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Future projections indicate that Indian Summer Monsoon Rainfall (ISMR) faces a "wetter and more variable" climate. However, the reasons remain uncertain. The Last Interglacial (LIG) climate provides a potential analog for future warming. Investigating ISMR responses to these two warming scenarios could help understand the causes of ISMR changes. Using PMIP4 simulations, we find that ISMR became "wetter and more stable" during the LIG, contrasting the future climate. The opposing changes in ISMR variability are related to divergent changes in the El Niño‐Southern Oscillation (ENSO) amplitudes, ENSO‐ISMR relationships, and ENSO‐induced large‐scale atmospheric circulation anomalies. During the LIG, orbital forcing weakened ENSO variability and its impacts on ISMR. A westward positioning of ENSO shifted the atmospheric circulation anomalies westward, suppressing extreme ISMR anomalies. These processes are supported by atmospheric model simulations. Our results suggest that different warming patterns (dynamic effects) are more critical than moisture‐increasing effects in controlling regional climate variability. Plain Language Summary: The Last Interglacial (LIG), approximately 129,000 to 116,000 years before the present, is a potential analog for future warming. We found that the variability of Indian Summer Monsoon Rainfall (ISMR) decreased while its mean state increased during the LIG, which is a "wetter and more stable" climate. This contrasts with the simultaneous increase in both the mean state and variability of ISMR projected in future warming scenarios. The opposing changes in ISMR variability during these two warm periods can be attributed to reverse changes in El Niño‐Southern Oscillation (ENSO) variability and its associated large‐scale circulation. During the LIG, reduced ENSO variability weakened the ENSO‐ISMR relationship. Sea surface temperature anomalies associated with ENSO extended westward in LIG, shifting precipitation and associated heating‐induced atmospheric circulation anomalies westward, which weakened the extreme ISMR anomalies, thus making the ISMR variability stable. This process is further supported by atmospheric general circulation model (CAM5) experiments. Our findings suggest that different external forcing‐induced warming patterns (dynamic effects) can be more critical than moisture‐increasing effects in contributing to regional climate variability change. Key Points: Indian Summer Monsoon Rainfall (ISMR) experienced a more stable climate during the LIG opposite to the change under anthropogenic warmingRelationship between ISMR and ENSO significantly weakened due to the waning ENSO variability induced by orbital forcingA westward positioning of ENSO during the LIG shifted the anomalous large‐scale circulation westward, reducing the extreme ISMR anomalies [ABSTRACT FROM AUTHOR]

The dominant influence of precession‐induced changes in summer insolation on orbital‐scale variability of the Asian summer monsoon (ASM) during the Holocene has been widely proposed; however, it remains unclear why the decline of the ASM started several thousand years after the peak summer insolation. Through comparisons of climate simulations and proxy records, our study reveals that the abrupt decline in the ASM coincided with an increase in spring insolation at the equator. The reduced spring insolation resulted in a cooler tropical Indian Ocean, which weakened and shifted northward the westerly jet due to decreased meridional thermal gradient. The South Asian high moved northward in conjunction with the westerly jet, causing anomalous upwards over northern South Asia, the Tibetan Plateau, as well as southwestern and northern China. The associated anomalous cyclone over the Tibetan Plateau enhanced the monsoonal moisture transport, subsequently intensifying the ASM circulation and precipitation. The ASM was enhanced by the decrease in spring insolation and was weakened by the opposite. The abrupt decline of the ASM was associated with an increase in spring insolation superimposed on a decrease in summer insolation. Consequently, orbital‐scale ASM variability is dominated by the precession not only via insolation changes in summer but also changes in spring. Plain Language Summary: It is widely acknowledged that orbital‐scale Asian summer monsoon (ASM) variability was controlled by precession‐dominated changes in Northern Hemisphere summer insolation. However, it is still not clear why the ASM did not weaken in response to the initial decrease in summer insolation (e.g., during the early to mid‐Holocene), as evidenced in numerous records. This study explores the underlying dynamics driving the decline of the ASM by comparing climate simulations with proxy records. Our findings reveal that an abrupt decline in the ASM commenced from minimum spring insolation at the equator, lagging the peak summer insolation by several thousand years. Reduced spring insolation had a prolonged impact on cooling of the tropical Indian Ocean in summer, leading to a decrease in meridional thermal gradient. Consequently, both westerly jet and South Asian high shifted northward, intensifying the ASM circulation and precipitation. The decreasing spring insolation slowed down the decline of the ASM, while the rising spring insolation accelerated it. Hence, an abrupt decline in the ASM was driven by increasing spring insolation superimposed on decreasing summer insolation. Key Points: An abrupt decline in the Asian summer monsoon (ASM) kept pace with the rise in equatorial spring insolationEquatorial spring insolation exerted a prolonged impact on the tropical Indian Ocean in the following summerThe ASM was modulated by the tropical Indian Ocean via shifting the Asian subtropical westerly jet [ABSTRACT FROM AUTHOR]

Toward the achievement of reliable global kilometer‐scale (k‐scale) climate simulations, we improve the Nonhydrostatic ICosahedral Atmospheric Model (NICAM) by focusing on moist physical processes. A goal of the model improvement is to establish a configuration that can simulate realistic fields seamlessly from the daily‐scale variability to the climatological statistics. Referring to the two representative configurations of the present NICAM, each of which has been used for climate‐scale and sub‐seasonal‐scale experiments, we try to find the appropriate partitioning of fast/local and slow/global‐scale circulations. In a series of sensitivity experiments at 14‐km horizontal resolution, we test (a) the tuning of terminal velocities of rain, snow, and cloud ice, (b) the implementation of turbulent diffusion by the Leonard term, and (c) enhanced vertical resolution. These tests yield reasonable convection triggering and convection‐induced tropospheric moistening, and result in better performance than in previous NICAM climate simulations. In the mean state, double Intertropical Convergence Zone bias disappears, and the zonal contrast of equatorial precipitation, top‐of‐atmosphere radiation balance, vertical temperature profile, and position/strength of subtropical jet are reproduced dramatically better. Variability such as equatorial waves and the Madden–Julian oscillation (MJO) is spontaneously realized with appropriate spectral power balance, and the Asian summer monsoon, boreal‐summer MJO, and tropical cyclone (TC) activities are more realistically simulated especially around the western Pacific. Meanwhile, biases still exist in the representation of low‐cloud fraction, TC intensity, and precipitation diurnal cycle, suggesting that both higher spatial resolutions and further model development are warranted. Plain Language Summary: In the near future, increasing computational power will make it possible to perform a global kilometer‐scale "cloud‐resolving" model (GCRM) simulation on the climate time scale, which is expected to reduce the uncertainty of cloud‐related processes in the climate system. In this sense, it is important to make GCRMs more reliable tools in the evaluation and prediction of the variabilities over a wide range of spatio‐temporal scales. With this perspective, we improve a Japanese GCRM, the Nonhydrostatic Atmospheric Icosahedral Model (NICAM), to achieve the realistic representation of both weather phenomena and climatological features in long‐term simulations. We revise the NICAM by the reconsideration of cloud microphysics properties, the implementation of diffusion processes around strong convection cores, and increased vertical layers. These revisions lead to the substantial improvements in the climatological mean precipitation distributions, radiative energy balance at the top of the atmosphere, westerly jets in the mid‐latitude, and temperature fields. We also find that weather phenomena such as the Asian summer monsoon and tropical cyclone (TC) genesis are simulated more realistically. We expect that, in addition to the above model improvements, kilometer‐scale horizontal resolutions can resolve a part of remaining issues of the representation of TC intensity and precipitation diurnal cycle. Key Points: We improve a global nonhydrostatic atmospheric model focusing on resolution‐independent errors that can exist even in k‐scale climate runsKey improvements are retuning of cloud microphysics properties, consideration of grid‐scale turbulent mixing, and increased vertical layersBiases in mean rainfall, radiation balance, and circulation as well as weather (monsoon, Madden–Julian oscillation, equatorial wave, tropical cyclone) are reduced [ABSTRACT FROM AUTHOR]

Estimates of the tropical cloud feedback of global climate models (GCMs) show a large inter‐model spread due to the small‐scale nature of convective cloud processes. Estimates from large‐eddy simulations (LES) are more consistent among themselves, but difficult to scale to the climate system. Here we consider a compromise between GCMs and LES, and study how tropical clouds over the Atlantic respond to a climate perturbation in a regional kilometer‐resolution model. We perform two 4‐year‐long simulations at 3.3 km horizontal grid spacing with the limited‐area model COSMO on a 9,000 × 7,000 km2 domain covering the tropical Atlantic: a control simulation and a climate change simulation using the pseudo‐global warming approach. In a previous publication we have demonstrated that this approach yields a credible representation of the tropical climate without the double‐ITCZ bias commonly seen in GCMs. Here we address the cloud feedback and find a reduction of ITCZ high‐cloud cover resulting in a negative longwave cloud feedback similar to the CMIP6 ensemble mean. We find a reduction of stratocumulus clouds, which we argue is primarily a thermodynamic response. More surprisingly, the shallow cumulus cloud cover over the West Atlantic increases, which we argue is due to increased stability resulting in weaker entrainment and a more humid boundary layer. The mean shortwave cloud feedback over the tropical Atlantic is positive, comparable to the CMIP6 ensemble mean. The emerging estimate of the total cloud‐radiative feedback over the Atlantic is slightly negative, consistent with CMIP6 GCMs, but it is substantially stronger than that of the driving GCM. Plain Language Summary: The response of tropical clouds to climate change is considered an important, but highly uncertain climate feedback mechanism. In this study, we perform high‐resolution climate simulations over the tropical Atlantic to obtain an estimate of tropical cloud changes over a large region based on a higher model resolution than typically used in global climate models (GCMs). This modeling approach yields a credible representation of the tropical climate with an improved representation of clouds compared to GCMs. The high‐resolution simulations project a reduction of high clouds in the deep tropics and a reduction of stratocumulus clouds in the East Atlantic in a warming climate. These results qualitatively agree with previous work. More surprisingly, the West Atlantic shallow cumulus cloud fraction increases with warming. The estimated longwave cloud feedback is more negative than in the analyzed CMIP6 GCMs while the shortwave cloud feedback is similar to the GCMs, resulting in a net cloud feedback comparable to the GCMs. However, the simulated feedback is substantially stronger than in the driving GCM. Key Points: We study tropical cloud changes and radiative feedbacks over the Atlantic in kilometer‐resolution climate‐change simulationsWe find a reduction of high and low clouds in most of the domain, while the West Atlantic shallow cumulus cloud fraction increasesThe emerging estimate of the cloud feedback is slightly negative, consistent with CMIP6 GCMs, but less negative than that of the driving GCM [ABSTRACT FROM AUTHOR]

In this study, the added value in using the sea level pressure field from the coupled higher‐resolution version of the Max Planck Institute Earth System Model (MPI‐ESM‐HR), compared to the lower‐resolution version (MPI‐ESM‐LR) for circulation typing, within the regional context of Western Europe was examined. The results show that the MPI‐ESM‐HR and the MPI‐ESM‐LR simulations can produce the classified circulation types (CTs) and their long‐term statistical characteristics as obtained from the ERA5 reanalysis. Overall, there are improvements in the composite maps, probability of occurrence and annual cycle of the simulated CTs in the MPI‐ESM‐HR compared to the MPI‐ESM‐LR. The model bias in simulating the structure of anticyclonic circulations over the Western European landmass was reduced by 14% under MPI‐ESM‐HR. Furthermore, under the shared socio‐economic pathways (SSP2‐4.5 and SSP5‐8.5) future emission scenarios, the historical CTs in the region of assessment were classified, suggesting that in Western Europe, the same historical CTs are present under future climate change scenarios. However, the frequency distribution and geographical structure of some of the CTs in Western Europe are projected to change by the MPI‐ESM model, especially under the higher future emission scenario. [ABSTRACT FROM AUTHOR]

Whether the South Asian summer monsoon (SASM) is controlled by local or remote insolation at the orbital band remains uncertain. Here, we perform a transient simulation forced by Earth's orbital parameters between 400 and 350 ka BP, a period characterized by significant contrast between local and remote insolation, to identify the SASM's response to insolation forcing. Simulation results suggest that the primary driver of orbital‐scale SASM variability is the Northern Hemisphere high‐latitude June insolation, as opposed to local insolation. High June insolation in the Southern Hemisphere might reduce the SASM intensity. Remote insolation influences the SASM by altering the latitudinal thermal gradient and, consequently, the meridional position of the South Asian high (SAH). The SAH is associated with intense convection and hence drives the meridional shift of the intertropical convergence zone and the SASM rain belt. Thus, orbital‐scale SASM variability is strongly related to remote insolation forcing. Plain Language Summary: Because the monsoon is directly related to the movement of the subsolar point, insolation changes are important in regulating the South Asian summer monsoon (SASM) intensity at an orbital timescale. However, it remains unclear whether the SASM is driven by local insolation that directly strikes southern Asia, or remote insolation in the high‐latitude Northern Hemisphere or the Southern Hemisphere at the precession band. We find a time window between 400 and 350 ka BP (ka = thousand years, BP = before present) when local and remote insolations differ significantly, allowing us to determine which insolation dominates the SASM at orbital timescales. We use an Earth system model with orbital forcing to run a transient simulation between 400 and 350 ka BP. Simulations suggest that the SASM is primarily influenced by Northern Hemisphere high‐latitude summer insolation rather than local insolation. Additionally, Southern Hemisphere insolation has a negative impact on orbital‐scale SASM variability. Remote insolation influences the SASM by inducing an anomalous meridional thermal gradient, which moves the South Asian high and thus the Intertropical Convergence Zone. Our findings are significant for future SASM projections because the obvious difference between remote and local insolation will reappear in the next 50 ka. Key Points: Local insolation is not the direct driver for orbital‐scale variability of the South Asian summer monsoon (SASM)The meridional shift of the South Asian high (SAH) affects orbital‐scale SASM variabilityRemote insolation influences the meridional shift in the SAH through altering the latitudinal thermal contrast [ABSTRACT FROM AUTHOR]

Clouds over tropical oceans are an important factor in the Earth's response to increased greenhouse gas concentrations, but their representation in climate models is challenging due to the small‐scale nature of the involved convective processes. We perform two 4‐year‐long simulations at kilometer‐resolution (3.3 km horizontal grid spacing) with the limited‐area model COSMO over the tropical Atlantic on a 9,000 × 7,000 km2 domain: A control simulation under current climate conditions driven by the ERA5 reanalysis, and a climate change scenario simulation using the Pseudo‐Global Warming approach. We compare these results to the changes projected in the CMIP6 scenario ensemble. Validation shows a good representation of the annual cycle of albedo, in particular for trade‐wind clouds, even compared to the ERA5 reanalysis. Also, the vertical structure and annual cycle of the intertropical convergence zone (ITCZ) is accurately simulated, and the simulation does not suffer from the double ITCZ problem commonly present in global climate models (GCMs). The response to global warming differs between the COSMO simulation and the analyzed GCMs. While both exhibit an overall weakening of the Hadley circulation, the narrowing of the ITCZ (known as the deep‐tropics squeeze) is not so pronounced in the kilometer‐resolution simulation, likely due to the absence of a double ITCZ bias. Also, there is a more pronounced intensification of the ITCZ at the equator in the kilometer‐resolution COSMO simulation, and a stronger associated increase in the anvil cloud fraction. Plain Language Summary: Tropical clouds are an important component of the climate system as they can either amplify or dampen human‐induced climate change. However, predicting how clouds will change in a warming climate is challenging due to their small‐scale nature. We perform high‐resolution atmospheric climate simulations over the tropical Atlantic to study what we can learn about tropical clouds from this relatively novel type of models. We validate the simulation under current climate conditions and find a good representation of tropical clouds in comparison to coarser climate models. In particular, the high‐resolution simulation does not suffer from the double intertropical convergence zone (ITCZ) problem commonly present in global climate models. We then study how tropical clouds will change in a warming climate and find differences between our high‐resolution simulation and coarser climate simulations. The tropical overturning (Hadley) circulation weakens in both model types, but the narrowing of the ITCZ (known as the deep‐tropics squeeze) is not so pronounced in the high‐resolution simulation, likely due to the absence of a double ITCZ bias. Key Points: We perform a km‐resolution climate simulation over the tropical Atlantic for current and future climate conditions using the Pseudo‐Global Warming approachWe find an accurate representation of the annual cycle of shallow cumulus clouds and a realistic structure of the intertropical convergence zone (ITCZ), without double ITCZThe ITCZ shows a stronger central intensification and weaker narrowing with warming than in the global climate models [ABSTRACT FROM AUTHOR]

The causes of the decreased intensity of the East Asian summer monsoon (EASM) over the past 150 years are still not fully understood, although several studies have linked the monsoon weakening to the warming of tropical oceans. Here, we use pine tree‐rings to reconstruct the precipitation total for April–August from 1810 to 2018, in south‐central Shandong Province, in the EASM region. The reconstruction accounts for 41.8% of the instrumental precipitation variance during 1965–2018. The EASM precipitation reconstruction shows extreme pluvial conditions in 1832, 1833, 1886, and 1998, and extreme droughts in 1878, 1901, and 1910, which correspond precisely to extreme climatic events recorded in historical documents. The reconstructed precipitation reveals a drying trend since the 1870s, which matches well with the decreasing trend of the EASM inferred from stalagmite oxygen isotope (δ18O) records and climate simulations. The trend of decreasing precipitation since the 1870s, indicated by our reconstruction, is significantly correlated with the spring sea surface temperature (SST) of the North Atlantic Ocean, which suggests that the EASM weakening was linked to North Atlantic SST variations during the past 150 years. This potential role of North Atlantic SST variability is supported by climate sensitivity simulations of the Community Earth System Model. North Atlantic SST variability induces two teleconnections of Rossby‐like wave propagation from the North Atlantic into East Asia, resulting in anomalous precipitation in this region. Key Points: A 209‐year precipitation reconstruction was established from the south‐central Shandong, the monsoonal eastern China used pine tree ringsSeveral historical severe droughts are captured by the reconstructed precipitation, and 20th century was dominated by dry conditionsThe trend of decreasing precipitation since the 1870s correlates significantly with spring sea surface temperature in the North Atlantic [ABSTRACT FROM AUTHOR]

Understanding millennial‐scale East Asian summer monsoon (EASM) variability is critical for climate projection in East Asia in the context of slowing Atlantic Meridional Overturning Circulation (AMOC) caused by global warming. This study performs two groups of sensitivity experiments at 8.2 and 4.2 ka BP, both forced by the same North Atlantic freshwater hosing and corresponding orbital parameters using the Community Earth System Model, to explore the orbital effect on millennial‐scale EASM variability. Our simulations reveal that EASM variability differs significantly between these two cold events. During the 8.2 ka BP (4.2 ka BP) (0 BP = 1950 AD) cold event, North Atlantic freshwater forcing weakens the EASM, generating a meridional tripole (dipole) pattern of EASM precipitation anomalies. Furthermore, the same freshwater discharge causes a greater decline in the EASM, contrasting to a slight weaker AMOC slowdown, at 4.2 ka BP than at 8.2 ka BP. This suggests orbital parameters significantly influence the EASM response to North Atlantic cold events. The East Asian subtropical westerly jet, whose meridional position and intensity are controlled by summer insolation on an orbital timescale, plays a key role in this orbital effect. The westerly jet's meridional position determines the spatial pattern of EASM precipitation anomalies, while its intensity affects the amplitude of the EASM's response to freshwater forcing. Because of a larger EASM decline due to freshwater hosing with lower summer insolation, we anticipate a profound declining EASM precipitation in the future with low summer insolation if the AMOC continues to weaken. Key Points: Millennial‐scale East Asian summer monsoon (EASM) variability is modulated by Earth's orbital parametersThe EASM weakens more pronounced in response to North Atlantic freshwater forcing under lower summer insolationSummer insolation influences the EASM response to North Atlantic freshwater forcing via the westerly jet [ABSTRACT FROM AUTHOR]

The features of monsoon systems in the Northern and Southern Hemispheres are analysed in climate simulations of two atmospheric models: the Brazilian Global Atmospheric Model version 1.2 (BAM‐v1.2) and the UK Met Office Hadley Centre Global Environment Model version 3 (HadGEM3). The results are compared to GPCP precipitation and ERA5 datasets. Although they have different configurations and parameterizations, the purpose is to evaluate their ability in representing key features of the global monsoon system. The spatial extent of the monsoon domains is well simulated by the models, as well as the main characteristics of the monsoons, although precipitation biases are noticed in the regions affected by the systems, consistent with vertical motion and moisture flux biases. The largest precipitation biases are found in the West Pacific Monsoon Region, extended to the east, and in the Australia Monsoon Region extended to the Maritime continent. Deficiencies in precipitation can be related to inaccuracy of vertical motion and humidity flux, as well as to the lack of air–sea interaction. However, the atmospheric circulation features at low and high levels are well represented in all monsoon regions, as well as the annual cycle of precipitation in those regions by both models. The divergence at high levels and convergence at low levels associated with ascending air movement and precipitation in monsoon regions are well represented by the models. An analysis of two monsoon indices at eight monsoon regions showed the models are generally able to simulate the relationship between precipitation and circulation features. In the majority of years, the signs of indices from the models agree with observations. Correlations of precipitation and circulation indices between models and observations show statistically significant values for some monsoon regions. The results obtained contribute to improving knowledge about global monsoon features and their representation in the two models. [ABSTRACT FROM AUTHOR]

Paleoclimatic records reveal spatially asynchronous changes of East Asian summer monsoon (EASM) precipitation during the Holocene, but the underlying mechanisms are not fully understood. This study explores the role of the zonal shift of the Asian westerly jet (AWJ) core on the spatial‐temporal variability of EASM precipitation based on Holocene climate simulations using the KCM and CESM forced by orbital variations. We analyzed the composite differences of summer precipitation and associated atmospheric circulations between the early (middle) and middle (late) Holocene. Simulations suggest a dipole pattern of summer precipitation with increasing (decreasing) precipitation in central (southern) China from the early to late Holocene, which was shaped by the eastward shift of the AWJ core. The eastward shift of the AWJ core and the accompanied eastward movement of the upper‐level convergence over the AWJ's right exit region weakened the low‐level downward motions over central China. Meanwhile, the low‐level upward motions over southern China were weakened by the concurrent eastward (westward) migration of the South Asian High (western Pacific subtropical High) during the Holocene. Consequently, summer precipitation increased (decreased) in central (southern) China from the early to late Holocene. The eastward shift of the AWJ core was primarily driven by amplified meridional insolation gradient at middle latitudes via strengthening upper‐level westerly intensity during the Holocene. In addition, land cover difference between East Asia and central Asia caused a greater enhancement of westerlies intensity in East Asia, further modulating the eastward movement of the AWJ core during the Holocene. Key Points: Our simulations reveal a dipole pattern of summer precipitation between central and southern China during the HoloceneThe dipole precipitation pattern was strongly modulated by zonal shift of the Asian westerly jet coreInsolation variation and land cover caused the eastward shift of the Asian westerly jet core during the Holocene [ABSTRACT FROM AUTHOR]

In order to understand the pure long‐term influence of single mega volcanic eruption (SMVE) of universal significance on global and polar region temperature changes, the AD 1258 Samalas mega volcanic eruption in Indonesia which is the largest eruption over the past millennium is selected as an ideal eruption for simulation study based on Community Earth System Model. Both reconstructions and simulations show that the Northern Hemisphere experienced nearly two decades of strong cooling after the Samalas mega eruption. The significant cooling in the Arctic lasts for 16 years, while the cooling in the Antarctic lasts only 2 years. As the volcanic aerosol gradually disappears, stronger cooling occurs in Arctic winter, and warming occurs in Antarctic winter. This asymmetric temperature changes over Arctic and Antarctic after SMVE (such as Samalas) are caused by the combined effects of albedo feedback and ocean‐atmosphere heat exchange related to sea ice. Plain Language Summary: Polar climate is the focus of earth system investigation because they are very sensitive to external forcings and its related impacts on global climate. Volcanic eruption is one of the important external factors affecting global and polar climate change. The AD 1258 Samalas mega volcanic eruption in Indonesia was the largest eruption over the past millennium, which makes it an ideal eruption to study pure long‐term climatic effects of single mega volcanic eruption (SMVE). Here, we use an Earth System Model and find that the duration of surface cooling caused by SMVE (such as Samalas) is longer than we generally believed before and varies in latitude. The Northern Hemisphere experienced nearly two decades of strong cooling after the Samalas event. The significant cooling in the Arctic lasts for 16 years, while the cooling in the Antarctic lasts only 2 years. The SMVE (such as Samalas) could expand Arctic sea ice for more than two decades, but the expansion of Antarctic sea ice lasts only 2–3 years. The asymmetric temperature changes over polar regions are influenced by the combined effects of albedo feedback and ocean‐atmosphere heat exchange related to sea ice. The knowledge gained from this research is critical for improved understanding of the potential long‐term impacts of SMVE on the projected future global and polar region temperature change. Key Points: Both reconstructions and simulations show that the NH experienced nearly two decades of strong cooling after the Samalas mega eruptionA single mega volcanic eruption will cause remarkable asymmetry of temperature variation and duration between the Arctic and AntarcticAsymmetric temperature changes are caused by the combined effects of albedo feedback and ocean‐atmosphere heat exchange related to sea ice [ABSTRACT FROM AUTHOR]

During spring 2011, an extreme flood occurred along the Richelieu River located in southern Quebec, Canada. The Richelieu River is the last section of the complex Richelieu basin, which is composed of the large Lake Champlain located in a valley between two large mountains. Previous attempts in reproducing the Richelieu River flow relied on the use of simplified lumped models and showed mixed results. In order to prepare a tool to assess accurately the change of flood recurrences in the future, a state‐of‐the‐art distributed hydrological model was applied over the Richelieu basin. The model setup comprises several novel methods and data sets such as a very high resolution river network, a modern calibration technique considering the net basin supply of Lake Champlain, a new optimization algorithm, and the use of an up‐to‐date meteorological data set to force the model. The results show that the hydrological model is able to satisfactorily reproduce the multiyear mean annual hydrograph and the 2011 flow time series when compared with the observed river flow and an estimation of the Lake Champlain net basin supply. Many factors, such as the quality of the meteorological forcing data, that are affected by the low density of the station network, the steep terrain, and the lake storage effect challenged the simulation of the river flow. Overall, the satisfactory validation of the hydrological model allows to move to the next step, which consists in assessing the impacts of climate change on the recurrence of Richelieu River floods. Plain Language Summary: In order to study the 2011 Richelieu flood and prepare a tool capable of estimating the effects of climate change on the recurrence of floods, a hydrological model is applied over the Richelieu basin. The application of a distributed hydrological model is useful to simulate the flow of all the tributaries of the Richelieu basin. This new model setup stands out from past models due to its distribution in several hydrological units, its high‐resolution river network, the calibration technique, and the high‐resolution weather forcing data set used to drive the model. The model successfully reproduced the 2011 Richelieu River flood and the annual hydrograph. The simulation of the Richelieu flow was challenging due to the contrasted elevation of the Richelieu basin and the presence of the large Lake Champlain that acts as a reservoir and attenuates short‐term fluctuations. Overall, the application was deemed satisfactory, and the tool is ready to assess the impacts of climate change on the recurrence of Richelieu River floods. Key Points: An advanced high‐resolution distributed hydrological model is applied over a U.S.‐Canada transboundary basinThe simulated net basin supply of Lake Champlain and the Richelieu River discharge are in good agreement with observations of the 2011 floodThe flow simulation is challenging due to the topographic and meteorological complexities of the basin and uncertainties in the observations [ABSTRACT FROM AUTHOR]

Extratropical cyclones, major contributors to precipitation in the midlatitudes, comprise mesoscale fronts and fine‐scale convective storms. Intense oceanic cyclones pose natural hazards, making reliable projections of their changes with global warming of great interest. Here, we analyze the first ever global climate simulations to resolve such mesoscale dynamics of extratropical cyclones. The present‐day structure, frequency, and precipitation of the oceanic extratropical cyclones compare well with reanalyses and new satellite datasets that resolve the multiscale cloud‐precipitation system. Simulated precipitation from intense oceanic cyclones increases at a rate of 7%/K1, following Clausius‐Clapeyron, with warming. The same scaling is apparent also in the interhemispheric contrast, suggesting that the latter could serve as a predictor of the former. Projected changes in precipitation from intense oceanic cyclones with warming may thus be testable using a reliable global observation network of precipitation in the present day. Plain Language Summary: Precipitation in midlatitudes is strongly governed by extratropical cyclones. Its future change is of great societal concern for adaptation to a warmer world. In this study, we use a new kind of global model and a new satellite dataset to resolve fine‐scale and frontal features of cyclones and their changes with warming. The simulation shows that the amount of precipitation around the intense oceanic cyclones will increase due to global warming, and furthermore, the rate of precipitation change around the intense oceanic cyclones is closely related to the precipitation contrast between the northern and southern hemispheres in the present climate. This suggests that the future precipitation change associated with intense oceanic cyclones could be inferred from the difference between the northern and southern hemispheres in the present climate. Key Points: The first global climate simulations to explicitly represent the mesoscale dynamics of extratropical cyclones are analyzedPrecipitation from intense cyclones scales with temperatures across hemispheres and with global warming following Clausius‐ClapeyronProjected change in precipitation from intense cyclones may thus be testable using global observations of precipitation in the present day [ABSTRACT FROM AUTHOR]

A subgrid parametrization scheme representing the enhancement of precipitation due to subgrid orography via the seeder–feeder (SF) effect has been modified to account for flow blocking in small Froude number situations. The scheme was validated in a set of limited‐area model simulations with a 1.5 km grid spacing, in which the orography was degraded by varying amounts. For simulations in which the largest orographic scales are still fairly well represented, the SF scheme was able to reduce the precipitation deficit by 30 to 70%. For simulations where the hills were completely subgrid, the SF scheme was still able to reduce the precipitation deficit by 10 to 30%. As well as increasing the integrated precipitation in global simulations with various grid spacings, some of the precipitation production was shifted from the convection scheme, with its very simple microphysical representation, to the microphysics scheme. In a long‐duration climate simulation, the SF scheme enhancements of orographic precipitation perturb the large‐scale hydrological cycle, as evidenced by the far‐field changes in both microphysical and convective precipitation. Changes over major mountain ranges were similar to those described for the case‐studies, so long as the upstream precipitation impinging on the mountains was not reduced by these changes in the global hydrological cycle. Increased atmospheric drying reduces column‐integrated resolved cloud water mixing ratios over mountains, reducing a positive bias in the amount of optically thick cloud with low‐ to mid‐level tops compared to ISCCP satellite observations. The associated reductions in cloud albedo slightly reduced the RMS error in the top‐of‐atmosphere outgoing short‐wave radiative fluxes over mountains compared to CERES satellite observations. [ABSTRACT FROM AUTHOR]

Atmospheric rivers (ARs) can significantly modulate surface hydrological processes through the extreme precipitation they produce. However, there is a lack of comprehensive evaluation of ARs' impact on surface hydrology. This study uses a high‐resolution regional climate simulation to quantify the impact of ARs on surface hydrological processes across the western U.S. watersheds. The model performance is evaluated through extensive comparison against observations. Our analysis indicates that ARs produce heavy precipitation but suppress evapotranspiration. Snowpack ablates more during ARs, with higher air temperature and increased longwave radiation playing the primary and secondary roles, respectively. At the 0 °C to 10 °C temperature range, ARs increase the probability of snow ablation from 0.33 to 0.57. The runoff‐to‐precipitation ratio is primarily controlled by antecedent soil moisture, but it almost doubles in the northwestern watersheds due to the intensification of snow ablation during AR events. From the analysis of the relationship between the hydrological responses and different meteorological factors, precipitation, temperature, and radiation are identified as the key drivers that distinguish the hydrologic responses between AR and non‐AR events. Lastly, analysis of ARs and total runoff at annual scale and 1 April snowpack and winter precipitation shows that ARs explain 30% to 60% of the variability of annual total runoff and sharpen the seasonality of water resources availability in the west coast mountain watersheds. Key Points: AR events intensify snow ablation and nearly double the runoff magnitude response to precipitation compared to non‐AR eventsAR events modulate temperature and radiation and induce rain‐on‐snow, which contributes 25% of runoff volume when snowpack existsARs explain 30% to 60% of the interannual variance and sharpen the seasonality of water resources in the west coast mountain watersheds [ABSTRACT FROM AUTHOR]

The article focuses on the climate change during the boring billion era in the history of Earth's deep-time evolution

We assess the effect of the Atlantic multidecadal variability (AMV) on the global monsoon using idealized simulations. Warm AMV phases are associated with a significant strengthening of monsoon precipitation over Northern Africa and India, and anomalously weak monsoon precipitation over South America. Changes in monsoon precipitation are mediated by a change in atmospheric dynamics, primarily associated with a shift in the circulation related to both an enhanced interhemispheric thermal contrast and the remote impact of AMV on the Pacific Ocean, through changes in the Walker circulation. In contrast, the thermodynamic changes are less important. Further experiments show that the impact of AMV is largely due to the tropical component of the sea surface temperature anomalies. However, the extratropical Atlantic also plays a role, especially for northern Africa. Finally, we show that the effect of AMV on monsoons is not linearly related to the magnitude of warming. Plain Language Summary: Global monsoon precipitation variability has substantial effects on about two thirds of the world's population. Therefore, understanding the factors that drive tropical precipitation is societally important. Here we focus on the effect of North Atlantic sea surface temperature (NASST) variability on global monsoon. To do so we use a set of climate model experiments, in which we add a surface temperature anomaly over the North Atlantic Ocean. The novelty of the analysis relies on the decomposition of precipitation changes to understand better their origins. We find that NASST changes have strong impacts on Sahel and Indian summer precipitation and monsoon domain sizes, through shifting northward the atmospheric patterns of moisture convergence. Changes involve increases in the large‐scale warming of the Northern Hemisphere and forcing of the eastern equatorial Pacific Ocean temperature. We highlight the tropical Atlantic basin as critical to explain the effects of NASST variability over the global monsoon. We found that changes in monsoon precipitation are sensitive to the magnitude of the NASST warming. Key Points: Changes in atmospheric circulation dominate the AMV effect on monsoons, while thermodynamic changes are moderateThe tropical North Atlantic largely forces AMV effects, by strengthening interhemispheric thermal gradients and the Walker circulationThe effects of AMV are not linearly related to the magnitude of warming [ABSTRACT FROM AUTHOR]

Abstract: Regional climate simulations over the continental United States were conducted for the 2011 warm season using the Weather Research and Forecasting model at convection‐permitting resolution (4 km) with two commonly used microphysics parameterizations (Thompson and Morrison). Sensitivities of the simulated mesoscale convective system (MCS) properties and feedbacks to large‐scale environments are systematically examined against high‐resolution geostationary satellite and 3‐D mosaic radar observations. MCS precipitation including precipitation amount, diurnal cycle, and distribution of hourly precipitation intensity are reasonably captured by the two simulations despite significant differences in their simulated MCS properties. In general, the Thompson simulation produces better agreement with observations for MCS upper level cloud shield and precipitation area, convective feature horizontal and vertical extents, and partitioning between convective and stratiform precipitation. More importantly, Thompson simulates more stratiform rainfall, which agrees better with observations and results in top‐heavier heating profiles from robust MCSs compared to Morrison. A stronger dynamical feedback to the large‐scale environment is therefore seen in Thompson, wherein an enhanced mesoscale vortex behind the MCS strengthens the synoptic‐scale trough and promotes advection of cool and dry air into the rear of the MCS region. The latter prolongs the MCS lifetimes in the Thompson relative to the Morrison simulations. Hence, different treatment of cloud microphysics not only alters MCS convective‐scale dynamics but also has significant impacts on their macrophysical properties such as lifetime and precipitation. As long‐lived MCSs produced 2–3 times the amount of rainfall compared to short‐lived ones, cloud microphysics parameterizations have profound impact in simulating extreme precipitation and the hydrologic cycle. [ABSTRACT FROM AUTHOR]

Abstract: In this two‐part paper, a description is provided of a version of the AM4.0/LM4.0 atmosphere/land model that will serve as a base for a new set of climate and Earth system models (CM4 and ESM4) under development at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL). This version, with roughly 100 km horizontal resolution and 33 levels in the vertical, contains an aerosol model that generates aerosol fields from emissions and a “light” chemistry mechanism designed to support the aerosol model but with prescribed ozone. In Part 1, the quality of the simulation in AMIP (Atmospheric Model Intercomparison Project) mode—with prescribed sea surface temperatures (SSTs) and sea‐ice distribution—is described and compared with previous GFDL models and with the CMIP5 archive of AMIP simulations. The model's Cess sensitivity (response in the top‐of‐atmosphere radiative flux to uniform warming of SSTs) and effective radiative forcing are also presented. In Part 2, the model formulation is described more fully and key sensitivities to aspects of the model formulation are discussed, along with the approach to model tuning. [ABSTRACT FROM AUTHOR]

Abstract: In Part 2 of this two‐part paper, documentation is provided of key aspects of a version of the AM4.0/LM4.0 atmosphere/land model that will serve as a base for a new set of climate and Earth system models (CM4 and ESM4) under development at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL). The quality of the simulation in AMIP (Atmospheric Model Intercomparison Project) mode has been provided in Part 1. Part 2 provides documentation of key components and some sensitivities to choices of model formulation and values of parameters, highlighting the convection parameterization and orographic gravity wave drag. The approach taken to tune the model's clouds to observations is a particular focal point. Care is taken to describe the extent to which aerosol effective forcing and Cess sensitivity have been tuned through the model development process, both of which are relevant to the ability of the model to simulate the evolution of temperatures over the last century when coupled to an ocean model. [ABSTRACT FROM AUTHOR]

The lifecycle of South American Monsoon System (SAMS) plays an important role on the duration of the rainy season over large areas of South America, affecting the economy through impacts on agriculture, water resources and energy management. Numerical model prediction of SAMS onset, demise and related atmospheric features is an important tool to be used in management decisions in these sectors. This information is still missing in seasonal predictions, and the purpose of this study is to examine results of a climate simulation using the CPTEC/INPE AGCM to verify its ability in simulating the SAMS onset and demise as well as the associated atmospheric features. The SAMS lifecycle is identified using an index of the zonal humidity flux in the monsoon core. The model captured the atmospheric changes associated with the SAMS lifecycle, although showing differences in intensity and maximum locations of some variables, such as the magnitude of humidity flux, sea level pressure and omega, compared to reanalysis. During the onset, the model simulated the humidity flux direction changes, the eastward shifting of the South Atlantic Subtropical High and the northwesterly moisture flux east of tropical Andes. During the demise, the model simulated the easterly moisture flux directed toward the Amazon region and the reduction of northerly/northwesterly flow over northern South America, as well as the increase of Sea Level Pressure over the continent. Results obtained using a previous version of CPTEC/INPE AGCM are discussed, mainly the improvements, in the new version, of atmospheric variables and annual cycle of precipitation. The model was able to represent the main observed features of the SAMS lifecycle. The method can be useful to identify the onset and demise dates and could be applied to results of seasonal prediction prior to the rainy season, adding information to planning and management actions. [ABSTRACT FROM AUTHOR]

ABSTRACT The lifecycle of South American Monsoon System ( SAMS) plays an important role on the duration of the rainy season over large areas of South America, affecting the economy through impacts on agriculture, water resources and energy management. Numerical model prediction of SAMS onset, demise and related atmospheric features is an important tool to be used in management decisions in these sectors. This information is still missing in seasonal predictions, and the purpose of this study is to examine results of a climate simulation using the CPTEC/ INPE AGCM to verify its ability in simulating the SAMS onset and demise as well as the associated atmospheric features. The SAMS lifecycle is identified using an index of the zonal humidity flux in the monsoon core. The model captured the atmospheric changes associated with the SAMS lifecycle, although showing differences in intensity and maximum locations of some variables, such as the magnitude of humidity flux, sea level pressure and omega, compared to reanalysis. During the onset, the model simulated the humidity flux direction changes, the eastward shifting of the South Atlantic Subtropical High and the northwesterly moisture flux east of tropical Andes. During the demise, the model simulated the easterly moisture flux directed toward the Amazon region and the reduction of northerly/northwesterly flow over northern South America, as well as the increase of Sea Level Pressure over the continent. Results obtained using a previous version of CPTEC/ INPE AGCM are discussed, mainly the improvements, in the new version, of atmospheric variables and annual cycle of precipitation. The model was able to represent the main observed features of the SAMS lifecycle. The method can be useful to identify the onset and demise dates and could be applied to results of seasonal prediction prior to the rainy season, adding information to planning and management actions. [ABSTRACT FROM AUTHOR]

ABSTRACT During the austral summer of 2014 and 2015, a severe drought occurred in southeastern Brazil at the same time when flooding conditions were registered in the state of Acre in the western Amazonia of Brazil. This study aimed the identification of the atmospheric and oceanic large-scale characteristics and regional features associated with these conditions, and verification of the Center of Weather Forecasting and Climate Studies/National Institute of Space Research (CPTEC/INPE) atmospheric global circulation model ability in reproducing the observed features. The state of Acre was chosen as a pilot area of the PULSE-Brazil project - a web platform tool that contains climate, ecological and health data for Brazil. The observational data and model results were analysed for the climatological period of 1981-2010. Correlation analyses between precipitation over west Amazon and atmospheric and oceanic variables indicated the main patterns in both data sets. Extreme wet and dry Januaries over west Amazon were selected to explore the regional and large-scale associated features. The general results of climate analyses indicated an opposite relation of precipitation between western Amazon and southeastern Brazil, in January, besides the typical precipitation dipole between the south Atlantic convergence zone and southeastern South America. This configuration is related to anomalous humidity flux at low levels and associated anomalous sea level pressure over southeastern South America induced by subsidence. The role of convection anomalies over the Pacific Ocean on South America anomalies is discussed. The wet and dry cases in Acre region display opposite atmospheric anomalies over South America that are linked to wavetrains over the Pacific Ocean, likely related to the opposite conditions of Indonesia-Pacific tropical convection. Similar patterns of the dry cases were observed during January of 2014 and 2015. The model reproduced some observed atmospheric patterns related to precipitation extremes and the results are discussed in terms of regional and large-scale climate variability. [ABSTRACT FROM AUTHOR]

The article reports on the study which examines the reversal of the common downscaling path from large-scale circulation patterns to local surface weather. The study applied re-sampling (RS) scheme to generate ensembles of future series by assembling segments from past time series. It also conducted a cross-validation experiment using global circulation model (GCM) to test whether changing statistics of temperature and circulation patterns are related to each other. It is concluded that most of the changes from the first to the second period can be assigned to the temperature evolution.

The article cites a study which looks at the characteristic features of the surface hydroclimatology concerning South Korean Peninsula's seven watersheds and the degree to which four modern-day climate models reproduce regional features of hydroclimatology. The findings of this study reveal that the surface climate variables analyzed show strong seasonal cycles with significant differences in mean and variability across watersheds and seasons. The results also develop a model for climate model simulations to establish hydroclimatology for means and variability of surface watershed variables for water resources planning in the South Korean Peninsula.

The article focuses on the use of a singular value decomposition (SVD) method to a 50-year climate simulation to explore the space-time connections between springtime soil moisture and summer precipitation over the continental U.S. It examines the influences of the relative importance of the land and ocean on precipitation changes with the seasons. A review of the coupling of Common Land Model (CLM) with National Center for Atmospheric Research Community Climate Model Version 3, which offers the soil moisture and precipitation data for the study, is presented.