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Winter extreme snowstorm events along the coast of the northeast United States have significant impacts on social and economic activities, and their potential changes under global warming are of great concern. Here, we adopted the pseudo–global warming approach to investigate the responses of 93 events identified in our previous observational analysis. The study was conducted by contrasting two sets of WRF simulations for each event: the first set driven by the ERA-Interim reanalysis and the second set by that data superimposed with mean-climate changes simulated from HiRAM historical (1980–2004) and future (2075–99; RCP8.5) runs. Results reveal that the warming together with increased moisture tends to decrease the snowfall along the coast but increase the rainfall throughout the region. For example, the number of events having daily snow water equivalent larger than 10 mm day−1 at Boston, Massachusetts; New York City, New York; Philadelphia, Pennsylvania; and Washington, D.C., is decreased by 47%, 46%, 30%, and 33%, respectively. The compensating changes in snowfall and rainfall lead to a total-precipitation increase in the three more-southern cities but a decrease in Boston. In addition, the southwestward shift of regional precipitation distribution is coherent with the enhancement (reduction) of upward vertical motion in the south (north) and the movement of cyclone centers (westward in 58% of events and southward in 72%). Finally, perhaps more adversely, because of the northward retreat of the 0°C line and the expansion of the near-freezing zone, the number of events with mixed rain and snow and freezing precipitation in the north (especially the inland area) is increased.

This study used both observations and global climate model simulations to investigate the characteristics of winter extreme snowfall events along the coast (the Interstate 95 corridor) of the northeast United States where several mega-cities are located. Observational analyses indicate that, during 1980–2015, 110 events occurred when four coastal cities—Boston, New York City, Philadelphia, and Washington, D.C.—had either individually or collectively experienced daily snowfall exceeding the local 95th percentile thresholds. Boston had the most events, with a total of 69, followed by 40, 36, and 30 (moving southward) in the other three cities. The associated circulations at 200 and 850 hPa were categorized via K-means clustering. The resulting three composite circulations are characterized by the strength and location of the jet at 200 hPa and the coupled low pressure system at 850 hPa: a strong jet overlying the cities coupled with an inland trough, a weak and slightly southward shifted jet coupled with a cyclone at the coast, and a weak jet stream situated to the south of the cities coupled with a cyclone over the coastal oceans. Comparative analyses were also conducted using the GFDL High Resolution Atmospheric Model (HiRAM) simulation of the same period. Although the simulated extreme events do not provide one-to-one correspondence with observations, the characteristics nevertheless show consistency notably in total number of occurrences, intraseasonal and multiple-year variations, snow spatial coverage, and the associated circulation patterns. Possible future change in extreme snow events was also explored utilizing the HiRAM RCP8.5 (2075–2100) simulation. The analyses suggest that a warming global climate tends to decrease the extreme snowfall events but increase extreme rainfall events.

Cloud dominates influence factors of atmospheric radiation, while aerosol-cloud interactions are of vital importance in its spatiotemporal distribution. In this study, a two-moment (mass and number) cloud microphysics scheme, which significantly improved the treatment of the coupled processes of aerosols and clouds, was incorporated into version 1.1 of the IAP/LASG global Finite-volume Atmospheric Model (FAMIL1.1). For illustrative purposes, the characteristics of the energy balance and cloud radiative forcing (CRF) in an AMIP-type simulation with prescribed aerosols were compared with those in observational/reanalysis data. Even within the constraints of the prescribed aerosol mass, the model simulated global mean energy balance at the top of the atmosphere (TOA) and at the Earth’s surface, as well as their seasonal variation, are in good agreement with the observational data. The maximum deviation terms lie in the surface downwelling longwave radiation and surface latent heat flux, which are 3.5 W m-2 (1%) and 3 W m-2 (3.5%), individually. The spatial correlations of the annual TOA net radiation flux and the net CRF between simulation and observation were around 0.97 and 0.90, respectively. A major weakness is that FAMIL1.1 predicts more liquid water content and less ice water content over most oceans. Detailed comparisons are presented for a number of regions, with a focus on the Asian monsoon region (AMR). The results indicate that FAMIL1.1 well reproduces the summer-winter contrast for both the geographical distribution of the longwave CRF and shortwave CRF over the AMR. Finally, the model bias and possible solutions, as well as further works to develop FAMIL1.1 are discussed.

Clouds strongly modulate regional radiation balance and their evolution is profoundly influenced by circulations. This study uses 2001–16 satellite and reanalysis data together with regional model simulations to investigate the spring shortwave cloud radiative effect (SWCRE) and the associated circulations over southeastern China (SEC). Strong SWCRE, up to −110 W m−2, persists throughout springtime in this region and its spring mean is the largest among the same latitudes of the Northern Hemisphere. SWCRE exhibits pronounced subseasonal variation and is closely associated with persistent regional ascending motion and moisture convergence, which favor large amounts of cloud liquid water and resultant strong SWCRE. Around pentad 12 (late February), SWCRE abruptly increases and afterward remains stable between 22° and 32°N. The thermal and dynamic effects of Tibetan Plateau and westerly jet provide appropriate settings for the maintenance of ascending motion, while water vapor, as cloud water supply, stably comes from the southern flank of the Tibetan Plateau and South China Sea. During pentads 25–36 (early May to late June), SWCRE is further enhanced by the increased water vapor transport caused by the march of East Asian monsoon systems, particularly after the onset of the South China Sea monsoon. After pentad 36, these circulations quickly weaken and the SWCRE decreases accordingly. Individual years with spring strong and weak rainfall are chosen to highlight the importance of the strength of the ascending motion. The simulation broadly reproduced the observed results, although biases exist. Finally, the model biases in SWCRE–circulation associations are discussed.

The WRF-simulated changes in clouds and climate due to the increased anthropogenic aerosols for the summers of 2002–08 (vs the 1970s) over eastern China were used to offline calculate the radiative forcings associated with aerosol–radiation (AR) and aerosol–cloud–radiation (ACR) interactions, which subsequently facilitated the interpretation of surface temperature changes. During this period, the increases of aerosol optical depth (ΔAOD) averaged over eastern China range from 0.18 in 2004 to 0.26 in 2007 as compared to corresponding cases in the 1970s, and the multiyear means (standard deviations) of AR and ACR forcings at the surface are −6.7 (0.58) and −3.5 (0.63) W m−2, respectively, indicating the importance of cloud changes in affecting both the aerosol climate forcing and its interannual variation. The simulated mean surface cooling is 0.35°C, dominated by AR and ACR with a positive (cooling) feedback associated with changes in meteorology (~10%), and two negative (warming) feedbacks associated with decreases in latent (~70%) and sensible (~20%) heat fluxes. More detailed spatial characteristics were analyzed using ensemble simulations for the year 2008. Three regions—Jing-Jin-Ji (ΔAOD ~ 0.63), Sichuan basin (ΔAOD ~ 0.31), and middle Yangtze River valley (ΔAOD ~ 0.26)—at different climate regimes were selected to investigate the relative roles of AR and ACR. While the AR forcing is closely related to ΔAOD values, the ACR forcing presents different regional characteristics owing to cloud changes. In addition, the surface heat flux feedbacks are also different between regions. The study thus illustrates that ACR forcing is useful as a diagnostic parameter to unravel the complexity of climate change to aerosol forcing over eastern China.

Our previous study found that the observed rainfall diurnal variation over Beijing–Tianjin–Hebei shows the distinct signature of the effects of pollutants. Here we used the hourly rainfall data together with satellite-based daily information of aerosols and clouds to further investigate changes in heavy rainfall and clouds associated with aerosol changes. Because of the strong coupling effects, we also examined the sensitivity of these changes to moisture (specific humidity) variations. For heavy rainfall, three distinguished characteristics are identified: earlier start time, earlier peak time, and longer duration; and the signals are robust using aerosol indicators based on both aerosol optical depth and cloud droplet number concentration. In-depth analysis reveals that the first two characteristics occur in the presence of (absorbing) black carbon aerosols and that the third is related to more (scattering) sulfate aerosols and is sensitive to moisture abundance. Cloud changes are also evident, showing increases in cloud fraction, cloud top pressure, the liquid/ice cloud optical thickness and cloud water path and a decrease in ice cloud effective radius; and these changes are insensitive to moisture. Finally, the mechanisms for heavy rainfall characteristics are discussed and hypothesized.

For East Asia, circulation responses to anthropogenic aerosol radiative forcing dominate aerosol-precipitation interactions. To gain insights, this study analyzed CESM simulated circulation changes related to the ‘north drought and south flood’ pattern caused by aerosol increases between two cases. One case was driven by the year-1850 global emission inventory, whereas the other used identical emissions for all regions except East Asia where anthropogenic emissions of aerosols and precursors of the year-2000 were imposed. Results show that the cooling caused by increased aerosols, which peaks at the middle latitudes, induces two intervened anomalous circulations in the troposphere. Near the surface, the increased land pressure weakens the southerlies and reduces the moisture transport for the entire eastern China. Meanwhile, in the free troposphere, the anomalous circulation exhibits remarkable meridional variations. While convergence occurs over 25°–45°N which partially compensates the decrease of moisture transport from lower levels, divergence develops over regions to the north which enhances the moisture deficiency. In addition, the southward shift of the jet stream stimulates anomalous rising and sinking motions over the south and north of 32°N. The combination of these changes leads to precipitation increase in the Yangtze River Valley but decrease over North China.

This paper describes the latest progress of a collaborative research program entitled “Modeling Aerosol Climate Effects over Monsoon Asia”, under the Climate Sciences agreement between the U.S. Department of Energy and the Chinese Academy of Sciences (in the early 1980s, Professor Duzheng YE played a critical role in leading and formalizing the agreement). Here, the rationale and approach for pursuing the program, the participants, and research activities of recent years are first described, and then the highlights of the program’s key findings and relevant scientific issues, as well as follow-up studies, are presented and discussed.

The WRF Model is used to investigate intraseasonal responses of the summer rainfall to aerosol direct and cloud-adjustment effects over East Asia, where the anthropogenic aerosol loading has been increasing in the past few decades. The responses are evaluated by comparing two cases for each year during 2002–2008: a control case imposing the observed aerosol optical depth of the corresponding year and a sensitivity case having anthropogenic components of the control case reduced by 75%. Analyses of multiple-year simulations reveal that aerosol-induced changes of rainfall and circulation exhibit strong intraseasonal variability, and that the spatial pattern of changes in the monthly rainfall is related to the intensification and westward extension of the western North-Pacific subtropical high (WNPSH) by increased aerosols. This perturbation of the WNPSH induces surface air divergence over the southeast China and convergence over regions to the north and west of the WNPSH, causing, respectively, decreased and increased rainfall. As the WNPSH migration path varies year by year, however, the variability of rainfall changes over subregions of the eastern China (e.g., North China) is large within the decade. Meanwhile, the pattern of summer-gross rainfall changes also shows large interannual variation, but the general pattern of wetter in the west and dryer in the east persists. Results also suggest that the aerosol increase tends to reduce the number of Tibet Plateau vortices, which indirectly influence summer rainfall over the eastern China.

This study uses 2001–2014 satellite observations and reanalyses to investigate the seasonal characteristics of Cloud Radiative Effects (CREs) and their associations with cloud fraction (CF) and precipitation over the Asian monsoon region (AMR) covering Eastern China (EC) and South Asia (SA). The CREs exhibit strong seasonal variations but show distinctly different relationships with CFs and precipitation over the two regions. For EC, the CREs is dominated by shortwave (SW) cooling, with an annual mean value of − 40 W m− 2 for net CRE, and peak in summer while the presence of extensive and opaque low-level clouds contributes to large Top-Of-Atmosphere (TOA) albedo (>0.5) in winter. For SA, a weak net CRE exists throughout the year due to in-phase compensation of SWCRE by longwave (LW) CRE associated with the frequent occurrence of high clouds. For the entire AMR, SWCRE strongly correlates with the dominant types of CFs, although the cloud vertical structure plays important role particularly in summer. The relationships between CREs and precipitation are stronger in SA than in EC, indicating the dominant effect of monsoon circulation in the former region. SWCRE over EC is only partly related to precipitation and shows distinctive regional variations. Further studies need to pay more attention to vertical distributions of cloud micro- and macro-physical properties, and associated precipitation systems over the AMR.

Our recent study found that, during 2002–2012, the diurnal variation of heavy rainfall over Beijing-Tianjin-Hebei (BTH) region exhibits different characteristics between clean and polluted environment. Here we use satellite cloud products together with meteorology and aerosol data to further examine the aerosol impact on the associated clouds focusing on its sensitivity to moisture. During the days with large aerosol loading, the characteristics of earlier starting time, earlier peak hour and the longer duration of heavy rainfall are usually accompanied by increased cloud fraction, reduced cloud top height and increased/reduced liquid/ice effective radius. However, the aerosol effects on the cloud top and liquid effective radius are distinct at lower and higher humidity. Different from the radiative effect that black carbon heats the lower troposphere and may generate the earlier start of heavy rainfall, the aerosol cloud effect enhances the efficiency of precipitation and advances the rainfall peak, which may be ascribed to increased cloud droplet number and cloud water, enhanced collision-coalescence and accelerated rainfall formation when the background moisture supply is sufficient. The speculation warrants further numerical experiment to verify.

We examine the characteristics (amplitude and phase) of the temporal variation in the rates of global-mean surface temperature change during the past millennium. The study was conducted by applying 20-, 30-, and 50-yr sliding windows to the observations of recent century and reconstructions of earlier times. The analysis focuses on the characteristics of the 20th century within the context of the millennium as well as their sensitivity to the low frequency variability of sea surface temperature (SST) and time scales. On 20-yr time scale, comparable rates to that of the 20th century in both amplitude and phase occur in earlier nine centuries. The peak in the amplitude of rates in the 20th century on 30-yr time scale, although is not the largest during the past millennium, but is the most persistent. On 50-yr time scale, the 20th century warming rates are the highest and the most persistent during the past millennium. The results also indicate that although the SST variability does not affect much the amplitude of the rates, but the phases is quite different, thus highlighting the importance of the role of oceans in affecting the rates. We also analyzed the characteristics from global climate model (1000–1999 AD) simulations with different climate (solar, volcanic, and greenhouse gases) forcing. Except for the one driven by the solar forcing, other forcing simulates similar amplitudes as the observed ones. However, only greenhouse gases (GHG) forcing can reproduce the persistent high warming rates of the 20th century.

Recently, Chen et al. used a combination of observations and WRF simulations to illustrate that the anthropogenic aerosol–cloud microphysics–radiation interactions over the southeast Pacific can potentially reduce the excessive shortwave radiation reaching the sea surface, a common bias identified in CMIP5 models. Here, with the aid of a mixed-layer ocean, the authors further study the implications of the shortwave radiation reduction to the underlying air–sea coupling, focusing on the SST sensitivity to the changes. Results show that responses of the air–sea coupling include two negative feedbacks (a large decrease in the latent heat flux and a small decrease in the sensible heat flux, both associated with the surface cooling) and a positive feedback (an increase in the cloud cover, caused by the increase in the relative humidity within the boundary layer, especially during the daytime). The 0.1°C (W m−2)−1 SST sensitivity is about half that documented in CMIP5 models. In addition, an effective daytime cloud fraction weighted with the solar diurnal cycle is proposed to facilitate diagnosing the intensity of cloud–radiation interactions in general circulation models.

This study investigates the effects of meteorological conditions and aerosols on marine stratocumulus in the southeastern Pacific using the Weather Research and Forecasting (WRF) Model. Two regimes with different temperature and moisture conditions in the finest model domain are investigated. The western regime is around 87°–79°W, while the eastern regime is around 79°–71°W. In both regimes, cloud fraction, liquid water path (LWP), cloud thickness, and precipitation show significant diurnal cycles. Cloud fraction can be 0.83 during the night and down to 0.29 during the day in the western regime. The diurnal cycles in the eastern regime have smaller amplitudes but are still very strong. Stratocumulus properties also differ in the two regimes. Compared to the western regime, the eastern regime has lower temperature, higher relative humidity, and a more coupled boundary layer, leading to higher cloud fraction (by 0.11) and lower cloud-base height. The eastern regime also has lower inversion height that causes lower cloud-top height and thinner clouds and, hence, lower LWP and less precipitation. Cloud microphysical properties are very sensitive to aerosols in both regimes. Increasing aerosols greatly increase cloud number concentration, decrease cloud effective radius, and suppress precipitation. Cloud macrophysical properties (cloud fraction, LWP) are not sensitive to aerosols in either regime, most notably in the eastern regime where precipitation amount is less. The changes in cloud fraction and LWP caused by changes in aerosol concentrations are smaller than the changes in the diurnal cycle and the spatial variability between the two regimes.

By using the radiosonde measurements collected at Shouxian, China, we examined the dynamics and thermodynamics of single- and two-layer clouds formed at low and middle levels. The analyses indicated that the horizontal wind speed above the cloud layers was higher than those within and below cloud layers. The maximum balloon ascent speed (5.3 m s−1) was located in the vicinity of the layer with the maximum cloud occurrence frequency (24.4%), indicating an upward motion (0.1–0.16 m s−1). The average thickness, magnitude and gradient of the temperature inversion layer above single-layer clouds were 117±94 m, 1.3±1.3°C and 1.4±1.5°C (100 m)−1, respectively. The average temperature inversion magnitude was the same (1.3°C) for single-low and single-middle clouds; however, a larger gradient [1.7±1.8°C (100 m)−1] and smaller thickness (94±67 m) were detected above single-low clouds relative to those above single-middle clouds [0.9±0.7°C (100 m)−1 and 157±120 m]. For the two-layer cloud, the temperature inversion parameters were 106±59 m, 1.0±0.9°C and 1.0±1.0°C (100 m)−1 above the upper-layer cloud and 82±60 m, 0.6±0.9°C and 0.7±0.6°C (100 m)−1 above the low-layer cloud. Absolute differences between the cloud-base height (cloud-top height) and the lifting condensation level (equilibrium level) were less than 0.5 km for 66.4% (36.8%) of the cases analyzed in summer.

Atmosphere–ocean general circulation models tend to underestimate the solar radiative forcing by stratocumulus over the southeast Pacific, contributing to a warm sea surface temperature (SST) bias. The underestimation may be caused by biases in either macro- or micro- (or both) physical properties of clouds. This study used the WRF Model (incorporated with a physics-based two-moment cloud microphysical scheme) together with the 2008 Variability of the American Monsoon Systems Ocean–Cloud–Atmosphere–Land Study (VOCALS) field observations to investigate the effects of anthropogenic aerosols on the stratocumulus properties and their subsequent effects on the surface radiation balance. The effects were studied by comparing two cases: a control case with the anthropogenic aerosols and a sensitivity case without the anthropogenic aerosols. Results show that the control case produced cloud properties comparable with the measurements by aircraft and that aerosol–cloud microphysical interactions play an important role in regulating solar cloud radiative forcing. As expected, the anthropogenic aerosols increase the cloud droplet number and decrease the cloud droplet size, resulting in an enhancement of solar cloud radiative forcing and a reduction in solar radiation reaching the sea surface, up to a maximum of about 30 W m−2 near the coast. Results also show that aerosol–cloud microphysics–radiation interactions are sensitive to cloud fraction, thus highlighting the role of cloud diurnal variation in studying the cloud–radiation interactions. Analysis of the high-resolution (3 km) model simulations reveals that there exists an inherent scale dependence of aerosol–cloud–radiation interactions, with coarser horizontal resolution yielding a weaker variability.

This paper documents version 1 of the Finite-volume Atmospheric Model of the IAP/LASG (FAMIL1), which has a flexible horizontal resolution up to a quarter of 1°. The model, currently running on the “Tianhe 1A” supercomputer, is the atmospheric component of the third-generation Flexible Global Ocean-Atmosphere-Land climate System model (FGOALS3) which will participate in the Coupled Model Intercomparison Project Phase 6 (CMIP6). In addition to describing the dynamical core and physical parameterizations of FAMIL1, this paper describes the simulated characteristics of energy and water balances and compares them with observational/reanalysis data. The comparisons indicate that the model simulates well the seasonal and geographical distributions of radiative fluxes at the top of the atmosphere and at the surface, as well as the surface latent and sensible heat fluxes. A major weakness in the energy balance is identified in the regions where extensive and persistent marine stratocumulus is present. Analysis of the global water balance also indicates realistic seasonal and geographical distributions with the global annual mean of evaporation minus precipitation being approximately 10−5 mm d−1. We also examine the connections between the global energy and water balance and discuss the possible link between the two within the context of the findings from the reanalysis data. Finally, the model biases as well as possible solutions are discussed.

An aerosol mass dataset simulated from a chemical transport model for the period 1850 to 2100 is used in an atmospheric general circulation model to investigate anthropogenic aerosol radiative forcing (RF) with a focus on East Asia. Compared to the pre-industrial era, the calculated strongest global mean direct RF (DRF) of −0.30 W m−2 at the all-sky top of the atmosphere (TOA) occurs in the 1980s and an indirect cloud albedo forcing (CAF) of −0.67 W m−2 in the 2000s; a maximum atmospheric DRF of 0.48 W m−2, mainly by black carbon absorption, is found in the 2010s. Much larger aerosol DRF and CAF values are distributed over East Asia until the 2010s, and the negative surface and positive atmospheric DRF in Eastern China is even projected to maintain a magnitude of 5.0 W m−2 until the 2030s. Increasing East Asian aerosol loading has shifted the anthropogenic aerosol RF centers to lower latitudes in the Northern Hemisphere since the 1980s, and this trend is more severe under future midand high-range emission scenarios. Further results indicate that larger DRF values over East Asia can be partly attributed to climatological summer atmospheric moisture that is higher relative to Norther American and European regions, which enhances the aerosol hygroscopic effect, then strengthens aerosol optical depth and DRF at clear-sky TOA and surface, and even influences their long-term changes. The observational comparisons reveal that present day simulated surface concentrations of key anthropogenic aerosol species and resulting optical depth are highly underestimated in Eastern China. Further research on simulated meteorology and aerosol features is therefore recommended to reduce the uncertainties in estimating aerosol RF over East Asia.

Nitrate as a rapidly increasing aerosol species in recent years affects the present climate and potentially has large implications on the future climate. In this study, the long-term direct radiative forcing (DRF) of nitrate aerosol is investigated using State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) atmospheric general circulation model (AGCM) and the aerosol dataset simulated by a chemical transport model with focus on East Asia. The DRF due to other aerosols, especially sulfate, is also evaluated for comparisons. Although the chemical transport model underestimates the magnitudes of nitrate and sulfate aerosols when compared with Chinese site observations, some insights into the significances of nitrate climate effects still emerge. The present-day global annual mean all-sky DRF of nitrate is calculated to be −0.025 W m−2 relative to the preindustrial era, which is much weaker than −0.37 W m−2 for sulfate. However, nitrate DRF may become increasingly important in the future especially over East Asia, given the expectation that decreasing trend in global sulfate continues while the projected nitrate maintains at the present level for a mid-range forcing scenario and even be a factor of two larger by the end of the 21st century for high emission scenarios. For example, the anthropogenic nitrate DRF of −2.0 W m−2 over eastern China could persist until the 2050s, and nitrate is projected to account for over 60 % of total anthropogenic aerosol DRF over East Asia by 2100. In addition, we illustrate that the regional nitrate DRF and its seasonal variation are sensitive to meteorological parameters, in particular the relative humidity and cloud amount. It thus remains a need for climate models to include more realistically nitrate aerosol in projecting future climate changes.

We present a study of summer precipitation changes over the Yangtze River Valley (YRV) and North China (NC) simulated from 20 models of the CMIP3 (phase 3 of the Coupled Model Intercomparison Project). It is found that the LASG-FGOALS-g1.0 (fgoals) model has the highest ability in simulating both the interannual variability of individual regions and the seesaw pattern of the two regions observed during the past few decades. Analyses of atmospheric circulations indicate that the variability in precipitation is closely associated with the 850 hPa meridional winds over the two regions. Wetness in the YRV and dryness in NC are corresponding to strong meridional wind gradient and weak meridional wind over these two regions, respectively. The ability of a coupled general circulation model (CGCM) to simulate precipitation changes in the YRV and NC depends on how well the model reproduces both observed associations of precipitation with overlying meridional winds and observed meridional wind features in summer. Analysis of future precipitation changes over the two regions projected by the fgoals model under the IPCC scenarios B1 and A1B suggests a significant increase of 7-15% for NC after 2040s due to the strengthened meridional winds, and a slight increase over the YRV due to less significant intensification of the Mei-yu front.

The Community Earth System Model is used to study the aerosol climate effects during the 1980s and 1990s in which the anthropogenic SO2 emissions decreased in North America and Western Europe and increased in East and South Asia. From the 100 year simulations, aerosol forcing results in cooler (−0.13 K) and drier (−0.01 mm/day) atmosphere with less shortwave radiation flux at the surface (−0.37 W/m2). The clear-sky shortwave radiation flux decreased over East Asia (−0.81 W/m2) and South Asia (−1.09 W/m2), but increased over Western Europe (+1.16 W/m2) and North America (+0.39 W/m2), consistent with aerosol loading changes. While changes in spatial distributions of all-sky shortwave radiation and surface temperature are closely related to cloud changes, the changes in wind and precipitation do not correspond to aerosol loading changes, indicating the complexity of aerosol-cloud circulation interactions. The East and South Asia monsoons were generally weakened due mainly to southward shift of the 200 hPa East Asia Jet (EAJ) and decrease in 850 hPa winds; annual precipitation decreased by 2% in South Asia but increased by 2% in Yangtze-Huai River Valley over East Asia. The uncertainties associated with aerosol climate effects are addressed within the context of model variability and the global warming effect. For the latter, while the aerosol effects decrease the greenhouse warming on the global mean, the regional responses are different. Nevertheless, the characteristics of aerosol climate effects, including the southward 200 hPa EAJ and weakened South Asia monsoon, still persist when the climate becomes warmer, although the strength and the geographical distribution are slightly modulated.

The direct radiative forcing (DRF) of sulfate aerosols depends highly on the atmospheric sulfate loading and the meteorology, both of which undergo strong regional and seasonal variations. Because the optical properties of sulfate aerosols are also sensitive to atmospheric relative humidity, in this study we first examine the scheme for optical properties that considers hydroscopic growth. Next, we investigate the seasonal and regional distributions of sulfate DRF using the sulfate loading simulated from NCAR CAM-Chem together with the meteorology modeled from a spectral atmospheric general circulation model (AGCM) developed by LASG-IAP. The global annual-mean sulfate loading of 3.44 mg m −2 is calculated to yield the DRF of �1.03 and �0.57 W m −2 for clear-sky and all-sky conditions, respectively. However, much larger values occur on regional bases. For example, the maximum all-sky sulfate DRF over Europe, East Asia, and North America can be up to�4.0 W m −2 . The strongest all-sky sulfate DRF occurs in the Northern Hemispheric July, with a hemispheric average of �1.26 W m −2 . The study results also indicate that the regional DRF are strongly affected by cloud and relative humidity, which vary considerably among the regions during different seasons. This certainly raises the issue that the biases in model-simulated regional meteorology can introduce biases into the sulfate DRF. Hence, the model processes associated with atmospheric humidity and cloud physics should be modified in great depth to improve the simulations of the LASG-IAP AGCM and to reduce the uncertainty of sulfate direct effects on global and regional climate in these simulations.

We present statistically reconstructed mean annual winter (December–February) temperatures from the middle and lower reaches of the Yangtze River (24° N–34° N, 108° E–123° E within mainland China) extending back to 1736. The reconstructions are based on information regarding snowfall days from historical documents of the Yu-Xue-Fen-Cun archive recorded during the Qing Dynasty (1644–1911). This information is calibrated with regional winter temperature series spanning the period from 1951 to 2007. The gap from 1912 to 1950 is filled using early instrumental observations. With the reference period of 1951–2007, the 18th century was 0.76 °C colder, and the 19th century was 1.18 °C colder. However, since the 20th century, the climate has been in a warming phase, particularly in the last 30 yr, and the mean temperature from 1981 to 2007 was 0.25 °C higher than that of the reference period of 1951–2007, representing the highest temperatures of the past 300 yr. Uncertainty existed for the period prior to 1900, and possible causes of this uncertainty, such as physical processes involved in the interaction between temperature and snowfall days and changing of observers, are discussed herein.

To improve the understandings on regional climatic effects of past human-induced land cover changes, the surface albedo changes caused by conversions from natural vegetation to cropland were estimated across northeastern China over the last 300 years, and its climatic effects were simulated by using the Weather Research and Forecasting (WRF) model. Essential natural vegetation records compiled from historical documents and regional optimal surface albedo dataset were used. The results show that the surface albedo decreased by 0.01–0.03 due to conversions from grassland to cropland in the Northeast China Plain and it increased by 0.005–0.015 due to conversions from forests to cropland in the surrounding mountains. As a consequence, in the Northeast China Plain, the surface net radiation increased by 4–8 W/m2, 2–5 W/m2, and 1–3 W/m2, and the climate was therefore warmed by 0.1°C–0.2°C、0.1°C–0.2°C、 0.1°C–0.3° in the spring, autumn and winter, respectively. In the surrounding mountain area, the net radiation d °C ecreased by less than 1.5 W/m2, and the climate was therefore cooled too slight to be detected. In summer, effects of surface albedo changes on climate were closely associated with moisture dynamics, such as evapotranspiration and cloud, instead of being merely determined by surface radiation budget. The simulated summer climatic effects have large uncertainties. These findings demonstrate that surface albedo changes resulted in warming climate effects in the non-rainy seasons in Northeast China Plain through surface radiation processes while the climatic effects in summer could hardly be concluded so far.

This study first used measurements to establish the association between the rainy season precipitation in the Yangtze River valley (YRV) and north China (NC) and the 850-hPa meridional wind, and then evaluated the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) models’ simulations of both the associations and precipitation amount. It is shown that there exists a statistically significant positive correlation in the June–July precipitation and wind gradient over the YRV, and in the July–August precipitation and wind over NC. These associations are robust at daily, monthly, and interannual scales. Although many models are found to be capable of simulating the associations, the precipitation amount is still quite inadequate when compared with observations, thus raising the issue of the importance of lower-level wind simulations.

Atmospheric circulation cells associated with anomalous East Asian Winter Monsoon (EAWM) were studied using the 1948/49 to 2002/03 NCEP/NCAR reanalysis and NCAR CAM3 AGCM simulations with monthly global sea surface temperatures from 1950 to 2000. Several atmospheric cells in the Pacific [i.e., the zonal Walker cell (ZWC) in the tropic, the Hadley cell in the western Pacific (WPHC), the midlatitude zonal cell (MZC) over the central North Pacific, and the Hadley cell in the eastern Pacific (EPHC)] are associated with anomalous EAWM. When the EAWM is strong, ZWC, WPHC, and MZC are enhanced, as opposed to EPHC. The anomalous enhanced ZWC is characterized by air parcels rising in the western tropical Pacific, flowing eastward in the upper troposphere, and descending in the tropical central Pacific before returning to the tropical western Pacific. The enhanced MZC has characteristics opposite those of the enhanced ZWC in the central North Pacific. The anomalous WPHC shows air parcels rising in the western Pacific, as in the case of ZWC, followed by flowing northward in the upper troposphere and descending in the west North Pacific, as in the case of the enhanced MZC before returning to the western tropical Pacific. The anomalous EPHC is opposite in properties to the anomalous WPHC. Opposite characteristics are found during the weak EAWM period. The model simulations and the observations show similar characteristics and indicate the important role of sea surface temperature. A possible mechanism is proposed to link interannual variation of EAWM with the central-eastern tropical Pacific sea surface temperature anomaly (SSTA).

Confirming the results of previous regional studies on changes in first bloom dates (FBD) in China, this study provides evidence that complements conclusions drawn from studies of phenological changes in other dynamic climate systems in the Northern Hemisphere. Furthermore, increased occurrences of yearly second blooms (YSB) further reinforce results derived from other studies indicating a recent trend of generalized climate warming across China. Additionally, ascertaining changes in FBD and YSB against a recent background not only provides a hitherto poorly formulated autumnal equivalent to the well-studied shifts in FBD, but also formulates both spring and autumn flowering changes in recent years. Data in this study are derived from observations made from 1963 to 2006 by the Chinese Phenological Observation Network (CPON)-a nationwide system of monitoring stations that has made observations of over 173 species from across China since 1963. At each site, the mean value of each species' annual deviation and spring mean surface temperatures were calculated. For each species, years and locations were also recorded for species in which second blooms (YSB) occurred. Of the 46 FBD samples, 31 showed advances from the mean, blooming earlier over the course of the study period. Notably, although only 8 of the 46 FBD samples showed significance levels of 0.1 or better, the average FBD did advance by 5.3 days. After the 1980s, the frequency of YSB occurrence remained steady, declining a little from the peak in the 1980s, but still exhibiting occurrences far more than were observed earlier. The data from this study clearly indicate that both the phenological advance of FBD in spring and the increased occurrence of YSB are consistent with climate warming.

Historical vegetation antedates current anthropogenic land use. It can therefore be used to reveal land use/cover changes due to human activities. We collected 197 records from Chinese historical documents, including gazettes, government files, private literature, and travel notes, to reveal vegetation status during the late seventeenth century to early twentieth century across Northeast China. The results indicate that woodland and grassland were the dominant landscapes, whereas swamps accounted for a small area. Woodland was composed of needleleaf deciduous forest, broadleaf deciduous forest, and mixed needleleaf and broadleaf forest. Mixed forest occupied the largest area. This forest type covered most of the Greater Khingan Range, Lesser Khingan Range, and Changbai Mountains. Grassland occupied the Songnen Plain, Liao River Plain, and Inner Mongolia Plateau, whereas swamps covered nearly the entire Sanjiang Plain. In addition, the data revealed that most current cropland was converted from grassland in the Northeast Plain, whereas a small area of cropland was converted from woodland and swamp.

Cloud radiative effects strongly depend on diurnal variations of insolation and cloud radiative properties. In general circulation models (GCMs), even when the daily-mean cloud properties agree with observations, errors in cloud diurnal cycle can still significantly impact the shortwave radiation and induce model biases. However, this aspect is overlooked in GCM evaluation and intercomparison programs (e.g., Coupled Model Intercomparison Project Phase 5 (CMIP5)), which mainly consider the daily-mean cloud fraction. This study presents a simple approach of using a diagnostic parameter, the “effective-daytime cloud fraction” which accounts for the concurrent variation of clouds and insolation, to reveal GCM biases in cloud diurnal variations. The usefulness of the approach is illustrated by the significant biases of cloud diurnal cycle in the Modern-Era Retrospective analysis for Research and Applications (MERRA) reanalysis when compared with that in the International Satellite Cloud Climatology Project (ISCCP) data. It is thus suggested that the parameter be included as one of the GCM diagnostics for evaluating cloud diurnal cycle in model intercomparisons.

Increasing cloud condensation nuclei (CCN) concentration usually leads to increasing cloud albedo and decreasing precipitation for warm clouds but its effect on the precipitation of mixed-phase clouds is less clear. Here, a bulk-formula semi-two-moment mixed-phase cloud scheme is incorporated with a regional model to study this aspect on a front system associated with convection. Although this cloud scheme is comparably simpler than most detailed bin-resolving cloud schemes used in cloud resolving models, certain features of CCN effects are reasonably simulated. Results show that both the first and the second indirect effects are simulated and that ice-phase precipitation effectively removes cloud water from the upper troposphere, leading to weaker first indirect effects. Sensitivity simulations show that although increasing CCN number results in more cloud drops and ice, its effect on surface precipitation depends on the interplay between the decreased warm-rain production and the decreased/increased ice-phase precipitation. The increase in cloud drops consequently enhances the diffusional growth of ice particles in water-subsaturated environments but inhibit it in water-supersaturated environments. Moreover, the change in riming depends on the balance between the enhancement due to more cloud drops and the suppression due to smaller cloud drops. For the case studied here, the precipitation responds nonlinearly to CCN number change, causing precipitation decrease in high CCN concentration environments but showing no clear tendency in low CCN concentration environments.

A two-moment (mass and number) warm cloud scheme together with ground and aircraft measurements over Beijing is used in a regional model to study the effects of aerosols on cloud radiative property and precipitation. Using a prescribed tri-modal lognormal aerosol size distribution, the aerosol numbers are calculated from prognostic aerosol masses, for which advection, diffusion, and cloud drop activation/deactivation are considered. Specifically, the accumulation mode of a tri-lognormal aerosol size distribution is fitted to the aircraft measured values for a cold front case passed through northern China during June 25–26, 2005. In the simulations, the warm cloud scheme simulates explicitly the cloud drops and subsequently affects the radiative heating and cooling, and circulations. Simulations with different initial conditions for being fitted with aircraft measurements, continental and maritime aerosol numbers were conducted. It is found that more aerosols result in more but smaller cloud drops and more cloud water, leading to an increase in albedo. The effects on rains are complex: smaller cloud drops have less efficient coagulation for raindrop to form (autoconversion), leading to fewer raindrop numbers and less rainwater; while more cloud water enhances the accretion for raindrop growth. Nevertheless, for the whole cloud system, the impact of increasing aerosols inhibits precipitation.

Studies of the effects of large volcanic eruptions on regional climate so far have focused mostly on temperature responses. Previous studies using proxy data suggested that coherent droughts over eastern China are associated with explosive low-latitude volcanic eruptions. Here, the authors present an investigation of the responses of summer precipitation over eastern China to large volcanic eruptions through analyzing a 1000-yr global climate model simulation driven by natural and anthropogenic forcing. Superposed epoch analyses of 18 cases of large volcanic eruption indicate that summer precipitation over eastern China significantly decreases in the eruption year and the year after. Model simulation suggests that this reduction of summer precipitation over eastern China can be attributed to a weakening of summer monsoon and a decrease of moisture vapor over tropical oceans caused by large volcanic eruptions.

We use measurements of recent decades, 1500-yr proxy data, and millennium model simulations with a variety of climate facings to study the temporal and spatial variability of summer precipitation over eastern China. Spectral analysis of the proxy data using multi-taper method reveals three statistically significant bidecadal (15–35-yr), pendadecadal (40–60-yr), and centennial (65–170-yr) oscillation bands. The results of wavelet filtering show that the amplitudes of these bands vary substantially through time depending on the temperature regimes. Weak centennial oscillation and strong pentadecadal oscillation occur in warm conditions, whereas the oscillations are both strong in cold conditions. A model/data intercomparison suggests that the centennial oscillation might be linked to the fluctuation of solar forcing (Gleissberg cycle), and the pentadecadal and bidecadal oscillations could be associated with internal variability of the climate system. It is also found that the increased frequency of drought-in-north/flood-in-south spatial pattern over eastern China during the last two decades is unusual in the past five centuries.