Southwesterly Winds Research Articles

Abstract The the Indian summer monsoon onset in Kerala (MoK) has large socioeconomic implications for the densely populated Indian subcontinent, yet understanding the associated air–sea interactions remains challenging for the scientific community. In this study, we first show that the preceding El Niño–Southern Oscillation (ENSO) accounts for approximately two-thirds of the interannual variability of the Arabian Sea mini warm pool (MWP), whereas the preceding Indian Ocean dipole (IOD) has minimal influence. Following an El Niño event, a strong anticyclone develops over the northern Arabian Sea from April to June due to the anomalous easterlies that weaken the mean southwesterly winds over the southeastern and central Arabian Sea. It, thus, simultaneously favors the MWP expansion in May and delays the MoK, establishing a positive correlation between the two (a strong MWP being statistically associated with a delayed onset). In contrast, after a La Niña event, the southwesterly monsoon winds remain strong, resulting in a weak or absent MWP. To examine the direct influence of the MWP on the MoK, we have employed a regional coupled atmosphere–ocean numerical model (RCM). The “noMWP” sensitivity experiments suggest that following an El Niño year, as the MWP intensifies, it draws winds toward the Kerala coast, enhancing convective activity and causing an early MoK. Consequently, the MWP helps advance the MoK, mitigating the delay that would otherwise be more pronounced after an El Niño. These findings underscore the importance of improving the observation and simulation of MWP dynamics to enhance monsoon forecasting.

Abstract From April 6 to 9, 2019, during the period between two cold fronts from Asian continent affecting Taiwan, the Pacific high-pressure system extended westward, causing weak southwesterly winds around Taiwan. During that time, PM2.5 event occurred in central Taiwan. We applied the WRF/CMAQ modeling system to explore the PM2.5 event, with a focus on the maximization of local pollution. The Integrated Process Rate (IPR) is employed to explore the contributions of various mechanisms to the PM2.5 concentration. At the north of central Taiwan, the increase in the PM2.5 concentration was caused mainly by horizontal advection (HADV) and to a limited degree by aerosol chemistry (AERO) and vertical diffusion (VDIF). In Taichung City, AERO, VDIF and vertical advection (ZADV) caused the increase in PM2.5 concentration. In the south of central Taiwan, HADV caused the decrease in the PM2.5 concentration. The calculated integrated reaction rate (IRR) indicated that gaseous HNO3 was produced by OH + NO2 during the day, accounting for almost all the HNO3 formed at noon. After sunset, heterogeneous reactions between N2O5 and water vapor dominated. Local pollution accounted for approximately half of the total amount of SO4 2−. The most important way to control local SO4 2− is to reduce the emission of SO2 or H2O2. Organic carbon (OC) reduction depends mainly on controlling OC produced via combustion. Another way is to reduce low-volatility/semivolatile primary organic aerosols (POAs). Additionally, the simulation indicated that the PM2.5 in central Taiwan was acidic, with pH values was below 2 at noon and between 3 and 5 at midnight. Graphical Abstract

Temporal variation of solar radiation with prevailing meteorological parameters focused on a specific location in the south-west Nigeria to provide detailed information required for climate studies and agricultural activities. Hourly and monthly solar radiation trends were analyzed using the variations in the temperature, relative humidity and wind speed from 2010 to 2013. This was with the purpose of determining the correction in the monthly trends of the solar radiation and meteorological parameters in Akure, south-west, Nigeria. Statistical analysis using Open Air project for R-statistics and the multiple linear regression (MLR) were carried out to establish correlation between solar radiation and prevailing meteorological parameters. Solar radiation has more significant impact on other meteorological parameter in the wet season at Akure while it drags other parameters with 1 – 2 months lag in the dry season. In the month August, which was characterized by the peak wet season, the station experiences rainfall break, extremely cloudy overcast and dominance of southwesterly wind. The cloudy atmosphere interrupts the incoming solar radiation with consequent effect of extremely humid and cold air temperature. This was why the low solar radiation aligned with high relative humidity and high wind speed in August while the temperature was the lowest. However, in dry season, the lag was as a result of onset of rainfall characterized by withdrawal of dry and cold northeasterly wind which interfered with response of boundary later to incoming radiation due to irregular heavy rainfall and rapid evaporation at this period. The results clearly aligned with predominant weather patterns in the tropical station influenced by back-and-forth movement of inter-tropical discontinuity during transition from dry to wet season.

Abstract The melting of sea ice in the Arctic has sparked research into how clouds form in exposed ice‐free zones. This study delves into the seasonal distribution of stratocumulus clouds over the Norwegian Sea‐Barents Sea region and presents a conceptual model for the underlying mechanisms. In spring, autumn, and winter, increased surface water vapor flux provides water vapor from the sea surface. Concurrently, warm air enters the area through the southwest wind of the Norwegian Strait. Under conditions of unstable stratification, the water vapor is lifted to the condensation level, promoting the formation of stratocumulus clouds. Conversely, in summer, evaporation is suppressed due to stable stratification, which hinders vertical vapor transport. Enhanced dry advection reduces the transport of water vapor, leading to a decrease in the amount of stratocumulus clouds during summer. This research enriches our understanding of the physical mechanisms influencing cloud formation and cloud‐climate feedbacks in the Arctic region.

Abstract Advances in uncrewed surface vehicles enable expanded observations in the critically undersampled Southern Ocean—a region vital for global heat uptake. Using data from three Saildrone missions that sampled the Pacific sector of the Southern Ocean in both summer and winter, we evaluate processes and spatiotemporal scales of decorrelation that drive sensible heat fluxes. Enhanced heat flux variability is primarily linked to synoptic‐scale southwesterly winds, with decorrelation scales of 50 km and 10 hr, consistent across seasons. These scales are influenced by both atmospheric forcing and oceanic variability, with sharp sea surface temperature changes occasionally driving pronounced shifts in sensible heat flux. Our results extend the observed relationship between wind direction and heat loss across the entire Pacific sector of the Southern Ocean, previously limited to three locations. Our data sets reveal over 8,000 temperature fronts ranging from <1 km to >20 km in width. These fine‐scale ocean processes contribute to the heat flux variability 35% of the time. While wind‐related variability dominates sensible heat flux changes across the smallest fronts, the ocean's role becomes increasingly significant with wider ocean fronts, particularly those over 4 km in width. However, due to their larger abundance, the total change of sensible heat flux over smaller (1 km) fronts is an order of magnitude greater than larger fronts (>4 km). These results highlight the role of fine‐scale atmosphere‐ocean interactions relating to heat flux variability in the Southern Ocean, offering valuable insights for enhancing flux estimates in this critical region.

The precision of ERA5 reanalysis datasets and their applicability in the mountainous regions of central China are essential for weather forecasting and climate change research in the transitional zone between northern and southern China. This study employs three months of continuous measurements collected from a high-precision remote sensing platform located in a representative mountainous valley (Xinyang city) in central China, spanning December 2024 to February 2025. Our findings indicate that both horizontal and vertical wind speeds from the ERA5 dataset exhibit diminishing deviations as altitude increases. Significant biases are observed below 500 m, with horizontal mean wind speed deviations ranging from −4 to −3 m/s and vertical mean wind speed deviations falling between 0.1 and 0.2 m/s. Conversely, minimal biases are noted near the top of the boundary layer. Both ERA5 and observations reveal a dominance of northeasterly and southwesterly winds at near-surface levels, which aligns with the valley orientation. This underscores the substantial impact of heterogeneous mountainous terrain on the low-level dynamic field. At an altitude of 1000 m, both datasets present similar frequency patterns, with peak frequencies of approximately 15%; however, notable discrepancies in peak wind directions are evident (north–northeast for observations and north–northwest for ERA5). In contrast to dynamic variables, ERA5 temperature deviations are centered around 0 K within the lower layers (0–500 m) but show a slight increase, varying from around 0 K to 6.8 K, indicating an upward trend in deviation with altitude. Similarly, relative humidity (RH) demonstrates an increasing bias with altitude, although its representation of moisture variability remains insufficient. During a typical cold event, substantial deviations in multiple ERA5 variables highlight the needs for further improvements. The integration of machine learning techniques and mathematical correction algorithms is strongly recommended as a means to enhance the accuracy of ERA5 data under such extreme conditions. These findings contribute to a deeper understanding of the use of ERA5 datasets in the mountainous areas of central China and offer reliable scientific references for weather forecasting and climate modelings in these areas.

Identifying hidden heavy metal sources in atmospheric dust of mining cities by integrating Cd isotopes and multivariate statistical method.

The Songnen Plain is a key region for Quaternary stratigraphic research in Northeast China. In this area, the Quaternary strata of the Bayan borehole reached a thickness of 58.00 m, offering excellent potential for investigation and research. A comprehensive analysis of the borehole was conducted using lithological characteristics, optically stimulated luminescence (OSL), electron spin resonance (ESR), magnetic susceptibility, grain-size distribution, and magnetostratigraphy. Based on these results, a polarity stratigraphic framework was established, subdividing the sequence into four units: the Holocene Series (0–1.50 m), Guxiangtun Formation (1.50–18.80 m), Harbin Formation (18.80–35.50 m), and Huangshan Formation (35.50–58.00 m). Chronostratigraphic and paleoenvironmental interpretations were derived to establish a Quaternary stratigraphic framework for the eastern Songnen Plain. Grain-size end-member analysis was applied to the Bayan borehole using the Analysize method to extract three effective grain-size components. EM1 (6.72 μm) corresponded to the atmospheric background dust; EM2 (21.20 μm) reflected the input from distal dust sources associated with southwesterly wind signals; and EM3 (45.60 μm) indicated the proximal deposition influenced by winter monsoon intensity. Comparative analysis of magnetic susceptibility (MS), mean grain size (Mz), grain-size end-members (EM), and marine isotope stages revealed strong correlations, identifying multiple climate response events. In the eastern Songnen Plain, the Middle Pleistocene was marked by a transition from dry-cold to cool-moist conditions, with a boundary at approximately 250 ka. During the Late Pleistocene, the region experienced alternating phases of dry-cold and cool-semi-humid conditions. The Holocene was characterized by a warm and semi-humid climate. These findings provide a robust data foundation for refining the Quaternary stratigraphy of the Songnen Plain and offer critical insights into its formation history, stratigraphic evolution, and paleoclimatic development.

Abstract Summer extreme rainfall frequently occurs in the Dabie Mountain (DM). The combined effects of synoptic patterns and local topography on the spatiotemporal variations of extreme rainfall in the summers from 2008 to 2020 have been investigated using an objective classification method. Results show that extreme rainfall in the DM mainly occurs under two typical synoptic patterns (P1 and P2). In the lower troposphere, the P1 type is characterized by southwesterly (easterly) winds south (north) to the DM, while the P2 type features southwesterly winds over the DM. These differences arise from the varying position of the Meiyu front. Under both types, extreme rainfall intensity reaches its diurnal maximum at around 09:00 local solar time (LST) because the low‐level southwesterly ageostrophic wind peaks in the early morning induced by inertial oscillation. The southwesterly ageostrophic winds bring abundant water vapor into the DM, resulting in the extreme rainfall along the windward slope. Extreme rainfall intensity decreases rapidly after 09:00 LST under the P2 type but sustains its maximum level for several hours under the P1 type. Two factors contribute to the prolonged high extreme rainfall intensity under the P1 type. One is the convergence between southwesterly and northeasterly ageostrophic flows over the DM. The other is the strengthening of the low‐level vortice over the DM from late morning to early afternoon. Overall, the synoptic patterns influence extreme rainfall by regulating the low‐level ageostrophic winds and the interactions between multi‐scale systems and the DM.

Few studies have investigated the potential drivers of high-resolution (daily and 24-hour scales) on ocean acidification (OA) and the carbonate system in a coastal estuary during an intense La Niña event. Therefore, we conducted the first high-resolution total scale pH (pHT) monitoring every three hours for 56 days (13 September to 7 November 2021) at the Colombian Pacific in El Muelle reef, Gorgona National Natural Park. Two moored autonomous submersible instruments (iSAMI-pH and CTD-Diver) were deployed at a depth of 2 m in an area influenced by extreme precipitation, river discharge, semi-diurnal tides, and southwest winds during La Niña 2020-2023. Total alkalinity was derived from salinity data and used alongside pHT to calculate sea surface seawater partial pressure of CO2 (pCO2w; μatm), dissolved inorganic carbon (DIC; μmol kg-1), and omega aragonite saturation (Ωa). The findings suggest that the observed low pH (7.93) and aragonite saturation state (Ωa = 2.22) values are likely attributed to increased precipitation. This enhanced precipitation resulted in higher river discharge, transporting naturally low-pH water to the island via mixing mechanisms (RiOMar type 2). Daily, decreasing solar radiation may reduce the seawater temperature, simultaneously elevating the pCO2w levels and reducing pHT. In contrast, elevated precipitation may reduce surface seawater salinity through freshwater dilution. Throughout the diurnal cycle, peak pHT values were recorded during late afternoon hours, likely driven by photosynthetic activity, while minimum values coincided with early morning periods of maximal respiratory activity. These results underscore the dynamic nature of this area and emphasize the need for long-term evaluation.

The Beibu Gulf’s ocean circulation system regulates regional marine ecosystems, sediment transport, and coastal geomorphology while also supporting vital economic activities. This study integrates one-year current observations from four in-situ current observation stations (B1−B4) with simulations using the Regional Ocean Modeling System (ROMS) to characterize circulation dynamics in the gulf. Observations show persistent northward subtidal currents west of Hainan Island year-round, primarily sustained by tidal-induced residual currents. These currents briefly reverse southward during strong northerly wind events, whereas subtidal currents in the northern Beibu Gulf are more wind-dependent, showing pronounced seasonal variations. Numerical results confirm that winter circulation is dominated by a basin-wide cyclonic gyre driven by northeasterly monsoons. In summer, circulation in the northern gulf is cyclonic under southeasterly winds, but turns anticyclonic when southwesterly winds prevail, indicating strong sensitivity to summer monsoon wind direction. By combining multi-station observations and numerical simulations, this study provides a systematic characterization of the seasonal circulation of the oceanic system in the Beibu Gulf, offering new insights into its dynamic mechanisms.

Wildland fires are a common and destructive natural disaster in Alaska. Recent active fires in Alaska were assessed and analysed for their associated synoptic-scale climatic conditions in this study. Hotspot (HS) data from satellite observations over the past 20 years since 2004 (total number of HS = 300,988) were used to identify active fire-periods, and the occurrence of Rossby wave breaking (RWB) was examined using various weather maps. Analysis results show that there are 13 active fire-periods of which 7 active fire-periods are related to RWB. The total number of HSs during the seven RWB-related fire-periods was 164,422, indicating that about half (54.6%) of the recent fires in Alaska occurred under fire weather conditions related to RWB. During the RWB-related fire-periods, two hotspot peaks with different wind directions occurred. At the first hotspot peak, southwesterly wind blew from high-pressure systems in the Gulf of Alaska. In the second hotspot peak, the Beaufort Sea High (BSH) supplied strong easterly wind into Interior Alaska. It was suggested that changes in wind direction during active fire-period and continuously blowing winds from BSH may affect fire propagation. It is hoped that this study will stimulate further research into active fires related to RWBs in Alaska.

In this paper, based on all the data from September 2021 to June 2024 collected by a 30 m meteorological tower and a differential image motion monitor (DIMM) at the Muztagh-Ata site located on the Pamir Plateau in western Xinjiang, China, we study the characteristics of the surface temperature inversion and its effect on astronomical seeing at the site. The results show the following: The temperature inversion at the Muztagh-Ata site is highly pronounced at night; it is typically distributed below a height of about 18 m; it weakens and disappears gradually after sunrise, while it forms gradually after sunset and remains stable during the night; and it is weaker in spring and summer but stronger in autumn and winter. Correlation studies with meteorological parameters show the following: increases in both cloud coverage and humidity weaken temperature inversion; the distribution of inversion with wind speed exhibits a bimodal distribution; southwesterly winds prevail at a frequency of 73.76% and are typically accompanied by strong temperature inversions. Finally, by statistical patterns, we found that strong temperature inversion at the Muztagh-Ata site usually bring better seeing by suppressing atmospheric optical turbulence.

In this work, we describe the inter-annual variability of the Barents Sea branch water (BSBW), which is one of the main branches of the Atlantic water that flows from the North Atlantic to the Western Arctic. We analyze an extensive data set of in situ data measurements performed during warm season from 1977 to 2024 in the northeastern part of the Barents Sea and in the St. Anna Trough. This region has experienced rapid climate change during recent decades, expressed by the decrease of sea ice and increasing heat inflow from the North Atlantic. Previously, BSBW effectively cooled in the Barents Sea and had a consistently negative temperature at its eastern boundary. However, significant warming was detected in the northeast part of the Barents Sea after 2000. We demonstrate that temperature of BSBW in the northeastern part of the Barents Sea and further in the St. Anna Trough largely increased during the last 20 years. In particular, BSBW with positive temperatures has been regularly observed in the St. Anna Trough since 2008. We reveal a link between the initial temperature of the Atlantic water masses at the western boundary of the Barents Sea on the one hand and BSBW temperature at the eastern boundary of the Barents Sea on the other hand. In addition, the temperature increase of BSBW is associated with (1) strengthening of local southwesterly winds, leading to decrease of ocean-atmosphere heat loss and (2) decreased intensity of cold dense water formation at the shallow banks of the Barents Sea. Finally, we confirm the results of previous model studies, which demonstrated the shift of the cooling zone from the Barents Sea to the St. Anna Trough. In particular, we show that during the recent years cooling of BSBW continues in the St. Anna Trough by mixing with cold dense water. The observed warming of BSBW accompanied by its salinity decrease, which is observed during the last 15 years, could significantly affect thermohaline structure and circulation in the Arctic Ocean.

Abstract Cold filaments (CFs) in the southwestern South China Sea (SCS), extend eastwards from the Vietnamese coast during summer and autumn, significantly influence hydrodynamic and ecological distributions in the region. By integrating multi‐source observations and reanalysis data from 2000 to 2023 (including sea surface temperature, sea level anomalies, surface currents, and wind fields), this study proposes an objective method for identifying CF areas and intensity using sea surface isotherms. Based on the changes of CFs, the impact of typhoons passing through the northern SCS on southwestern CFs is investigated. Statistical results revealed that 66 typhoons over the past 24 years have exerted enhanced effects on CFs. These findings demonstrate that typhoons traversing the northern SCS can enhance the CFs located over 10 latitudes south of the typhoon tracks. This indicates that typhoons not only directly affect oceanic dynamic processes along their paths but also exert significant remote influences on coastal dynamics in other regions. The mechanism analysis shows that typhoons primarily enhance the CFs through two pathways: (a) Intensifying southwest winds over Vietnam's eastern coast, thereby increasing the wind stress curl and triggering stronger‐than‐climatological upwelling that brings deep cold water to the surface; (b) altering the dipole distribution pattern in the southwestern SCS through enhanced southwesterly winds, which strengthen cold eddies and intensify offshore currents, transporting more coastal cold water to the open sea. These combined effects ultimately amplify the intensity of the CFs and expand their coverage.

Abstract Long‐term changes of extreme precipitation have been a big concern in various regions. Previous studies are mostly concerned with trends of seasonal frequency and intensity of extreme precipitation and interpret those trends based on long‐term changes in seasonal mean moisture. Present study analyzes trends of extreme precipitation frequency in sub‐periods of the rainy season (June and July) in central eastern China and roles of atmospheric circulation changes. It is found that the trends of extreme precipitation frequency have prominent subseasonal changes in central eastern China. The frequency of extreme precipitation displays an increasing trend in early June and early and middle July, but a decreasing trend in middle and late June and late July. The trends of extreme precipitation frequency are attributed to those of corresponding atmospheric circulation patterns in sub‐periods of the rainy season. Increasing (decreasing) trends of extreme precipitation frequency are associated with increasing (decreasing) lower‐level southwesterly winds over southeastern China, westward extending (eastward retreating) western North Pacific subtropical high and strengthening (weakening) East Asian trough. The mean atmospheric circulation trends play a role in the subseasonal changes in the trends of extreme precipitation frequency in central eastern China. The change in the mean moisture availability cannot explain subseasonal changes in the trends of extreme precipitation frequency. Present study suggests the necessity of analyzing extreme precipitation trends and roles of atmospheric circulation trends during sub‐periods of seasons.

In the context of high anthropogenic pressure and eutrophication of the waters in the southeastern Baltic Sea, it is important to monitor the plume of highly productive waters from the Kaliningrad Lagoon through the Baltic Strait. Seasonal and interannual variability in plume propagation was estimated using satellite data from January 2020 to October 2024, and was then compared with expeditionary salinity measurements. The plume area was largest during the flood period (February–March) and the summer period (June–July), when strong winds contributing to plume dissipation were absent. Analysis of wind conditions and plume movement direction showed that, in most cases, the plume propagates along the coast to the northeast towards Cape Taran, predominantly in response to southwest and southeast winds. In autumn, dominant westerly winds press the plume to the coast. The hydrophysical structure of the plume corroborates the findings derived from satellite data.

Abstract The space‐time variations of thermo‐hydrodynamics and underlying mechanisms in Lake Nam Co, the third largest lake over Tibetan Plateau, are investigated using the simulations from a three‐dimensional lake‐ice coupled model during 2007–2017. The model well reproduces the seasonal lake thermodynamics, highlighting the phases of summer‐autumn warm thermal stratification, late‐autumn overturning, winter‐spring inverse thermal stratification, and late‐spring overturning. Heat budget analysis underscores the importance of lateral heat transport and ice freeze‐thaw processes in shaping the horizontal thermal variability. During 2007–2017, lake surface temperature, as well as the duration, onset and end of warm thermal stratification, show significant interannual variations related to the surface air temperature and ice conditions. During winter‐spring, the lake water flow speed shows strong interannual variability related to wind speed and ice conditions. Nevertheless, a consistent circulation pattern is found, featuring a dominant mid‐lake cyclonic gyre, upwelling along the western coast, and strong coastal currents driven by the prevailing southwesterly winds during December–January, followed by weakened lake water motions during February–April when the packed ice inhibits the wind stress input. In contrast, the summer‐autumn lake circulation is weaker but more variable, with the mid‐lake circulation shifting between being cyclonic (caused by the combined effects of southwesterly winds, positive wind stress curl and density effects) and occasionally anti‐cyclonic (due to the presence of negative wind stress curl).

Abstract Extreme precipitation events (EPEs) without severe convective weather signatures such as frequent lightning may be more difficult to forecast and potentially more dangerous. This study investigates the differences in the macro‐ and micro‐structures between EPEs with and without lightning over eastern and southern China, as well as their underlying environmental conditions. EPEs are defined as convective features with maximum hourly rain rate reaching the gauge‐based climatological extreme precipitation threshold (99.9%). Results show that EPEs with lightning (EPE_LIG) account for 51%, and the other 49% EPEs have no lightning (EPE_NoLIG), whose fractional maxima are located along the coast. Most EPE_NoLIGs are embedded in large organized precipitation systems, although their convective cores are smaller than EPE_LIGs. The parent systems of both EPE types are multicellular in nature, but those of EPE_NoLIGs are more likely to produce multiple extreme precipitation centers. EPE_LIGs have the most intense convection, which is stronger than regular thunderstorms (NonEPEs with lightning), while the convective intensity of EPE_NoLIGs is just close to NonEPEs. Microphysical processes of the two types of EPEs differ significantly. The downward increasing radar reflectivity profiles and drop size distribution analyses suggest that warm‐rain processes highly dominate (94.1%) in the formation of extreme precipitation in EPE_NoLIGs. Even for EPEs with very active ice‐based processes (EPE_LIGs), warm‐rain processes still contribute significantly (83.31%). The large‐scale environments of EPE_NoLIGs are featured by a relatively convectively stable but deep moist troposphere and enhanced low‐level southwesterly winds, highlighting the importance of excessive moisture transport and convergence in these events.

The South Asian Summer Monsoon is a vital part of the broader Asian monsoon system, heavily influencing atmospheric circulation, regional climate, and water resources across South Asia. Nepal, located on the southern slopes of the Himalayas, receives approximately 80% of its annual rainfall during the summer monsoon (June-September), which significantly impacts agriculture, water availability, and disaster risks. This study focuses on analyzing the diurnal variation, spatial distribution, and intensity of extreme precipitation events in Nepal during the 2022 monsoon season. Using hourly precipitation data from 63 meteorological stations across Nepal, the study investigates rainfall patterns from June to September 2022. The monsoon season of 2022 began earlier than usual on June 5th, extending for 134 days, the longest on record in Nepal. Despite its extended duration, the total rainfall was not significantly higher than average, with western Nepal experiencing below-normal precipitation and eastern regions receiving slightly above-normal rainfall. The analysis of spatial variation revealed considerable disparities in rainfall distribution, with the Lumle area recording the highest precipitation (3133 mm) and several western districts observing minimal rainfall. Diurnal analysis highlighted a consistent pattern of nighttime precipitation dominance, with the highest rainfall occurring around 9 PM and the lowest around 6 AM. Approximately 60% of the total monsoon rainfall occurred during nighttime hours. This diurnal cycle was consistent across Nepal’s major regions, suggesting large-scale atmospheric influences like monsoon troughs and southwesterly winds. The study also assessed extreme precipitation events, defined as rainfall exceeding 40 mm/h. These events were widespread across Nepal, with central and eastern regions experiencing a higher frequency of extreme rainfall compared to western areas. The findings emphasize significant spatial variability in precipitation intensity and duration, critical for understanding regional monsoon dynamics and improving disaster preparedness.