Isotopic evidence for twentieth-century weakening of the Pacific Walker circulationZhongfang Liu and Zhimin Jian and Christopher J. Poulsen and Liang Zhao.Earth and Planetary Science Letters:2019,507,85 - 93摘要The strength of the Pacific Walker circulation (WC) over the historical period is uncertain and strongly debated, largely due to the limited length of reliable instrumental records. Tropical Pacific corals provide continuous, highly-resolved records that can be used to overcome the limitations of the instrumental records. Here we combine coral δ18O records from the western Pacific Warm Pool (WPWP) and tropical central-eastern Pacific (CEP) to develop a coral WC index back to 1886. Our coral WC index is in good agreement with post-1950 instrumental records, justifying both a direct comparison with earlier instrumental records and an evaluation of twentieth century WC trends. Our results show that pre-1950 instrumental records appear to underestimate WC variability. The coral WC index reveals a significant weakening of the WC over the twentieth century in response to development of El Niño like SST pattern in the tropical Pacific and enhanced hydrological cycle over the CEP under greenhouse warming. Our results provide new evidence for twentieth century WC variability and offer an observational constraint for improving models and their prediction of future WC behavior.
Summer ozone variation derived from FY3/TOU satellite data and impacts of East Asian summer monsoonZhang Yan, Zhao Liang*, Wang Weihe, Tang Shihao, Huang Fuxiang.Proceedings of SPIE:2018/10/25,10776摘要下载全文The daily dataset of coherent total column ozone were created from FY3/TOU from 2008 to 2017. Using total column ozone from FY3/TOU and tropospheric and stratospheric column ozone from AURA OMI/MLS satellite data, the seasonal variations of the climatological ozone in the region (40ºE-160ºE, 0-60ºN) are analyzed for the
total, tropospheric and stratospheric column, respectively. Differences of ozone and circulation pattern between strong and weak East Asian summer monsoon year are also investigated. Variation of total, tropospheric and stratospheric column ozone is dominated by a low value center over the Tibetan Plateau and abnormal distribution
in the monsoon region. There are significant differences of ozone concentration and circulation pattern during strong and weak monsoon in summer. The combination of the monsoon anomaly and the upper westerly jet anomaly affects obviously distribution of the tropospheric and stratospheric ozone during summer in the East Asia and the western Pacific regions.
Preferred solar signal and its transfer in the Asian--Pacific subtropical jet regionLi Delin，Xiao Ziniu，Zhao Liang.Climate Dynamics:2018(Oct)摘要下载全文Solar impact on the tropospheric subtropical jet (SJ) has been identified previously from a zonally averaged perspective. The SJ was observed to be weaker in the high solar activity winters. However, some regional features of solar-induced SJ variations might remain unrecognized. Here it is found that the regional solar signal in wintertime Asian--Pacific zonal wind at 200 hPa, which exhibits a tripolar banded structure, greatly resembles the second internal mode of zonal wind within the same sector. Significant response of the Asian--Pacific SJ (APSJ) to increased solar forcing in boreal winter exclusively marks its center region, showing a deceleration in westerlies. Further exploration suggests two possible top--down routes to interpret this particular manifestation of solar signal in APSJ center, a tropical route and a middle--high latitude route. Regarding the tropical route, during the cold season, driven by the solar-associated reduction in Brewer--Dobson circulation, ozone concentration in tropical lower stratosphere increases notably and merely within the zonal range of APSJ center. This heats the air here and the tropical tropospheric regional upwelling is thereby suppressed. Consequently, a significant weakened APSJ center is produced via local Hadley cell. Regarding the middle--high latitude route, in early winter, solar-related pronounced westerly anomalies in the mid-latitude stratosphere only appear in the longitudinal range of APSJ center. Meanwhile, the upward propagating planetary waves from the troposphere could be reflected back downward by this intensified stratospheric westerlies. As winter progresses, through wave mean flow interactions, a resultant weakened APSJ center markedly presents in the middle of winter.
Amplification of the solar signal in the summer monsoon rainband in China by synergistic actions of different dynamical responsesZhao Liang, Wang Jingsong, Liu Haiwen, Xiao Ziniu.Journal of Meteorological Research:2017,31(1),61--72摘要下载全文A rainband meridional shift index (RMSI) is defined and used to statistically prove that the East Asian summer monsoon rainband is usually significantly more northward in the early summer of solar maximum years than that of solar minimum years. By applying continuous wavelet transform, cross wavelet transform, and wavelet coherence, it is found that throughout most of the 20th century, the significant decadal oscillations of sunspot number (SSN) and the RMSI are phase-locked and since the 1960s, the SSN has led the RMSI slightly by approximately 1.4 yr. Wind and Eliassen–Palm (EP) flux analysis shows that the decadal meridional oscillation of the June rainband likely results from both a stronger or earlier onset of the tropical monsoon and poleward shift of the subtropical westerly jet in high-solar months of May and June. The dynamical responses of the lower tropical monsoon and the upper subtropical westerly jet to the 11-yr solar cycle transmit bottom-up and top-down solar signals, respectively, and the synergistic actions between the monsoon and the jet likely amplify the solar signal at the northern boundary of the monsoon to some extent.
A stable snow--atmosphere coupled modeZhao Liang, Yuxiang Zhu, and Haiwen Liu and Zhongfang Liu, Yanju Liu, Xiuping Li, and Zhou Chen.Climate Dynamics:2016,47(7),2085-2104摘要下载全文Snow is both an important lower boundary forcing of the atmosphere and a response to atmospheric forcing in the extratropics. It is still unclear whether a stable snow–atmosphere coupled mode exists in the extratropics, like the ENSO in the tropics. Using Sliding Correlation analysis over Any Window, the present study quantitatively evaluates the stability of coupling relationships between the major modes of winter snow over the Northern Hemisphere and the winter atmospheric Arctic Oscillation (AO), the Antarctic Oscillation (AAO) and the Siberian High over the period 1872–2010, and discusses their possible relationships for different seasons. Results show that the first mode of the winter snow cover fraction and the winter AO together constitute a stable snow–atmosphere coupled mode, the SNAO. The coupled mode is stronger during recent decades than before. The snow anomaly over Europe is one key factor of the SNAO mode due to the high stability there, and the polar vortex anomaly in the atmosphere is its other key factor. The continuity of signals in the SNAO between autumn and winter is weaker than that between winter and spring. The second winter snow mode is generally stably correlated with the winter AAO and was more stable before the 1970s. The AAO signal with boreal snow has a strong continuity in seasonal transition. Generally, through these coupled modes, snow and atmosphere can interact in the same season or between different seasons: autumn snow can influence the winter atmosphere; the winter atmosphere can influence spring snow.
Robust response of the East Asian monsoon rainband to solar variabilityZhao Liang, Wang Jingsong*.J. Climate:2014,21,3043-3051摘要下载全文This study provides evidence of the robust response of the East Asian monsoon rainband to the 11-yr solar cycle and first identify the exact time period within the summer half-year (1958–2012) with the strongest correlation between the mean latitude of the rainband (MLRB) over China and the sunspot number (SSN). This period just corresponds to the climatological-mean East Asian mei-yu season, characterized by a large-scale quasi-zonal monsoon rainband (i.e., 22 May–13 July). Both the statistically significant correlation and the temporal coincidence indicate a robust response of the mei-yu rainband to solar variability during the last five solar cycles. During the high SSN years, the mei-yu MLRB lies 1.2° farther north, and the amplitude of its interannual variations increases when compared with low SSN years. The robust response of monsoon rainband to solar forcing is related to an anomalous general atmospheric pattern with an up–down seesaw and a north–south seesaw over East Asia.
Statistical tests for a correlation between decadal variation in June precipitation in China and sunspot numberWang Jingsong, Zhao Liang*.Journal of Geophysical Research:2012,117(D23),D23117摘要下载全文Six different statistical methods (i.e., correlation, difference, prominent period, variance contribution, scale-averaged spectrum, and cross spectrum) are used to test for regional differences in the relationship between the 11 year sunspot cycle and June precipitation in China during the 20th century. In the Huaihe River basin (HRB) of central China, located at the marginal region of the East Asian summer monsoon (EASM), there exists a reliable positive-correlation relationship between the 11 year sunspot cycle and June precipitation; whereas, possible negative and very weak positive correlations in the south of the middle–lower Yangtze River Region and the HeTao Basin (HTB), located in the interior of the EASM and the westerlies, respectively. The reasons for these regional differences are investigated, revealing that the marginal region of EASM may be more sensitive to solar forcing than is its interior, which results in the HRB becoming the most susceptible (strongest correlation) region. That is to say, in June during the high sunspot number (SSN) years, the influence of the EASM is significantly greater and more to the north than that in June during the low SSN years, causing the HRB to be mainly influenced by the EASM (westerlies) in June during the high (low) SSN years. The northward expansion of the June EASM probably resulted from enhancement of the low-level southwesterly monsoon flow over the northern tropical Indian Ocean, combined with an expansion of the western Pacific subtropical high at times of high SSN.
Signature of the solar cycle on decadal variability in monsoon precipitation over ChinaZhao Liang, Jingsong Wang*, Haijuan Zhao.Journal of the Meteorological Society of Japan:2012,90(1),1-9摘要下载全文Monthly high-resolution land surface precipitation data from 1901 to 2006 associated with sunspot number (SSN) data is investigated for the relationship between summer precipitation in China and the decadal solar variability. Generally, on a national scale, precipitation is poorly correlated with SSN. However, in many regions, the long-period (＞8 years) variability in summer precipitation is significantly (at ＞95% confidence level) correlated to SSN. Absolute value correlation coefficient can exceed 0.48 (at ＞99% confidence level) in some regions. If only the decadal (9–13 years) precipitation component is considered, the correlation becomes stronger with a maximum (minimum) correlation coefficient of 0.73 (–0.73) (at ＞99.9% confidence level). Considering that the decadal component is the most important factor among precipitation’s low-frequency signals in the high correlation areas (because it explains more than 50% of the precipitation’s low-frequency variance), it can be concluded that solar variability seems to dominate the long-period variation of summer precipitation in these areas. Furthermore, in these high correlation areas, temporal variation patterns in the power spectrum of summer precipitation is similar to that of SSN, strongly suggesting that there is a very likely physical link between solar variability and precipitation in these regions. More convincing and direct evidence shows the significant difference of low-level monsoon flow between high and low solar activity years, which may cause the higher precipitation rate for high, rather than low, solar activity years in central China.
The preliminary analysis of sunshine durations with meteorological data for the Chinese giant solar telescope site surveyLiu Yu, Zhao Liang.Monthly Notices of the Royal Astronomical Society:2013,434(2),1674-1680摘要Using meteorological data is fundamental in any site survey for astronomical instruments. As
a first step, the analyses of sunshine duration for candidate sites are crucial for remote site
survey for solar observing instruments. In western China, some ground-based meteorological
stations have collected daily sunshine data from only partial-sky area since they had to be
constructed in valley. One aim of this study is to demonstrate the geographical properties of
those meteorological stations. Our goal is to investigate the true sunshine durations obtained
if the stations are installed at the top of nearby mountain without screen effect. We make use
of the three-dimensional geographical data from the Google Earth software and the statistical
meteorological data from the National Meteorology Administration and the meteorological
stations. All the 76 national basic meteorological observing stations with altitude over 3000 m
located in western China are measured. Since astronomical instruments tend to be installed at
the top of a mountain, we need to take into account the loss of the sunshine durations in making
the remote site survey. Our results, after the compensation, show that the condition of sunshine
duration in the Hengduan-Shan Mountains (HSM) area can meet the basic requirement of at
least 2500 h yr−1 for the Chinese Giant Solar Telescope (CGST) site survey.
The response of winter Pacific North American pattern to strong volcanic eruptionsZhongfang Liu, Kei Yoshimura, Nikolaus H. Buenning, Zhimin Jian, Zhao Liang.Climate Dynamics:2016,1-16摘要The impact of volcanic eruptions on large-scale atmospheric circulation patterns has been well studied, but very little effort has been made on relating the response of Pacific North American (PNA) pattern to strong volcanic eruptions. Here we investigate the response of winter PNA to the largest volcanic eruptions using three different reanalysis datasets. We demonstrate a significant positive PNA circulation response to strong volcanic forcing in the first winter following the eruptions. This circulation pattern is associated with enhanced southwesterly winds advecting warm air from the tropical/subtropical Pacific into northwestern North America and leads to a significant warming in the region. However, no significant PNA signal is found for the second post-eruption winter. The PNA responses to volcanic forcing depend partly upon the modulation of the El Ni?o Southern Oscillation (ENSO) events. When the ENSO influence is linearly removed, this positive PNA signal is still robust during the first post-eruption winter, albeit with slightly decreased magnitude and significance. Our findings provide new evidence for volcanic forcing of the Pacific and North American climates. The results presented here may contribute to deconvolving modern and past continental-scale climate changes over North America.
Binary mesovortex structure associated with southwest vortexZhou Kuo, Liu Haiwen, Zhao Liang Zhu Yuxiang, Lin Yihua, Zhang Fuying, Fu Ning.Atmospheric Science Letters:2017-May-12,18/6,246--252摘要Previous work has concluded that the southwest vortex (SWV) is a single mesoscale vortex. Applying the National Centers for Environmental Prediction Final Operational Global Analysis, the Interim European Centre for Medium-Range Weather Forecasts Re-Analysis, and the non-hydrostatic mesoscale Advanced Research Weather Research and Forecasting (WRF) model to a case study, we discovered a new type of SWV associated with another coexisting mesoscale warm and moist vortex. In the case study, meso-β-scale vortex-A was generated at 1800 UTC 17 July, and dissipated around 0500 UTC 18 July 2013, with a lifespan of approximately 11 h. Vortex-B occurred at 0600 UTC 17 July and moved out of the Sichuan Basin at 0800 UTC 18 July 2013, remaining over the basin for approximately 26 h. Stronger atmospheric upward motion and two mesoscale rainbelts associated with each of the vortices further demonstrate the binary mesoscale vortex structure related to the SWV using the WRF model. The quasi-geostrophic balance of the two mesoscale cyclonic circulations is responsible for the generation and maintenance of the two closed mesoscale vortices.
Investigations on moisture transports, budgets and sources responsible for the decadal variability of precipitation in southern ChinaHu Yamin, Si Dong, Liu Yanju, Zhao Liang.Journal of Tropical Meteorology:2016,22(3),402-412摘要In the context of global warming,apparent decdal-interdecdal variabilities can be detected in summer precipitation in southern China.Especially around the 1990 s,precipitation in South China experienced a phase transition from a deficiency regime to an abundance regime in the early 1990 s,while the Yangtze River Valley witnessed a phase shift of summer precipitation from abundance to deficiency in the late 1990 s.Pertinent analyses reveal a close relationship between such decadal precipitation shifts and moisture budgets,which is mainly modulated by the meridional component.This relationship can be attributed to large-scale moisture transport anomalies.Further,the HYSPLIT model is utilized to quantitatively evaluate relative moisture contributions from diverse sources during different regimes.It can be found that during the period with abundant precipitation in South China,the moisture contribution from the source of Indochina Peninsula-South China Sea increased significantly,while during the deficient precipitation regime in the Yangtze River Valley,moisture from local source,western Pacific and Indochina Peninsula-South China Sea contributed less to precipitation.It means some new features of relative moisture contributions from diverse sources to precipitation anomaly in southern China took shape after 1990s.