Summer Climate In China Research Articles

A preliminary attempt on decadal prediction of the East Asian summer monsoon

The East Asian summer monsoon (EASM) is one of the major synoptic systems that affect the summer climate in China. Decadal prediction of the EASM is of great significance, yet few attempts have been made by far. This study represents a preliminary attempt that uses the decadal increment method to predict the decadal variability of the EASM. The 3-year increment of the decadal EASM (DI_EASMI) is firstly predicted by the leading 4 years tropical ocean and the leading 5 years sea ice over Barents Sea. These two leading predictors with quasi-10-year oscillation can explain most variance of the DI_EASMI, especially in recent decades. The predicted DI_EASMI is combined with the observed EASM at 3 years ago to get the final prediction result. The results of cross-validation and independent hindcast show that the decadal increment method can well predict decadal variability of the EASM during the recent century. The real-time prediction results show that the chance for the occurrence of strong decadal EASM would be rare in 2021. The method developed in the present study provides a new approach for decadal prediction of the EASM.

The Position of the Current Warm Period in the Context of the Past 22,000 Years of Summer Climate in China

AbstractIdentifying the position of the Current Warm Period (CWP) in the context of the long‐term climatic trend is vital for understanding the impact of human activity on climate change. Reconstructions of summer temperature and precipitation in eight subregions of China over the past 22,000 years show that the CWP summer temperature and precipitation in these subregions are all lower than in the Early to Middle Holocene. The timing of the Holocene temperature and precipitation peaks in northern China (including Northwest China, North China, and Northeast China) is mainly determined by orbital forcing. Greenhouse gas forcing and the land ice‐sheet help to fine‐tune the timing of the climate maxima. These findings show that the climate since the Last Glacial Maximum in northern China is more sensitive to nonanthropogenic external forcings, whereas the summer precipitation in Southwest China since the early 20th century is controlled more by anthropogenically forced changes.

Verification and Improvement of the Ability of CFSv2 to Predict the Antarctic Oscillation in Boreal Spring

The boreal spring Antarctic Oscillation (AAO) has a significant impact on the spring and summer climate in China. This study evaluates the capability of the NCEP’s Climate Forecast System, version 2 (CFSv2), in predicting the boreal spring AAO for the period 1983–2015. The results indicate that CFSv2 has poor skill in predicting the spring AAO, failing to predict the zonally symmetric spatial pattern of the AAO, with an insignificant correlation of 0.02 between the predicted and observed AAO Index (AAOI). Considering the interannual increment approach can amplify the prediction signals, we firstly establish a dynamical–statistical model to improve the interannual increment of the AAOI (DY AAOI), with two predictors of CFSv2-forecasted concurrent spring sea surface temperatures and observed preceding autumn sea ice. This dynamical–statistical model demonstrates good capability in predicting DY AAOI, with a significant correlation coefficient of 0.58 between the observation and prediction during 1983–2015 in the two-year-out cross-validation. Then, we obtain an improved AAOI by adding the improved DY AAOI to the preceding observed AAOI. The improved AAOI shows a significant correlation coefficient of 0.45 with the observed AAOI during 1983–2015. Moreover, the unrealistic atmospheric response to March–April–May sea ice in CFSv2 may be the possible cause for the failure of CFSv2 to predict the AAO. This study gives new clues regarding AAO prediction and short-term climate prediction.

Impact of Tropospheric Ozone on Summer Climate in China

The spatial distribution, radiative forcing, and climatic effects of tropospheric ozone in China during summer were investigated by using the regional climate model RegCM4. The results revealed that the tropospheric ozone column concentration was high in East China, Central China, North China, and the Sichuan basin during summer. The increase in tropospheric ozone levels since the industrialization era produced clear-sky shortwave and clear-sky longwave radiative forcing of 0.18 and 0.71 W m–2, respectively, which increased the average surface air temperature by 0.06 K and the average precipitation by 0.22 mm day–1 over eastern China during summer. In addition, tropospheric ozone increased the land–sea thermal contrast, leading to an enhancement of East Asian summer monsoon circulation over southern China and a weakening over northern China. The notable increase in surface air temperature in northwestern China, East China, and North China could be attributed to the absorption of longwave radiation by ozone, negative cloud amount anomaly, and corresponding positive shortwave radiation anomaly. There was a substantial increase in precipitation in the middle and lower reaches of the Yangtze River. It was related to the enhanced upward motion and the increased water vapor brought by strengthened southerly winds in the lower troposphere.

Substantial impacts of landscape changes on summer climate with major regional differences: The case of China

China's rapid socioeconomic development during the past few decades has resulted in large-scale landscape changes across the country. However, the impacts of these land surface modifications on climate are yet to be adequately understood. Using a coupled process-based land-atmospheric model, therefore, we quantified the climatic effects of land cover and land management changes over mainland China from 2001 to 2010, via incorporation of real-time and high-quality satellite-derived landscape representation (i.e., vegetation fraction, leaf area index, and albedo) into numerical modeling. Our results show that differences in landscape patterns due to changes in land cover and land management have exerted a strong influence on summer climate in China. During 2001 and 2010, extensive cooling of up to 1.5°C was found in the Loess Plateau and 1.0°C in northeastern China. In contrast, regional-scale warming was detected in the Tibetan Plateau (0.3°C), Yunnan province (0.4°C), and rapidly expanding urban centers across China (as high as 2°C). Summer precipitation decreased in the northeastern region, with patchy reduction generally <1.8mm/day, but increased in the Loess Plateau, with local spikes up to 2.4mm/day. Our study highlights that human alterations of landscapes have had substantial impacts on summer climate over the entire mainland China, but these impacts varied greatly on the regional scale, including changes in opposite directions. Therefore, effective national-level policies and regional land management strategies for climate change mitigation and adaptation should take explicit account of the spatial heterogeneity of landscape-climate interactions.

Simulation on the impacts of the street tree pattern on built summer thermal comfort in cold region of China

The phenomenon of global warming and urban heat island has raised the attention for the outdoor thermal comfort. Vegetation in the improvement of urban micro-climate has been confirmed by a large number of scholars. The problem of the uncomfortable summer climate in China's Cold region didn't get enough research. In this paper, the summer thermal comfort of the street canyon has been studied. The main research intent is to analyze the relationship between the street tree pattern and the thermal comfort of street canyon.It’s demonstrated that, in north-south street, it is suitable for the arrangement of street tree to be at the centre on one side of the street. The higher the height of the street tree, the more comfortable thermal environment the street gets. However, when the ratio of the street tree height to the street building is greater than 10:18, the improvement effect decreases. In east-west street, planting the street tree clinging to the street buildings can provide a better thermal comfort improvement effect.The result of this study can serve as a guide to the greening design in China B-cold region and other regions with similar climatic conditions.

Impacts of urbanization on summer climate in China: An assessment with coupled land‐atmospheric modeling

AbstractChina has experienced unprecedented urbanization since the 1980s, resulting in substantial climatic effects from local cities to broad regions. Using the Weather Research and Forecasting model dynamically coupled to an urban canopy model, we quantified the summertime climate effects of urban expansion in China's most rapidly urbanizing regions: Beijing‐Tianjin‐Hebei (BTH), Yangtze River Delta (YRD), and Pearl River Delta (PRD). High‐resolution landscape data of each urban agglomeration for 1988, 2000, and 2010 were used for simulations. Our results indicated summertime urban warming of 0.85°C for BTH, 0.78°C for YRD, and 0.57°C for PRD, which was substantially greater than previous estimates. Peak summer warming for BTH, YRD, and PRD was 1.5°C, 1°C, and 0.8°C, respectively. In contrast, the loss of moisture was greatest in PRD, with maximum reduction in 2 m water vapor mixing ratio close to 1 g/kg, followed by YRD and BTH with local peak humidity deficits reaching 0.8 g/kg and 0.6 g/kg, respectively. Our results were in better agreement with observations than prior studies because of the usage of high‐resolution landscape data and the inclusion of key land‐atmospheric interactions. Our study also demonstrated that the warming impacts of polycentric urban forms were less intense but more extensive in space, whereas large concentrated urban aggregations produced much stronger but localized warming effects. These findings provide critical knowledge that improves our understanding of urban‐atmospheric interactions, with important implications for urban landscape management and planning to alleviate the negative impacts of urban heat islands.

Interdecadal Variations of Meridional Winds in the South China Sea and Their Relationship with Summer Climate in China*

Abstract Analysis of the NCEP and 40-yr ECMWF Re-Analysis (ERA-40) data and the Xisha Island station observation indicates that the low-level meridional wind (LLMW) over the South China Sea (SCS) experienced an interdecadal variation since the late 1970s. The LLMW change is associated with the reduction of tropospheric temperature in midlatitude East Asia. A mechanism is put forward to explain the triggering and maintenance of the tropospheric cooling. The enhanced convective heating over the southern South China Sea results in a meridional vertical overturning circulation, with anomalous descending motion appearing over continental East Asia. The anomalous descending motion reduces the local humidity through both anomalous low-level divergence and dry vertical advection. The decrease of the local tropospheric humidity leads to the enhanced outgoing longwave radiation into space and thus cold temperature anomalies. The decrease of the temperature and thickness leads to anomalous low (high) pressure and convergent (divergent) flows at upper (lower) levels. This further enhances the descending motion and leads to a positive feedback loop. The fall in tropospheric temperature over continental East Asia reduces the land–sea thermal contrast and leads to the weakening of cross-equatorial flows and the LLMW over SCS. A further diagnosis indicates that the LLMW is closely linked to the summer precipitation and temperature variations in China on interdecadal time scales. A weakening of the LLMW after 1976 is associated with a “−, +, −” meridional rainfall pattern, with less rain in Guangdong Province and north China but more rain in the Yangtze and Huaihe River basins and northeast China, and a “+, −, +” temperature pattern, with increased (decreased) surface temperature in the south and north (central) China.

Anomalous summer climate in China influenced by the tropical Indo-Pacific Oceans

Possible influences of three coupled ocean–atmosphere phenomena in the Indo-Pacific Oceans, El Niño, El Niño Modoki and the Indian Ocean Dipole (IOD), on summer climate in China are studied based on data analysis for the summers of 1951–2007. Partial correlation/regression analysis is used to find the influence paths through the related anomalous mid- and low-level tropospheric circulations over the oceanic region and East Eurasia, including the western North Pacific summer monsoon (WNPSM). Among the three phenomena, El Niño Modoki has the strongest relationship with the WNPSM. When two or three phenomena coexist with either positive or negative phase, the influences exerted by one phenomenon on summer climate in different regions of China may be enhanced or weakened by other phenomena. In 1994 when both El Niño Modoki and IOD are prominent without El Niño, a strong WNPSM is associated with severe flooding in southern China and severe drought in the Yangtze River Valley (YRV). The 500 hPa high systems over China are responsible for heat waves in most parts of China. In 1983 when a strong negative phase of El Niño Modoki is accompanied by moderate El Niño and IOD, a weak WNPSM is associated with severe flooding in the YRV and severe drought in southern China. The 500 hPa low systems over China are responsible for the cold summer in the YRV and northeastern China. For rainfall, the influence path seems largely through the low-level tropospheric circulations including the WNPSM. For temperature, the influence path seems largely through the mid-level tropospheric circulations over East Eurasia/western North Pacific Ocean.

Effects of vegetation cover on summer climate in China during 1982–2001

In this paper, we apply lagged correlation analysis to study the effects of vegetation cover on the summer climate in different zones of China, using NOAA/AVHRR normalized difference vegetation index (NDVI) data during the time period from 1982 to 2001 and climate data of 365 meteorological stations across China (precipitation from 1982 to 2001 and temperature from 1982 to 1998). The results show that there are positive correlations between spring NDVI and summer climate (temperature and precipitation) in most zones of China; these suggest that, when the vegetation cover increases, the summer precipitation will increase, and the lagged correlations show a significant difference between zones. The stronger correlations between NDVI in previous season and summer climate occur in three zones (Mid-temperate zone, Warm-temperate zone and Plateau climate zone), and this implies that vegetation changes have more sensitive feedback effects on climate in the three zones in China.

Projecting the Summer Climate of Mainland China in the Middle 21st Century: Will the Droughts in North China Persist?

Since no consensus has been reached in previous studies about how the summer climate in China will evolve in the first half of the 21st century, this issue is addressed here through sensitivity experiments by forcing an atmospheric general circulation model (AGCM), the Geophysical Fluid Dynamics Laboratory (GFDL)’s Atmospheric Model Version 2.0 (AM2) with projected sea surface temperature (SST) trend. A total of two SST trends from the Intergovernmental Panels on Climate Change (IPCC) Special Report on Emissions Scenario (SRES) A1B are used. The two trends are from two coupled climate system models, the National Center for Atmospheric Research (NCAR) Community Climate System Model Version 3.0 (CCSM3) and the GFDL Climate Model Version 2.0 (CM2), respectively. Results consistently suggest a substantial warming and drying trend over much of China, with a surface air temperature increase of 1.0 2.0 ℃ and a 10% 20% decrease in rainfall. Exceptions are the areas from northwestern China to western North China as well as the southern Tibetan Plateau, which are projected to be wetter with a rainfall anomaly percentage increase of 10% 50%. The drying in eastern North China has not been documented to date but appears to be reasonable. Physically, it is attributed to anomalous northeasterly winds at the rear of a low-level cyclone over the South China Sea, the Philippines and the subtropical western North Pacific. These conditions, which govern the climate of eastern China, are forced by the northward shift of convection over warm waters due to additional warming.

Precursory SST anomalies associated with the convection over the western Pacific warm pool

The convection over the tropical western Pacific warm pool influences significantly the atmospheric circulation and climate in East Asia. Thus, the precursory signals of the convection may be used in the forecast of summer climate in China. According to the present results, the June-July-August (JJA) mean convection intensity over the warm pool is significantly related to the precursory positive and negative sea surface temperatures (SSTs) in the warm pool and in the equatorial central and eastern Pacific, respectively. It is also related to the simultaneous negative surface temperatures west to the Philippines. The analysis on the SSTs associated with the convection over the warm pool in individual month of summer shows that for the convection in June and July, there are precursory SST signals in the warm pool and the equatorial central and eastern Pacific. Therefore, this study shows that only the convection in June and July, rather than that in August, has precursory SST signals, despite the existence of the precursory signals of the JJA mean convection. Accordingly, it is implied that the interaction among the warm pool, equatorial central and eastern Pacific, and the region west to the Philippines may exhibit distinct features in the precursory period (preceding winter and spring) and in the simultaneous period.