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- Correction to: Low‑frequency variability enhancement of the midlatitude
climate in an eddy‑resolving coupled ocean–atmosphere model—part II:
ocean mechanisms-
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PubDate: 2023-06-04
- Precipitation variability using GPCC data and its relationship with
atmospheric teleconnections in Northeast Brazil-
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Abstract: The present study investigates the influence of different atmospheric teleconnections on the annual precipitation variability in Northeast Brazil (NEB) based on the annual precipitation data from the Global Precipitation Climatology Center (GPCC) from 1901 to 2013. The objective of this study is to analyze the influence of different atmospheric teleconnections on the total annual precipitation of NEB for the 1901–2013 period, considering the physical characteristics of four subregions, i.e., Mid-north, Backwoods, Agreste, and Forest zone. To analyze the influence of different atmospheric teleconnections, GPCC data were used, and the behavior of the teleconnections was assessed using Pearson correlation coefficient, Rainfall Anomaly Index (RAI), and cross-wavelet analysis. The Pearson correlation was used to analyze the influence on the annual precipitation for the studied region. RAI was used to calculate the frequency of atmospheric patterns and drought episodes. The cross-wavelet analysis was applied to identify similarity signals between precipitation series and atmospheric teleconnections. The results of the Pearson correlation assessed according to Student's t test and cross-wavelet analysis showed that the Atlantic Multidecadal Oscillation (AMO) exerts a more significant influence on the Backwoods region at an interannual scale. In contrast, the Pacific Decadal Oscillation (PDO) exerts greater control over the modulation of the climatic patterns in NEB. The results of the study are insightful and reveal the differential impacts of teleconnections such as the AMO, PDO, MEI, and NAO on precipitation in the four sub-regions of NEB. The Atlantic circulation patterns strongly influence the interannual and interdecadal precipitation in the Agreste, Backwoods, and Mid-north regions, possibly associated with the Intertropical Convergence Zone (ITCZ) position. Finally, this study contributes to understanding internal climatic variability in NEB and planning of water resources and agricultural activities in such a region. Graphic abstract 
PubDate: 2023-06-04
- Projected trends in hydro-climatic extremes in small-to-mid-sized
watersheds in eastern Nepal based on CMIP6 outputs-
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Abstract: Quantifying the extent of change in climatic and hydrological variables in the past and the future is essential for climate change-resilient development, especially in the climate change sensitive region of Nepal. This paper analyzed future climatic trends and extremes, historical hydrological extremes and their linkage with historical precipitation extremes, and discussed the impacts of climate change on various sectors in the less-studied Small and Medium-sized Eastern River Basins (SMERB) of Nepal. Applying an ensemble of five Coupled Model Intercomparison Project phase 6 (CMIP6) global climate models (GCMs), we evaluated 10 precipitation and 13 temperature extreme indices using Climpact2 for the historical (1979–2020), near-future (2021–2045), mid-future (2046–2070) and far-future (2071–2100) under two Shared Socioeconomic Pathway (SSP), SSP245 and SSP585. Hydrological extreme indices were assessed using Indicators of Hydrologic Alteration tool. Projected climate revealed significant increase (9–73%) in annual and seasonal rainfall except winter; frequent intense rainfall extremes but prolonged dry spells; significant increasing minimum and maximum temperature trends (0.4–5 °C); rise in extreme heat events; increasing minimum and maximum discharge extreme trends in most hydrological stations; as well as strong association between maximum 1 day precipitation (Rx1day) and 1 day max flow for all stations. Growing dry periods but intense rainfall in few wet days, coupled with warming pattern all-over SMERB with frequent extreme events indicate high risk for future climate-related disasters. The harsher climate will potentially have damaging implications, especially in climate-induced disasters, food security, and water and sanitation infrastructure.
PubDate: 2023-06-04
- Relationships among Arctic warming, sea-ice loss, stability, lapse rate
feedback, and Arctic amplification-
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Abstract: The Arctic warms much faster than other places under increasing greenhouse gases, a phenomenon known as Arctic amplification (AA). Arctic positive lapse-rate feedback (LRF) and oceanic heating induced by sea-ice loss have been considered as major causes of Arctic warming and AA, and Arctic high atmospheric stability has been considered as a key factor for the occurrence of the bottom-heavy warming profile and thus positive LRF in the Arctic. Here we analyze model simulations with and without large AA and sea-ice loss and long-term changes in ERA5 reanalysis data to examine the relationships among Arctic sea-ice loss, stability, LRF, Arctic warming, and AA. Results show that the Arctic bottom-heavy warming profile and the resultant positive LRF are produced primarily by increased oceanic heating of the air due to sea-ice loss in Arctic winter, rather than high atmospheric stability. Without the oceanic heating induced by sea-ice loss, most Arctic climate feedbacks weaken greatly, and all other processes can only produce slightly enhanced surface warming and thus weak positive LRF under stable Arctic air. A non-convective Arctic environment allows the oceanic heating to warm near-surface air more than the upper levels, resulting in large positive LRF that roughly doubles the surface warming compared with the case without the LRF. We conclude that enhanced cold-season oceanic heating due to sea-ice loss is the primary cause of Arctic large positive LRF, which in turn allows the surface heating to produce more Arctic warming and large AA.
PubDate: 2023-06-02
- Using an ensemble nonlinear forcing singular vector data assimilation
approach to address the ENSO forecast uncertainties caused by the
“spring predictability barrier” and El Niño diversity-
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Abstract: An ensemble data assimilation approach for El Niño-Southern Oscillation (ENSO) forecasting is proposed by embedding nonlinear forcing singular vector-data assimilation (NFSV-DA) in the Zebiak–Cane model. This approach generalizes the NFSV-DA performed over a long time series of sea surface temperature anomaly (SSTA) to an ensemble NFSV-DA (EnNFSV-DA) that combines useful precursory signals existed additionally on different decades for ENSO predictions. With the EnNFSV-DA of the Zebiak–Cane model, the SSTA associated with ENSO events during 1961–2020 is predicted. It is shown that the ENSO forecasts made by the EnNFSV-DA outperform the control forecasts generated by a coupled initialization procedure and also the forecasts made by the NFSV-DA, and with the lead times of skillful forecasting being extended from less than 6 months in the control forecast and 10 months in the NFSV-DA to more than 12 months in the EnNFSV-DA. Furthermore, the “spring predictability barrier” (SPB) that severely limits ENSO forecasting becomes very weak in the predictions generated by the EnNFSV-DA of the Zebiak–Cane model. It is also encouraging that the use of the EnNFSV-DA can identify the warm signal in the equatorial central Pacific at a lead time of 8 months, which has a strong capacity to distinguish the types of El Niño events in predictions. Therefore, the EnNFSV-DA could be a useful DA approach to address both initial and model error effects and to significantly reduce the SPB phenomenon, especially in recognizing the types of El Niño in predictions.
PubDate: 2023-06-01
- How do the characteristics of monsoon low pressure systems over India
change under a warming climate' A modeling study using the NCAR CESM-
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Abstract: In this study, using the NCAR Community Earth System Model (CESM1.2.2), we investigate the changes in the characteristics of the summer monsoon low pressure systems (LPS) over India in a twenty-first century climate change simulation corresponding to the RCP8.5 scenario. A slight weakening in monsoon circulation and an increase in mean summer monsoon precipitation over India are simulated in a warmer climate, consistent with several previous studies. The weakening of the monsoon circulation is associated with a pair of anticyclonic anomalies straddling the equator in the low level, weakening the cross-equatorial monsoonal flow from the southern hemisphere. These low-level circulation anomalies appear to be robust features in the equatorial Indian Ocean under climate change. An increase in moisture flux is also simulated over the Indian subcontinent. However, we find no significant change in the number of LPS or their spatial distribution under the RCP8.5 scenario. This is attributed to a small but non-significant decrease in the low-level meridional cyclonic shear in zonal winds. An increase in the intensity and frequency of extreme precipitation over India in a warmer world is simulated and is likely associated with an increase in moisture content. Our study shows that the fractional contribution of LPS to mean and extreme precipitation over India in a warmer world is likely unchanged, but the frequency and intensity of extreme events are larger. Because of the diversity in the results from single model studies on LPS characteristics in a warmer world, a future study that uses CMIP6 multi-model data would be valuable to assess the robustness and the uncertainty in changes in LPS activities under climate change.
PubDate: 2023-06-01
- Correction to: Persistent freshening of the Arctic Ocean and changes in
the North Atlantic salinity caused by Arctic sea ice decline-
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PubDate: 2023-06-01
- CMIP6 captures the satellite-era jet slowdown and Arctic amplification,
yet projects future jet speedup and tropical amplification-
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Abstract: The polar-to-subtropical temperature gradient in the free troposphere is a key driver of the extratropical jet stream response to climate change. Climate models tend to steepen this gradient in response to large greenhouse gas increases, due to very strong subtropical upper-level warming. This strengthens the simulated jets. However, multiple lines of observational evidence point to a slowing northern jet over the satellite era, driven by enhanced Arctic free-tropospheric warming and weakening of the gradient. Here, we reconcile these seemingly contradictory results by showing that the CMIP6 ensemble successfully simulates both the observed satellite-era slowdown/weakening, and the speedup/strengthening with strong global warming. Specifically, the observed gradient weakening from 1980–1997 to 1997–2014 appears inconsistent (p < 0.05) with the simulated gradient changes for just 6 of 45 models using Microwave Sounding Unit observations, and for just 5 of 45 models using reanalysis estimates. The observed jet slowdown appears inconsistent with the simulated jet changes for just 1 of 45 models. In fact, a clear majority of the CMIP6 models weaken the gradient and slow down the jet over this interval. Yet a strong majority of the models reverse course under a high-emissions future-type scenario, simulating gradient strengthening and jet speedup. Future work will seek to clarify the cause(s) of this unexpected difference between past and future atmospheric responses.
PubDate: 2023-05-31
- Atmospheric controls on the Terra Nova Bay polynya occurrence in
Antarctica-
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Abstract: Polynyas, or ice-free regions within the sea ice pack, are a common occurrence around Antarctica. A recurrent and often large polynya is the Terra Nova Bay Polynya (TNBP), located on the western side of the Ross Sea just off Victoria Land. In this study, we investigate the atmospheric conditions leading to the occurrence of the TNBP and its spatial variability, as estimated using satellite-derived ice surface temperature and sea ice concentration data. A cluster analysis revealed that katabatic winds descending the Transantarctic Mountains, account for about 45% of the days when the TNBP exceeded its 2010–2017 mean extent plus one standard deviation. Warmer and more moist air intrusions from lower-latitudes from the Pacific Ocean, which are favoured in the negative phase of the Southern Annular Mode, play a role in its expansion in the remaining days. This is more frequent in the transition seasons, when such events are more likely to reach Antarctica and contribute to the occurrence and the widening of the polynya. In-situ weather data confirmed the effects of the mid-latitude air intrusions, while sea ice drifts of up to 25 km day−1 cleared the ice offshore and promoted the widening of the polynya starting from the coastal areas. Knowing the atmospheric factors involved in the occurrence of coastal polynyas around Antarctica is essential as it helps in improving their representation and predictability in climate models and hence advance the models’ capabilities in projecting Antarctic sea ice variability.
PubDate: 2023-05-31
- Which ENSO index best represents its global influences'
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Abstract: Knowledge about the El Niño-Southern Oscillation (ENSO) is the scientific foundation for short-term climate prediction, due to its global influence. In operation and research communities, the ENSO state is often represented by various ENSO indices. However, it is unclear which index is the strongest for capturing ENSO’s global climate influence. By examining the correlations of eleven ENSO indices with monthly mean global precipitation and surface temperature (TS), we illustrate the similarities and differences in the connections, identify the strongest index, and discuss the physics behind the differences. For the global average, the Niño3.4 and relative Niño3.4 indices are the two strongest indices and the warm pool index is the weakest one for capturing the impact of ENSO on global precipitation, while the Niño4 and Niño3.4 indices are the two strongest indices and the Modoki index is the weakest one for capturing the ENSO’s influence on TS variations. In addition to the dependence on the variables and ENSO indices, the representations of climate variability associated with ENSO depend on the region. For example, in Australia, the southern oscillation index has the most significant correlations with precipitation and its correlations with TS are relatively weaker than those of some of the other indices. These differences associated with the various ENSO indices may be due to their representation of the deep convection in the tropical Pacific. These results can serve as a benchmark to understand the global picture of monthly mean precipitation and TS influenced by ENSO and to verify model’s ability in capturing these connections.
PubDate: 2023-05-29
- The interannual impact of the North Atlantic sea surface temperature on
the surface air temperature over southern China in February-
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Abstract: Prolonged low temperature significantly threatens transportation and planting in populous areas and is closely linked to slowly varying forcing such as sea surface temperature (SST). In this study, we reveal the impact of the north–south dipole pattern in extra-tropical North Atlantic SST (DNA) anomaly on surface air temperature (SAT) over southern China in February. The positive phase of the DNA is favorable for a positive North Atlantic Oscillation-like pattern at the troposphere via synoptic eddy vorticity forcing and triggers a southeastward-propagating Rossby wave train associated with the deepened East Asian trough and the strengthened Siberian high, which are conducive to enhancement of the East Asian winter monsoon. A stronger monsoon leads to lower-than-normal SAT over southern China by intensifying southward cold air outbreaks. Considerably, the extremely low temperature over southern China in February 2022 is explainable by this physical mechanism. Furthermore, experiments with a linear baroclinic model verify that the proposed downstream propagating Rossby wave train is mainly associated with the midlatitude North Atlantic SST anomaly. These results emphasize that the extra-tropical North Atlantic SST anomaly should be focused when interpreting and predicting the late winter SAT over southern China.
PubDate: 2023-05-26
- Impacts of land-surface heterogeneities and Amazonian deforestation on the
wet season onset in southern Amazon-
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Abstract: Continued Amazonian deforestation perturbs the surface turbulent fluxes which are important for building the conditions for the wet season onset in the southern Amazon. This work evaluates the impacts of tropical deforestation on the onset and development of the Amazonian rainy season using a weather typing approach. We use 19-year simulations (2001–2019) with the Regional Earth System Model from the Institute Pierre Simone Laplace (RegIPSL) with twin control/deforestation experiments. RegIPSL represents the dominant modes or the atmospheric circulation patterns (CPs) of the daily-to-decadal circulation variability in tropical South America, and the evolution of atmospheric and surface conditions along the dry-to-wet transition period. According to RegIPSL, forests and crops contribute differently to the onset. During the dry-to-wet transition period, croplands/grasslands present a stronger shallow convection driven by a higher atmospheric temperature. Large-scale subsidence suppresses low-level convection in the region and deep convection only persists over forests where the atmosphere presents more convective potential energy. After the onset and the establishment of large-scale rainfall structures, both land covers behave similarly in terms of surface fluxes. Deforestation decreases the frequency of the CP typically linked to the onset. Changes in the spatial structure and frequency of the wet season CPs reinforce the hypothesis of a deforestation-induced dry season lengthening. Variations in the CP frequency and characteristic rainfall have opposite effects on accumulated rainfall during the dry-to-wet transition period. Whereas alterations in frequency are associated with a regional circulation response, changes in the CP characteristic rainfall correspond to a local response to deforestation.
PubDate: 2023-05-26
- Observed and projected changes in snow accumulation and snowline in
California’s snowy mountains-
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Abstract: The Sierra Nevada and Southern Cascades—California’s snowy mountains—are primary freshwater sources and natural reservoirs for the states of California and Nevada. These mountains receive precipitation overwhelmingly from wintertime storms including atmospheric rivers (ARs), much of it falling as snow at the higher elevations. Using a seven-decade record of daily observed temperature and precipitation as well as a snow reanalysis and downscaled climate projections, we documented historical and future changes in snow accumulation and snowlines. In four key subregions of California’s snowy mountains, we quantified the progressing contribution of ARs and non-AR storms to the evolving and projected snow accumulation and snowlines (elevation of the snow-to-rain transition), exploring their climatology, variability and trends. Historically, snow makes up roughly a third of the precipitation affecting California’s mountains. While ARs make up only a quarter of all precipitating days and, due to their relative warmth, produce snowlines higher than do other storms, they contribute over 40% of the total seasonal snow. Under projected unabated warming, snow accumulation would decline to less than half of historical by the late twenty-first century, with the greatest snow loss at mid elevations (from 1500 to 3300 m by the mountain sub-regions) during fall and spring. Central and Southern Sierra Nevada peaks above 3400 m might see occasionally extreme snow accumulations in January–February resulting entirely from wetter ARs. AR-related snowlines are projected to increase by more than 700 m, compared to about 500 m for other storms. We discuss likely impacts of the changing climate for water resources as well as for winter recreation.
PubDate: 2023-05-25
- Moisture sources for precipitation variability over the Arabian Peninsula
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Abstract: We apply the Lagrangian-based moisture back trajectory method to two reanalysis datasets to determine the moisture sources for wet season precipitation over the Arabian Peninsula, defined as land on the Asian continent to the south of the Turkish border and west of Iran. To accomplish this, we make use of the evaporative source region between 65°W–120°E and 30°S–60°N, which is divided into twelve sub-regions. Our comparison of reanalyses and multiple observations allows us to validate datasets and highlight broad-scale similarities in characteristics, notwithstanding some inconsistencies in the southwest AP. The results indicate north-to-south spatiotemporal heterogeneity in the characteristics of dominant moisture sources. In the north, moisture for precipitation is mainly sourced from midlatitude land and water bodies, such as the Mediterranean and Caspian Seas. Areas further south are dependent on moisture transport from the Western Indian Ocean and parts of the African continent. The El Niño-Southern Oscillation (ENSO) exhibits an overall positive but sub-seasonally varying influence on the precipitation variability over the region, with noticeable moisture anomalies from all major source regions. A significant drying trend exists over parts of the Peninsula, which both reanalyses partially attribute to anomalies in the moisture advection from the Congo Basin and South Atlantic Ocean. However, considerable uncertainty in evaporation trends over the terrestrial evaporative sources in observations warrants additional modeling studies to further our understanding of key processes contributing to the negative trends.
PubDate: 2023-05-25
- Western disturbances vs Non-western disturbances days winter precipitation
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Abstract: While studying the Western Disturbances (WDs) and associated precipitation forming mechanism in changing time, we found that there is significant amount of precipitation received during Non-WDs days too. In addition, it is also highlighted that all the WDs don’t precipitate. And hence cumulative winter precipitation is kind of summation of all the available precipitation and NOT only of WDs days’ precipitation. Thus here understanding of WDs vs Non-WDs days precipitation dynamics, linkages and changes in last three decades are deliberated. Threshold for evaluating non-precipitating and precipitating day(s) is chosen as < 0.1 mm/d and = or > greater than 0.1 mm/d, respectively. The present finding shows decreasing trend (p-value 0.039) of WDs days precipitation and intriguingly increasing trend (p-value 0.57) of Non-WDs days precipitation. These trends, though statistical not significant, are based on Mann–Kendall test. Further, Non-WDs days precipitation over the western Himalayas (WH) is less studied and researched. Thus dynamics of WDs vs Non-WDs precipitating days precipitation is evaluated and corresponding precipitation and moisture sources days are assessed. As knowingly, WDs precipitation is mainly from western sources and Arabian Sea (AS); whereas Non-WDs days precipitation derive moisture from Bay of Bengal (BoB). Present work presents preliminary investigation for Non-WDs days precipitation.
PubDate: 2023-05-25
- The onset and cessation of rainy season over the Hengduan Mountains
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Abstract: In this study, the onset and cessation of rainy season over the Hengduan Mountains (HM) are determined by an objective method. The onset and cessation of climatological rainy season are largely controlled by large-scale circulation systems, such as the Indian summer monsoon (ISM), 200 hPa subtropical jet, and the South Asian high. Both onset and cessation dates exhibit strong interannual variability. For late onset, the lower-level northeasterly anomalies over the north Indian Ocean (IO) delay the advance of moisture transported by ISM, and are excited by the positive SST anomalies over the southwest IO. In accord with late cessation, the equatorial west IO cooling adjusts the zonal overturn circulation and causes the west side wet anomalies, which trigger the north IO cyclonic wind anomalies and the northwest Pacific anticyclonic wind anomalies following Gill response. These two anomalous flows merge, turn southerly, and continuously transport moisture to the HM, prolonging the rainy season. At upper levels, the late onset and cessation related circulation anomalies are almost mirror images and highly resemble the Silk Road pattern. The anomalous upper and lower-level circulation cooperate and favor the dynamical and thermodynamical processes, which contribute to the vertical motion anomalies and finally affect the onset and cessation dates. Especially, the 200 hPa geopotential height anomaly center on the north side of the Arabian Sea (AS) is stronger than the other centers both for late onset and cessation, and coincides well with the nearby Rossby wave source, which are reinforced via the planetary vorticity stretching term due to the upper-level wind anomalies induced by the IO SST anomalies.
PubDate: 2023-05-23
- Process-based analysis of the impacts of sea surface temperature on
climate in CORDEX-SEA simulations-
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Abstract: This paper investigates the process behind climate model biases, especially in rainfall, during the southwest (June to August; JJA) and northeast monsoon (December to February; DJF) seasons over the Philippines using the downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations of the Southeast Asia Regional Climate Downscaling/Coordinated Regional Climate Downscaling Experiment-Southeast Asia (SEACLID/CORDEX-SEA). Biases in the surface and near-surface climate are assessed over land in eastern (EastPH) and western (WestPH) Philippines using observation and reanalysis datasets. Results show that models with well-represented sea surface temperature (SST) provided better added values after downscaling. Although the CMIP5-driven models tend to overestimate both surface energy and water partitioning, simulations with well-represented SST have better surface energy partitions. In contrast to the reference simulation driven by ERA-Interim reanalysis, the CMIP5-driven simulations tend to underestimate (overestimate) moisture flux convergence during the DJF (JJA) season, which might have contributed to the overall underestimation (overestimation) of rainfall in this season. Further investigation along a vertical transect shows the differences in governing mechanisms for each season. During DJF (JJA) season, the simulation with underestimated (overestimated) SST, near-surface air temperature, and mixing ratio results in underestimated (overestimated) rainfall over EastPH (WestPH). In addition, the CMIP5-driven models were found to overestimate low-level winds, which may have induced the deep convection regardless of season, suggesting the role of low-level winds in the convection scheme used in RegCM4 aside from topography and land cover.
PubDate: 2023-05-23
- Impacts of Pacific Ocean SST on the interdecadal variations of tropical
Asian summer monsoon onset: new eastward-propagating mechanisms-
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Abstract: Understanding the variability and mechanisms of monsoon onset is extremely prominent for water management and rain-fed agriculture. Previous studies have shown a significant interdecadal advance in Asian summer monsoon (ASM) onset after the late-1990s and attributed it to the sea surface temperature anomalies (SSTA) in the tropical Pacific. However, the westward-propagating mechanisms revealed by previous studies (Walker circulation, equatorial Rossby wave response) are gradually decaying westward, which cannot explain the observational facts of stronger low-level winds over the Arabian Sea than the South China Sea. Based on longer datasets and multiple methods, this study reveals the influences of Pacific SST on the interdecadal changes of ASM onset through two eastward-propagating mechanisms: the equatorial Kelvin wave response to the SSTA in the equatorial central Pacific, and the extratropical Rossby wave train associated with SSTA in the subtropical North Pacific. These two eastward-propagating mechanisms mainly modulate the ASM onset via altering the meridional temperature gradient, which is more evident over the Arabian Sea and is more consistent with the observations. Special attention has been paid to the generation and maintenance of the extratropical Rossby wave train, which is less understood compared to the other mechanisms. This Rossby wave train can be excited by the upper-level divergence associated with the warm SSTA in the subtropical North Pacific. In addition, it can effectively gain available potential energy and kinetic energy from the basic flow, and exhibits strong positive interactions with the synoptic-scale eddies. This Rossby wave train is a newly recognized mechanism by which the extratropical Pacific SSTA influences the tropical ASM.
PubDate: 2023-05-22
- Atlantic decadal-to-bidecadal variability in a version of the Kiel Climate
Model-
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Abstract: Atlantic decadal-to-bidecadal variability (ADV) is described from a multimillennial control integration of a version of the Kiel Climate Model (KCM). The KCM’s ADV is the second most energetic mode of long-term North Atlantic variability in that simulation, whereas the Atlantic multidecadal variability (AMV) is the leading mode that has been described in a previous study. The KCM’s ADV can be regarded as a mixed oceanic gyre-overturning circulation mode that is forced by the North Atlantic Oscillation. The extratropical North Atlantic sea surface temperature (SST) anomalies associated with the model’s ADV initially exhibit a tripolar structure in the meridional direction, which is linked to the gyre circulation. After some years, the SST-anomaly pattern turns into a monopolar pattern located in the subpolar North Atlantic. This transition is related to the overturning circulation. The AMV and the ADV co-exist and share some similarities. Both modes of variability rely on the upper-ocean heat transport into the subpolar North Atlantic. They differ in the importance of the gyre and overturning circulations. In the ADV, gyre and overturning-heat transports into the subpolar North Atlantic are equally important in contrast to the AMV where the overturning contribution dominates.
PubDate: 2023-05-20
- Performance evaluation of CMIP6 GCMs for the projections of precipitation
extremes in Pakistan-
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Abstract: Extreme weather events are more detrimental to human culture and ecosystems than typical weather patterns. A multimodel ensemble (MME) of the top-performing global climate models (GCMs) to simulate 11 precipitation extremes was selected using a hybrid method to project their changes in Pakistan. It also compared the benefits of using all GCMs compared to using only selected GCMs when projecting precipitation extremes for two future periods (2020–2059) and (2060–2099) for four shared socioeconomic pathways (SSPs), SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5. Results showed that EC-Earth3-Veg, MRI-ESM2-0 and NorESM2-MM performed best among GCMs in simulating historical and projecting future precipitation extremes. Compared to the MME of all GCMs, the uncertainty in future projections of all precipitation indices of the selected GCMs were significantly smaller. The MME median of the selected GCMs showed increased precipitation extremes over most of Pakistan. The greater increases were in RX1day by 6–12 mm, RX5day by 12–20 mm, Prcptot by 40–50 mm, R95ptot by greater than 30 mm, R99ptot by more than 9 mm, R4mm ≥ 4 mm by 0–4 days, R10mm by 2–6 days, R20mm by 1–3 days, and SDII by 1 mm/day, CWD by one day, CDD by 0–4 days in the northern high elevated areas for SSP5-8.5 in the late future. These results emphasize the greater influence of climate change on precipitation extremes in the northern, high-elevation areas, which provide the majority of the country’s water. This emphasizes the necessity to adopt suitable climate change mitigation strategies for sustainable development, particularly in the country's northern regions.
PubDate: 2023-05-20
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Hybrid journal (It can contain Open Access articles)
