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Climate Dynamics
Journal Prestige (SJR): 2.445
Citation Impact (citeScore): 4
Number of Followers: 44  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1432-0894 - ISSN (Online) 0930-7575
Published by Springer-Verlag Homepage  [2467 journals]
  • Correction to: Impacts of the strengthened Atlantic meridional overturning
           circulation on the North Atlantic sea surface temperature: mean state

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      PubDate: 2023-01-30
       
  • Assessment of the changing role of lower tropospheric temperature
           advection under arctic amplification using a large ensemble climate
           simulation dataset

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      Abstract: Abstract The role of temperature advection in the Arctic lower troposphere under changing level of global warming is investigated using a large-ensemble climate simulation dataset. Taking the 30-year climatology of the non-warming simulation (HPB-NAT) as a reference, we examined the difference in temperature advection under changing basic states of the historical experiment (HPB) and 2 K and 4 K warming experiments (HFB-2K and HFB-4K) and decomposed them into terms related to dynamical changes, thermodynamical changes and the eddy term which is a covariance term related to the effect of sub-monthly transient eddies. Under the HPB experiment, it was found that the total change in advection hangs in a balance between the positive signal located along the sea-ice boundary in the North Atlantic and along the Eurasian continent driven by a stronger dynamical term and a negative signal in the thermodynamical term and eddy term. It is found that with the progression of global warming the dynamical term of advection increases due to changes in the large-scale atmospheric circulation, but the thermodynamical term and eddy term decrease due to weaker temperature gradient and increased sensible heat flux from the newly opened ice-free ocean, respectively. Atmospheric temperature advection terms related to large-scale atmospheric circulation partially cancels one another, and the relative importance of the eddy term diverging locally induced sensible heat from the newly opened ice-free ocean dominates as global warming progresses.
      PubDate: 2023-01-30
       
  • Evaluation of the convection-permitting regional climate model
           CNRM-AROME41t1 over Northwestern Europe

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      Abstract: Abstract Since a decade, convection-permitting regional climate models (CPRCM) have emerged showing promising results, especially in improving the simulation of precipitation extremes. In this article, the CPRCM CNRM-AROME developed at the Centre National de Recherches Météorologiques (CNRM) since a few years is described and evaluated using a 2.5-km 19-year long hindcast simulation over a large northwestern European domain using different observations through an added-value analysis in which a comparison with its driving 12-km RCM CNRM-ALADIN is performed. The evaluation is challenging due to the lack of high-quality observations at both high temporal and spatial resolutions. Thus, a high spatio-temporal observed gridded precipitation dataset was built from the collection of seven national datasets that helped the identification of added value in CNRM-AROME. The evaluation is based on a series of standard climatic features that include long-term means and mean annual cycles of precipitation and near-surface temperature where CNRM-AROME shows little improvements compared to CNRM-ALADIN. Additional indicators such as the summer diurnal cycle and indices of extreme precipitation show, on the contrary, a more realistic behaviour of the CNRM-AROME model. Moreover, the analysis of snow cover shows a clear added-value in the CNRM-AROME simulation, principally due to the improved description of the orography with the CPRCM high resolution. Additional analyses include the evaluation of incoming shortwave radiation, and cloud cover using satellite estimates. Overall, despite some systematic biases, the evaluation indicates that CNRM-AROME is a suitable CPRCM that is superior in many aspects to the RCM CNRM-ALADIN.
      PubDate: 2023-01-30
       
  • Impact of sea ice transport on Beaufort Gyre liquid freshwater content

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      Abstract: Abstract The Arctic Ocean’s Beaufort Gyre (BG) is a wind-driven reservoir of relatively fresh seawater, situated beneath time-mean anticyclonic atmospheric circulation, and is covered by mobile pack ice for most of the year. Liquid freshwater accumulation in and expulsion from this gyre is of critical interest due to its potential to affect the Atlantic meridional overturning circulation and due to the importance of freshwater in modulating vertical fluxes of heat, nutrients and carbon in the ocean, and exchanges of heat and moisture with the atmosphere. Here, we investigate the hypothesis that wind-driven sea ice transport into/from the BG region influences the freshwater content of the gyre and its variability. To test this hypothesis, we use the results of a coordinated climate response function experiment with four ice-ocean models, in combination with targeted experiments using a regional setup of the MITgcm, in which we rotate the surface wind forcing vectors (thereby changing the ageostrophic component of these winds). Our results show that, via an effect on the net thermodynamic growth rate, anomalies in sea ice transport into the BG affect liquid freshwater adjustment. Specifically, increased ice import increases freshwater retention in the gyre, whereas ice export decreases freshwater in the gyre. Our results demonstrate that uncertainty in the ageostrophic component of surface winds, and in the dynamic sea ice response to these winds, has important implications for ice thermodynamics and freshwater. This sensitivity may explain some of the observed inter-model spread in simulations of Beaufort Gyre freshwater and its adjustment in response to wind forcing.
      PubDate: 2023-01-26
       
  • Internal variability plays a dominant role in global climate projections
           of temperature and precipitation extremes

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      Abstract: Abstract Climate projection uncertainty can be partitioned into model uncertainty, scenario uncertainty and internal variability. Here, we investigate the different sources of uncertainty in the projected frequencies of daily maximum temperature and precipitation extremes, which are defined as events that exceed the 99.97th percentile. This is done globally using large initial-condition ensembles. For maximum temperature extremes, internal variability that generates deviations about the ensemble average, dominates in the next 2 decades. Around the middle of the twenty-first century model and scenario uncertainty become the dominant contribution in the tropics but internal variability remains dominant in the extra-tropics. Towards the end of the century, model and scenario uncertainty increase to near equal contributions of \(\sim \) 40% each globally with large regional fluctuations. For precipitation extremes, internal variability dominates throughout the twenty-first century, except for some tropical regions, for example, West Africa. In regions where internal variability constitutes the major source of uncertainty, the potential impact of reducing model uncertainty on the signal-to-noise ratio of the climate projection is estimated to be small. We discuss the caveats of the methodology used and impact of our findings for the design of future climate models. The importance of internal variability found here emphasizes that large ensembles are a vital tool for understanding climate projections.
      PubDate: 2023-01-25
       
  • Spatiotemporal characteristics of clear-air turbulence (CAT) potential in
           China during 1979–2020

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      Abstract: Abstract Air turbulence, especially the clear-air turbulence (CAT), always affects flight safety. Based on six CAT diagnostics and ERA5 reanalysis data, the spatiotemporal characteristics of CAT potential in the middle and upper troposphere in China during 1979–2020 and the possible mechanisms are analyzed in this study. The results show that CAT occurs the most frequently in winter and spring at 250–300 and 200–225 hPa, respectively. In general, CAT occurs relatively less in summer and autumn. Moreover, the CAT potential decreases with altitude in each season, and the high-magnitude centers gradually move northward and eastward accompanied with a rising motion from winter to summer. During 1979–2020, the CAT potential shows clear increasing trends in most of China in winter, while decreasing trends in most regions in summer. In the “high CAT frequency region (HCFR, 75–135° E, 25–45° N)”, the CAT potential has been significantly increasing in winter and decreasing in summer. Mechanism analysis indicates that the spatiotemporal distribution of East Asian subtropical westerly jet is well correlated with the CAT potential in the HCFR, with the spatial (temporal) correlation coefficients greater than 0.75 (0.54). In addition, the geopotential height pattern in various regions, the zonal circulation in the Eurasia and Atlantic, the Polar Vortex, the Subtropical High, and the sea surface temperature all have significant impact on the CAT in the HCFR.
      PubDate: 2023-01-25
       
  • Intermodel uncertainty in response of the Pacific Walker circulation to
           global warming

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      Abstract: Abstract The Pacific Walker circulation (PWC) is one of the major atmospheric circulations that plays an essential role in ocean-atmosphere interactions and global climate. The response of the PWC to greenhouse warming remains a mystery and model results are inconsistent. Based on multimodel simulations from the Coupled Model Intercomparison Project phase 6 (CMIP6), this study explores the intermodel uncertainty of the change in the PWC under global warming. The combination of the El Niño-like warming pattern and the interbasin warming contrast between the Indian and Pacific Oceans strengthens (weakens) the west (east) branch of the Pacific trade winds, resulting in a structural shifting of the PWC. By conducting a set of Atmosphere General Circulation Model (AGCM) experiments, we demonstrate that the western Pacific warming plays a critical role in driving the PWC shift. An intensified western Pacific warming counteracts the effect of Indian Ocean warming on the PWC, leading to a uniformly weakened PWC in the tropical Pacific due to the SST gradient. In contrast, a decreased warming in the western Pacific strengthens the west branch of the PWC, shifting the turning longitude of zonal wind changes eastward. Our finding highlights that the relative warming pattern in the Indian and Pacific Oceans is coupled with the PWC change in a warmer climate.
      PubDate: 2023-01-24
       
  • Causes of the persistent merging of the western North Pacific subtropical
           high and the Iran high during late July 2022

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      Abstract: Abstract During late July 2022, the western North Pacific subtropical high (WNPSH) and the Iran high merge persistently, leading to concurrent extreme climate events over multiple regions. Such extraordinary circulation results from two extreme anticyclonic anomalies centered over the WNP–South Asia and Central Asia, respectively. The WNP–South Asia anticyclonic anomaly is related to La Niña SSTA pattern and the enhanced convection over the tropical eastern Indian Ocean (TEIO). SSTA serves as a seasonal-mean background, with abnormally cold tropical central Pacific (TCP) favoring the anticyclonic anomaly through Rossby wave response. The TEIO convection is extremely strong during late July and induces the anticyclonic anomaly via Kelvin wave response and a local Hadley circulation. The TEIO convection anomaly during late July results from different time scales, with the seasonal mean accounting for 30% and the 25–90-day intraseasonal oscillation (ISO) for 50%. The seasonal mean TEIO convection anomaly is related to La Niña, triggered by not only the local positive SSTA but also the negative TCP SSTA through the Walker circulation. The 25–90-day ISO features a northward-propagating convection dipole over the Indian Ocean. An enhanced ISO convection center develops over the TEIO during late July, which moves northward and is gradually replaced by suppressed convection. On the other hand, the Central Asia anticyclonic anomaly is associated with the Silk Road pattern propagating eastward along the westerly jet. During late July, a remarkable anticyclonic node moves across Central Asia, cooperating with the enhanced TEIO convection to facilitate the merging of the WNPSH and the Iran high.
      PubDate: 2023-01-23
       
  • What added value of CNRM-AROME convection-permitting regional climate
           model compared to CNRM-ALADIN regional climate model for urban climate
           studies ' Evaluation over Paris area (France)

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      Abstract: Abstract The convection-permitting regional climate model CNRM-AROME was applied on a spatial domain restricted to the northern half of France for analyzing its performances in simulating the urban climate of Paris region, and its potential added value compared to the regional climate model CNRM-ALADIN. In addition to its fine horizontal resolution (2.5 km compared to 12.5 km for CNRM-ALADIN), CNRM-AROME has the advantage of integrating the urban canopy model TEB into its land-surface modeling system. A hindcast simulation was performed for the past period 2000–2017, following an evaluation configuration for which CNRM-AROME was driven by CNRM-ALADIN, driven itself by the ERA-Interim reanalyses. Long-term gridded observations with kilometric resolution allowed a fine spatial scale evaluation of the atmospheric variables simulated by both models. They showed in particular a significant overestimation of spring precipitation, but an improvement of summer precipitation in CNRM-AROME compared to CNRM-ALADIN. Above all, thanks to its horizontal resolution and the use of a dedicated urban model, CNRM-AROME was shown to offer significant added value for the simulation of urban heat islands, for the mapping of heat-warming areas, and for representing the effects of the city on precipitation. It is a promising tool to diagnose climatic and impact indicators at the city scale, and their evolution in a changing climate.
      PubDate: 2023-01-23
       
  • Predictability of spatial distribution of pre-summer extreme precipitation
           days over southern China revealed by the physical-based empirical model

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      Abstract: Abstract Southern China is prone to floods during the wet season, and regional extreme precipitation is expected to become more frequent given the context of climate change. However, the prediction skills and predictability of the spatial distribution of extreme precipitation days (EPDs) over southern China remain unclear. To address this issue, through observational diagnosis and numerical experiment, the present study revealed the formation mechanisms of the two leading modes of pre-summer (May and June) EPDs in southern China, and established a physical-based empirical model (P-E model) to predict the distribution of EPDs in the region. The results revealed the following: (1) the first mode of pre-summer EPDs in southern China displayed a uniform pattern, while the second mode presented a meridional dipole pattern. The uniform pattern of the first mode is associated with the tropical western North Pacific anomalous anticyclone (TWPAC), whereas the meridional dipole pattern of the second mode is related to the subtropical western North Pacific anomalous anticyclone (SWPAC); (2) the spring North Atlantic tripole sea surface temperature (SST) pattern, the northern North America surface air temperature, and the snow cover depth over central Siberia contribute to the variation of the first mode and TWPAC, whereas the spring extratropical North Atlantic dipole SST pattern and the spring change of sea ice concentration over the Barents and Kara seas are physically linked with the variation of the second mode and SWPAC; (3) based on these predictors, the established P-E model demonstrated predictive skill with regard to the principal components of the first two modes, and the spatial distribution of EPDs in southern China was reconstructed. The areal mean temporal correlation coefficient skill for the independent prediction period (2011–2021) was 0.34, while for the pattern correlation coefficient skill averaged over the entire period was 0.28. In comparison with the maximum attainable skills, both metrics indicate potential for improvement. The findings of this study represent a reference for the prediction and predictability of the spatial distribution of pre-summer EPDs in southern China.
      PubDate: 2023-01-23
       
  • Mechanisms of tropical cyclone response under climate change in the
           community earth system model

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      Abstract: Abstract Climate change induces a myriad of effects which influences the global tropical cyclone (TC) genesis frequency. Here we explore how North Atlantic and Western Pacific TCs are affected under climate change using a present-day and a future (1% pCO2 scenario) ensemble of high resolution simulations. We find that the number of TCs decreases ( \(-45\%\) ) in the North Atlantic but increases ( \(+15\%\) ) in the Western Pacific. Part of these opposing variations are linked to differences in the ocean’s meridional overturning circulation, which gives rise to a different sea surface temperature response and air-sea fluxes between the two basins. The results show the important role of oceanic climate change on TC response.
      PubDate: 2023-01-22
       
  • Tropical cyclone strength, precipitation, and environment in variable
           resolution CAM-MPAS simulations over Western North Pacific

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      Abstract: Abstract The multi-year simulation of tropical cyclones (TCs) over the Western North Pacific (WNP) in the variable resolution (VR) CAM-MPAS model is studied. Experiments with the global quasi-uniform low resolution of 120 km (MPAS-UR) and the variable resolution mesh of 30–120 km refined over East Asia (MPAS-VR) are integrated from 1980 to 2005 following the Atmospheric Model Intercomparison Project protocol. By utilizing an objective detection method, TCs in ERA5 reanalysis and model simulations are tracked and compared against observations. MPAS-VR shows significant advantages over MPAS-UR as indicated by more realistic TC counts, intensities, lifetime distribution, and seasonal variation. The large-scale circulation and precipitation patterns associated with TCs are also improved in MPAS-VR relative to MPAS-UR. Based on the theory of Dynamic Genesis Potential Index, the multi-year TC records are further used to quantify the dependence of TC genesis on various dynamical environmental factors from the perspective of seasonal variation. We find that in ERA5, the relative contribution of the 500 hPa vertical pressure velocity term to TC genesis exceeds that of the 200–850 hPa vertical wind shear term, which is responsible for the August peak and strong seasonal variation of TC genesis. MPAS-UR fails to capture such relationship while MPAS-VR performs much better in this regard, suggesting that the higher skills in simulating the relative contributions from different dynamical environmental factors to the simulated seasonal cycle of TC genesis may explain the improvements from MPAS-UR to MPAS-VR.
      PubDate: 2023-01-22
       
  • Indian Ocean dynamic sea level, its variability and projections in CMIP6
           models

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      Abstract: Abstract The regional sea level variability and its projection amidst the global sea level rise is one of the major concerns for coastal communities. The dynamic sea level plays a major role in the observed spatial deviations in regional sea level rise from the global mean. The present study evaluates 27 climate model simulations from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) for their representation of the historical mean states, variability and future projections for the Indian Ocean. Most models reproduce the observed mean state of the dynamic sea level realistically; however, consistent positive bias is evident across the latitudinal range of the Indian Ocean. The strongest sea level bias is seen along the Antarctic Circumpolar Current (ACC) regime owing to the stronger than observed south Indian Ocean westerlies and its equatorward bias. This equatorward shift of the wind field also results in a stronger positive windstress curl across the southeasterly trade wind regime in the southern tropical basin and an easterly wind bias along the equatorial waveguide. Owing to the anomalous easterly equatorial winds, the thermocline in the eastern tropical basin is shallower in the models than observed, resulting in enhanced variability there. Such spurious variability in the eastern part of the basin causes models to become biased towards the dipole zonal mode or Indian Ocean dipole patterns in the tropics. In the north Indian Ocean, the summer monsoon winds are weak in the model leading to weaker coastal upwelling and positive sea level bias along the western Arabian Sea. Further, it is noted that the high-resolution models compare better in simulating the sea level variability, particularly in the eddy-dominated regions like the ACC regime in interannual timescale. However, these improved variabilities do not necessarily produce a better mean state likely due to the spurious enhanced mixing driven by parametrizations set in these high-resolution models. Finally, the overall pattern of the projected dynamic sea level rise is similar for the mid (SSP2-4.5) and high-end (SSP5-8.5) scenarios, except that the magnitude is higher under the high emission situation. Notably, the projected dynamic sea level change is milder when only the best-performing models are used compared to the complete ensemble.
      PubDate: 2023-01-21
       
  • Evolution of high-temperature extremes over the main Euro-Mediterranean
           airports

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      Abstract: Abstract The increasing intensity and frequency of high-temperature events in response to climate change can potentially impact the aviation industry, since aircraft takeoff and landing performances depend on near-surface air temperature. Previous studies have combined climate data with aircraft technical data to estimate the future impact of rising high temperatures on aircraft takeoff. They found a decrease of maximum takeoff weights and the lengthening of takeoff distances. The Mediterranean region is a climate change “hot spot” area, specially concerned by extreme high-temperatures increase. In this study, the magnitude and trends of the daily maximum near-surface temperature extremes in summer were analysed over major airports in Southwestern Europe. Trends in the period 1961–2014 were analysed from observations and reanalysis. Future changes by 2021–2050 and 2071–2100, with respect to 1961–2005, were analysed from simulations performed with Regional and Global Climate Models (RCMs and GCMs). Before assessing future climate projections, climate models were evaluated in present climate, and the RCM and GCM ensembles were compared to each other. No clear added value was found for RCMs over GCMs in present climate at the airport scale in these terms. GCMs project larger temperature changes than RCMs over the same locations. Multi-model ensemble mean projected changes under the RCP8.5 scenario range between + 1.7 and + 3.2  \(^{\circ }\) C by the near term, and between + 4.9 and + 8.5  \(^{\circ }\) C by the long term, across the airports and the RCM and GCM ensembles. This increase of high-temperature extremes would impact airport operations. Adaptation or mitigation policies would become necessary.
      PubDate: 2023-01-20
       
  • Asymmetric impacts of El Niño–Southern Oscillation on the winter
           precipitation over South China: the role of the India–Burma Trough

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      Abstract: Abstract The winter precipitation over South China (SCWP) can exert great impacts on the local ecosystem and human livelihood. Previous studies suggested that the inter-annual variability of SCWP can be affected by the El Niño-Southern Oscillation (ENSO) via the Northwest Pacific anticyclone (NWPAC). The present study investigates the role of the India–Burma Trough (IBT) in mediating the teleconnection between ENSO and the SCWP. During the El Niño mature winter, the slowdown of Walker circulation is evident over the tropical Indian Ocean (TIO). The low-level easterly wind anomaly is pronounced from the warm pool to the western TIO, which turns into the westerly wind anomaly over the northern TIO basin and then enhances IBT. Meanwhile, the Kelvin wave in the upper troposphere stimulated by El Niño propagates eastward toward Indian Ocean and induces the tropospheric warming over TIO. The resultant increase of the meridional temperature gradient leads to the southward shift of the westerly jet stream which favors the strengthening of IBT and the increase of SCWP. It is further shown that the IBT change is unclear in La Niña. This nonlinear feature can be largely attributed to the asymmetry in both ENSO amplitude and ENSO-related circulation anomalies. The present findings highlight the role of IBT, in addition to the well-known NWPAC, in bridging ENSO and SCWP.
      PubDate: 2023-01-19
       
  • Radiative effects of observationally constrained tropical upper-level
           clouds in a radiative-convective equilibrium model

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      Abstract: Abstract Tropical upper-level clouds (TUCs) control the radiation budget in a climate system and strongly influence surface temperatures. This study examines global mean surface temperature changes due to the percent change in TUC cover, which is referred to as the tropical upper-level cloud radiative effect (TUCRE, in units of Kelvin per %). We use a radiative-convective equilibrium model that can control both upper- and lower-level cloud layers separately in three idealized regions (extratropics, tropical moist, and tropical dry regions) and two sub-regions (clear-moist and cloudy-moist regions) within the tropical moist regions. In the simulation, tropical reflectivity based on the TUC fraction assumes a primary role in determining the TUCRE. Accurate estimate of the TUCRE requires careful prescriptions according to actual satellite observations. We use the extent of TUC fraction and reflectivity obtained from 18 years (2003–2020) of satellite data on daily MODIS cloud properties. Our results show that the estimated net TUCRE ranges from 0.19 to 0.33 K/%, with a higher TUC fraction leading to higher temperatures (a warming effect) in the climate system. This means that a longwave TUCRE dominates over a shortwave TUCRE. When upper- and lower-level clouds interplay in the model, the range of the TUCRE was greater with a combination of two cloud layers, although all values were positive. The TUCRE is greater by 0.22 to 0.40 K/% when upper- and lower-level clouds are negatively coupled, because the Earth warms due to a decline in the reflectance of solar radiation. When upper- and lower-level clouds are positively coupled, the TUCRE is lower by 0.14 to 0.30 K/%, as less radiation reaches the Earth through combined cloud layers. Finally, we test the sensitivity of the TUCRE with five TUC fractions and 15 combinations of tropical reflectivity. Comparing our results with the TUCREs estimated from climate models will help us understand how TUC cover affects climate, and should greatly reduce uncertainty associated with cloud feedback.
      PubDate: 2023-01-18
       
  • Multifaceted characteristics of summer heat and affected population across
           China under climate change

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      Abstract: Abstract Excessive heat can cause discomfort, stress even mortality to humans. We investigate the multifaceted characteristics of summer heat and the affected population across China using a composite heat index (HI) based on meteorological observations and the Coupled Model Intercomparison Project Phase 6 climate models. We highlight that HI is only applicable when maximum air temperature is above 26.7 ℃. From 1961 to 2014, China has experienced increasing heat days (1.05 day/10a) and severity (0.15 ℃/10a) with more population influenced by expanding heat extent. Simultaneously, increases in the frequency (7.58–14.80 times), duration (0.46–1.23 days) and intensity (1.00–1.42 ℃/day) of heat events are detected with increased population exposure (9.33 × 105–5.59 × 106 times·persons). In the future, increases in heat severity, spatial extent, and the affected population would be aggravated from 1.5 to 2 to 3 ℃ warming. Dangerous heat events would experience increases in frequency (12.67–70.81 times), duration (0.85–7.21 days), intensity (1.78–8.57 ℃/day), and population exposure (2.06 × 106–3.18 × 107 times·persons) under a warming climate. Some regions over the Tibetan Plateau and southwest China would be affected by expanding cautionary and extremely cautionary heat. Northwest China would experience intensified dangerous heat events whereas southeastern China would face longer-lasting heat events with stronger intensity. Precautionary strategies are essential for these regions under risk.
      PubDate: 2023-01-17
       
  • Revised cloud processes to improve the simulation and prediction skill of
           Indian summer monsoon rainfall in climate forecast system model

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      Abstract: Abstract The performance of six-class weather research forecasting (WRF) single moment (WSM6) cloud microphysical scheme in the National Centre for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2) at T126 (~ 100 km) horizontal resolution in the simulation and prediction skill of the Indian summer monsoon (ISM) is investigated with 34 years of hindcast runs with 10 ensemble members. The results reveal that the revised version of CFSv2 (EXPT) shows relative improvement in summer monsoon precipitation, its variability, rainfall annual cycle, rainfall probability distribution function, synoptic and intraseasonal variance, etc. over ISM region compared to standard CFSv2 (CTRL). Robust representation of cloud hydrometeors in the WSM6 microphysics scheme leads to better large-scale precipitation distribution compared to CTRL simulation which resulted in realistic northward propagation of rainfall bands in the EXPT. The interannual variability of rainfall in EXPT simulation suggests improved prediction skill of summer monsoon than CTRL run and comparable to higher resolution (T382; ~ 38 km) version of CFSv2. The above improvements are mainly attributed to the better simulation of vertical and spatial distribution of cloud hydrometeors in the EXPT simulation. Further, the cold bias in sea surface temperature (SST) in CTRL simulation is replaced with slightly warm bias in EXPT run which has resulted in wet bias in precipitation over the tropical oceanic region. Introduction of more physically based cloud physics parameterization helps to improve the cloud hydrometeor, cloud variability, and the rainfall variability.
      PubDate: 2023-01-17
       
  • Robustness of precipitation Emergent Constraints in CMIP6 models

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      Abstract: Abstract An Emergent Constraint (EC) is a physically-explainable relationship between model simulations of a past climate variable (predictor) and projections of a future climate variable (predictand). If a significant correlation exists between the predictand and the predictor, observations of the latter can be used to constrain model projections of the former and to narrow their uncertainties. In the present study, the EC technique has been applied to the analysis of precipitation, one of the variables most affected by model uncertainties and still insufficiently analysed in the context of ECs, particularly for the recent CMIP6 model ensemble. The main challenge in determining an EC is establishing if the relationship found is physically meaningful and robust to the composition of the model ensemble. Four precipitation ECs already documented in the literature and so far tested only with CMIP3/CMIP5, three of them involving the analysis of extreme precipitation, have been reconsidered in this paper. Their existence and robustness are evaluated using different subsets of CMIP5 and CMIP6 models, verifying if the EC is still present in the most recent ensemble and assessing its sensitivity to the detailed ensemble composition. Most ECs considered do not pass this test: we found one EC not to be robust in both CMIP5 and CMIP6, other two exist and are robust in CMIP5 but not in CMIP6, and only one is verified and is robust in both model ensembles.
      PubDate: 2023-01-17
       
  • The South Atlantic Ocean as a moisture source region and its relation with
           precipitation in South America

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      Abstract: Abstract We explore the South Atlantic as a moisture source for South America and its relationship with the precipitation variability in southeastern South America (SESA) during the 1982–2015 period. Based on diagnostic calculation with a Semi-Lagrangian analytical model, three regions of the South Atlantic acting as moisture sources for South America were studied: the Tropical Atlantic (15° N–5° S), Subtropical Atlantic (30° S–5° S), and Southwestern Atlantic (21° S–50° S; 30° W to the further west). The Tropical and Subtropical Atlantic are important sources of moisture for the Amazon, and occasionally for SESA. The Southwestern Atlantic contributes mainly locally, although in summer it also has a role in increasing precipitation over Uruguay and southern Brazil. Approximately 17% of the observed precipitation over the La Plata basin comes from the three regions identified as moisture source in the South Atlantic. Sea surface temperature variability is related to the moisture contribution from the South Atlantic to the continent. In summer, a significant positive correlation between the sea surface temperature leading-mode and the precipitation contribution from the Tropical Atlantic and La Plata Basin is found. A significant negative correlation between the sea surface temperature leading-mode and contribution in terms of precipitation from the Southwest Atlantic was found, as warm anomalies are associated with an anomalous cyclonic circulation over the Southwest Atlantic that favors moisture transport to SESA. Finally, the study of individual precipitation events identified contributions from the Subtropical and Southwest Atlantic to particular daily precipitation events in SESA. Climatological contributions from the Southwestern Atlantic are low, however, in events such as these, their contribution can increase up to 40% on the synoptic scale.
      PubDate: 2023-01-17
       
 
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