Lianchun Song

Projected Changes in Temperature and Precipitation Extremes in China by the CMIP5 Multimodel Ensembles

AbstractThis paper presents projected changes in temperature and precipitation extremes in China by the end of the twenty-first century based on the Coupled Model Intercomparison Project phase 5 (CMIP5) simulations. The temporal changes and their spatial patterns in the Expert Team on Climate Change Detection and Indices (ETCCDI) indices under the RCP4.5 and RCP8.5 emission scenarios are analyzed. Compared to the reference period 1986–2005, substantial changes are projected in temperature and precipitation extremes under both emission scenarios. These changes include a decrease in cold extremes, an increase in warm extremes, and an intensification of precipitation extremes. The intermodel spread in the projection increases with time, with wider spread under RCP8.5 than RCP4.5 for most indices, especially at the subregional scale. The difference in the projected changes under the two RCPs begins to emerge in the 2040s. Analyses based on the mixed-effects analysis of variance (ANOVA) model indicate that by ...

Guiding the Creation of A Comprehensive Surface Temperature Resource for Twenty-First-Century Climate Science

Surface temperature data – observed primarily for weather-related purposes – are disparate, originating from ever evolving instrument types and observational practices. Although several global databases are in use internationally, no comprehensive global repository exists and many data are undigitized or restricted. Scientists have painstakingly obtained vast quantities of data, carefully removed random errors and accounted for systematic biases. The 21st Century demands go further - requiring highly detailed (spatially and temporally), globally complete, long-term products, with quantified uncertainties, and created from freely available, fully traceable data. Many decisions of substantial socio-economic importance rely on the accuracy of such products. An international meeting was held to plan how best to facilitate such efforts. A central repository is to be created, where data are traceable from their origins to final product. Strategies are outlined to rescue non-digitized data and move towards entirely freely available data. Creation of multiple methodologically independent products is recommended for quantifying uncertainty. Methods of benchmarking and assessing multiple products to aid inter-comparison and end-user product selection are described. Data-products would be obtained and visualized using in-house tools from the planned data-portal. Structure and governance include engagement with bodies such as WMO and, importantly, with experts other than climatologists.

Changes in Mean and Extreme Temperature and Precipitation over the Arid Region of Northwestern China: Observation and Projection

This paper reports a comprehensive study on the observed and projected spatiotemporal changes in mean and extreme climate over the arid region of northwestern China, based on gridded observation data and CMIP5 simulations under the RCP4.5 and RCP8.5 scenarios. The observational results reveal an increase in annual mean temperature since 1961, largely attributable to the increase in minimum temperature. The annual mean precipitation also exhibits a significant increasing tendency. The precipitation amount in the most recent decade was greater than in any preceding decade since 1961. Seasonally, the greatest increase in temperature and precipitation appears in winter and in summer, respectively. Widespread significant changes in temperature-related extremes are consistent with warming, with decreases in cold extremes and increases in warm extremes. The warming of the coldest night is greater than that of the warmest day, and changes in cold and warm nights are more evident than for cold and warm days. Extreme precipitation and wet days exhibit an increasing trend, and the maximum number of consecutive dry days shows a tendency toward shorter duration. Multi-model ensemble mean projections indicate an overall continual increase in temperature and precipitation during the 21st century. Decreases in cold extremes, increases in warm extremes, intensification of extreme precipitation, increases in wet days, and decreases in consecutive dry days, are expected under both emissions scenarios, with larger changes corresponding to stronger radiative forcing.

Tropospheric wet refractivity tomography based on the BeiDou satellite system

This paper presents a novel approach for assessing the precision of the wet refractivity field using BDS (BeiDou navigation satellite system) simulations only, GPS, and BDS+GPS for the Shenzhen and Hongkong GNSS network. The simulations are carried out by adding artificial noise to a real observation dataset. Instead of using the d and s parameters computed from slant wet delay, as in previous studies, we employ the Bias and RMS parameters, computed from the tomography results of total voxels, in order to obtain a more direct and comprehensive evaluation of the precision of the refractivity field determination. The results show that: (1) the precision of tropospheric wet refractivity estimated using BDS alone (only 9 satellites used) is basically comparable to that of GPS; (2) BDS+GPS (as of current operation) may not be able to significantly improve the data’s spatial density for the application of refractivity tomography; and (3) any slight increase in the precision of refractivity tomography, particularly in the lower atmosphere, bears great significance for any applications dependent on the Chinese operational meteorological service.

The Boreal Summer Intraseasonal Oscillation Simulated by Four Chinese AGCMs Participating in the CMIP5 Project

The performances of four Chinese AGCMs participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) in the simulation of the boreal summer intraseasonal oscillation (BSISO) are assessed. The authors focus on the major characteristics of BSISO: the intensity, significant period, and propagation. The results show that the four AGCMs can reproduce boreal summer intraseasonal signals of precipitation; however their limitations are also evident. Compared with the Climate Prediction Center Merged Analysis of Precipitation (CMAP) data, the models underestimate the strength of the intraseasonal oscillation (ISO) over the eastern equatorial Indian Ocean (IO) during the boreal summer (May to October), but overestimate the intraseasonal variability over the western Pacific (WP). In the model results, the westward propagation dominates, whereas the eastward propagation dominates in the CMAP data. The northward propagation in these models is tilted southwest-northeast, which is also different from the CMAP result. Thus, there is not a northeast-southwest tilted rain belt revolution off the equator during the BSISO’s eastward journey in the models. The biases of the BSISO are consistent with the summer mean state, especially the vertical shear. Analysis also shows that there is a positive feedback between the intraseasonal precipitation and the summer mean precipitation. The positive feedback processes may amplify the models’ biases in the BSISO simulation.

Human Influence on the 2015 Extreme High Temperature Events in Western China

Introduction. The 2015 summer (June–August) was historically the hottest in western China (west of 105°E), setting new records for the regionally averaged seasonal mean temperature, annual maxima of daily maximum (TXx), and daily minimum (TNx) temperatures. Many stations set new record high temperatures as well. During the period of 12 June–10 August, the daily high temperature above 38°C covered an area of about 753 000 km2, with the highest temperature of 47.7°C recorded in Dongkan station (42.83°N, 89.25°E) of Turpan. The long-lasting extreme high temperature events exerted serious impacts on agriculture and other sectors, resulting in severe heat damage for different crops such as corn, wheat, and fruit trees (CMA 2016).

Preliminary Results of Tropospheric Wet Refractivity Tomography Based on GPS/GLONASS/BDS Satellite Navigation System

Up until the end of October 2012, the Chinese BeiDou navigation satellite system (BDS) had launched 16 satellites, and then started providing formal operation services for China and surrounding regions from the beginning of 2013. It is of theoretical and practical significance to do research on Tropospheric wet refractivity tomography based on BeiDou system. The simulation experiment is conducted based on the ephemeris obtained from two line elements (TLE) and SDP4 model, Shenzhen-Hongkong GNSS network and standard atmosphere. The multiplicative algebraic reconstruction techniques (MART) are used to solve tomography equations to obtain tropospheric wet refractivity field. The results show that for the Shenzhen-Hongkong area the tomography precision has not improved obviously by the signals fusion of GPS/GLONASS/BeiDou, and the tropospheric wet refractivity field can be obtained with high precision based purely on the BeiDou system when GPS/GLONASS become unavailable due to certain factors.