Wind Circulation Research Articles

Intraseasonal Variability and Physical Characteristics of the Break and Active Phases of the Mainland Indochina Southwest Monsoon

ABSTRACTThe term ‘break’ is traditionally meant only for dry spells occurring after monsoon onset in the region. Simply put, the daily rainfall of the monsoon pauses across the region for a few days, which is called a ‘break spell’, and the revised pattern is called ‘active’. Researchers have suggested that standardised anomalies of three consecutive days of rainfall prevail when categorising active and break spells. This study examined break spells and active spells at interannual, intraseasonal, and decadal scales by examining the frequency and spatial distribution of three consecutive days of rainfall occurrences of different intensities linked to break and active events over the mainland Indochina region. The difference in the surface‐to‐upper wind circulation between active spells with excessive moist convection and intense break events with less rainfall was explained by various atmospheric parameters. During active phases, the easterly jet migrated south, while subtropical westerly entered lower latitudes during the break. During break spellings, the upper and lower troposphere jet winds will be weaker and dislocated over the study area but stronger during active time. La Niña encourages more break days than active days and distinguishing between vertical meridional circulation and intense break events with a heat trough‐type circulation and active spells with moist convection is crucial for developing suitable prediction tools.

The Distinct Spatial Patterns and Physical Mechanisms of Coastal Boundary Layer Jets over the Northern South China Sea

Abstract Two distinct spatial patterns of coastal boundary layer jets in the northern South China Sea (CBLJ-NSCS) in June 2015–22 are investigated using hourly output data from the Weather Research and Forecasting Model with a horizontal grid spacing of 9 km and ERA5 data. Spatial pattern 1 shows a high-incidence core on the east side of Hainan Island, while pattern 2 features dual high-incidence cores covering both the east side of Hainan Island and the waters south of Guangdong, with the latter being stronger and more extensive. Unique diurnal cycles have been observed in different high-incidence cores of CBLJ-NSCS: the western core, on the east side of Hainan Island, peaks at night and shows a secondary afternoon subpeak, while the eastern core, located south of Guangdong, reaches its maximum intensity at night with a morning subpeak. Inertial oscillations triggered by large-scale perturbation wind circulation and momentum propagation from upstream Indochina Peninsula CBLJs explain the nocturnal enhancement of both cores. The thermal effect exerted by Hainan Island largely contributes to the afternoon enhancement in the western core. The formation of the morning subpeak of the eastern core results from strong convergence and lifting in the northeast region of it. When upstream CBLJs along the Annamite Range intensify, more momentum is propagated to the eastern core instead of the western one due to wind field changes, which promotes the transition from spatial pattern 1 to pattern 2. Significance Statement Two spatial patterns of coastal boundary layer jets in the northern South China Sea have been identified. Spatial pattern 1 shows a high-incidence core on the east side of Hainan Island, while pattern 2 features dual high-incidence cores covering both the east side of Hainan Island and the waters south of Guangdong. The transition between these two spatial patterns is related to low-level westerly winds along the coast of the Annamite Range. This study has uncovered the novel spatial pattern of coastal boundary layer jets in the northern South China Sea and provides new insights into precipitation research in southern China, considering the substantial influence of these jets on coastal weather.

Surface temperature modulations induced by Rossby Wave Breaking over Indian region

Abstract Upper-level Rossby Wave Breaking (RWB) significantly affects surface weather patterns in the subtropical Indian region through influencing wind circulation often resulting in extremes in rainfall and surface temperatures. While the impact of RWB on rainfall is relatively well understood, its role in modulating surface temperatures within the Indian subcontinent is less explored. This study examines the link between pre-monsoon (March to May) RWB events and the occurrence of extreme surface temperatures and heatwaves by considering long-term data of 43 years between 1979 and 2021. We identify 139 RWB events using a potential vorticity (PV) contour searching algorithm over the Indian sub-continent. Our analysis reveals a significant amplification in temperature both to the west and east of the breaking PV streamers. These temperature anomalies, which last for 3–4 days during the breaking events, strongly correlate with the maximum day of breaking. Further, regression analyses explain the reasons behind the temperature enhancement mainly on the western and eastern flank of RWB. It indicates a positive association between upper-level PV anomalies and anticyclonic circulations at 250 hPa, along with subsidence at 500 hPa, leading to drier conditions in the western and eastern regions of the PV streamers. Additionally, the decomposition of temperature anomalies during RWB events reveals that surface warming is primarily driven by diabatic heating on both sides of the centroid, with stronger adiabatic heating in regions of upper-level anticyclonic circulation and significant temperature advection predominantly on the western side of the centroid, resulting in dry weather and the poleward movement of warm air toward the ridges near the PV streamers.

Are Atmospheric Models Too Cold in the Mountains? The State of Science and Insights from the SAIL Field Campaign

Abstract Mountains play an outsized role in water resource availability, and the amount and timing of water they provide depend strongly on temperature. To that end, we ask the question: How well are atmospheric models capturing mountain temperatures? We synthesize results showing that high-resolution, regionally relevant climate models produce 2-m air temperature (T2m) measurements colder than what is observed (a “cold bias”), particularly in snow-covered midlatitude mountain ranges during winter. We find common cold biases in 44 studies across global mountain ranges, including single-model and multimodel ensembles. We explore the factors driving these biases and examine the physical mechanisms, data limitations, and observational uncertainties behind T2m. Our analysis suggests that the biases are genuine and not due to observation sparsity or resolution mismatches. Cold biases occur primarily on mountain peaks and ridges, whereas valleys are often warm biased. Our literature review suggests that increasing model resolution does not clearly mitigate the bias. By analyzing data from the Surface Atmosphere Integrated Field Laboratory (SAIL) field campaign in the Colorado Rocky Mountains, we test various hypotheses related to cold biases and find that local wind circulations, longwave (LW) radiation, and surface-layer parameterizations contribute to the T2m biases in this particular location. We conclude by emphasizing the value of coordinated model evaluation and development efforts in heavily instrumented mountain locations for addressing the root cause(s) of T2m biases and improving predictive understanding of mountain climates.

Asian summer monsoon responses under RCP4.5 and RCP8.5 scenarios in CESM large ensemble simulations

The response of the Asian Summer Monsoon (ASM) circulation to the Representative Concentration Pathway 4.5 and 8.5 (RCP4.5 and RCP8.5) forcing scenarios is examined using the CESM1 state-of-the-art global circulation model from 2021 to 2050. The projections show that monsoon precipitation will increase over East Asia, the North Pacific Ocean, the Indian Peninsula, and the Bay of Bengal under the RCP4.5 scenario. Conversely, the South Indian Ocean, West Asia, the Middle East, and the Central Pacific Ocean exhibit a decreasing trend in precipitation. Under the RCP8.5 scenario, precipitation is projected to increase over a wider swath of the Indian Ocean and the Middle East Asia. In the RCP4.5 scenario, the low-level wind circulation is likely to strengthen over the entire northern Indian Ocean, extending to the South China Sea, thereby increasing moisture transport from the Indian Ocean to peninsular India and the South China Sea. Conversely, in the RCP8.5 scenario, easterly winds strengthen over the South Indian Ocean, leading to an increase in moisture transport from the equatorial West Pacific Ocean to the Indian Ocean. A weak (strong) cyclonic circulation in response to the east-centered (west-centered) low sea level pressure trend over the North Pacific in RCP4.5 (RCP8.5) scenario is projected to help maintaining a strong (weak) ASM circulation from the India to east Asia. Internal climate variability is also calculated, revealing that the North Pacific Ocean near the Bering Sea is likely to play a dominating role and contribute significantly to the future ASM dynamics. In both scenarios, internal variability is found to substantially contribute to changes in monsoon circulation over the Indian Ocean.

Computational aspects of calculating vertical velocity in a wind circulation model

Computational aspects of calculating vertical velocity in a wind circulation model

Decadal preference of seasonal ENSO transition through a southern hemisphere climate mode

El Niño Southern Oscillation (ENSO) is the leading interannual coupled climate mode in the tropical Pacific. The seasonal transition of ENSO from boreal winter to the following summer can significantly affect the global climate. One of the major hurdles in understanding the seasonal transition of ENSO is the spring predictability barrier. Here, we show that ENSO’s seasonal transition is modulated by a multidecadal climate mode of boreal spring sea-level pressure (SLP) in the extratropical Southern Hemisphere. This ENSO transition mode (ETM), when characterised by a decrease in SLP and associated clockwise circulation of the surface winds centred over the southeastern subtropical Pacific Ocean, produces westerly anomalies at the equator. These wind anomalies in the equatorial eastern Pacific aid the seasonal warming of Niño3.4 sea surface temperature anomalies (N34SST) from boreal winter to the following summer. The ETM time series shows prominent multidecadal variations at around 50 years. This creates a conducive environment for alternate cold and warm seasonal transitions leading to multidecadal variations in boreal summer N34SST. Thus, ETM provides a physical insight into the seasonal transition of ENSO and leads to a new paradigm for ENSO evolution beyond its peak. This has implications for seasonal ENSO forecasts and decadal climate predictions.

Investigating Wind Characteristics and Temporal Variations in the Lower Troposphere over the Northeastern Qinghai–Tibet Plateau Using a Doppler LiDAR

Knowledge of wind field characteristics and variation principles in complex topographical regions is of great importance for the development of numerical prediction models, aviation safety support, and wind energy utilization. However, there has been limited research focused on the lower-tropospheric wind fields in the Qinghai-Tibet Plateau. This paper aims to study the wind characteristics, vertical distributions, and temporal variations in the northeast of the plateau by analyzing a four-year continuous dataset collected from a Doppler wind LiDAR deployed in Xining, Qinghai Province of China. The results indicate that the prevailing horizontal wind direction in the low levels is primarily influenced by the mountain-valley wind circulation. However, as the altitude increases, the prevailing winds are predominantly affected by the westerlies. From a diurnal perspective, noticeable transition processes between up-valley and down-valley winds can be observed. The west-northwest wind (down-valley wind) dominates from late night to morning, while the east-southeast wind (up-valley wind) prevails from afternoon to early evening. The vertical winds in the low levels exhibit a downward motion during the daytime and an upward motion during the nighttime. In this plateau valley, the wind shear exponent is found to be highest in spring and lowest in winter, and it is generally lower during the daytime compared to the nighttime.

Formation mechanism and development potential of wind energy resources on the Tibetan plateau

It is important to understand whether the wind energy resources on the Tibetan Plateau have power potential suitable for development. To this end, we conducted sodar wind measurement experiments in areas of typical terrain, analyzed radiosonde and surface meteorological observations, and performed mesoscale numerical model simulations to study the characteristics and formation mechanisms, and to assess the technical potential, of the wind energy resources on the Tibetan Plateau. Results showed that the wind energy resources on the Tibetan Plateau are very abundant and of high quality with enormous development potential. The total technical potential of the wind energy resources at 100-m height above ground level is 1.02 billion kW, accounting for 26 % of the total technical potential of China's wind energy resources. The technical potential of the wind energy resources at very rich and rich levels accounts for 63 % of the total. The strengthening effect of the superposition of valley wind circulations and the synoptic-scale background wind field is the fundamental formation mechanism of the abundant wind energy resources on the Tibetan Plateau.

Statistical downscaling of GCMs wind speed data for trend analysis of future scenarios: a case study in the Lombardy region

Near-surface wind speed is a key climatic variable, affecting many sectors, such as energy production, air pollution, and natural hazard. Lombardy region of Italy is among the European areas with lowest average wind speed, leading generally to low air quality and wind energy potential. However, it is also one of the most affected area by tornadoes in Italy. Here we investigate possible changes in wind circulation as due to prospective global warming. We analysed wind speed WS under future scenarios (SSP1-2.6 and SSP5-8.5) from six Global Climate Models (GCMs) until 2100, tuned against observed WS data. We employed a statistical downscaling method, namely Stochastic Time Random Cascade (STRC) to correct locally GCMs outputs. Three statistical tests, i.e. Linear Regression, Mann Kendall, Moving Window Average, were carried out to analyse future trends of: annual WS averages, 95th quantile (as an indicator of large WS), and the number of days of calm wind per year (NWC). The proposed STRC algorithm can successfully adjust the mean, standard deviation, and autocorrelation structure of the GCM outputs. No strong trends are found for the future. The chosen variables would all display non-stationarity, and the 95th percentile display a positive trend for most of the stations. Concerning NWC, notable discrepancies among GCMs are seen. The STRC algorithm can be used to successfully adjust GCMs outputs to reflect locally observed data and to then generate credible long-term scenarios for WSs as a tool for decision-making.

Temperature Inversion and Particulate Matter Concentration in the Low Troposphere of Cergy-Pontoise (Parisian Region)

This study aims to elucidate the influence of meteorological conditions on particle levels in Cergy-Pontoise. It explores the temporal variability of PM10 pollution days by associating them with the vertical temperature profile derived from conventional radiosondes from 2013 to 2022 (regional station). The results indicate that nearly 80% of exceedance days were associated with thermal inversions, primarily observed in winter and typically lasting 1 to 3 days. Analysis of winter thermal inversion characteristics suggests that those linked to pollution primarily occur near the ground, with higher intensity in December (12.1 °C) and lower in February (10.3 °C). Persistent inversions (extended nocturnal by diurnal inversion) account for 91.4% of the total inversions associated with high concentrations. Captive balloon soundings and temperature measurements at different altitudes were conducted during the winter of 2022/2023 to clarify thermal inversion in the Oise Valley at the center of Cergy-Pontoise. The results highlight three nocturnal wind circulation mechanisms in the valley, including downslope flow, circulation influenced by an urban heat island, and mechanical air evacuation under an inversion layer towards the less steep East side of the valley. Analysis of PM with the temperature gradient in the Oise Valley shows a significant correlation, suggesting an increase in concentrations during locally detected inversions and a decrease during atmospheric disturbance.

Numerical investigation of thermal patterns and local wind circulations to characterize Urban Heat Island during a heatwave in Turin

Heatwaves are annually increasing in terms of intensity and frequency. In urban areas, the impact could be further exacerbated by the Urban Heat Island (UHI) effect. This work carries out an urban microclimate numerical analysis to evaluate the behavior of the UHI in the city of Turin (Italy) during a heatwave event. Turin is located in the North-West region of Italy, boarded by the Alps mountain ranges in the west and hills in the East. The study utilizes the WRF/MLUCM model and considers the heatwave period in June 2019. The high-resolution urban land use/land cover data is generated from local climate zone (LCZ) generator tool provided by the World Urban Database and Access Portal Tools (WUDAPT) portal. The simulation is validated with the data provided by ARPA (Regional Environmental Protection Agency) meteorological stations located over the region. The lower root mean squared error of air temperature and higher index of the agreement show that the simulation is in good agreement with the observational data. The simulation results are then used to analyze the rural-urban temperature distributions over the diurnal cycle and local wind circulations. According to the simulated results, the city of Turin has higher near-surface UHI intensity during the night and early morning (with maximum intensity greater than 5 °C), whereas the intensity is diminishing during the mid-day hours. The simulated wind patterns show a significant reduction in wind intensity over the urban areas. This reveals the potential of creating wind ventilation inside the city to minimize UHI effect and enhance air quality. Ultimately, this research contributes valuable insights into addressing the challenges posed by heatwaves and urban heat islands in Turin and offers a foundation for the development of sustainable urban climate strategies.

Modern‐Type Eolian Regime and Global Cooling‐Modulated Dust Provenance in the Late Paleogene of Central‐East Asia

AbstractAtmospheric mineral dust is a poorly constrained yet extremely important component of the climate system. Provenance studies from geologic dust archives are crucial to understand the drivers of the dust cycle over long time scales. Our multi‐technique provenance analysis of a rare Paleogene (35–27 Ma) eolian dust sequence from Ulantatal, ∼400 km northwest of the Chinese Loess Plateau (CLP), shows that Paleogene dust transporting winds generally varied between northwesterly and westerly, the same as those in the late Neogene‐Quaternary bipolar icehouse. We propose that, as today, westerly wind circulation patterns would have been modulated by an Arctic Oscillation (AO)‐like situation, and that the warm Eocene favored a long‐term negative phase of AO, leading to meridional westerly circulation and the dominance of a northwesterly dust transport pathway. After the Eocene‐Oligocene transition (EOT), long‐term positive phase of AO‐like conditions initiated, leading to stronger and more zonal westerlies. The Siberian High (SH) also formed or strengthened at the EOT and started to control dust storm activity along the northwesterly transport pathway. We argue that increased Paleogene Northern Hemisphere (NH) ice volume was the ultimate driver of this modern‐type dust transport regime in the Ulantatal region, possibly also controlling initial Ulantatal dust sequence formation via the development of the SH and modern‐type eolian regime. The similarity between the Ulantatal and late Neogene northern CLP dust provenance signals suggests that the increased NH ice volume, via its control on the northwesterly dust transport, could have promoted increased loess formation also in the late Miocene.

Intensity duration and frequency of Heat wave in different phases of MJO over India

The Madden-Julian Oscillation (MJO) is an important tropical atmospheric phenomenon that plays a significant role in modulating weather patterns across India. Heat Waves (HW) are extreme weather events that have severe impacts on human health, agriculture, and various socio-economic sectors. This research paper aims to investigate the dynamical relationship between MJO phases, as measured by the Real-time Multivariate MJO (RMM) index, and the occurrence of HW in India, as defined by the Indian Meteorological Department. This paper demonstrated the relationship among three aspects, i.e., intensity, duration, frequency of HW during the different MJO phases. The differential dynamics associated for about two-fold rise in the HW occurrence in the South East, Eastern and North West India in the MJO active phase. Inactive phase witnessed enhancement (suppression) of HW during wet (dry) over the regions. The novel finding of this paper is that, the weaker the MJO, the higher probability of HW occurrence in respective regions depending on the position of the MJO convection center. The maximum duration is observed to be significantly decreased by about 2 days in the active MJO phase over NW and north central parts of the country. It is also inferred from this study that there is a significantly decrease of 0.5 °C in HW intensity during the active wet phase of MJO over the NW India. To explain the linkage of HW with MJO, geopotential height (GPH), wind circulation, velocity potential (VP), sea surface temperature (SST) and outgoing longwave radiation (OLR) composite anomalies have been computed and used in the analysis. It is observed that all these parameters have a direct impact on the evolution, strength and spread of the HW in India. This dynamical study mechanism can be prescribed in the numerical weather prediction models for the improved prediction of such extreme weather events during summer for proactive disaster management.

Effects of urbanization and topography on thermal comfort during a heat wave event: A case study of Fuzhou, China

Urbanization intensifies urban heat and compromises thermal comfort. However, few studies have examined the interactions of Urban Heat Island (UHI) between neighboring cities and the impacts of expanding satellite towns on central urban areas (CUA). We conducted a series of WRF/BEP-BEM simulations during a summer heat wave in Fuzhou, China, to understand how extensive urbanization and complex topography affect thermal comfort. Control runs reveal an intense UHI centered on Fuzhou’s CUA. Comparisons with scenarios where urban land use and terrain are altered demonstrate that urbanization degrades thermal comfort citywide by elevating heat stress while valley-basin topography worsens midday heat but alleviates nighttime humidity. The urban heat island circulation above the CUA suppresses the valley wind circulation and prevents the sea breeze front from advancing inland in the afternoon. Notably, CUA urbanization enhances sea breezes in a satellite town, inducing afternoon “cool islands”. Interactions between CUA and satellite towns appear minimized, with urbanization impacts confined locally. Future expansion according to the “Fuzhou 2035” Master Plan shows negligible effects on thermal comfort in CUA. Our findings enhance understanding of intra-urban UHI dynamics in complex terrains. The outcomes directly inform urban planning and climate adaptation strategies to promote Fuzhou’s livability and resilience.

Fine particulate matter (PM2.5) exposure assessment among active daily commuters to induce behaviour change to reduce air pollution

Fine particulate matter (PM2.5), a detrimental urban air pollutant primarily emitted by traffic and biomass burning, poses disproportionately significant health risks at relatively limited exposure during commuting. Previous studies have mainly focused on fixed locations when assessing PM2.5 exposure, while neglecting pedestrians and cyclists, who often experience higher pollution levels. In response, this research aimed to independently validate the effectiveness of bicycle-mounted low-cost sensors (LCS) adopted by citizens, evaluate temporal and spatial PM2.5 exposure, and assess associated health risks in Ljubljana, Slovenia. The LCS quality assurance results, verified by co-location field tests by air quality monitoring stations (AQMS), showed comparable outcomes with an average percentage difference of 21.29 %, attributed to humidity-induced nucleation effects. The colder months exhibited the highest air pollution levels (μ = 32.31 μg/m3) due to frequent thermal inversions and weak wind circulation, hindering vertical air mixing and the adequate dispersion of pollutants. Additionally, PM2.5 levels in all sampling periods were lowest in the afternoon (μ = 12.09 μg/m3) and highest during the night (μ = 61.00 μg/m3) when the planetary boundary layer thins, leading to the trapping of pollutants near the surface, thus significantly affecting diurnal and seasonal patterns. Analysis of exposure factors revealed that cyclists were approximately three times more exposed than pedestrians. However, the toxicological risk assessment indicated a minimal potential risk of PM2.5 exposure. The collaborative integration of data from official AQMS and LCS can enhance evidence-based policy-making processes and facilitates the realignment of effective regulatory frameworks to reduce urban air pollution.

Analysis of methods for assimilating fire perimeters into a coupled fire-atmosphere model

Correctly initializing the fire within coupled fire-atmosphere models is critical for producing accurate forecasts of meteorology near the fire, as well as the fire growth, and plume evolution. Improperly initializing the fire in a coupled fire-atmosphere model can introduce forecast errors that can impact wind circulations surrounding the fire and updrafts along the fire front. A well-constructed fire initialization process must be integrated within coupled fire-atmosphere models to ensure that the atmospheric component of the model does not become numerically unstable due to excessive heat fluxes released during the ignition, and that realistic fire-induced atmospheric circulations are established at the model initialization time. The primary objective of this study is to establish an effective fire initialization method in a coupled fire-atmosphere model, based on the analysis of the impact of the initialization procedure on the model’s ability to resolve fire-atmosphere circulations and fire growth. Here, we test three different fire initialization approaches leveraging the FireFlux II experimental fire, which provides a comprehensive suite of observations of the pyroconvective column, local micrometeorology, and fire characteristics. The two most effective fire initialization methods identified using the FireFlux II case study are then tested on the 380,000-acre Creek Fire, which burned across the central Sierra Nevada mountains during the 2020 Western U.S. wildfire season. For this case study, simulated pyroconvection and fire progression are evaluated using plume top height observations from MISR and airborne fire perimeter data, to assess the effectiveness of different initialization methods in the context of establishing pyroconvection and resolving the fire growth. The analyses of both the experimental fire simulation and the wildfire simulation indicate that the spin-up initialization method based on historical fire progression that masks out inactive fire regions provides the best results in terms of resolving the fire-induced vertical circulation and fire progression.

Significant increase in humidity since 2003 in Qinghai Province, China: evidence from annual and seasonal precipitation.

Recently, extreme climate events have become more frequent under global warming, resulting in increasingly severe disaster losses. Essentially, the variability in precipitation is more uncertain compared to temperature. In this study, monthly precipitation data from 30 stations in Qinghai Province from 1960 to 2020 were selected to investigate the spatial-temporal variations in precipitation via linear tendency estimation, variability, cumulative anomaly, Mann-Kendall test, and spatial interpolation methods. The conclusions are as follows. (1) The annual and four seasons' average precipitation in Qinghai Province showed an increasing trend over the last 61 years, and the enhancement of summer and spring average precipitation contributed more to the annual. (2) There are increasing trends from northwest to southeast in the annual and seasonal mean precipitation, whose distributions are jointly controlled by the East Asian summer monsoon (EASM), the westerlies, and geomorphological features. (3) It is reasonable to conclude that the annual and four seasons' average precipitation has increased significantly since 2003 by integrating the results of variability, cumulative anomaly, and Mann-Kendall test. In other words, the significant intensification of humidity in Qinghai since 2003 is closely related to the ongoing intensification of the EASM and the westerly wind circulation, with the latter contributing considerably. These findings confirm the view of warming and humidification in northwest China and provide a reliable time point for discussing warming and humidification in northwest China.

Role of local absorbing aerosols in modulating Indian summer monsoon rainfall

Absorbing aerosols and their impact on the Indian monsoon system is highly complex and demands more scientific understanding. Our study using a chemistry-coupled regional climate model (RegCM 4.5) with idealized experiments observed that natural and anthropogenic absorbing aerosols (i.e., dust and carbonaceous aerosols) reduce monsoon precipitation in a seasonal time scale. More than 1 mm day−1 decline in mean summertime rainfall was observed over parts of the central Indian region and Indo-Gangetic plane for dust aerosol. A substantial reduction in the land-sea pressure gradient and lower tropospheric moisture distribution were found to control the observed modulation in rainfall. Near-surface wind circulation responded distinctly to natural (dust) and anthropogenic (carbonaceous) aerosols. The dust forcing weakened the monsoon trough by creating an anomalous anticyclonic circulation. The Northern Arabian Sea acted as a moisture source for the carbonaceous aerosol forcing. Intraseasonal rainfall over central India appeared to have a sharp reduction for dust forcing during early June, with a moderate increase for carbonaceous aerosols. Such quantification is essential for understanding the impact of aerosol forcing on regional climate change and the water cycle and has implications for emissions management and mitigation policies.

Role of updraft in dry‐season torrential rainfall in Greater Jakarta, Indonesia

AbstractCoastal urban areas in tropical regions, such as Greater Jakarta (GJ) in Indonesia, are susceptible to flood hazards from torrential rainfall. Efforts to understand the convective mechanisms leading to this type of rainfall have been carried out extensively, especially for events occurring in the wet season. However, hydrometeorological risks persist even in the dry season, when the rainfall is more closely correlated with the diurnal wind circulation. Among the aspects of convective activities and this diurnal circulation, the details of the updraft remain the least studied and open for discussion. We investigate the role of the updraft in urban torrential rainfall over GJ, using data from a C‐band Doppler radar and reanalysis dataset during the dry season of 2018–2019. Employing back‐trajectory calculations, we locate updraft origins corresponding to the peak of daytime inland rainfall. Most updraft origins are localized at an NW–SE‐oriented front nearly parallel to the coastline on the low‐lying plain, suggesting a region of atmospheric destabilization favorable for convective activity. The dry‐season torrential rainfall over GJ may involve convective activity from this front, that from earlier updrafts originating above the densely populated area, and further enhancement coming from orographic contributions. Our findings suggest the important role of updrafts in the rainfall generation, providing insights into the convective mechanism over GJ.