Abstract Thermal remote sensing is a valuable tool for assessing Surface Urban Heat Islands (SUHI). To quantify the SUHI intensity, the Urban Thermal Field Variance Index (UTFVI) is increasingly used as a proxy for urban heat distribution, e.g., by public authorities in Germany. The UTFVI is an ordinal-scaled metric that shows the spatial variability of LST in relation to the average LST of an area of interest. Numerous scientific studies utilize the UTFVI for detecting spatiotemporal increases in SUHI intensities attributed to Land Use/Land Cover (LULC) changes, such as rapid urbanization. However, UTFVI analyses often rely on only a few time steps over extended periods, ignoring the effects of weather patterns on actual UTFVI distributions. To address this research gap, this study investigates the influence of weather conditions of varying durations (up to 21 days) on seasonal UTFVI distributions in four Hessian municipalities (Germany) with less than 300,000 inhabitants and only minor LULC changes in the urban area over time. The analysis is based on more than 100 Landsat 4–9 Level‑2 datasets spanning a 40-year period. To reduce rural influences, only urban areas are considered. Results reveal high seasonal and intra-seasonal variability in UTFVI. Statistical tests (Friedman and Wilcoxon) show significant differences of UTFVI distributions even within one summer (2023). Spearman’s rank correlation coefficients indicate that spatial patterns of the UTFVI are influenced by the temperature intensity of preceding weather phases: short-term warming leads to an increase of the UTFVI categories indicating high LST levels, while they are less frequent during prolonged warmth. The presented study provides for the first time a comprehensive analysis of long-term UTFVI developments that focusses on factors altering the UTFVI which have not been investigated so far. These new insights support a better understanding and a more distinct interpretation of the UTFVI for potential users.

Abstract This study investigates large-scale circulation patterns associated with the characteristics and origins of intraseasonal precipitation variability in Northeast China (NEC) during the dry-to-wet transitional season (April–June) over 1979–2022. Spectral analysis shows that the 10–30-day period dominates the intraseasonal precipitation variability in NEC and explains 58.29% of total precipitation variability. Two distinct circulation patterns (CP1 and CP2) associated with 10–30-day precipitation variability are identified based on self-organizing map clustering analysis. CP1 is associated with a meridional dipole pattern that propagates southeastward, affecting precipitation extending from NEC to southern China. CP2 is characterized by a zonal dipole pattern that propagates eastward, impacting precipitation mainly over NEC. Further, the moisture budget diagnosis for the preconditioning period shows that moisture increases associated with the two CPs are mainly due to the interaction between the background westerly flow and the 10–30-day moisture anomalies. Additionally, the 10–30-day vertical advection of background moisture by the intraseasonal upward motion plays a dominant role in maintaining precipitation. Tracking the origins of the CPs shows that CP1 is influenced by wave trains from the central North Atlantic and the Barents Sea, and CP2 is linked to the wave trains from the Baffin Island–Iceland–western Europe region. Both CPs’ upstream wave trains lead the initial phase of intraseasonal precipitation events by 2 weeks, providing predictive signals for intraseasonal precipitation in NEC.

Our planet is warming rapidly, accompanied by an increase in the frequency and intensity of marine heatwaves (MHWs). Beyond their impacts on marine ecosystems, MHWs can also modulate regional climate systems, including the Asian monsoon. Here, we investigate the variability, drivers, and monsoon impacts of MHWs in the North Indian Ocean using detrended sea surface temperature anomalies over the period 1982–2024. An Empirical Orthogonal Function (EOF) analysis of MHW intensity identifies two leading modes of variability. The first mode (PC1), explaining 22% of the variance, is characterized by basin-wide MHWs with enhanced intensity in the Arabian Sea and is associated with weakened monsoon winds, reduced evaporation and cloud cover, and enhanced shortwave radiation, leading to upper-ocean warming. The second mode (PC2), accounting for 8% of the variance, exhibits a dipole structure, with intensified MHWs in the Bay of Bengal and suppressed activity in the Arabian Sea during its positive phase, and the opposite pattern during its negative phase. Large-scale climate modes modulate these patterns. Basin-wide MHWs resembling PC1 are usually associated with the mature phase of El Niño, coinciding with the transition from active to break phases of the Monsoon Intraseasonal Oscillation (MISO). Under similar MISO conditions, La Niña tends to favor PC2 + -type warming. These modes are accompanied by distinct rainfall responses: PC1 and PC2 + are linked to wetter conditions over southern India and drier conditions in the north, whereas PC2 − corresponds to more widespread dryness. The termination of MHWs is associated with the re-intensification of monsoon winds, which both suppresses further ocean warming and enhances rainfall through increased evaporation and moisture transport. Together, these results point to a potential interaction between MHWs, monsoon intraseasonal variability, and ENSO and suggest that certain climate conditions may favor the transition of MISO-related ocean warming into marine heatwaves, with implications for monsoon predictability in a warming climate.

Abstract During July and August, a secondary westerly jet exists near 70°N, collocated with a thermally direct circulation. This thermally driven jet is accompanied by intraseasonal variability of zonal-mean zonal wind 5°-10° north of its core, which exceeds that of the winter midlatitude jet. This Arctic jet variability is driven first by eddy momentum flux in the upper troposphere, followed by poleward heat flux near the surface. This sequence is opposite to that of the canonical baroclinic lifecycle. During its westerly phase, this eddy-driven jet peaks at 76°N, and the climatological thermally driven jet disappears altogether. This transient jet is referred to here as the Arctic eddy-driven jet (AEJ). In this study, the dynamics of this AEJ is explored using observational analysis. At the initial stage of development, the zonal mean flow satisfies the Rayleigh-Kuo criterion for barotropic instability. The region of negative potential vorticity (PV) gradient is located at the local jet minimum, centered at ~60°N, between the midlatitude jet and the climatological thermally driven jet. Consistently, across the region of the negative PV gradient and the positive PV gradient to its north, the eddies tilt against the meridional shear of the zonal wind. This eddy tilt drives the AEJ. Once the AEJ is established, anomalously positive poleward heat fluxes emerge in the low troposphere. A thermodynamic energy budget analysis reveals that the overturning circulation induced by the initial momentum forcing contributes to the formation of subsequent heat flux anomalies. The easterly phase follows a similar sequence with opposite signs but, during its development, lacks the signatures of barotropic instability.

• Persistent southwestward current extends 750 km along northern South China Sea continental slope in summer. • The southwestward slope current appears locally generated and maintained in geostrophic balance. • Two underlying dynamic mechanisms contribute to this current: mesoscale Kuroshio eddies and wind stress curl. The summertime slope current in the northern South China Sea (SCS) constitutes a dynamically distinctive yet inadequately understood component of the regional circulation system. This study synthesizes extensive in-situ hydrographic measurements, multi-year mooring current records, satellite altimetry products, surface drifter trajectories, and numerical model outputs to provide a comprehensive physical description of the slope current and to investigate its underlying dynamical forcing mechanisms. Observations reveal a persistent southwestward flow along the continental slope isobaths at depths between approximately 200 and 2000 m, spanning approximately 750 km from the Dongsha Plateau to the southeastern waters off Hainan Island. The current is roughly 100 km wide, reaches depths of at least 500 m, and exhibits maximum mean along-slope velocities exceeding 10 cm/s, with substantial synoptic to intraseasonal variability. Dynamically, the current appears locally generated and sustained, governed by a cross-slope pressure gradient in geostrophic balance. This pressure structure is associated with a pronounced, elongated ridge in absolute dynamic topography aligned with the outer shelf and upper slope. The ridge is likely maintained by warm, saline water mass, sourced from mesoscale Kuroshio eddies. Although positive wind stress curl over the northern SCS favors a basin-scale cyclonic circulation, with the southwestward slope current forming its northern limb. Yet mooring observations show the current emerges prior to the onset of dominant wind forcing. This temporal mismatch suggests that wind stress curl alone cannot sustain its persistence. We therefore identify two underlying dynamical drivers contributing to this flow: mesoscale Kuroshio eddies and wind stress curl. Given its documented geographic extent and distinct dynamics, we propose redesignating this historically localized “Dongsha Current” as the “Yue-Qiong Slope Current”, a name that accurately reflects its full pathway along the continental slope regions off Guangdong (Yue) and Hainan (Qiong).

Intraseasonal variation of sea surface temperature and its primary mechanism in Bohai Sea

Tropical Instability Waves (TIWs) dominate intraseasonal variability in the tropical Pacific Ocean, strongly impacting climate variability and marine ecosystems. However, their response to greenhouse warming remains uncertain because most current climate models cannot resolve them well. Using a suite of high-resolution climate model simulations capable of representing TIWs, we identify two consistent and distinct mechanisms driving the response of TIWs to CO2 increases. North of the equator, TIW activity intensifies under higher CO2 due to enhanced meridional shear of the prevailing zonal currents during boreal fall. Along the equator, TIW activity weakens and shifts slightly westward, driven by a reduced meridional temperature gradient and shoaling of the Equatorial Undercurrent. These changes result in a robust decrease in TIW-driven temperature variability and associated eddy dynamical heating along the equator, underscoring their importance for constraining both the magnitude and spatial pattern of future tropical Pacific warming.

Abstract The response of the Australian Summer Monsoon (AUSM) onset to global warming remains a critical and unresolved question. Here, using Coupled Model Intercomparison Project Phase 6 (CMIP6) multi‐model simulations under the SSP5‐8.5 scenario, we project a robust earlier onset by about 5 days by the late 21st century. Unlike traditional explanations that invoke mean‐state sea surface temperature changes, our results highlight the important role of the Madden–Julian Oscillation (MJO). Because the AUSM onset is typically preceded by the first austral‐spring MJO event entering the Australian sector, an earlier monsoon onset under warming is closely linked to the earlier arrival of this event. This shift is likely associated with a projected acceleration of the MJO's eastward propagation. These findings underscore the influence of intraseasonal variability on future regional climate changes and provide new insight into monsoon predictability under global warming.

In the context of global warming, abrupt transitions between extreme temperature states (extreme temperature variability events) pose severe threats to both ecosystems and socioeconomic systems. However, previous studies have primarily focused on the regulatory effects of atmospheric intraseasonal oscillation (ISO) on extreme temperatures from the perspective of a single scale, leaving the synergistic driving mechanisms of multi-scale ISO on extreme temperature variability poorly understood. This study investigates the synergistic influence mechanisms of 10–30-day and 30–60-day ISO on extreme temperature variability events in eastern China. Utilizing ERA5 reanalysis data from 1979 to 2024, the record-breaking extreme winter of 2023–2024 is employed as a representative case study to systematically elucidate these mechanisms. The results indicate that the winter of 2023–2024 was marked by a record-high surface air temperature variance, accompanied by two prominent extreme temperature variation processes. Wavelet and empirical orthogonal function (EOF) analyses reveal that both ISOs were anomalously strong during this winter and exhibited significant positive correlations with temperature variance, with the 10–30-day ISO playing a more dominant role. Phase evolution analysis demonstrates that phase-locking between the leading 10–30-day modes precedes extreme temperature events by approximately 5 days, whereas the 30–60-day ISO modulates the monthly-scale persistent warm or cold backgrounds. Dynamic diagnosis shows that the ISO-related wave activity flux drives the evolution of key circulation systems, such as the Ural blocking high and the East Asian trough, thereby governing the abrupt temperature reversals. Thermodynamic budget analysis highlights the dominant role of diabatic heating, particularly in the northern key region, where its 10–30-day component is crucial for rapid temperature reversals. Critically, a synergistic effect significantly amplifies the intensity and frequency of extreme temperature variations when both ISOs are in positive phases concurrently. This study advances the understanding of the multi-scale dynamical mechanisms underlying extreme temperature variability and provides a scientific foundation for the extended-range forecasting of such events. Moreover, the findings offer critical insights for enhancing regional climate resilience and informing risk mitigation strategies for major urban clusters in eastern China.

Abstract In summer 2022, the Yangtze–Huaihe River Basin (YHRB) experienced an extreme drought accompanied by persistent heatwaves. Previous studies have highlighted the influence of the Western Pacific subtropical high (WPSH). However, a similarly strong and westward‐extended WPSH also occurred in summer 2020, when the YHRB instead received excessive rainfall, implying that the WPSH anomaly alone cannot explain the 2022 precipitation deficit and heat extremes. We show that the 2022 drought was more directly linked to a robust mid‐to‐upper‐tropospheric continental anticyclone (heat dome) that exhibited pronounced intraseasonal variability yet persisted for nearly a month in August. Using the Multiscale Window Transform (MWT) and localized multiscale energetics diagnostics, we find that the heat dome was primarily maintained by enhanced Tibetan Plateau (TP) thermal forcing. The in‐phase relationship between intraseasonal temperature and meridional wind anomalies, acting on an intensified background temperature gradient associated with TP heating, favored baroclinic instability and enabled efficient transfer of available potential energy from the background (>64 days) to the intraseasonal window (16–64 days). The resulting barotropic high caused a severe precipitation deficit over the YHRB throughout August, intensifying the 2022 summer drought. Further analysis shows that spring–summer TP mid‐tropospheric temperature is strongly correlated with YHRB heatwave variability, and a linear baroclinic model reproduces the observed heat‐dome response to TP thermal forcing. Overall, our results highlight the critical role of TP thermal conditions in shaping YHRB drought and heatwave extremes.

ABSTRACT Sunshine duration (SDU) is a fundamental climatological variable with broad applications in agriculture, energy, health and tourism. However, despite its importance, Brazil lacks comprehensive country‐scale assessments, mainly due to deficiencies in the irregular and sparse in situ observation network. To overcome these limitations, this study employed the high‐resolution satellite‐based CMSAF SARAH‐3.0 SDU dataset for the 1983–2020 period, enabling a spatially consistent evaluation across Brazil. The analysis combined regional and gridded climatologies, Empirical Orthogonal Function (EOF) decomposition and robust trend assessment. Climatological results reveal strong regional contrasts: the Northeast records the highest and most regular SDU, while the South exhibits the lowest values. The largest (smallest) seasonal amplitude occurs in the North (Southeast). Also, the Central‐West exhibits a marked monsoonal cycle. EOF analysis identifies three leading modes of variability, associated with the South American Monsoon System, the Atlantic Intertropical Convergence Zone and a regional mode linked to intraseasonal variability over southeastern Brazil, the La Plata Basin and the adjacent South Atlantic. Long‐term analyses indicate generalised increases in SDU, with statistically significant positive trends in the Central‐West and Northeast, while the North and South display weaker and spatially heterogeneous tendencies. These findings fill a critical gap in Brazil's SDU climatology and underscore the need for continued monitoring to better understand the mechanisms driving observed changes and their implications for climate‐sensitive sectors.

Abstract Understanding changes in intraseasonal rainfall variability is critical for improving sub-seasonal prediction. While the amplification of intraseasonal rainfall variability across Australia has been reported, the spatial heterogeneity of this intensification has been overlooked. Here, we observe that the intraseasonal rainfall variability has been intensified, particularly over northeastern Australia during the wet season (November–April) over the past four decades. The intensified intraseasonal rainfall variability is primarily attributed to enhanced intensity of precipitation events, rather than drier spells. Moisture budget analysis indicates that the intensification of intraseasonal abnormal rainfall events over northeastern Australia is primarily due to the strengthened vertical advection of background moisture caused by the intraseasonal vertical motion anomalies. In this process, the strengthening of intraseasonal vertical velocity driven by changes in intraseasonal wind convergence plays a dominant role, accounting for over 90%, whereas the effect of background moisture changes is relatively less significant. Our findings highlight northeastern Australia as a hotspot for amplified intraseasonal rainfall variability, rather than the whole of Australia. This study provides fundamental insights into northern Australia’s changing climate, and highlights the important role of intraseasonal circulation on northeastern Australia rainfall variability.

Long-term Atlantic Ocean and Gulf Stream (GS) variability were linked in past studies to coastal sea level (CSL) change along the U.S. East Coast – a weakening GS can lead to rise in CSL and increased coastal flooding. However, high frequency variability (HFV) in CSL is, in most cases, attributed to atmospheric weather events. This study is focused on HFV (intraseasonal variations with periods between ~ 1 week and ~ 2 months) in the GS and in CSL. First, wavelet and spectral analysis of observations of the Florida Current transport and CSL characterized the HFV in the data, and then idealized numerical simulations were conducted to study the response of CSL to imposed GS variations with known frequencies. Three experiments were conducted: a control run with constant surface and boundary forcing, and two experiments with imposed oscillations in the Florida Current transport into the model domain- a “high-frequency experiment” (HFE) and a “low-frequency experiment” (LFE), where the period of the GS oscillations were ~ 1–2 weeks and ~ 1–2 months, respectively. The observations and the model show statistically significant anticorrelation between the GS flow and the CSL, but the LFE resulted in higher GS-CSL correlations and was more like the observations than the HFE was. The results also show large spatial differences in the CSL response to GS variations - the South-Atlantic Bight (SAB) responded more strongly to the LFE while the Mid-Atlantic Bight (MAB) responded more strongly to the HFE. Power spectra of the model simulations show that even small, imposed GS oscillations at high frequency, can interact with natural variability to excite unpredictable CSL variabilities over a wide range of frequencies, including oscillations at much longer time scales than the forcing. The variability in the Florida Current flow generated a northward propagating signal along the GS path and a southward propagating sea level signal along the coast. However, the topography near Cape Hatteras seems to partly block communication between the MAB and the SAB. The study demonstrates the important contribution of high frequency GS variability to CSL variability - better understanding of the role of remote forcing on coastal sea level can help to improve prediction of coastal sea level variations and associated flooding.

Robust Increase in Indian Summer Monsoon Intraseasonal Variability in a Warmer Climate

Year-round variations of contaminants of emerging concern (CECs, also known as emerging contaminants) were examined in river water, dam water, and treated municipal wastewater in the South African setting. UPLC-MS/MS identified CECs belonging to different categories such as pesticides, licit and illicit recreational drugs, and particularly pharmaceuticals. Concentrations of up to 6 µg/L were identified but greatly varied spatially and temporally. Treated municipal wastewater was a harbinger for CECs (e.g., 6,055 ± 434 ng/L for efavirenz an HIV drug), while high CECs concentrations were also observed in river water (e.g., 3,228 ± 114 ng/L for acetaminophen). The high concentration for antiretroviral medication reflects the HIV/AIDS crisis in Sub-Saharan Africa and likely medicine misuse for illicit drug (whoonga/nyaope) manufacturing. Large intra-seasonal and intra-annual (seasonal) variations were observed (e.g., caffeine in dam water ranged from 73 ± 6 ng/L to 1,492 ± 30 ng/L), with overall high intra-seasonal and intra-annual variations (coefficient of variations up to 1.08 and 1.52, respectively) being observed. Individual risk quotients of up to 30 suggested high ecotoxicological risk potential. CECs pollution is apparent in South Africa, and likely across Sub-Saharan Africa and the Global South where similar problems persist, suggesting the need for effective wastewater treatment and policy intervention to curb CECs releases in freshwater.

Abstract. During the southwest monsoon, seasonal storms bring torrential rainfall to the South Asian subcontinent and the northern Indian Ocean. Dense cloud cover limits the amount of sunlight that reaches the ocean surface, and sediment-laden river runoff limits the depths to which light can penetrate. Changing light availability should affect phytoplankton primary productivity and its dependent biogeochemical processes, yet little is known about how subtropical weather is linked to ecosystem processes below the ocean’s surface. Here, using novel physical and bio-optical measurements from an array of free-drifting, autonomous systems in the Bay of Bengal, we show that the onset of cloudy conditions associated with “active” monsoon conditions led to >50 % reduction in gross chlorophyll productivity (GCP) near the subsurface chlorophyll maximum (SCM) relative to sunny “break” conditions. Optical backscatter measurements confirm chlorophyll fluorescence fluctuations correspond to biomass variability of a similar scale. Simultaneous bioacoustic measurements collected onboard the autonomous platforms suggest this intraseasonal variability in SCM chlorophyll and biomass generated a response in higher trophic levels. Long-term measurements from biogeochemical (BGC) Argo floats in the bay confirm the presence of intraseasonal oscillations in chlorophyll a concentration with days-to-weeks variability in magnitude similar to the regional annual cycle in the region. Our findings demonstrate that intraseasonal subtropical air-sea variability modulates important regional biogeochemical ocean processes in the Northern Indian Ocean with implications for the Indian Ocean carbon cycle.

Abstract The northward propagation of the Monsoon Intraseasonal Oscillations (MISOs) in the Bay of Bengal (BoB) is an intrinsic characteristic of the Indian summer monsoon (ISM). Previous studies have demonstrated the critical role of air‐sea interactions in modulating MISO propagation. This study elucidates the intraseasonal variability of ocean heat content (OHC) in the upper 200 m of the BoB and its dynamic relationship with MISO. Similar to sea surface temperature (SST), the positive OHC anomalies lead MISO's northward propagation, showing two prominent maxima located east of Sri Lanka and in the northwestern BoB. The OHC anomalies are stronger east of Sri Lanka, penetrating the thick barrier layer during MISO events, whereas temperature anomalies in the northwestern BoB remain confined to the mixed layer. Diagnostic analyses reveal that the intraseasonal OHC variability, unlike that of SST, stems from intensified downward vertical advection driven by intraseasonal vertical velocity. In contrast to the wind‐dominated intraseasonal vertical velocity in NBOX, the pronounced intraseasonal OHC variability east of Sri Lanka stems from sea level anomaly generated by both westward‐propagating Rossby waves and MISO‐related winds. Subsequently, with the arrival of MISO, upward vertical advection and thick barrier layer prolong warm SST anomalies east of Sri Lanka, providing additional heat and moisture to enhance MISO convection and rainfall intensity. These results highlight the essential role of the memory effect of upper ocean heat exchange and redistribution processes in sustaining MISO propagation.

The present study determines pecan tree transpiration using the sap flow technique in a microirrigated pecan orchard. It documents for the first time the contribution of pecan tree transpiration to the orchard’s water use in the hot and humid climate of Georgia. The tree transpiration is derived from sap flow data on a daily basis and calibrated against tree transpiration using a combination of eddy-covariance and microlysimeter measurements. Results show that trees consumed 46% to 84% of the monthly water use of the orchard during the June–October period. The pattern of intraseasonal variation of pecan transpiration is associated with the influence of weather conditions, especially the vapor pressure deficit. The present study suggests that high pecan transpiration took place from June through August (nut sizing and early kernel filling stages) with peak values reaching ∼4.5 mm/day in the first half of July (mid nut sizing). The transpiration decreased in September during late kernel filling and post-kernel filling. The results also suggest that the crop coefficient increased throughout the growing season, possibly reflecting the influence of crop load: the relative evaporative demand becomes higher with crop load development. This information represents a step forward in understanding how pecan trees use water in the humid southeastern United States.

Salinity is an emerging constraint for Mediterranean coastal agriculture, where shallow groundwater, seawater intrusion, and summer evapo-concentration generate relevant intra-seasonal variability in soil electrical conductivity. Camelina [Camelina sativa (L.) Crantz] has been proposed as a diversification oilseed for constrained environments, but its field performance under realistic, dynamic salinity in Mediterranean soils remains unexplored. This two season on farm study compared three commercial camelina lines at an inland non-saline site and a coastal saline–sodic site in northeastern Italy, combining agronomic measurements with phenology aligned monitoring of soil saturated paste electrical conductivity (ECe). At the saline site, ECe increased from 1.8 dS m−1 at the vegetative stage to 6.2 dS m−1 at seed filling, while camelina completed its cycle earlier than at the inland site. Despite similar aboveground and root biomass yield at flowering across lines, performance diverged during the reproductive phase. Two lines maintained similar seed yields (1.30 Mg ha−1) at the coastal site compared with the inland site, whereas one line declined from 1.45 Mg ha−1 to 0.40 Mg ha−1. Differences among lines in seed yield under salinity were accompanied by contrasting responses in seed oil composition. Oil yield at the saline site was more strongly associated with the increase in ECe from flowering to seed filling than with absolute ECe at seed filling. These results provide the first field-based evidence of line-specific salinity responses in camelina and highlight its potential to diversify moderately salt-affected Mediterranean coastal cropping systems, while emphasizing the need to account for temporal salinity dynamics in genotype selection and crop planning.

The frequency and intensity of tropical cyclones (TCs) in the Arabian Sea have increased in recent decades, heightening concerns regarding regional vulnerability and forecasting difficulties. This study examines the impact of the Madden–Julian Oscillation (MJO) on TCs activity—formation, frequency, and severity—over the Arabian Sea from 1982 to 2021. This study analyzes variations in convection, vertical wind shear (VWS), sea level pressure (SLP), and relative humidity (RH) across different MJO phases utilizing the best-track data from the India Meteorological Department (IMD), the Real-Time Multivariate MJO (RMM) index, and reanalysis datasets from the National Oceanic and Atmospheric Administration (NOAA) and the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR). Results show that more than 80% of TCs form during the convectively active phases of the MJO (P1–P4). These phases have the most noticeable negative outgoing longwave radiation (OLR) anomalies, as well as higher mid-level moisture and low-pressure anomalies, which are good for cyclogenesis. On the other hand, suppressed phases (P6–P8) have positive outgoing longwave radiation, dry air in the middle troposphere, and high-pressure anomalies, which make it harder for TCs to form. While VWS is predominantly favorable during both active and inactive phases, thermodynamic and convective factors principally regulate the modulation of TC activity. The simultaneous presence of active MJO phases with positive Indian Ocean Dipole (pIOD) and neutral or El Niño conditions markedly increases TC frequency, highlighting a combined influence link between interannual–El Niño–Southern Oscillation (ENSO) and IOD– and intraseasonal (MJO) variability. Additionally, the association between MJO and the Indo-Pacific Warm Pool (IPWP) reveals that TC activity peaks during convectively active MJO phases under the second twenty years of this study, emphasizing the influence of large-scale oceanic warming on TC variability. These findings underscore the critical function of the MJO in regulating TC activity variability in the Arabian Sea and stress its significance for enhancing intraseasonal forecasting and disaster preparedness in the area.