"kkZ dk izfr:i.k djus ds fy, ¶yksfjMk jkT; fo’ofo|ky; ds lhfer {ks= iwokZuqeku fun’kZ dk mi;ksx fd;k x;k gS A bl fun’kZ dks {kSfrt fxzM ij vk/kk fMxzh v{kka’k@ns’kkraj vkSj Å/okZ/kj esa 16 flxek Lrjksa ij O;kogkfjd cukus ds fy, iz;qDr fd;k x;k gSA v/;;u okys bu o"kksZa esa ck<+ ykus okys o"kkZ&rwQkuksa ds fy, mRrjnk;h lkekU; flukWfIVd fLFkfr] bu mRrjh caxykns’k esa mRrjkfHkeq[kh v{kka’k ij ekSleh ekulwu nzks.kh ds v{k dh vofLFkfr vkSj cM+s iSekus ij ifjlapj.k dh folaxfr;ksa ds izHkkoLo:Ik mi;qZDr fLFkfr;ksa esa fLFkj ikbZ xbZ gSA lhfer {ks= fun’kZ ls o"kkZ ds iwokZuqeku 24 ?kaVksa vkSj 48 ?kaVksa dh iwokZuqeku vof/k;ksa esa izkIr gq, gS tks izsf{kr o"kkZ forj.k ds laca/k esa lqlaxr ik, x, gSaA  A diagnostic study of flood producing heavy rainfall in Bangladesh during the southwest monsoon period has been carried out.  The study focuses on identifying the synoptic situations leading to persistent heavy rainfall within Bangladesh and in the upstream portions of the river basins of Bangladesh.  Case studies are carried out in respect of heavy rainstorms in the two most outstanding excess rainfall and flood years 1987 and 1998.  The weather maps for diagnostic analysis are prepared from ECMWF ERA-40 Reanalysis data sets downloaded from their ftp site.  A limited area forecast model based on Florida State University has been used for simulating the precipitation in short range.  The model has been customized to run on half degree Lat./Long. horizontal grid and 16 sigma levels in the vertical.  The common synoptic situation responsible for flood producing rainstorms in the years examined is the positioning of the axis of seasonal monsoon trough in a northerly latitude over north Bangladesh and persistence of the above conditions under the influence of large scale circulation anomalies. The limited area model produced precipitation forecasts in 24h and 48h forecast ranges, which were reasonably well placed with reference to the observed rainfall distribution.

scholarly journals Prediction and Diagnosis of Tropical Cyclone Formation in an NWP System. Part III: Diagnosis of Developing and Nondeveloping Storms

2007 ◽  
Vol 64 (9) ◽  
pp. 3195-3213 ◽  
Author(s):  
K. J. Tory ◽  
N. E. Davidson ◽  
M. T. Montgomery
Keyword(s):  
Tropical Cyclone ◽  
Large Scale ◽  
Deep Convection ◽  
Weather Prediction ◽  
Vertical Wind Shear ◽  
Forecast Model ◽  
Vertical Shear ◽  
Limited Area ◽  
Vortex Interactions ◽  
Secondary Mechanism

Abstract This is the third of a three-part investigation into tropical cyclone (TC) genesis in the Australian Bureau of Meteorology’s Tropical Cyclone Limited Area Prediction System (TC-LAPS), an operational numerical weather prediction (NWP) forecast model. In Parts I and II, a primary and two secondary vortex enhancement mechanisms were illustrated, and shown to be responsible for TC genesis in a simulation of TC Chris. In this paper, five more TC-LAPS simulations are investigated: three developing and two nondeveloping. In each developing simulation the pathway to genesis was essentially the same as that reported in Part II. Potential vorticity (PV) cores developed through low- to middle-tropospheric vortex enhancement in model-resolved updraft cores (primary mechanism) and interacted to form larger cores through diabatic upscale vortex cascade (secondary mechanism). On the system scale, vortex intensification resulted from the large-scale mass redistribution forced by the upward mass flux, driven by diabatic heating, in the updraft cores (secondary mechanism). The nondeveloping cases illustrated that genesis can be hampered by (i) vertical wind shear, which may tilt and tear apart the PV cores as they develop, and (ii) an insufficient large-scale cyclonic environment, which may fail to sufficiently confine the warming and enhanced cyclonic winds, associated with the atmospheric adjustment to the convective updrafts. The exact detail of the vortex interactions was found to be unimportant for qualitative genesis forecast success. Instead the critical ingredients were found to be sufficient net deep convection in a sufficiently cyclonic environment in which vertical shear was less than some destructive limit. The often-observed TC genesis pattern of convection convergence, where the active convective regions converge into a 100-km-diameter center, prior to an intense convective burst and development to tropical storm intensity is evident in the developing TC-LAPS simulations. The simulations presented in this study and numerous other simulations not yet reported on have shown good qualitative forecast success. Assuming such success continues in a more rigorous study (currently under way) it could be argued that TC genesis is largely predictable provided the large-scale environment (vorticity, vertical shear, and convective forcing) is sufficiently resolved and initialized.

scholarly journals Characteristics of monsoon inversions over the Arabian Sea observed by satellite sounder and reanalysis data sets

2016 ◽  
Vol 16 (7) ◽  
pp. 4497-4509 ◽  
Author(s):  
Sanjeev Dwivedi ◽  
M. S. Narayanan ◽  
M. Venkat Ratnam ◽  
D. Narayana Rao
Keyword(s):  
Arabian Sea ◽  
Monsoon Season ◽  
Measurement Data ◽  
Southwest Monsoon ◽  
Reanalysis Data ◽  
Indian Region ◽  
Data Sets ◽  
Atmospheric Infrared Sounder ◽  
Data Set ◽  
Strength Based

Abstract. Monsoon inversion (MI) over the Arabian Sea (AS) is one of the important characteristics associated with the monsoon activity over Indian region during summer monsoon season. In the present study, we have used 5 years (2009–2013) of temperature and water vapour measurement data obtained from satellite sounder instrument, an Infrared Atmospheric Sounding Interferometer (IASI) onboard MetOp satellite, in addition to ERA-Interim data, to study their characteristics. The lower atmospheric data over the AS have been examined first to identify the areas where MIs are predominant and occur with higher strength. Based on this information, a detailed study has been made to investigate their characteristics separately in the eastern AS (EAS) and western AS (WAS) to examine their contrasting features. The initiation and dissipation times of MIs, their percentage occurrence, strength, etc., has been examined using the huge database. The relation with monsoon activity (rainfall) over Indian region during normal and poor monsoon years is also studied. WAS ΔT values are  ∼  2 K less than those over the EAS, ΔT being the temperature difference between 950 and 850 hPa. A much larger contrast between the WAS and EAS in ΔT is noticed in ERA-Interim data set vis-à-vis those observed by satellites. The possibility of detecting MI from another parameter, refractivity N, obtained directly from another satellite constellation of GPS Radio Occultation (RO) (COSMIC), has also been examined. MI detected from IASI and Atmospheric Infrared Sounder (AIRS) onboard the NOAA satellite have been compared to see how far the two data sets can be combined to study the MI characteristics. We suggest MI could also be included as one of the semipermanent features of southwest monsoon along with the presently accepted six parameters.

scholarly journals The Okhotsk-Japan Circulation Pattern and the Heavy Rainfall in Beijing in 2012 Summer

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Yafei Wang ◽  
Jianzhao Qin ◽  
Lijuan Zhu
Keyword(s):  
Heavy Rainfall ◽  
Large Scale ◽  
Circulation Pattern ◽  
Northern China ◽  
Reanalysis Data ◽  
Heavy Rainfall Event ◽  
Baikal Lake ◽  
Ural Mountains ◽  
Pressure System ◽  
Blocking High

Using station precipitation and reanalysis data, we examined the evolution of the large-scale circulations associated with the heavy rainfall event that occurred around July 21, 2012 (721 heavy rainfall). This study focuses on a role that the large-scale circulations named “the Okhotsk-Japan (OKJ) circulation pattern” played in causing the heavy rainfall case. We found that the 721 heavy rainfall occurred under a background of the OKJ circulation that persisted for about 10 days. However, the pattern was different from the normal OKJ circulation, for this circulation pattern accompanied a blocking high between the Ural Mountains and the Baikal Lake. This difference resulted from the seasonal change of the basic flow. The related Rossby wave propagated eastward during the persisting period of the dominated OKJ pattern. This caused the development of a low-pressure system around the Baikal Lake and the weakening of a ridge around the Okhotsk Sea. The slow evolution of the OKJ circulation created a favorable environment for the moisture transport to northern China, assisting in the generation of the 721 heavy rainfall.

scholarly journals An update on global atmospheric ice estimates from satellite observations and reanalyses

2018 ◽  
Vol 18 (15) ◽  
pp. 11205-11219 ◽  
Author(s):  
David Ian Duncan ◽  
Patrick Eriksson
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Principal Component ◽  
Reanalysis Data ◽  
Data Sets ◽  
Diurnal Variability ◽  
Weather Forecasts ◽  
Earth Observing System ◽  
The Difference ◽  
Ice Water

Abstract. This study assesses the global distribution of mean atmospheric ice mass from current state-of-the-art estimates and its variability on daily and seasonal timescales. Ice water path (IWP) retrievals from active and passive satellite platforms are analysed and compared with estimates from two reanalysis data sets, ERA5 (European Centre for Medium-range Weather Forecasts Reanalysis 5, ECMWF) and MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications 2). Large discrepancies in IWP exist between the satellite data sets themselves, making validation of the model results problematic and indicating that progress towards a consensus on the distribution of atmospheric ice has been limited. Comparing the data sets, zonal means of IWP exhibit similar shapes but differing magnitudes, with large IWP values causing much of the difference in means. Diurnal analysis centred on A-Train overpasses shows similar structures in some regions, but the degree and sign of the variability varies widely; the reanalyses exhibit noisier and higher-amplitude diurnal variability than borne out by the satellite estimates. Spatial structures governed by the atmospheric general circulation are fairly consistent across the data sets, as principal component analysis shows that the patterns of seasonal variability line up well between the data sets but disagree in severity. These results underscore the limitations of the current Earth observing system with respect to atmospheric ice, as the level of consensus between observations is mixed. The large-scale variability of IWP is relatively consistent, whereas disagreements on diurnal variability and global means point to varying microphysical assumptions in retrievals and models alike that seem to underlie the biggest differences.

scholarly journals Comparison of large-scale dynamical variability in the extratropical stratosphere among the JRA-55 family data sets

2017 ◽  
Author(s):  
Masakazu Taguchi
Keyword(s):  
Large Scale ◽  
Weather Prediction ◽  
Polar Vortex ◽  
Numerical Weather Prediction Model ◽  
Reanalysis Data ◽  
Family Data ◽  
Data Sets ◽  
Polar Night ◽  
Standard Product ◽  
Northern Winter

Abstract. This study compares large-scale dynamical variability in the extratropical stratosphere, such as major stratospheric sudden warmings (MSSWs), among the Japanese 55-year Reanalysis (JRA-55) family data sets. The JRA-55 family consists of three products: a standard product of the JRA-55 reanalysis data, and two sub-products of JRA-55C and JRA-55AMIP. JRA-55C assimilates only conventional observations, whereas JRA-55AMIP runs the same numerical weather prediction model without assimilation of observational data. A comparison of the occurrence of MSSWs in Northern winter shows that compared to the standard product, JRA-55C delays several MSSWs by one to four days and also misses a few MSSWs. JRA-55C also misses the Southern Hemisphere MSSW in September 2002. JRA-55AMIP shows much fewer MSSWs in Northern winter, and especially lacks MSSWs of high aspect ratio of the polar vortex. A further examination of daily geopotential height differences between JRA-55 and JRA-55C reveals occasional peaks in both hemispheres. The delayed and missed MSSW cases have smaller height differences in magnitude than such peaks. The differences include large contributions from the zonal component, which are consistent with underestimations in the weakening of the zonal mean polar night jet in JRA-55C. We also explore strong planetary wave forcings and associated polar vortex weakenings for JRA-55 and JRA-55AMIP. It shows a lower frequency of strong wave forcings and weaker vortex responses to such wave forcings in JRA-55AMIP, consistent with the lower MSSW frequency.

scholarly journals Aerosol effects on clouds and precipitation during the 1997 smoke episode in Indonesia

2009 ◽  
Vol 9 (2) ◽  
pp. 743-756 ◽  
Author(s):  
H.-F. Graf ◽  
J. Yang ◽  
T. M. Wagner
Keyword(s):  
Large Scale ◽  
Convective Cloud ◽  
Reanalysis Data ◽  
Cumulus Parameterization ◽  
Convective Precipitation ◽  
Limited Area ◽  
Convective Rainfall ◽  
High Background ◽  
Convective Clouds ◽  
The Mean

Abstract. In 1997/1998 a severe smoke episode due to extensive biomass burning, especially of peat, was observed over Indonesia. September 1997 was the month with the highest aerosol burden. This month was simulated using the limited area model REMOTE driven at its lateral boundaries by ERA40 reanalysis data. REMOTE was extended by a new convective cloud parameterization mimicking individual clouds competing for instability energy. This allows for the interaction of aerosols, convective clouds and precipitation. Results show that in the monthly mean convective precipitation is diminished at nearly all places with high aerosol loading, but at some areas with high background humidity precipitation from large-scale clouds may over-compensate the loss in convective rainfall. The simulations revealed that both large-scale and convective clouds' microphysics are influenced by aerosols. Since aerosols are washed and rained out by rainfall, high aerosol concentrations can only persist at low rainfall rates. Hence, aerosol concentrations are not independent of the rainfall amount and in the mean the maximum absolute effects on rainfall from large scale clouds are found at intermediate aerosol concentrations. The reason for this behavior is that at high aerosol concentrations rainfall rates are small and consequently also the anomalies are small. For large-scale as well as for convective rain negative and positive anomalies are found for all aerosol concentrations. Negative anomalies dominate and are highly statistically significant especially for convective rainfall since part of the precipitation loss from large-scale clouds is compensated by moisture detrained from the convective clouds. The mean precipitation from large-scale clouds is less reduced (however still statistically significant) than rain from convective clouds. This effect is due to detrainment of cloud water from the less strongly raining convective clouds and because of the generally lower absolute amounts of rainfall from large-scale clouds. With increasing aerosol load both, convective and large scale clouds produce less rain. At very few individual time steps cases were found when polluted convective clouds produced intensified rainfall via mixed phase microphysics. However, these cases are not unequivocal and opposite results were also simulated, indicating that other than aerosol-microphysics effects have important impact on the results. Overall, the introduction of the new cumulus parameterization and aerosol-cloud interaction reduced some of the original REMOTE biases of precipitation patterns and total amount.

scholarly journals Large Scale Processes for Understanding Extreme Rain Storm Over Rangamati on 12 June 2017- A Case Study

2020 ◽  
Vol 11 (2) ◽  
pp. 87-97
Author(s):  
Samarendra Karmakar ◽  
Mohan Kumar Das ◽  
Haripada Sarker
Keyword(s):  
Bay Of Bengal ◽  
Heavy Rainfall ◽  
Large Scale ◽  
Early Period ◽  
Analysis Data ◽  
Southwest Monsoon ◽  
Monsoon Depression ◽  
Heavy Rainfall Event ◽  
Strong Wind ◽  
Synoptic Conditions

Attempts have been made to study the large-scale surface and upper air synoptic processes associated with a monsoon depression during 11-12 June 2017. In this study, Grid Analysis and Display System (GrADS) software has been used to prepare the large-scale sea level pressure and upper flow patterns by analyzing the FNL re-analysis data. In this analysis, FNL dataset is used to characterize the rainstorms, with key hydrometeorological variables describing the prior conditions of the very heavy rainfall event presented the study. National Center for Environmental Prediction (NCEP) Final (FNL) analysis data of 1o by 1o grids for every 6 hours are used for large scale synoptic analysis. The disastrous event was a strong monsoon depression in the early period of southwest monsoon 2017. Due to this depression, very heavy rainfall occurred in the southeastern Bangladesh. Rangamati recorded 343 mm of rainfall in the 24 hours on 12 June 2017. Massive landslides occurred in three districts such as Rangamati, Bandarban and Chittagong. The analysis of surface and upper air synoptic conditions has revealed that a well-marked low was formed over the northwest Bay of Bengal within the low-pressure belt passing from Somalia coast extending through southern Pakistan, and India up to east central Bay of Bengal and adjoining Bangladesh. The wind speed is calculated from the pressure distribution and is found to be 24.23ms-1, which is at par with the observed one. The well-marked low was subsequently intensified into a depression and moved northeastwards over Bangladesh. Strong southsouthwesterly winds were associated in the eastern side of the depression, especially over Chittagong Hill Tracts. The depression was found to extend up to 500 hPa level as seen from the distribution of geopotential and strong circulation around the centre. Winds were advecting from large continental and Ocean areas over the South Asia. Strong winds and moisture influx, strong narrow coma-like trough from a micro low at the surface to 500 hPa level as well as strong wind shear were responsible for the heavy rainfall, disastrous effects and massive landslides over Rangamati and adjoining areas. Journal of Engineering Science 11(2), 2020, 87-97

scholarly journals DIAGNOSTIC ANALYSIS OF CATASTROPHIC FLOOD OVER EASTERN INDIA IN JULY 2017 - A CASE STUDY

MAUSAM ◽  
2021 ◽  
Vol 71 (3) ◽  
pp. 513-522
Author(s):  
Sharma R S ◽  
Mandal B K ◽  
Das G K
Keyword(s):  
Heavy Rainfall ◽  
West Bengal ◽  
Monsoon Season ◽  
Geographical Location ◽  
River Basins ◽  
Southwest Monsoon ◽  
Eastern India ◽  
Monsoon Period ◽  
Indian States ◽  
South West Monsoon

Floods are very common in eastern India during southwest monsoon season. It brings a lot of misery to the people of this region. Every year eastern Indian states namely West Bengal, Odisha and Bihar witness such types of flood during monsoon period. Major river basins in eastern India are Ganga river basin in Bihar and West Bengal area, Odisha has three river basins namely Mahanadi, Subarnarekha, Brahmani and Baitarani        [Fig. 1(a)]. As majority of tributary rivers of Ganga passing through Bihar and West Bengal; these two states are more prone to massive flood during monsoon season. The abnormal occurrence of rainfall generally causes floods. It occurs when surface runoff exceeds the capacity of natural drainage. The heavy rainfall is frequently occurring event over the area during South-West Monsoon (SWM) every year. The geographical location of the area, orography and its interaction with the basic monsoon flow is considered as one of prime factors of these heavy rainfall activities. Synoptically, the latitudinal oscillation of eastern end of the Monsoon Trough and the synoptic disturbances formed or passing over the eastern India region and / or its neighbourhood that brings moisture laden Easterly or South-Easterly winds over the area are the main causes responsible for heavy rainfall in this area.

scholarly journals Aerosol effects on clouds and precipitation during the 1997 smoke episode in Indonesia

2007 ◽  
Vol 7 (6) ◽  
pp. 17099-17116 ◽  
Author(s):  
H.-F. Graf ◽  
J. Yang ◽  
T. M. Wagner
Keyword(s):  
Large Scale ◽  
Convective Cloud ◽  
Reanalysis Data ◽  
Cumulus Parameterization ◽  
Convective Precipitation ◽  
Limited Area ◽  
High Background ◽  
Convective Clouds ◽  
Era40 Reanalysis ◽  
Instability Energy

Abstract. In 1997/98 a severe smoke episode due to extensive biomass burning, especially of peat, was observed over Indonesia. September 1997 was the month with the highest aerosol burden. This month was simulated using the limited area model REMOTE driven at its lateral boundaries by ERA40 reanalysis data. REMOTE was extended by a new convective cloud parameterization mimicking individual clouds competing for instability energy. This allows for the interaction of aerosols and convective clouds and precipitation. Results show that convective precipitation is diminished at all places with high aerosol loading, but at some areas with high background humidity precipitation from large-scale clouds may over-compensate the loss in convective rainfall. At individual time steps, very few cases were found when polluted convective clouds produced intensified rainfall via mixed phase microphysics. However, these cases are not unequivocal and opposite results were also simulated, indicating that other than aerosol-microphysics effects have important impact on the results. Overall, the introduction of the new cumulus parameterization and of aerosol-cloud interaction improved the simulation of precipitation patterns and total amount.

scholarly journals Evaluation of a new convective cloud field model: precipitation over the maritime continent

2006 ◽  
Vol 6 (5) ◽  
pp. 10217-10246
Author(s):  
H.-F. Graf ◽  
J. Yang
Keyword(s):  
Large Scale ◽  
Field Model ◽  
Convective Cloud ◽  
Atmospheric Model ◽  
Reanalysis Data ◽  
Convective Precipitation ◽  
Limited Area ◽  
Maritime Continent ◽  
Simulated Precipitation ◽  
Set Up

Abstract. A convective cloud field model (CCFM) is substituted for a standard mass flux parameterisation of convective clouds in a limited area atmospheric model (REMO) and is tested for a whole annual cycle (July 1997 to June 1998) over the Maritime Continent. REMO with CCFM is run in 0.5-degree resolution and the model at the boundaries is forced 6-hourly by ECMWF reanalysis data. Simulated precipitation from runs with the standard convection parameterisation and with CCFM is compared against two sets of observations. The use of CCFM clearly improves the simulated precipitation patterns and total rainfall over the whole model domain. The distribution between large-scale and convective precipitation becomes more realistic. CCFM shows to be a useful concept to describe convective cloud spectra in atmospheric models, although there are still similar problems with occasionally extreme precipitation as in the original set-up of REMO.

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