Laboratory for Climate Studies

Beijing, China

Laboratory for Climate Studies

Beijing, China
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Wang Z.,Laboratory for Climate Studies | Yang S.,Sun Yat Sen University | Zhou B.,Nanjing University of Information Science and Technology
International Journal of Climatology | Year: 2017

As two major types of icing, rime and glaze, especially those with long persistency and extensive coverage, cause great economic and social damages for China. Based on 28 persistent and extensive rime events and 19 glaze events in China, this article examined their preceding features and relationship with large-scale climate factors. The results show that the pronounced preceding signals for these events include the Ural and Okhotsk blocking highs, major East Asian trough, cold air actives, southwesterly moisture transportation and upper-level jet stream. They intensify greatly 5-7 days ahead, indicating the forthcoming icing events and weaken significantly foretelling the ending of the events. Large-scale climate factors such as negative phase of the Arctic Oscillation, strong Siberian high, La Niña background and low sea surface temperature from the tropical Indian Ocean to the tropical western Pacific favour the occurrence of glaze events in China by intensifying the East Asian winter monsoon and exciting the southward outbreak of cold airs. In the meantime, deep wintertime semi-permanent trough in the southern branch of westerlies is crucial for the northward moisture transportation. However, only the low sea surface temperature from the tropical Indian Ocean to the tropical western Pacific and the deep wintertime semi-permanent trough in the southern branch of westerlies are significantly related to the occurrence of rime events in China. Although weak Australian low and strong western Pacific subtropical high also favour water vapour transportation, they are observed only during a small portion of icing events. © 2017 Royal Meteorological Society.

Hardiman S.C.,UK Met Office | Lin P.,Princeton University | Scaife A.A.,UK Met Office | Dunstone N.J.,UK Met Office | Ren H.-L.,Laboratory for Climate Studies
Geophysical Research Letters | Year: 2017

The strength of the Brewer-Dobson circulation (BDC) is predicted to increase due to climate change. However, this increase has yet to be robustly detected in observational analyses. In this study a long control simulation is used to calculate the Time of Emergence of the BDC trend and how much of that trend may be masked by dynamical variability in current observations. A Time of Emergence of around 30 years is found (assuming a 2%/decade trend in the BDC), similar to the length of current reanalysis data sets. However, the discrepancies in vertical velocities between different reanalysis products remain far larger than any predicted trend. Furthermore, dynamical variability can completely mask the BDC trend on time scales shorter than around 12 years. Thus, more robust observational analyses of vertical velocity are likely to be needed for at least the next decade before detection of a statistically significant trend can be expected. © 2017. American Geophysical Union.

Ren F.,Laboratory for Climate Studies | Liang J.,Nanjing University | Wu G.,CAS Institute of Atmospheric Physics | Dong W.,Beijing Normal University | Yang X.,Nanjing University
Journal of Climate | Year: 2011

Data homogeneity has become a significant issue in the study of tropical cyclones (TCs) and climate change. In this study, three historical datasets for the western North Pacific TCs from the Joint Typhoon Warning Center (JTWC), Japan Meteorological Agency (JMA), and China Meteorological Administration (CMA) are compared with a focus on TC intensity. Over the past 55 years (1951-2005), significant discrepancies are found among the three datasets, especially between the CMA and JTWC datasets. The TC intensity in the CMA dataset was evidently overestimated in the 1950s and from the late 1960s to the early 1970s, while it was overestimated after 1988 in the JTWC dataset, especially during 1993-2003. Large discrepancies in TC tracks exist in two periods of 1951-early 1960s and 1988-1990s. Further analysis reveals that the discrepancies are obviously related to the TC observational techniques. Before the era of meteorological satellites (1951-the early 1960s), and after the termination of aircraft reconnaissance (since 1988), large discrepancies exist in both TC intensity and track. That the intensity discrepancy was smallest during the period (1973-87) when aircraft reconnaissance data and the Dvorak technique were both available suggests that availability of the aircraft reconnaissance and the Dvorak method helps in reducing the TC intensity discrepancy. For those TCs that were included in all the three datasets, no significant increasing or decreasing trend was found over the past 50 years. Each of the three TC datasets has individual characteristics that make it difficult to tell which one is the best. For TCs that affect China, the CMA dataset has obvious advantages such as more complete and more accurate information. © 2011 American Meteorological Society.

Ren F.,Laboratory for Climate Studies | Cui D.,Laboratory for Climate Studies | Cui D.,Lanzhou University | Gong Z.,Laboratory for Climate Studies | And 5 more authors.
Journal of Climate | Year: 2012

An extreme weather and climate event does not only mean that an extreme occurs at an individual point (station), but more generally it has a certain impacted area and duration, which means that it is a regional extreme event (REE). How to identify a REE is the basis for studies in this area. An objective identification technique for REE (OITREE), which is based on the model of "the string of candied fruits,"is proposed in this study. This technique consists of five steps: to select a daily index for individual points (stations), to partition natural daily abnormality belts, to distinguish the event's temporal continuity, to establish an index system for regional events, and to judge extremity for regional events. In the index system developed specially for regional events, there are five single indices, namely extreme intensity, accumulated intensity, accumulated area, maximum impacted area and duration, as well as an integrated index and the spatial location. In this study, the proposed method was first applied to examine four types of REEs in China: heavy precipitation, drought, high temperature, and low temperature. Results show that the technique is skillful in identifying REEs, demonstrating the usefulness of the proposed method in detecting and studying of REEs and operational application. © 2012 American Meteorological Society.

Tan G.-R.,Nanjing University of Information Science and Technology | Ren H.-L.,Laboratory for Climate Studies | Chen H.,Nanjing University of Information Science and Technology
International Journal of Climatology | Year: 2014

Using a linear dynamic operator and the daily National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data, the linearized part of the synoptic eddy feedback onto the low-frequency flow (SELF) associated with cold/warm events in January over China is investigated. Composite stream function differences between the cold and warming events show that the anomalous temperature events are linked closely to the teleconnection pattern which is related to North Atlantic Oscillation (NAO) and accompanied with remarkable anomalies over Ural Mountain and the areas south to Lake Baikal. The significant eddy feedback exists as the episodes occur, which tends to induce a similar circulation pattern to the anomalous low-frequency flow associated with the temperature episodes. Further, a linear SELF operator is used to estimate quantitatively the linearized part of the eddy feedback on the low-frequency flow for the temperature events. Results show that the magnitude of the stream function anomalies (SFAs) induced by eddy forcing is bigger at higher latitudes than lower latitudes. The positive (negative) SFA can be induced where eddy-vorticity fluxes converge (diverge) into the anomalous cyclonic (anticyclonic) circulation. Further analysis of differences in eddy feedback strength suggests that synoptic eddy feedback is more effective for the cold events than that for the warm events over North Atlantic, Ural Mountain, and the areas south to Lake Baikal. The SFA anomaly pattern over Ural Mountain and Lake Baikal associated with the anomalous temperature events in China will disappear without considering the eddy feedback. It suggests that the eddy feedback plays a very important role in maintaining the low-frequency flow during the January anomalous temperature events. © 2014 Royal Meteorological Society.

Ren H.-L.,University of Hawaii at Manoa | Ren H.-L.,Laboratory for Climate Studies | Jin F.-F.,University of Hawaii at Manoa | Gao L.,University of Hawaii at Manoa | Gao L.,Laboratory for Climate Studies
Journal of the Atmospheric Sciences | Year: 2012

A method of eddy structure decomposition is proposed to detect how low-frequency flow associated with the North Atlantic Oscillation (NAO) organizes systematically synoptic eddy (SE) activity to generate inphase and upstream feedbacks. In this method, a statistical eddy streamfunction (SES) field, defined by the three-point covariance of synoptic-scale streamfunction, is introduced to characterize spatiotemporal SE flow structures. The SES field is decomposed into basic and anomalous parts to represent the climatological SE flow structure and its departure. These two parts are used to calculate the basic and anomalous eddy velocity, eddy vorticity, and thus eddy vorticity flux fields, in order to elucidate those two SE feedbacks onto the NAO. This method is validated by the fact that the observed anomalous eddy vorticity flux field can be reproduced well by two linear terms: the basic eddy velocity field multiplied by anomalous eddy vorticity field and the anomalous eddy velocity field multiplied by basic eddy vorticity field. With this method, it is found that, in the positive and negative phases, the NAO flow tends to induce two different types of anomalous SE flow structure, which are largely responsible for generating the net meridional and zonal eddy vorticity fluxes that, in return, feed back onto the NAO. The two processes that are related to these two different types dominate in the in-phase and upstream feedbacks, which are delineated conceptually into two kinematic mechanisms associated with zonal-slanting and meridional-shifting changes in the SE structure. The present observational evidence supports the theory of eddy-induced instability for low-frequency variability and also provides insights into the reason for the asymmetry between the SE feedbacks onto the two NAO phases. © 2012 American Meteorological Society.

Hua L.,University of Chinese Academy of Sciences | Zhong L.,CAS Institute of Atmospheric Physics | Ke Z.,Laboratory for Climate Studies
International Journal of Climatology | Year: 2016

Dynamic recycling model (DRM) and reanalysis data were used to study the interaction between the land surface and atmosphere during the warm season from 1979 to 2010 across the arid and semi-arid regions of China. The nonlinear trends common to the key land-atmosphere interaction variables were extracted. For the whole study region, the precipitation recycling ratio showed an increasing trend, especially in the period before the 1990s. Simultaneously, increasing trends were also found in variables regionally related to precipitation, such as soil moisture, evaporation, precipitation efficiency, low-level cloud and precipitable water. However, the moisture transport due to westerly moisture flux showed a remarkable weakening throughout the whole study region. Based on significantly positive correlation between the precipitation efficiency and precipitation recycling ratio under relatively low moisture advection, it was concluded that the precipitation recycling process should not been ignored, for both direct and indirect precipitation processes, in the study region. The spatial patterns of nonlinear trends in land-atmosphere interaction variables indicated reverse tendencies in two sub-regions divided by the meridional boundary at approximately 110°E. For the western sub-region, although decreasing westerly moisture flow was found, the strengthening southerly moisture flux mainly resulted in an increase of precipitable water. Positive relationships among precipitable water, low cloud, precipitation, soil moisture, evaporation and the precipitation recycling ratio were also found. The soil becoming wetter and the precipitation recycling process becoming enhanced suggested the existence of positive land-atmosphere interaction in the western sub-region. However, the opposite tendencies were found in the eastern sub-region, where a weakening of advected moisture convergence was caused by decreases in both westerly and southerly moisture transport. Furthermore, less evaporation and warming temperatures suggested the climate in the eastern sub-region shifted towards relatively warmer and drier conditions throughout the course of the study period. © 2016 Royal Meteorological Society.

Wu J.,Laboratory for Climate Studies | Gao X.-J.,Laboratory for Climate Studies
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2013

A new gridded daily dataset with the resolution of 0.25° latitude by 0.25° longitude, CN05.1, is constructed for the purpose of high resolution climate model validation over China region. The dataset is based on the interpolation from over 2400 observing stations in China, includes 4 variables: daily mean, minimum and maximum temperature, daily precipitation. The "anomaly approach" is applied in this interpolation. The climatology is first interpolated by thin-plate smoothing splines and then a gridded daily anomaly derived from angular distance weighting method is added to climatology to obtain the final dataset. Intercomparison of the dataset with other three daily datasets, CN05 for temperature, and EA05 and APHRO for precipitation is conducted. The analysis period is from 1961 to 2005. For multi-annual mean temperature variables, results show small differences over eastern China with dense observation stations, but larger differences (warmer) over western China with less stations between CN05.1 and CN05. The temperature extremes are measured by TX3D (mean of the 3 greatest maximum temperatures in a year) and TN3D (mean of the 3 lowest minimum temperatures). CN05.1 in general shows a warmer TX3D over China, while a lower TN3D in the east and greater TN3D in the west are found compared to CN05. A greater value of annual mean precipitation compared to EA05 and APHRO, especially to the latter, is found in CN05.1. For precipitation extreme of R3D (mean of the 3 largest precipitations in a year), CN05.1 presents lower value of it in western China compared to EA05.

Bao B.,Chinese Academy of Meteorological Sciences | Bao B.,University of Chinese Academy of Sciences | Bao B.,Laboratory for Climate Studies | Ren G.,Laboratory for Climate Studies
Continental Shelf Research | Year: 2014

Based on monthly mean HadISST data, climatological characteristics and long-term changes of sea surface temperature (SST) over marginal seas of China are analyzed for the time period 1870-2011. The results show that (1) The smallest and largest spatial SST differences among various areas are seen in August and January respectively, with the coolest month occurring in February for all of the seas and the warmest month occurring in August for all but South China Sea (SCS); (2) The warming trends of the marginal seas of China during the time periods analyzed are generally larger than the global and hemispheric averages, with the East China Sea seeing the largest warming of all seas; (3) All of the sea areas see significant rising trends of annual mean SST in the last 140 years and the last 50 years, with larger and more significant warming generally occurs in autumn and winter; (4) The last 30 years especially the last 14 years undergo a slowdown of warming in the marginal seas of China, and the slowdown in the last 14 years is more evident than the global and northern hemispheric averages; (5) A weak upwelling current exists in western SCS, and the upwelling intensity has a significant positive correlation with the SCS summer monsoon index, with both seeing a decreasing trend in the last 64 years. © 2014 .

Peng Y.,Lanzhou University | Peng Y.,Laboratory for Climate Studies | Shen C.,Albany State University | Wang W.-C.,Albany State University | Xu Y.,Laboratory for Climate Studies
Journal of Climate | Year: 2010

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. © 2010 American Meteorological Society.

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