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- Arctic–midlatitude–tropics interactions in January 2020: linkages to
precipitation extremes over Indian region-
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Abstract: Abstract The prolonged positive phase of the Arctic Oscillation (AO) and associated quasi-stationary equivalent barotropic Euro-Atlantic blocking high (EABH) and the Siberian high (SH) existed during January 2020. The presence of the persistent quasi-stationary barotropic high resulted in higher (lower) than normal surface temperatures in most parts of northern (southern) Eurasia. The large-scale analysis suggests the detouring of the mid-latitudinal westerlies from EABH and the formation of the west–east trough from East Atlantic to Northwest Pacific across North Africa, the Middle East, North India and China. The convergence of the moisture and positive convection anomalies along the region of the trough is perceived from the analysis. In the backdrop of this large-scale circulation anomalies, higher than normal precipitation was received in most of the central and north Indian regions with thunderstorms/hailstorm events. The variations in the AO index (AOI) and EABH were found to be in concurrence with the precipitation anomalies over the Indian region. The detailed analysis of a selected thunderstorm/hailstorm case suggests that the lowering of the 0 °C isotherm due to the intrusion of mid-latitudinal westerlies and the development of atmospheric instability with moisture supply from the adjacent seas facilitated the occurrence of the thunderstorms/Hailstorm events during January 2020.
PubDate: 2023-11-22
- Prediction and forecast of surface wind using ML tree-based algorithms
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Abstract: Abstract This study focuses on the importance of reliable surface wind forecasts for various sectors, particularly energy production. Traditional numerical weather prediction models are facing limitations and increasing complexity, leading to the development of machine learning models as alternatives or supplements. The research consists of two stages. In the first stage, the ERA5 database is used to evaluate the long-term performance of different combinations of features and two tree-based algorithms for predicting surface wind characteristics (speed and direction) in Cairo. The XGBoost algorithm slightly outperforms the Random Forest algorithm, especially when combined with appropriate feature selection. Even three years after the training period, the results remain very good, with an RMSE of 0.59 m/s, rRMSE of 17%, and R2 of 0.84. The second stage assesses the multivariate approach's ability to forecast wind speed evolution at different time horizons (1–12 h) during a week characterized by significant wind dynamics. The forecasts demonstrate excellent agreement with observations at a 1-h time horizon, with an RMSE of 0.35 m/s, rRMSE of 7.6%, and R2 of 0.98, surpassing or comparable to other literature results. However, as the time lag increases, the RMSE (0.86, 1.14, and 1.51 m/s for 3, 6, and 12 h, respectively) and rRMSE (18.7%, 24.8%, and 32.9% for 3, 6, and 12 h, respectively) also increase, while R2 decreases (0.86, 0.79, and 0.60). Furthermore, the wind variations' amplitude is underestimated. To address this bias, a simple correction method is proposed.
PubDate: 2023-11-20
- Role of radiation and canopy model in predicting heat waves using WRF over
the city of Bhubaneswar, Odisha-
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Abstract: Abstract The heat waves (HW) are more frequent with upsurge intensity and spread in the recent warming era over Bhubaneswar, the capital city of Odisha state in India. The city has experienced HW more than four events per year and reported casualties are higher during the recent era as compared to the past century. In addition, the HW caused ecosystem mortality and affected significantly the agriculture and water resource sectors. The city notably grows with urban areas in recent decades, thus, in this study, we explored the potential role of various radiation and urban canopy model schemes with different initial conditions (48, 24, and 12 h lead time) to assess the predictability of HW over Bhubaneswar using the Weather Research and Forecasting (WRF) model. A large number of simulations were carried out with three nested domains at a resolution of 4.5, 1.5, and 0.5 km for the three HW events. The model forecasts have been validated against the Indian Monsoon Data Assimilation and Analysis. The WRF model satisfactorily predicted the spatial distributions and timing of an HW with the Community Atmospheric Model (CAM) radiation and Single-Layer Urban Canopy Model (UCM) urban schemes over the Bhubaneswar urban region 2 days in advance. However, the performance of radiation and urban canopy model schemes varies from event to event. The composite of statistical errors and skill score analysis confirm that the CAM radiation scheme and UCM urban scheme performed well. Overall, CAM and UCM have around 30% and 20% lower percentages of errors, respectively. This study emphasizes the behavior of various radiation and urban canopy model schemes in predicting HW, specifically in the urban agglomeration of Bhubaneswar.
PubDate: 2023-11-10
- Feasibility of forecasting convective rain by diagnosing intracloud
lightning jumps-
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Abstract: Abstract This study conducted a comparison of the data quality of Earth Networks (EN) and Taiwan Power Company’s Total Lightning Detection System (TLDS) and evaluated the feasibility of using intracloud (IC) lightning to issue convective rain warnings. The results indicate uncertainties in the TLDS positioning of IC lightning. When forecasting convective rain on the basis of IC lightning jumps using EN data, the mean prefigurance and postagreement scores were 0.8 and 0.67, respectively, which were more favourable than the respective TLDS scores of 0.65 and 0.47. In regions with high TLDS positioning uncertainties, the use of EN data increased the number of prefigurance and postagreement hits in each analysis zone and raised the prefigurance and postagreement scores to 0.3 and 0.5, respectively. This indicates that analyses using EN data can reduce the risk of missed convective rain warnings when diagnosing IC jumps and can reduce the false alarm rate. In this study, IC jumps preceded convective rains by a maximum of 27.5–39.3 min on average in all analysis zones across Taiwan. The results suggest that diagnosing IC jumps to forecast convective rain is feasible, but until the uncertainties in the positioning of IC lightning using TLDSs have been remedied, EN data are the more suitable diagnostic choice.
PubDate: 2023-11-07
- Variability in episodic precipitation concentration in the Asian megacity
of Dhaka, Bangladesh-
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Abstract: Abstract Changes in episodic and extreme rainfall events are the prime concern for waterlogging issues in major Asian cities such as Dhaka, Bangladesh. The present study analyzed the characteristics of episodic and non-episodic rainfall and their trend over the 1976–2015 period in Dhaka, Bangladesh. The study used the daily rainfall data of the Dhaka meteorological station of Bangladesh to estimate episodic and non-episodic rainfall events, seasonal and annual precipitation concentrations. The Mann-Kendal Test and Sen’s slope were used to calculate rainfall trends over the study period. Results indicate that the monsoon rainfall has increased, whereas the annual rainfall has decreased. Results suggest that seasonal daily average and total rainfall have decreased, except for monsoon, which is insignificant. However, the number of post-monsoon rainfall days is increasing. In addition, the number of episodes and episodic rainfall has increased during the monsoon and post-monsoon, although these are not statistically significant. Episodic rainfall has a strong positive relationship with extreme rainfall events, although the number of extreme rainfall events has decreased. The study noticed substantial irregularities in precipitation concentration during the winter and post-monsoon periods, while the monsoon has an almost uniform precipitation concentration. This research found that episodic rainfall had inter-annual variability before the 2000s, whereas decadal variability was detected in recent decades. This study could help policymakers better understand the characteristics of rainfall patterns and their contribution to waterlogging in similar areas of Bangladesh and elsewhere.
PubDate: 2023-11-03
- Origin and maintenance of upper tropospheric inversion over the northern
Indian Ocean during boreal winter of 2018-
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Abstract: Abstract Radiosonde observations over the Indian Ocean on board ORV Sagar Kanya showed the presence of a sharp thermal inversion layer in the upper troposphere during the onward leg of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) ship cruise in winter 2018 (12° N–2° S, 75° E; 16–24 January 2018). This temperature inversion layer having a thickness of ~ 300 m, referred to as upper tropospheric inversion (UTI) observed near 15 km altitude at 12° N showed a gradual descent towards the equator reaching about 13 km altitude at 2° S. Daily radiosonde observations at a nearby island station Minicoy (8.27° N, 73.05° E) revealed similar UTI structure for about 20 days during the period 5–24 January 2018, indicating that the UTI features observed during the cruise period were temporal in nature. The persistent inversion layer which is situated on the top of a ~ 2 km thick moist layer is characterised by a large vertical gradient in potential temperature, high wind speed, large wind shear and minimum in ozone mixing ratio. The mean magnitude of UTI (~ 1.5 K) and its persistence (life time) is found to be much higher than the temperature inversions reported elsewhere in boreal winter season. Analysis of background meteorological parameters and estimated radiative heating profiles indicates that the presence of the moist layer solemnly could not produce the observed magnitude of thermal inversion. From further analysis, we conjecture that the observed UTI with higher magnitude is a result of the combined influence of radiative cooling due to the tropical moist air and the overlaying warm subtropical air by means of Rossby wave intrusion from the extra-tropics.
PubDate: 2023-11-03
- On the nature of drag coefficient over a tropical coastal station
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Abstract: Abstract The turbulent flow over a coastal region is investigated to study the drag coefficient ( \(C_D\) ) behavior during on-shore and off-shore winds. The analysis of turbulent data over 2 years is carried out to examine the dependence of \(C_D\) on mean wind speed ( \(\overline{U}\) ) and stability parameter ( \(\zeta\) ). The drag coefficient is found to show a parabolic dependence with wind speed for on-shore flows and a slightly linear trend for off-shore flows for neutral and weakly unstable cases. Only for strongly unstable and stable cases ( \(\zeta >0\) ), high values of \(C_D\) are observed for low wind speed ( \(\overline{U}<2\text {ms}^{-1}\) ). The likely cause for high values of \(C_D\) during low wind speed is attributed to an increase in turbulent intensity caused due to the presence of coherent structures. On further analysis of \(C_D\) with \(\zeta\) , it is found that under stable conditions ( \(\zeta >0\) ), \(C_D\) shows a systematic decrease with increasing \(\zeta\) . On the contrary, for unstable cases ( \(\zeta <0\) ), the values of \(C_D\) peaks around \(\zeta \approx -0.13\) , before decreasing with increasing \(-\zeta\) .
PubDate: 2023-10-30
- The impact of carbon dioxide removal on temperature parameters over West
Africa-
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Abstract: Abstract Removal of atmospheric carbon dioxide is being considered a suitable option for reducing the recent global rise in atmospheric temperature. The impact of the removal on some climate parameters—near-surface air temperature (TAS), maximum near-surface air temperature (TASMAX), minimum near-surface air temperature (TASMIN) and surface temperature (TS) over West Africa was assessed in this paper. We used CNRM-ESM1-C1 model simulation output consisting of 1%yr−1 CO2 removal from the atmosphere which was compared with CRU observational dataset. Four climatological periods 1990–2019 (reference period), 2040–2069, 2070–2099 and 2100–2129 were considered, and hence the impacts levels in each of the two West African regions, Sahel and Guinea, were estimated in each period with respect to the reference period. The comparison with CRU demonstrated that CNRM-ESM1-C1 model captured temperature variations within major locations in Mauritania, Mali, Niger, Burkina Faso and Senegal with an indication of an underestimation of temperature at locations above 18° N. The value of each parameter was projected to decrease progressively the periods and much impacts were also projected in the last period for the two regions. Time of retreat to 2 °C reduction target is projected a decade before the year 2100 and will occur earlier with greater impact in the Guinea region than in Sahel region. The root mean square deviation of each ensemble member was found at RMSD < 0.5 with respect to the model ensemble mean per parameter, although RMSD > 0.5 was found with GFDL-ESM4 model for TAS and TS.
PubDate: 2023-10-27
- Evaluation of the FY-3E microwave temperature sounding data assimilation
on forecasting Typhoon Chanthu (2021)-
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Abstract: Abstract Fengyun-3E is the first early-morning-orbit polar-orbiting satellite launched by China, which carries the third generation of Microwave Temperature Sounder (MWTS-3). This instrument has 17 channels and it can provide rich atmospheric temperature observation information at different altitudes. To explore the application value of the MWTS-3 data in assimilation, we selected Typhoon Chanthu in 2021 in this study to evaluate the effect of the MWTS-3 data assimilation on the forecasts of typhoons affecting China. The results show that the simultaneous assimilation of the conventional data and MWTS-3 data can effectively correct the westward error of the typhoon track forecasted by the experiments without assimilation and well predict the track of Typhoon Chanthu along the east coast of China and its stay on the ocean area east of Shanghai. Therefore, the characteristics of the heavy rainfall caused by the typhoon only affecting Shanghai and northeastern Zhejiang are also well reproduced. Compared with the conventional data assimilation, the assimilation of the Fengyun-3E MWTS-3 data provides a more noticeable improvement in the typhoon intensity forecasts, thus allowing better forecasts of the spiral rain belt of the typhoon. The results of the rolling test also proved that MWTS-3 data assimilation has a stable improvement effect on typhoon track forecasts and the forecast skill of precipitation heavier than 5 mm.
PubDate: 2023-10-12
- Long-term spatio-temporal analysis and trends of precipitation over
semi-arid region of Rajasthan-
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Abstract: Abstract Assessing the spatial and temporal variability of climate data is one of the basic requirements for solving water and water management problems. This study performed a comprehensive data quality test, a precipitation concentration index (PCI), Sen’s slope, Mann–Kendall (MK) trend test, and an analysis of the symptoms of drought using rainfall anomaly index (RAI) and standardized precipitation index (SPI). The standard homogeneity test (SNHT), Pettitt test, Buishand range test, and von Neumann scale were used for homogeneity analysis, and most tehsils (administrative boundary) showed the same weather character. PCI annual estimates show high local and temporary variability or irregularity in rainfall distribution. MK tests showed a marked increase in the tendency to high temperatures; however, the trend of annual and extreme rain events was not significant for most of the stations. The extreme dry conditions in 101 years (IMD) were found at Sujangarh. Analysis of size statistics and the trend of rainfall anomaly indices and spatial variability of climate data are important in the integration of water resource planning and management decisions. Rajasthan is an agricultural state in India, the monsoon rainfall largely controls the production of crops, and the proper implementation of regional agro-water management and rainwater harvesting can contribute significantly to agricultural potential. This study paves the way for further exploration of inter-regional hydrological modeling to sustain livelihoods. The mean yearly precipitation has shown a minimal non-significant positive pattern over the dryland ecosystem. Amazingly, 3 year running average has shown a cyclic example of mean yearly precipitation under the changing climatic conditions and in dry and wet conditions at different time scales. The western, northern, and southern parts of the dryland ecosystem have encountered wetter conditions (significant at 95% certainty level), while north-eastern, eastern, and south-eastern regions have seen expanded drier circumstances. Overall, most of the areas are suffering from hyperarid conditions, which needs extreme water management for a below normal-to-normal arid cropping.
PubDate: 2023-09-28
- Trivariate risk analysis of meteorological drought in Iran under climate
change scenarios-
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Abstract: Abstract The aim of this study is to analyze the trivariate risk of meteorological drought using copula functions under climate change scenarios in Iran. For this purpose, SPI-12 is calculated for the historical and future periods and the drought characteristics [severity (S)–duration (D) and magnitude (M)] are extracted and the trend analysis of drought characteristics is performed using Mann–Kendall trend test. Then, trivariate risk analysis of drought variables is performed for historical and future periods. The results of the trend test indicate that the precipitation trend decreased mostly in the northwest and west regions of Iran, while these changes in the future period will be observed in the central regions. According to the results, no significant trend in precipitation and drought characteristics will be observed in the future compared to the historical period. Trivariate risk analysis for the given values of (D = 6, S > 40, M = 2) and (D = 12, S > 40, M = 2) shows that for the given values of severity and duration, increasing duration from D = 6 to D = 12 months, decreases the probability of drought occurrence and return period. Therefore, the conditional risk will increase in Iran under future climate change scenarios.
PubDate: 2023-09-25
- Future photovoltaic solar power resources in Zambia: a CORDEX-CORE
multi-model synthesis-
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Abstract: Abstract The exploration of renewable energy such as wind and solar radiation has the potential of reducing reliance on fossil fuels, thus cutting emissions of carbon dioxide, particulate matter, and several other greenhouse gasses. However, recent findings indicate that wind speed across Zambia is very slow, it is increasing but remains unlikely to support large commercial wind farms. In this study, we explore the future impacts of climate change on solar photovoltaic resources. To do this, we examine the new high-resolution (25 km) Coordinated Regional Climate Downscaling Experiment—CORDEX-CORE simulations for the African domain, using two different emission scenarios until 2100. At an annual scale, results indicate a weak but steady decrease in PVRes of around 0.02 W/m2 per annum under RCP2.6 and about 0.005 W/m2 per annum under RCP8.5. Results further show that at an average of ~ 237 ± 3.3 W/m2 and 212 ± 2.5 W/m2, respectively, RCP2.6 comes along with 12 ± 3% more PVRes than RCP8.5. Thus RCP2.6, a greener and climate-friendly pathway, points towards a higher renewable energy potential across Zambia compared to the business-as-usual pathway.
PubDate: 2023-09-23
- Role of ocean–atmosphere interactions on contrasting characteristics of
two cyclones over the Arabian Sea-
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Abstract: Abstract The role of ocean–atmosphere interaction in modulating the track and intensity of two cyclonic storms, Nisarga and Nanauk, which originated from almost similar locations in June in the Arabian Sea with completely different tracks, is investigated in this study. Sea surface temperature (SST), steering flow, relative vorticity, latent heat flux (LHF), specific humidity, vertical wind shear (VWS), outgoing longwave radiation (OLR), convective available potential energy (CAPE), and Madden–Julian oscillation (MJO) phases are analyzed to elucidate the causes of contrasting characteristics of these two cyclones. During the progression and intensification of the storm Nanauk, SST decreased drastically (magnitude of ~ 4 °C), while VWS anomaly is found to be increased (~ 8 ms−1), followed by entrainment of dry air leading to a decrease in upward LHF anomaly (~ 3.5 to 4 J m−2) hindering further moisture supply. Moreover, just before the storm initiation, the CAPE anomaly was around − 800 to − 1000 J kg–1 and the MJO condition was also unfavorable for the continuous intensification of the cyclone. All these factors contributed to the quick dissipation of cyclone Nanauk. However, high SST (~ 31 °C) along with other favorable atmospheric conditions contrary to cyclone Nanauk provided a conducive environment for Nisarga to intensify and prevail. A high-pressure anticyclonic circulation at the eastern side of Nisarga over Indian land dragged the storm north-eastwards across the Maharashtra coast. The convective phase of MJO (magnitude > 1) along with the strong lower tropospheric westerly wind at the west side of the convective system also helped cyclone Nisarga to propagate eastward.
PubDate: 2023-08-31
DOI: 10.1007/s00703-023-00987-w
- A comparison study between the use of single-point versus areal-mean
rainfall values from a high-resolution model when verified against
satellite retrievals for three typhoons hitting the Philippines-
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Abstract: Abstract In this study, effects of using areal-mean instead of single-point output values from a cloud-resolving model to verify its quantitative precipitation forecasts (QPFs) in terms of the categorical 2 × 2 matrix against satellite rainfall retrievals are assessed for three typhoons that hit the Philippines. The motivation behind this work stemmed from the fact that categorical measures are point-to-point methods but satellite estimates are considered areal-mean values. Overall, we find that using areal-mean values have small but positive impacts on categorical statistics, mainly due to a better overall agreement between satellite-derived rainfall and model outputs after areal averaging with a smoothing effect. These impacts are also statistically significant up to high thresholds of roughly ≥ 350 mm. Using areal means from the model, the threat scores (TSs) improve at low thresholds by about 0.02–0.05, primarily owing to increases in the probability of detection (POD) of observed rainfall events, so the smoothing effect helps convert some misses into hits. In cases with low frequency bias, similar improvements in TSs also occur across middle and even high thresholds (up to 500–750 mm) as both POD and success ratio (SR) rise, with the latter indicative of a lowered false alarm ratio (FAR). Toward the extreme thresholds, results are more mixed and the confidence level of significance drops, but the TSs there are already low (≤ 0.08) against the satellite data regardless of the method adopted.
PubDate: 2023-08-30
DOI: 10.1007/s00703-023-00985-y
- Suitable thermodynamic indices for the prediction of thunderstorm events
for different cities throughout India-
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Abstract: Abstract We have studied the thermodynamic stability indices and their effectiveness in predicting premonsoon thunderstorms for different cities all over India. For that purpose, we have studied 10 thermodynamic stability indices for 24 cities all over India. We have analyzed the upper air radiosonde data at 00 UTC during the premonsoon season of 2016-2018. The mean, standard deviation, and range of variation of the indices have been obtained separately for thundery and nonthundery days. For each of the indices, we have determined the optimum threshold values that give the best prediction skill for each location. Further, we have identified a list of suitable indices that are more effective in predicting thunderstorms for each location. Finally, we have proposed a scheme for premonsoon binary thunderstorm prediction, i.e., whether thunderstorms will occur or not at a particular place, on the basis of optimum consensus among the suitable indices.
PubDate: 2023-08-30
DOI: 10.1007/s00703-023-00984-z
- A simulation study on the recirculation effect of land–sea breeze flows
on atmospheric dispersion of airborne releases in Southeast coast of India
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Abstract: Abstract This study aims to examine the recirculation effect of land and sea breeze flows on atmospheric releases from Chennai and Kalpakkam stations in Southeast coast of India using the WRF and FLEXPART models. High-resolution (2 km) simulations conducted with WRF for 4–6 April 2016 and 13–16 July 2016 showed development of sea breeze circulation under strong land–sea temperature contrast across the coast during daytime. Simulations conducted with FLEXPART in two scenarios of (1) 24 h continuous release, (2) release during sea breeze hours for SO2 from industrial sources at Manali in Chennai and routine low-level Ar-41 from a nuclear power reactor at Kalpakkam stations for 5 April and 14 July indicated considerable differences in SO2/Ar-41 concentrations in the two simulation cases. The simulated plume for 24 h release case showed wide dispersion pattern during flow transition compared to the case in which release is confined to onshore sea breeze hours. The recirculation effect is confirmed from low recirculation factor (0.1–0.3), simulated plume trajectory and particle distributions in the 24 h release case. The simulated SO2 concentrations are about 21 µg/m3 to 2 µg/m3 higher from release location to ~ 20 km in the 24 h release case compared to the release case during sea breeze. Simulated SO2 and Ar-41 concentration/doses at monitor locations during the flow transition period indicated better comparison with monitor data by 24-h release case compared to the release case during sea breeze. Although both simulations underestimated the concentration/dose due to stronger simulated winds, the 24 h release case produced higher concentration/cloud gamma dose by representing the recirculation effect. Overall, simulations suggest that the recirculation effect can lead to increase in the concentration /dose over land by 40% during the wind transition period at the coast.
PubDate: 2023-08-29
DOI: 10.1007/s00703-023-00983-0
- Moisture transport associated with southwest monsoon rainfall over Sri
Lanka in relatively wet and dry rainfall years-
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Abstract: Abstract Atmospheric moisture transport is the most important part of the atmospheric branch of the water cycle, and its anomalies strongly influence rainfall variability. Atmospheric moisture transportation associated with southwest monsoon (SWM) years over Sri Lanka is still not fully understood. Using ERA5 daily data, we investigated the role of moisture transport in relatively wet (SWMWet) and dry (SWMDry) SWM years. Based on composite analysis, seven wet (SWMWet) and nine dry (SWMDry) years were selected from 1985 to 2015. We observe positive (negative) anomalous rainfall in SWMWet (SWMDry) years, while the strong anomalous rainfall is concentrated on the western and southwest parts of Sri Lanka. In SWMWet years, strengthened moisture-laden low-level jets from the Arabian Sea bring excess moisture toward Sri Lanka, while a contrasting pattern is observed in SWMDry years. As a consequence, the climatological mean of net moisture flux (9.46 × 105 kg s−1) over the study domain is increased by 12.37 × 105 kg s−1, resulting in above-average rainfall in SWMWet Years. The results show a decrease in the net moisture flux (5.37 × 105 kg s−1), prescribed below-average rainfall in SWMDry years. The strong relationship (r = 0.63) between net moisture flux and SWM rainfall may explain the observed SWM rainfall variability over the country. Compared to the climatological Vertically Integrated Moisture Flux Convergence (VIMFC, 8.56 × 10−4 kg m−2 s−1), positive anomalous VIMFC (2.63 × 10−4 kg m−2 s−1) in SWMWet years and negative anomalous VIMFC (− 3.70 × 10−5 kg m−2 s−1) in SWMDry years are recorded. These results indicate that the free-tropospheric moisture and moisture flux convergence contributes to strong SWM rainfall by creating environments favorable for producing and maintaining moist absolutely unstable layers. This study helps us understand that the dynamic processes of the atmosphere are more important in regulating the variability of SWM rainfall over the country.
PubDate: 2023-08-28
DOI: 10.1007/s00703-023-00986-x
- Synoptic conditions triggering extreme flood events in Bintan Island in
early January 2021-
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Abstract: Abstract Bintan Island has experienced two consecutive record-breaking rainfall events that took place on 1-2 and 9-10 January 2021, and devastating floods that caused significant losses. This research studied the events to understand the synoptic conditions in which they occurred and to anticipate future incidents. Hourly rainfall data from the Kijang station and Global Satellite Mapping of Precipitation (GSMaP) were used. OLR (outgoing longwave radiation) was also explored as a proxy of convection. Rainfall measurements showed extreme rainfall during both flood events. Anomalies of moisture convergence were observed in the vicinity of Bintan Island during both events. The two extreme rainfall events were the results of interactions among several synoptic phenomena. The first event was associated with strong cold surges and the Borneo Vortex (BV), while the second event involved a moderate cold surge, the Madden-Julian Oscillation (MJO), and the BV. During both extreme rainfall events, the two BV locations were similar and close to Bintan Island, although their initial locations were different. The first BV was formed in the northern South China Sea and then propagated to the equator, due to the southward vorticity advection associated with a strong cold surge, while the second BV stagnated in the west of Borneo. Information on the important factors that triggered extreme events should be useful to manage the coastal environment for future island development.
PubDate: 2023-08-22
DOI: 10.1007/s00703-023-00982-1
- Analysis of the different influence between initial/boundary and physical
perturbation during ensemble forecast of fog-
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Abstract: Abstract To explore the different effects of initial/boundary condition (ICBC) and physical perturbation during fog ensemble forecast, ensemble forecast experiments are done for a heavy fog episode from December 31, 2016 to January 2, 2017. Three ensemble schemes [ICBC, multi-physics (MPY), and a combination of ICBC and MPY (COM)] were compared. Their forecast performances are analyzed in detail and compared with the reference deterministic forecast. The results show that all ensemble schemes, especially the COM, are able to noticeably improve fog prediction. The TS score of ensemble-based fog forecast with 50% probability threshold is higher than that of the control deterministic prediction by ~ 26%. Compared with the ICBC scheme, the MPY scheme can produce a larger ensemble spread and has more skill in fog and the near-surface variables forecast. When ICBC and MPY are combined (the COM scheme), the ensemble spread is enhanced and the prediction performance is also further improved. The sensitivity experiments of different physical parameterization schemes are also analyzed among microphysics, planetary boundary layer, and land surface. The fog forecast is found to be most sensitive to the land surface scheme, followed by planetary boundary layer scheme, and the least sensitive to microphysics.
PubDate: 2023-08-07
DOI: 10.1007/s00703-023-00981-2
- Interactions among Cold Surge, Cross-Equatorial Northerly Surge, and
Borneo Vortex in influencing extreme rainfall during Madden–Julian
oscillation over the Indonesia Maritime Continent-
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Abstract: Abstract The effect of Cold Surge (CS), Cross-Equatorial Northerly Surge (CENS), and Borneo Vortex (BV) on extreme rainfall in the Indonesia Maritime Continent (the IMC) during the wet season (November–March) under active and inactive Madden–Julian Oscillation (MJO) has been evaluated using observational data from 3108 weather stations and gridded GSMaP data. The results showed that the effect of these three phenomena on extreme rainfall in the IMC is significantly modulated by MJO conditions, with the magnitude of the impact varying among regions. The analysis was done by dividing into three groups: single events, double events, and three events. When CS occurs singly, there is an increase in PCE along the CS pathway from the southeastern Philippines when MJO is active and vice versa when MJO is inactive. However, there was an increase in PCE in several other areas in IMC when MJO was inactive. The pattern of PCE increase when CENS is single in active MJO is almost the same as during inactive MJO, namely from Java Island to Nusa Tenggara and along the Indian Ocean in the southern region of Java Island. However, the intensity is higher when the inactive MJO, which suggests that the role of the MJO is to reduce the influence of CENS on extreme rainfall in the area. The effect of BV in the South China Sea on extreme rainfall is higher when inactive MJO than active MJO due to the role of MJO in reducing the frequency of BV events. CS and CENS tend to attenuate their effects on oceanic rainfall extremes mutually. However, they mutually reinforced their influence on the mainland when the inactive MJO. CENS and BV reinforce each other’s influence on each other’s locations when active MJO. However, it’s the other way around when inactive MJO. CS and BV reinforce each other’s influence on extreme rainfall when they occur together, either when the MJO is active or inactive, but CS is more likely to strengthen the development of BV. MJO has the property of weakening the influence of CS + CENS + BV around Java Island and the southern IMC if they occur together.
PubDate: 2023-07-17
DOI: 10.1007/s00703-023-00978-x
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