Xia Qu

An Enhanced Influence of Tropical Indian Ocean on the South Asia High after the Late 1970s

The tropical Indian Ocean (TIO)’s influence on the South Asia high (SAH)’s intensity experiences a decadal change in the late 1970s; after (before) the decadal shift, the influence is significant (insignificant). The present study investigates the role of tropospheric temperature in relaying the impact of sea surface temperature (SST) to the SAH and the change in the TIO’s influence. During the two epochs, the local tropospheric temperature responses to the TIO warming are distinct—more significant during the second epoch. It is inferred that this change may be responsible for the strengthening of the TIO’s influence on the SAH. Encouragingly, the ensemble simulations accurately capture the time of the decadal change, indicating that the enhanced influence is attributed to the SST forcing. There are two possible reasons for the change in the TIO‐SAH relationship. The first reason is the change in the locations of the SST anomalies in the TIO. During the second epoch, positive SST anomalies lie in the Indian Ocean warm pool. Through the background vigorous convection and moist adjustment, the SST anomalies affect largely the tropospheric temperature and thus the SAH. The second reason is the decadal change in mean SST and the SST variability. During the recent decades, both the background SST and the variability of the TIO SST increase, which enhance the influence of the SST anomalies on the atmosphere. The influence of the remote oceanic forcing on the enhanced TIO‐SAH relationship and its comparison with the contribution of the TIO SST are also discussed.

Interdecadal Variations in ENSO Influences on Northwest Pacific-East Asian Early Summertime Climate Simulated in CMIP5 Models

The present study investigates interdecadal modulations of the El Nino-Southern Oscillation (ENSO) influence on the climate of the northwest Pacific (NWP) and East Asia (EA) in early boreal summer following a winter ENSO event, based on 19 simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). In the historical run, 8 out of 19 models capture a realistic relationship between ENSO and NWP early summer climate-an anomalous anticyclone develops over the NWP following a winter El Nino event- and the interdecadal modulations of this correlation. During periods when the association between ENSO and NWP early summer climate is strong, ENSO variance and ENSO-induced anomalies of summer sea surface temperature (SST) and tropospheric temperature over the tropical Indian Ocean (TIO) all strengthen relative to periods when the association is weak. In future projections with representative concentration pathways 4.5 and 8.5, the response of TIO SST, tropospheric temperature, and NWP anomalous anticyclone to ENSO all strengthen regardless of ENSO amplitude change. In a warmer climate, low-level specific humidity response to interannual SST variability strengthens following the Clausius-Clapeyron equation. The resultant intensification of tropospheric temperature response to interannual TIO warming is suggested as the mechanism for the strengthened ENSO effect on NWP-EA summer climate.

Consistent responses of East Asian summer mean rainfall to global warming in CMIP5 simulations

East Asia summer rainfall is of great social–economic importance. Based on observations, reanalysis and simulations of 16 Coupled Models Intercomparison Project phase 5 (CMIP5) models, the responses of East Asia summer precipitation, as well as some relevant features, to global warming are investigated. The CMIP5 historical simulation reasonably reproduces the climatology of summer rainfall, the associated circulation, the moisture and its transportation, and the mid-troposphere horizontal advection of temperature as well. Under global warming, the rainfall enhancement is robustly projected in the state-of-the-art models over North China, Northeast China, northern coast of Japan and the Kuroshio. As well, the total summer rainfall over East Asia is consistently increased in the models. For the consistent responses, the moisture budget analysis based on the simulations shows that two factors are responsible: one is increased moisture. As East Asia is a climatological ascent region in northern summer, increased moisture induced by global warming leads to more moisture transported upward and thus the rainfall rise. The other is enhanced evaporation, which may be caused by surface warming and provides more precipitable water to the atmosphere column. Furthermore, the results may provide some implications to the long-term variability of East Asia summer rainfall over the last several decades.

The global warming hiatus—a natural product of interactions of a secular warming trend and a multi-decadal oscillation

The globally-averaged annual combined land and ocean surface temperature (GST) anomaly change features a slowdown in the rate of global warming in the mid-twentieth century and the beginning of the twenty-first century. Here, it is shown that the hiatus in the rate of global warming typically occurs when the internally generated cooling associated with the cool phase of the multi-decadal variability overcomes the secular warming from human-induced forcing. We provide compelling evidence that the global warming hiatus is a natural product of the interplays between a secular warming tendency due in a large part to the buildup of anthropogenic greenhouse gas concentrations, in particular CO2 concentration, and internally generated cooling by a cool phase of a quasi-60-year oscillatory variability that is closely associated with the Atlantic multi-decadal oscillation (AMO) and the Pacific decadal oscillation (PDO). We further illuminate that the AMO can be considered as a useful indicator and the PDO can be implicated as a harbinger of variations in global annual average surface temperature on multi-decadal timescales. Our results suggest that the recent observed hiatus in the rate of global warming will very likely extend for several more years due to the cooling phase of the quasi-60-year oscillatory variability superimposed on the secular warming trend.

Changes in the characteristics of precipitation over northern Eurasia

Based on observed daily precipitation data, this study investigates the changes in the characteristics of precipitation over northern Eurasia during 1951–2010. Over the majority of northern Eurasia (east of 20° E), the light precipitation days and amounts decrease, but those for the moderate, heavy, and very heavy precipitation increase. Moreover, the precipitation intensity increases, which is responsible for the decrease in light precipitation days and amount and increase in relatively more intense precipitation since there is no significant trend in total precipitation days. However, the precipitation characteristics are opposite over the Iberian Peninsula. We find that the changes in precipitation characteristics are possibly due to the changes in static stability. In the majority region (the Iberian Peninsula), the static stability weakens (strengthens) during 1951–2010. When static stability weakens (strengths), the upward motion increases (decreases) and thus the precipitation intensity increases (decreases). Accordingly, the light precipitation events decrease (increase) and heavy precipitation events increase (decrease).

Different influences of two types of El Niños on the Indian Ocean SST variations

By comparing correlation of sea surface temperature (SST) and vertical circulation with canonical El Niño and El Niño Modoki, we find that El Niño Modoki has an effect on the Indian Ocean different from traditional El Niño. There exists obvious Indian Ocean basin mode (IOBM) after canonical El Niño, while insignificant SST anomalies exist in the Indian Ocean after El Niño Modoki. Anomalous downdraft and updraft appear over the eastern and western Indian Ocean, respectively, during canonical El Niño, while anomalous updraft is weak over the Indian Ocean during El Niño Modoki. Besides, the strength of El Niño Modoki is slightly weaker than that of canonical El Niño. According to previous studies, two mechanisms can explain IOBM after canonical El Niño: tropospheric temperature (TT) mechanism and ocean dynamics. However, both of them do not exist during El Niño Modoki. Comparing with the complicated oceanic processes, it is convenient to verify the observed TT anomalies and test the possible mechanism using the simple model. Therefore, we pay more attention on the question why TT mechanism does not work during El Niño Modoki. Using a linear barocinic model (LBM), we demonstrate that the strength of SST anomalies and cold SST anomalies in the eastern Pacific have an influence on TT anomalies. Especially, cold SST anomalies in the eastern Pacific cancel the effects of warm SST anomalies in the central Pacific on TT anomalies. It suggests that the SST anomalies in the eastern Pacific are important for the TT mechanism in two types of El Niño.

Spatial and temporal features of summer extreme temperature over China during 1960–2013

Based on daily air temperature data from 772 stations in China, the present study uses absolute index and percentile index to investigate the spatial and temporal features of summer extreme temperature over China during the period 1960–2013. The analysis indicates that Xinjiang and southeastern China are two major domains where extreme heat events frequently occur and that the number of heat day (NHD) and the frequency of heat wave (FHW) both show an increasing trend throughout the country except for Shandong and Henan provinces where a decreasing trend is identified. Although the two leading empirical orthogonal function (EOF) modes of the NHD and the FHW based on the absolute index and percentile index have differences, the time series of the first principal components (PC1) are consistent; PC1 depicts opposite trends from 1960 to late 1990s and during the late 1990s to 2013. According to the climatology and EOF modes, four sub-regions are chosen: Chuanyu, Huanghuai, Southeast, and Xinjiang area. The inter-decadal variation over the four sub-regions differs, but the NHD and the FHW significantly increase after the mid-1990s. Based on Mann-Kendall method, it is found that the NHD and the FHW over Chuanyu exhibited abrupt shifts in 1978 and 2000; sudden shifts occurred in 1973 and 2000 over Huanghuai; an abrupt shift occurred over the Southeast area in 2003.

The Global Warming–Induced South Asian High Change and Its Uncertainty

AbstractBased on models from phase 5 of the Coupled Model Intercomparison Project (CMIP5), the present study investigates the South Asian high (SAH) change in response to global warming. Under global warming, the selected 16 coupled general circulation models all feature an elevation of geopotential height at 100 hPa to the south of the SAH climatological position; an easterly response is found over the northern Indian Ocean in all the models, while a westerly response is found over subtropical Asia. The ridges of the SAH shift equatorward in 75% of models. Using the linear baroclinic model, it is found that the combined effects of latent heating and the mean advection of stratification change (MASC) are mainly responsible for those responses. The MASC mainly leads to the aforementioned easterly and westerly responses; the latent heating contributes to the geopotential height response and the easterly response over the northern Indian Ocean. The most important intermodel diversity is found in the 100-hPa ...

The decadal variability of the tropical Indian Ocean SST–the South Asian High relation: CMIP5 model study

Based on Coupled Model Intercomparison Project phase 5 (CMIP5) models, present study investigates the decadal variability of the tropical Indian Ocean (TIO) sea surface temperature (SST)–the South Asian High (SAH) relation (hereafter TSR) as well as its responses to the global warming. Out of the 17 CMIP5 models, only one (GFDL-CM3) reproduces reasonably the influence of the TIO SST on the SAH. In the historical simulations of GFDL-CM3, the TSR features fluctuations modulated by the western Pacific SST and the Indian subcontinent precipitation. When the TIO warming is accompanied by warm western Pacific, the western Pacific SST-induced tropospheric warming propagates westwards, warms the troposphere surrounding the Indian Ocean, enhances SAH and leads to higher TSR; when accompanied by not so warmed western Pacific, the TSR is lower. While, if the TIO warming is accompanied by negative rainfall anomalies over the Indian subcontinent, the rainfall-induced upper-troposphere cyclone over the subtropical Asia weakens the response of the SAH and leads to lower TSR; if not accompanied by negative rainfall anomalies, the TSR is higher. The decadal variability of the TSR is not subject to the global warming. In RCP45 and RCP85 scenarios, the TSR is also not directly affected by global warming. The rainfall over the Indian subcontinent is still a factor modulating the TSR. While, the western Pacific SST is invalid in the influences of the TIO SST on the SAH.

Southern European rainfall reshapes the early-summer circumglobal teleconnection after the late 1970s

The summer circumglobal teleconnection (CGT), which crucially affects mid-latitude climate in the Northern Hemisphere, is generally characterized by a mid-latitude wave train along the strong upper-tropospheric westerly jet. In this study a significant change is identified in the spatial pattern of the early-summer CGT after the late 1970s: An additional high-latitude wave train has occurred over northern Eurasia. Based on observational evidences and simulation results with a linear baroclinic model, it is proposed that the post-1970s CGT change is induced by enhanced impact of rainfall over southern Europe (SE) after the late 1970s. Specifically, the mid-latitude wave train of CGT in early summer is dominated by Indian rainfall before the late 1970s but by both rainfall over India and SE after the late 1970s; the high-latitude wave train of CGT occurring after the late 1970s, however, is induced only by the SE rainfall. The coupled Indian and SE rainfall after the late 1970s, which is probably due to the basic flow change over the North Atlantic, induce both mid-latitude and high-latitude wave trains of the CGT.