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- Impact of stratospheric polar vortex variability on Antarctic sea ice in
CMIP6 models-
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Abstract: The stratospheric polar vortex (SPV) is a potential source of variability for Antarctic sea ice at interannual timescales. While the downward influence of the SPV on the lower troposphere is relatively well-documented, its impact on sea ice is still uncertain. Here, we evaluate how this link between the SPV, the troposphere and sea ice is simulated by 23 CMIP6 models, highlighting the robust features and examining the related processes. We define years in which the springtime SPV is relatively weak, average or strong. We then build composites of atmospheric and sea ice anomalies with respect to neutral conditions (average strength) and present results from the multi-model mean. When the SPV is weakened, we find an overall decrease of sea ice extent in late spring, followed by an increase in summer. We suggest that this switch in the integrated response over the Southern Ocean is related to different regional characteristics. The initial decrease in spring is dominated by anomalous melting in the Ross sector driven by meridional winds, with potential contributions from temperature perturbations descending from the stratosphere in this specific region. In turn, the summer increase is mostly associated with surface winds in the Weddell Sea acting during both spring and summer. The response to a strengthened SPV is largely symmetric, namely with opposite-signed anomalies, though the atmospheric response is lagged by about one month. While the modelled signal is robust, some inconsistencies emerge in the observations, possibly due to the different sample size and period.
PubDate: 2025-07-04
- Interannual variability of summertime quasi-biweekly East Asia-Pacific
teleconnection-
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Abstract: Quasi-biweekly (QBW) variations account substantially for the intra-seasonal variability of the East Asia-Pacific (EAP) teleconnection, exerting significant impacts on East Asian summer weather. However, its year-to-year variability and underlying mechanisms remain unclear. Here we demonstrate that the activity of QBW EAP events exhibits significant interannual variability from 1979 to 2020, primarily attributed to event intensity rather than event frequency. In summers with enhanced QBW EAP events, active centers across the East Asian coast are enhanced and prolonged, forming a dipole pattern over the western North Pacific (WNP) in the lower troposphere during the events. Using reanalysis data and numerical simulations, we investigate the interannual variability of QBW EAP from the perspectives of triggering and maintenance mechanisms, revealing a notable modulation by tropical central-eastern Pacific (CEP) warming. In summers characterized by stronger QBW EAP activity, CEP warming induces a summer-mean cyclonic anomaly over the Philippine Sea and westerly anomalies over the tropical western Pacific (WP) at lower levels. These anomalies cause moisture convergence, ascending motion, and easterly vertical shear over the southern Philippine Sea, promoting convection which enhances the Rossby Wave Source, leading to more intense QBW EAP event. Besides, the cyclonic anomaly over the Philippine Sea and the anticyclonic anomaly east of Japan enhance the meridional shear of zonal wind between them, facilitating the transfer of barotropic kinetic energy from mean flow to sustain QBW EAP events. Our findings provide insights for improving subseasonal forecasts of East Asian summer weather and climate.
PubDate: 2025-07-04
- Quantitative evaluation of decadal scale climatic variability in the
Chambal River Basin; focus on the Banas Badlands-
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Abstract: The present study investigates rainfall variability within the Chambal River basin over the past four decades (1980–2024), focusing on its major sub-basins: Upper Chambal, Banas, Parbati, Kalisindh, and Lower Chambal. The gridded precipitation and temperature datasets were used to compute multiple drought indices- Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), and Reconnaissance Drought Index (RDI). Cross Wavelet Analysis (CWA) and correlation- regression methods were employed to examine the precipitation teleconnections with large-scale climatic indices such as; Southern Oscillation Index (SOI), Sea Surface Temperature (SST), Indian Ocean Dipole (IOD), and Multivariate ENSO Index (MEI). The analysis revealed widespread extreme drought conditions in 1987 and 2002 across all sub-basins, with Banas basin experiencing most severe impacts. Other notable drought years include 1984, 1989, 2000, 2006, 2009 and 2017 across specific sub-basins. In contrast, severe and extreme wet events were recorded in 2013, 2019 and 2024, with intense flooding in the various sub-basins of Chambal. The CWA and correlation- regression results indicated strong correlation between MEI and precipitation during drought years and between SST/IOD during flood years, underscoring the influence of global climatic oscillations on precipitation variability. Furthermore, extensive Badlands have also been identified in the Banas River basin, where tectonic uplift and/or intense monsoonal erosion has caused deep gullies and ravines. The land degradation and deep channel incision have rendered large areas unsuitable for agriculture, leading to significant socio-economic losses. Given the alarming rate of land degradation, the policymakers and researchers need to prioritize the reclamation strategies to address land degradation in the Chambal Basin.
PubDate: 2025-06-27
- El Niño southern oscillation and tropical basin interaction in
idealized worlds-
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Abstract: In this study we present a set of global, coupled climate model simulations with idealised geometries of the tropical ocean basins and land with a focus on important characteristics of El Niño Southern Oscillation (ENSO) type of variability and tropical basin interaction. In a series of 15 simulations, we first vary the zonal width of a single tropical ocean basin from 50° to 360°, while the rest of the tropical zone is set as land. Further we discuss different simplified configurations of two or three tropical ocean basins. The results show remarkable changes in ENSO characteristics as a function of basin width and due to the interaction with other basins that challenge our current understanding of ENSO dynamics. A single basin ENSO has an optimal basin width of about 150° (width of the Pacific) at which ENSO’s preferred period is the longest, the wind stress feedback is the strongest and variability is stronger than in all other basin widths, expect for the 350° basin. Tropical basin interactions substantially affect ENSO strength, periodicity, feedbacks, non-linearity, spatial scale and pattern. In experiments with two or three identical ocean basins we find highly synchronized ENSO modes that are identical between basins and far more energetic and oscillatory than the single basin modes. The results challenge our current understanding of core ENSO dynamics. The framework of these experiments can help to better understand the atmospheric dynamics of ENSO and should help to formulate an ENSO theory that incorporates tropical basin interactions as a core element.
PubDate: 2025-06-26
- Soil-moisture-atmosphere coupling hotspots and their representation in
seasonal forecasts of boreal summer-
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Abstract: This study examines soil-moisture-atmosphere coupling “hotspots” across the Northern Hemisphere during the summer months and evaluates their representation in seasonal forecasting systems. Using hindcasts from the Copernicus Climate Change Service (C3S) multi-model seasonal forecast ensemble, the analysis explores the predictability of land–atmosphere interactions related to soil moisture anomalies. The results indicate that regions with strong soil-moisture-atmosphere coupling, such as parts of western North America, southern Europe, and Central Asia, exhibit potential for predicting seasonal temperature and precipitation patterns a season or more in advance. However, significant uncertainty exists in estimates of the soil-moisture initial conditions and soil-moisture persistence timescales. Moreover, while some regions exhibit realistic coupled behaviour, others, including a large swathe of North America, Eastern Europe, and Northern India display exaggerated coupling, resulting in systematic errors in temperature forecasts. This study underscores the potential for predicting the atmosphere in summer based on memory of soil-moisture initial conditions whilst highlighting the need to improve the representation of soil-moisture atmosphere feedbacks in order to enhance the skill of seasonal climate predictions over land.
PubDate: 2025-06-26
- On the role of AMOC weakening in shaping wintertime Euro-Atlantic
atmospheric circulation-
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Abstract: Climate change simulations project the slowdown of the Atlantic Meridional Overturning Circulation (AMOC) in the 21st century, though the rate and extent of the decline vary across models. In the Euro-Atlantic region, where the AMOC strongly influences sea surface temperature (SST) variability, climate projections also show significant uncertainty in the evolution of large-scale atmospheric circulation. We hypothesise that the decline of the AMOC and the uncertainty in Euro-Atlantic atmospheric circulation are interconnected. To test this, we analyse three coordinated experiments from the CMIP6 archive (SSP2$$-$$4.5, SSP5$$-$$8.5 and abrupt-4xCO2) adopting a storyline approach. In particular, we compare groups of models projecting a larger AMOC decline to groups of models projecting a smaller AMOC decline. Our results indicate that a stronger AMOC weakening is associated with an intensification of the North Atlantic storm track and jet stream, as well as an increased frequency of the NAO$$+$$ weather regime. We link these atmospheric changes to the influence of a reduced warming of the subpolar North Atlantic, known as the North Atlantic Warming Hole (NAWH), associated with the AMOC weakening. To further support our findings, we conduct an additional experiment using the EC-Earth3 model, comparing an abrupt-4xCO2 experiment with one where the AMOC is fixed at preindustrial levels. This experiment corroborates the CMIP6 analysis and validates our hypothesis. We conclude that the AMOC plays a critical role in driving atmospheric changes over the Euro-Atlantic region. Improved monitoring and better constraints on future AMOC decline would help reduce uncertainty in predictions of atmospheric circulation and climate impacts over Europe.
PubDate: 2025-06-25
- The role of the Westward Equatorial Undercurrent in feeding the
Seychelles–Chagos Thermocline Ridge upwelling-
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Abstract: Indian Ocean water exchange is vital for energy and material exchange across the ocean basin. So far, knowledge of the freshwater exchange between the equator and the Southwest Indian Ocean remains limited. By examining volume transport and salinity variations during 1994–2020, this study suggests that the westward Equatorial Undercurrent (wEUC) provides freshwater for the Seychelles–Chagos Thermocline Ridge (SCTR) upwelling during boreal summer–autumn. During June–August, the wEUC occurs in the western Indian Ocean, and transports freshwater to the subsurface of the main region of the SCTR with a lag time of one month, followed by upwelling to the upper surface layer. On interannual timescales, the enhanced wEUC during negative Indian Ocean Dipole years and strong equatorial winds years provides more freshwater for intensified upwelling in the SCTR. This research contributes to our knowledge of freshwater exchange in the tropical Indian Ocean and may provide a new perspective on the branch of the shallow meridional overturning circulation in the Indian Ocean.
PubDate: 2025-06-24
- Tropical Indian Ocean warming drives an increase in bering sea ice
concentration-
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Abstract: Arctic sea ice has undergone rapid changes in recent decades and exhibited significant interannual variability. Factors such as changes in greenhouse gas concentrations, sea ice-albedo feedback, and cloud feedback are known to influence Arctic sea ice variability. Both the Pacific and the Atlantic oceans have been reported to impact Arctic sea ice through atmospheric and oceanic processes. However, limited research has focused on the influence of the Indian Ocean on Arctic sea ice, partly due to the considerable distance between the Indian and Arctic Ocean basins. This study investigates the influence of tropical Indian Ocean warming on the Arctic sea ice concentration (SIC). Through statistical analysis and numerical experiments, we demonstrate that tropical Indian Ocean warming can increase Bering Sea SIC in boreal winter (December–January–February, DJF). The warming excites a Rossby wave train that propagates into the high-latitude Pacific Ocean, resulting in an anomalous low-pressure center over the Bering Strait. The associated cyclonic circulation induces a pronounced southwestward drift of sea ice from the Bering Sea to the high-latitude North Pacific, extending from the Bering Strait to about 60°N over the North Pacific, contributing to the increase in Bering Sea SIC. This result establishes a robust linkage between the Indian Ocean and the Arctic, which may largely influence the predictability and the future projection of Arctic climate. Moreover, given that Arctic sea ice may provide feedback to the Indian monsoon system, these two areas thus form an interactive system that requires further investigation.
PubDate: 2025-06-24
- Zonal expansion of global land monsoon domain under future changing
climate from a probabilistic perspective-
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Abstract: The potential impact of future changes in the monsoon domains due to climate change on two-thirds of the global population should not be overlooked. However, the performance of the NEX-GDDP-CMIP6 dataset in identifying the monsoon domain has not been evaluated. The assessments of the spatial shift of the future monsoon domain are lacking. In this study, projections from 20 state-of-the-art climate models from NEX-GDDP-CMIP6 under four scenarios were assessed and used to detect future climatological and spatial changes of the monsoon domain coverage. The impact of future monsoons on global land is demonstrated through probability perspective by using a multivariate probabilistic framework. Future shift of the global land monsoon domain was detected by probability changes. Results showed that the coverage of the global land monsoon domain derived from NEX-GDDP-CMIP6 projections had only a 5% bias compared to the GPCC dataset (based on globally observed station-level data). The uncertainty between projections of the NEX-GDDP-CMIP6 model was minimal. According to these projections, global land monsoon coverage is expected to increase in the future, with significant increases in the near-term (2021–2040) and mid-term (2041–2060), while the rate of growth is expected to slow down in the long-term (2081–2100). The largest increase (7.2%) in coverage occurred under the high-emissions scenario (SSP5-8.5). The probability would increase at the boundary in most monsoon regions, indicating an expansion change. The expansion of the global land monsoon domain can result in increased precipitation and unstable weather systems. Hence, the projected shift in the global land monsoon domain under future climate change is crucial for formulating climate change response strategies.
PubDate: 2025-06-23
- ENSO phase space dynamics in CMIP models
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Abstract: This study analyses the El Niño-Southern Oscillation (ENSO) phase space as simulated by the Coupled Model Intercomparison Projects (CMIP) 5 and 6 models. In the framework of the ENSO phase space, the ENSO cycle is described as a two-dimensional representation of the sea surface temperature anomaly in the eastern equatorial Pacific (T) and the equatorial mean thermocline depth anomaly (h). We find that the characteristics out-of-phase cross-correlation between T and h is shifted to negative values in CMIP models, suggesting that the coupling between T and h is regionally shifted. If we consider the CMIP models with h estimated shifted further to the eastern Pacific, then the models have better agreements with the observed characteristics. While the models can capture some of the observed asymmetries with high correlations, they do largely underestimate the strength of non-linear ENSO aspects. They underestimate the likelihood of extreme El Niño and discharge states, they cannot capture the enhanced growth rates during the recharge state, the enhanced decay after the discharge state nor the slower phase transitions after the La Niña phase. Further, we found no indication of significant improvements from the CMIP 5 to 6 ensemble, suggesting that the two ensembles are essentially the same in terms of their ENSO dynamics. There is, however, a large spread within the model ensembles, with only a few CMIP models accurately simulating the observed asymmetries of the ENSO phase space, leading to models with quite different ENSO dynamics.
PubDate: 2025-06-23
- Key local atmospheric processes of the heat extreme over the middle-lower
Yangtze River basin in August 2022-
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Abstract: The unprecedented heat event over the middle-lower Yangtze River Basin (YRB) in August 2022 had disastrous socioeconomic impacts. Based on the general mechanism of multi-year surface air temperature (SAT) variation in August, this study focuses on the key local atmospheric processes responsible for the record-breaking event in 2022. We firstly propose that through hydrostatic adjustment, the local atmospheric perturbation thickness (APT) between 1000 and 500 hPa is the most crucial factor dynamically influencing the SAT over the YRB in August. Net diabatic heating from the surface affects the SAT thermodynamically at the same time. Analysis of the geopotential thickness tendency reveals that vertical motion ($$\omega$$) and diabatic heating (Q) within the air column significantly affect the thickness of the air column in August, highlighting the pivotal role of the interaction among local APT,$$\omega$$, and Q. The specific performance is that the downward motion and enhanced Q within the air column lead to increased local APT. Meanwhile, the increased APT and downward motion amplified the Q above the surface by reducing cloud cover. Therefore, thermodynamic processes are initiated by dynamic processes and exert a reciprocal influence on them. The results exhibit that this heat event was driven by both the hydrostatic adjustment of dynamic processes and diabatic heating of thermodynamic processes, with the dynamic processes playing a dominant role. Moreover, the APT and $$\omega$$ serve as crucial bridges through which upper-level atmospheric circulation affects the SAT. Additionally, despite these large-scale interannual processes, synoptic regional foehn effect should be taken into consideration.
PubDate: 2025-06-23
- Climate drivers of spatio-temporal variability of july–october rainfall
in cameroon (1981–2023) under climate warming-
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Abstract: Global warming and climate change have had a considerable impact on hydrometeorological variables. This has resulted in rainfall and temperature changes that offer significant difficulties to local ecosystems and rain-dependent agriculture in West Africa, including Cameroon. Despite the vital necessity of understanding long-term rainfall patterns in combatting climate change and promoting socioeconomic development, this region has received insufficient attention due to much focus on environmental issues such as deforestation and degradation and lack of reliable station data. The spatio-temporal changes in temperature and precipitation are critical for regional environmental preservation and policymaking. This study investigates the spatio-temporal patterns in rainfall and temperature throughout the primary rainy season (July to October) from 1981 to 2023, using daily Climate Hazards Group Infrared Precipitation with Station data (CHIRPS) and the ERA-5 reanalysis dataset respectively. CHIRPS has a superior performance compared to other datasets, while ERA-5 is a more advanced and sophisticated reanalysis dataset. To analyze statistical trends and significant shifts, the Mann–Kendall test and change-point analysis were used respectively. To assess correlations between variables, the Pearson’s correlation coefficient was then employed. Our findings show a steady increase in mean annual temperature and a decrease in average annual rainfall, with the Southern regions of Cameroon being the most affected and the Northern regions experiencing increased rainfall. Multiple drought periods (1981–1990 and 2001–2010) contributed to lower seasonal rainfall, coinciding with rising temperatures and indicating significant shifts. Key climate drivers, particularly the WASM and SSTs have a considerable influence on these patterns. This study emphasizes the significance of spatio-temporal variability in rainfall and temperature, providing a scientific foundation for building effective climate responses in Cameroon, such as disaster preparedness, agricultural planning, energy production, and water resource management.
PubDate: 2025-06-19
- Characterization of Western US hydrologic processes linked to atmospheric
rivers in two sets of seasonal global retrospective forecasts-
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Abstract: Atmospheric rivers (ARs) are narrow filaments of high water vapor content that have considerable influence on the western United States (US) hydroclimate. ARs provide significant amounts of annual precipitation and snowfall and affect mountain snowpack via snow water equivalent (SWE) accumulation and ablation. With ARs projected to become increasingly key players in western US hydrology, water resource managers will rely progressively more on AR seasonal forecasts to infer flood/drought risks and make informed decisions about water supply allocation. However, precisely how well current seasonal climate prediction systems capture ARs and their associated hydrologic variables is still an open question. Here, we evaluate the ability of high (HR) and low resolution (LR) CCSM4 and CESM1 seasonal global retrospective forecasts to characterize precipitation, snowfall, and SWE changes associated with western US landfalling ARs. HR forecasts more accurately represent hydrologic variables than LR forecasts, however, CCSM4-HR underestimates AR-related snowfall, causing enhanced AR-related SWE ablation. Further investigation reveals amplified onshore positive temperature advection by south-southwesterly biased AR winds causes ARs in CCSM4-HR to be embedded within thicker air columns, yielding increased freezing level heights, reduced snowfall, and increased SWE loss. Results suggest both HR and LR global seasonal forecast models are capable of characterizing AR distribution and frequency, but HR models are needed for proper precipitation, snowfall, and SWE representation. Furthermore, models used to assess AR-related hydrological processes must contain accurate wind fields, as even minor biases can have a profound effect on a model’s ability to simulate AR precipitation and SWE accumulation/ablation rates.
PubDate: 2025-06-18
- Interannual variations of persistent extreme cold events in northeastern
China-
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Abstract: The interannual variations of persistent extreme cold events (ECE) in northeastern China (NEC) and associated tropical and high-latitude forcings were investigated through both observational analyses and idealized numerical model experiments. The yearly accumulated ECE number exhibits a marked interannual fluctuation at a dominant period of 2–3 years. During the more frequent ECE winters, the NEC is controlled by a local cyclonic anomaly. This cyclonic anomaly is a part of a quasi-barotropic Rossby wave train with an alternated cyclone-anticyclone-cyclone pattern across the Eurasian Continent. Accompanied with this Rossby wave train are positive sea surface temperature (SST) anomalies in the Barents Sea ($$\:{\text{S}\text{S}\text{T}}_{\text{B}\text{A}\text{S}}^{{\prime\:}}$$) and enhanced precipitation over the Maritime Continent ($$\:{\text{P}\text{R}\text{E}}_{\text{M}\text{C}}^{{\prime\:}}$$). The possible roles of the two forcing factors in triggering the Rossby wave train were further demonstrated through idealized general circulation model experiments. The results show that $$\:{\text{S}\text{S}\text{T}}_{\text{B}\text{A}\text{S}}^{{\prime\:}}$$ stimulates a southeastward Rossby wave activity flux through induced local positive geopotential height anomalies, whereas $$\:{\text{P}\text{R}\text{E}}_{\text{M}\text{C}}^{{\prime\:}}$$ tends to force a northeastward wave activity flux with anticyclonic anomalies in southern China and cyclonic anomalies over the northeastern Asia. The numerical experiments indicate that the effect of $$\:{\text{S}\text{S}\text{T}}_{\text{B}\text{A}\text{S}}^{{\prime\:}}$$ is about 20–30% stronger than that of $$\:{\text{P}\text{R}\text{E}}_{\text{M}\text{C}}^{{\prime\:}}$$.
PubDate: 2025-06-18
- Sources of predictability and skill in late summer precipitation forecasts
of eastern China: insights from EC-S2S-
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Abstract: Using the Sub-seasonal to Seasonal (S2S) data from the European Centre for Medium-Range Weather Forecasts (ECMWF), this study investigates the most predictable modes and prediction skills of late summer precipitation in eastern China, as well as their associated sources of predictability. By employing the maximum signal-to-noise empirical orthogonal function (MSN EOF) analysis on late summer precipitation predictions in eastern China, the results identify the most predictable mode as featuring a strong precipitation signal over the Yangtze River Basin, characterized by a meridional triple pattern. This pattern is significantly linked to sea surface temperature (SST) variations in the equatorial central eastern Pacific and the southern Indian Ocean. During this period, the SST evolution plays a crucial role in driving anomalous circulations over the northwest Pacific, acting as a key source of the predictability. The second predictable mode is characterized by a strengthening signal over the northwest Pacific, a weakening signal in the central western Pacific, and warming in the Indian Ocean. The MSN EOF method effectively captures the ocean-atmosphere interactions underlying these precipitation modes. The main predictable modes and their sources of predictability are further utilized to develop calibration schemes. By selecting high-skill modes, the prediction models are reconstructed to eliminate internal forecast biases, thereby improving precipitation prediction skills. The corrected temporal correlation coefficients indicate significant improvements in forecasts for central and eastern mainland China, offering a potential pathway for improving late summer precipitation predictions in the region.
PubDate: 2025-06-18
- How is the future climate linked to mean temperature changes over the west
coast of India' Part-II: precipitation changes and drought severity from
CMIP6 projections-
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Abstract: This study examines the projected changes in precipitation patterns and droughts over the west coast of India (WCI) during the period 2024–2050. Bias-corrected, downscaled data from the coupled model inter-comparison project phase-6 (CMIP6) under multiple shared socioeconomic pathways (SSPs), as discussed in the companion paper (Part-I; Haridas et al. in Clim Dyn, 2025), are employed for the analysis. The self-calibrating Palmer Drought Severity Index (scPDSI) is used to assess drought severity over the WCI, including the southern Indian State of Kerala. The projections indicate a 10 mm increase in post-monsoon and 300 mm in monsoon seasonal rainfall over northern coastal and far-leeward regions under all SSPs. While central Kerala is projected to experience a significant increase of 225 mm in mean monsoon rainfall under SSP3-7.0, along with up to 250 mm of post-monsoon rainfall at the 90% confidence level, pre-monsoon rainfall in northern Kerala may rise only marginally (5–25 mm) and south-central Kerala could witness a 5–10 mm decrease. Although the mean rainfall is projected to rise, an increase in standard deviation suggests a heightened intensity of extreme events. The projected scPDSI revealed that severe and extreme droughts will increase, with the eastern hilly regions facing prolonged (> 90 cumulative months) extreme droughts, under SSP2-4.5 and SSP5-8.5. Given the growing evidence of convective intensification and increased vulnerability over the WCI, a detailed projection of future precipitation patterns is essential for better preparedness and adaptation.
PubDate: 2025-06-17
- Comments on “Consistent climate fingerprinting"by McKitrick (2025)
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Abstract: We provide comments on McKitrick (Consistent climate fingerprinting. Manuscript, 2025) Consistent Climate Fingerprinting, outlining our views on some keys points of the paper.
PubDate: 2025-06-16
- Dominant modes and drivers of interannual variability of surface air
temperature in boreal summer over Europe-
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Abstract: This study investigates the dominant modes and drivers of interannual variability of summer surface air temperature (SAT) over Europe. The first Empirical Orthogonal Function Mode (EOF1) of interannual variability of summer SAT over Europe shows a northeast-southwest dipole pattern with large SAT warming over central and northeastern Europe and SAT cooling of weaker extent and amplitude over southwestern Europe. The EOF2 shows a tripole pattern with warming over central Europe and cooling over southwestern and northeastern Europe. The EOF3 shows a meridional dipole pattern. Atmospheric changes contribute to SAT anomalies of the three EOF modes via wind-induced temperature advection and cloud-induced radiation changes. Specifically, EOF1 is related to the East Atlantic/Western Russia pattern (EA/WR). The EA/WR-generated anticyclonic (cyclonic) anomaly and associated meridional wind anomalies over central and eastern (western) Europe lead to less (more) cloud cover, more (less) downward shortwave radiation, and warm (cold) advection, thus resulting in SAT warming (cooling) there. The EOF2 is associated with the British-Baikal Corridor pattern (BBC). The BBC-induced anticyclonic anomaly over central-northern Europe and cyclonic anomaly on its eastern and western sides contribute to the zonal tripole SAT anomaly pattern. The Scandinavian pattern has a marked contribution to the EOF3 by generating anticyclonic anomaly over the Scandinavian peninsula and cyclonic anomaly on its southwestern side. Further analysis shows that EOF1 is also associated with sea surface temperature (SST) anomalies in the equatorial central-eastern Pacific, southern Atlantic, and mid-latitude North Atlantic. EOF2 is related to SST anomalies in the equatorial central Pacific and high-latitude North Pacific. EOF3 is associated with SST anomalies in the North Atlantic and the tropical Indian Ocean. Several coupled climate models can well simulate the first three EOF modes of summer SAT anomalies over Europe and the associated atmospheric circulation anomalies. These results contribute to a better understanding of the interannual variability and drivers of European SAT.
PubDate: 2025-06-16
- Meteorological conditions associated with different categories of monsoon
inversions over Salalah (17.0° N, 54.1° E), a station on the west coast
of the Arabian Sea-
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Abstract: The monsoon inversion (MI) layer over the western part of the Arabian Sea (AS) from June to September serves as one of the semi-permanent features of the Indian summer monsoon which plays an essential role in pollution dispersion and exchange between the atmospheric boundary layer (ABL) and free troposphere (FT). The analysis focuses on characterizing the inversion layers over Salalah (17.0oN, 54.1oE), a station on the west coast of the AS, using radiosonde and Indian monsoon data assimilation and analysis (IMDAA) datasets at 00 UTC during 2016–2020. The ABL over Salalah at 00 UTC is characterized as the stable boundary layer (SBL) at ~ 0.3 ± 0.15 km and residual layer (RL) at ~ 1.25 ± 0.35—1.5 ± 0.4 km from October to May while and MI layer at ~ 1.25 ± 0.25 km during June to September. MI strength highly varies on a day-to-day scale which is characterized into five different categories based on the temperature change (ΔT) between the 950 and 850 hPa levels. The threshold limit ΔT > 2.7 K, 2.7 ≥ ΔT > 0 K, 0 ≥ ΔT > − 2.5 K, − 2.5 ≥ ΔT > − 5 K, and ΔT ≤ − 5 K signifies the different categories C1, C2, C3, C4, and C5, respectively that are found to be 14% (2%), 9% (10%), 16% (23%), 29% (43%), and 32% (22%) out of 586 (610) radiosonde (IMDAA) profiles from June- September during 2016–2020. The strength and thickness of the MI increase from the C1 to C5 categories. The mean temperature and relative humidity profiles of these categories reveal that the stronger the MI, the shallower it is and the drier the layer aloft and vice versa. The advective term indicates warm advection below MI layer and cold advection aloft it which becomes stronger with increasing horizontal windspeed from C1 to C5 categories. The convective term indicates warm air within the MI layer overlaid by the cold subsiding air which remains sustained almost equally for the different categories. The saturation pressure deficit suggests the cloudy layer below the MI whose extension decreases from C1 to C5. It is observed that MI and FT almost contribute equally to the total integrated water vapor essential for cloud formation.
PubDate: 2025-06-14
- Improving CMIP6 projections of daily precipitation using a mean-adjusted
time variability correction technique-
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Abstract: Daily precipitation time series exhibit intermittent periods of high variability separated by periods of no rain, posing challenges to correct projected precipitation. To improve projected changes in probabilities of flooding and drought, it is critically important to improve temporal correlations of the precipitation time series. Previous work introduced a Time Variability Correction (TVC) method, which quantified and corrected time variability errors at differing time scales. This study extends TVC to post-process daily precipitation projections from 28 CMIP6 models over Australia, introducing a new mean adjustment procedure to eliminate negative precipitation values while ensuring that both the mean and variability of the final series aligns with the observations in the historical training period. The new TVC mean-adjusted (TVC-ma) method preserves each model’s projected change in timescale covariances, and our analysis reveals interesting differences among CMIP6 projections of changes in time-scale-dependent variances. TVC-ma is evaluated using a leave-one-out model-as-truth setup. Results reveal that, in most cases, TVC-ma significantly improves the mean, variance, lag correlations, and projections of climate indices related to persistent, heavy, and low rainfall extremes compared to raw models. When applied to future precipitation projections for Australia, TVC-ma projects pronounced increases in prolonged dry periods and maximum 1-day and 5-day precipitation amounts under the high-emission scenario relative to the low-emission scenario. Compared to the historical period, corrected projections under the high-emission scenario show drier conditions in parts of Western Australia, greater variability, extended durations of consecutive dry days and increased multi-day precipitation extremes across most regions of the continent.
PubDate: 2025-06-14
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