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Diurnal temperature range (DTR), as a core indicator of the Earth system, exhibits obvious temporal and spatial variations, which is not entirely consistent over global. The historical simulation capabilities of 19 Coupled Model Intercomparison Project 6 (CMIP6) models for DTR were firstly evaluated against CRU_TS v4.04 data. Future changes under three shared socioeconomic pathways (SSP1-2.6, SSP2-4.5, SSP5-8.5) in DTR were projected using a multi-model ensemble mean (MME), and its interannual variations were seasonally explored through empirical orthogonal function (EOF) analysis. The results indicated that CMIP6 models could reflect the decreasing trend of DTR during 1901–2014, with the global spatial correlation coefficient between models and observation ranging from 0.4 to 0.7. MME outperformed individual models in both spatial and temporal variations, indicating higher accuracy and reliability. The future changes of DTR exhibited significantly decrease across the northern hemisphere and increase in the South America, and change magnitude enlarged with time extension and emission intensity, especially by more than 0.4 °C under SSP5-8.5. The decreasing trend of global DTR was kept in SSP2-4.5 and SSP5-8.5, while SSP1-2.6 changed increasing trend during 2015–2100. DTR showed seasonal variations and was mainly influenced by colder months. The dominant modes of interannual DTR and their relationship with the 500 hPa geopotential height, the 200 hPa U wind, and the outgoing longwave radiation showed higher features in tropical regions. The highly positive correlation between the first mode of DTR and the Niño3.4 index in December/January/February (DJF) is 0.67, indicating significant influence of the El Niño-Southern Oscillation on DTR. [ABSTRACT FROM AUTHOR]

A severe flooding hit southern China along the Yangtze River in summer 2020. The floods were induced by extreme rains, and the associated dynamic and thermodynamic conditions are investigated using daily gridded rainfall data of China and NCEP-NCAR reanalysis. It is found that the June–July rainfall over the Yangtze River Basin (YRB) experienced pronounced subseasonal variation in 2020, dominated by a quasi-biweekly oscillation (QBWO) mode. The southwestward-moving anomalous QBWO circulation was essentially the fluctuation of cold air mass related to the tropospheric polar vortex or trough-ridge activities over the mid-high latitude Eurasian in boreal summer. The southwestward-transport of cold air mass from mid-high latitudes and the northeastward-transport of warm and moist air by the strong anomalous anticyclone over the western North Pacific provided important large-scale circulation support for the extreme rainfall in the YRB. The analysis of streamfunction of water vapor flux demonstrates that a large amount of water vapor eastward zonal transport from the Bay of Bengal and Indo-China and northward transport from the South China Sea provided the background moisture supply for the rainfall. The quasi-biweekly anomalies of potential and divergent component of vertically integrated water vapor flux played an important role in maintaining the subseasonal variability of rainfall in June–July of 2020. The diagnosis of moisture tendency budget shows that the enhanced moisture closely related to the quasi-biweekly fluctuated rainfall was primarily attributed to the moisture convergence. Further analysis of time-scale decomposition in the moisture convergence indicates that the convergence of background mean specific humidity by the QBWO flow and convergence of QBWO specific humidity by the mean flow played dominant roles in contributing to the positive moisture tendency. In combination with adiabatic ascent over the YRB induced by the warm temperature advection, the boundary layer moisture convergence strengthened the upward transport of water vapor to moisten the middle troposphere, favoring the persistence of rainfall during June–July. The vertical moisture transport associated with boundary layer convergence was of critical importance in causing low-level tropospheric moistening. By comparison, the horizontal moisture advection played a secondary important role in the quasi-biweekly oscillation of rainfall in June–July 2020. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Understanding the contributions of large-scale atmospheric circulation and local land surface processes to precipitation is essentially important for the climate prediction. This study adopts a dynamic adjustment (DA) approach based on constructed circulation analogs to quantitatively isolate the contribution of atmospheric circulation to summer land precipitation (Pr) over Asian mid-low latitudes during 1980–2019. The atmospheric circulation factor is represented by the 500 hPa geopotential height (Z500), and the residual component after DA is regarded as the contribution from land surface processes via evaporation mainly resulting from soil moisture (SM). The results indicate that the key SM-Pr feedback areas are mainly located in northeast China and the northern Indian Peninsula. The key influencing area of Z500 on the land Pr anomaly shows a "- + -" tripole pattern in the mid-latitude region. Atmospheric circulation determines the magnitude of summer land Pr, while the residual components reflect the land–atmosphere coupling effect and dominate Pr trend. This conclusion is helpful for better understanding the evolution mechanism of summer climate over Asia mid-low latitudes and may also have application value for climate prediction. [ABSTRACT FROM AUTHOR]

This study examines the linear orthogonal modes associated with monthly precipitation in the northeastern United States, from CESM1 LENS (35 ensemble members, 1979–2005) and two reanalysis datasets (ERA5, 1950–2018 and NOAA-CIRES-DOE 20CRv3, 1950–2015). Calendar months are aggregated together, and any linear trends in data are removed. Using region-averaged precipitation anomaly time series and monthly anomalies for several global 2D atmospheric fields, a linear orthogonal decomposition method is implemented to iteratively extract time series (based on field and geographic location) of absolute maximum correlation. Linear modes associated with this method are then projected onto the full set of 2D fields to provide physical insight into the mechanisms involved in generating precipitation. In this region, the first mode is associated with vapor transport from the Atlantic seaboard, the second mode is characterized by westward vapor transport associated with extratropical cyclones, and the third mode captures vapor transport from the Gulf of Mexico during the fall and winter. However, the third mode is less robust in the spring and summer. Results are generally consistent across the datasets, and applying multiple linear regression with the linear modes to predict the precipitation anomalies produces R-squared values of around 0.54–0.65 for CESM1 LENS, and around 0.58–0.88 for reanalysis, with the lowest values generally in the spring and late summer. The influence of low-frequency climate variability on the modes is considered for CESM1 LENS, and the modes in late winter can be predicted with some success via a combination of several, prominent large-scale teleconnection patterns. [ABSTRACT FROM AUTHOR]

The East Asian summer monsoon (EASM) has significant impacts on local and global hydrological and climatic systems. However, most current atmospheric and coupled models have difficulty in capturing the climatological mean state of the EASM. The present study investigated the possible improvement of EASM simulation via coupling the Stochastic Multicloud Model (SMCM) to the state-of-the-art ECHAM6.3 atmosphere model. Evaluated by the pattern correlation coefficient and root-mean-square error, the modified ECHAM6.3, i.e., with SMCM coupling, showed better performance in simulating the EASM in terms of the precipitation pattern and intensity, the pattern of the western North Pacific subtropical high, the monsoon onset, and its seasonal evolution. Analyses also revealed that the modified ECHAM6.3 outperformed the default ECHAM6.3 in terms of large-scale circulation and vertically integrated moisture transport. Finally, it was that the intensified land–sea thermal contrast in both the meridional and zonal directions, as well as the stronger meridional temperature gradient in the upper troposphere and enhanced diabatic heating over the Tibetan Plateau, which are associated with the stochastic cloud, were the main reasons for the better performance of the modified ECHAM6.3 in simulating the EASM. [ABSTRACT FROM AUTHOR]

Vertically resolved multi-layer cloud distributions over the globe using 4 years of CloudSat/CALIPSO observations during 2007-2010 are discussed. The quantitative information on the frequency of occurrence of one- to five-layered clouds across the globe is established, which are of immense importance from the global climate standpoint. After segregating the CloudSat observations into different seasons, the 4 years of mean global maps of frequency of occurrence of one to five-layered clouds are discussed in details. These global maps provide much needed quantification of vertically resolved multi-layer clouds by revealing when and where the frequency of occurrence of multi-layer clouds are maximum including the number of layers. On an average, it is observed that over the globe one-, two-, three-, four- and five-layer clouds occur 53, 20, 3.5, 0.4 and 0.04 % of the time respectively. High fraction of single layer clouds is observed over the descending limbs of Hadley cell where relatively large lower tropospheric stability is found. The regions where multi-layer clouds are more frequent are identified and discussed along with large scale circulation. Apart from quantifying the frequency of occurrence of multi-layer clouds, the latitudinal distribution of zonal mean occurrence of cloud base and top altitudes of each cloud layer is constructed for boreal winter and summer. These analyses provide the cloud base and top altitudes of one to five-layered clouds, which are important to understand the vertical structure of the multi-layered clouds. The significance of the present study lies in establishing the global distribution of vertically resolved multi-layer clouds and the role of large-scale dynamics in controlling their distribution for the first time. [ABSTRACT FROM AUTHOR]

Upper tropospheric water vapor (UTWV) plays a critical role in amplifying global warming caused by increasing greenhouse gases, yet it is one of the most poorly simulated quantities in climate models. It is not clear what physical processes play a central role in controlling the model errors in UTWV. We diagnose the UTWV simulation errors from AMIP models submitted to the CMIP5 project by using 'A-Train' satellite observation and reanalysis data. We identify the relative contributions of errors in relative humidity (RH), temperature, and large-scale circulation (represented by vertical pressure velocity at 500 hPa, ω) to the modeled UTWV errors over the tropics (30°N-30°S). It is found that models generally have positive biases in UTWV, except over the continental convective regions where negative biases predominate. The errors in the patterns and amplitudes of climatological UTWV are highly correlated with those in RH and ω. The fractional UTWV errors show large positive errors over the large-scale descending regimes (0 < ω < 40 hPa/day) where large model spreads also exist. The seasonal cycle of hemispherically averaged UTWV closely resembles that of ω. The errors for UTWV interannual anomalies are abundant over the climatologically deep convective regions (SST > 300 K or ω < −30 hPa/day) and these errors are positive (negative) where anomalous descent (ascent) occurs during El Niño. We find that the water vapor errors are dominated by the errors in RH rather than in temperature throughout the troposphere, while temperature errors play an important role for water vapor errors near the tropopause. [ABSTRACT FROM AUTHOR]