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    The 12th Workshop on Antarctic Meteorology and Climate
    Matthew A. LAZZARA, Jordan G. POWERS, Carol A. COSTANZA, David H. BROMWICH, Scott CARPENTIER, Steve R. COLWELL
    DOI: 10.1007/s00376-018-8061-2
    Abstract   ( 15 ) PDF (1011KB) (9)
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    Increasing Flash Floods in a Drying Climate over Southwest China
    Chan XIAO, Peili WU, Lixia ZHANG, Robin CLARK
    DOI: 10.1007/s00376-018-7275-7
    Abstract   ( 35 ) PDF (1321KB) (23)
    In a globally warming world, subtropical regions are generally expected to become drier while the tropics and mid--high latitudes become wetter. In line with this, Southwest China, close to 25°N, is expected to become increasingly prone to drought if annual mean precipitation decreases. However, despite this trend, changes in the temporal distribution of moisture supply might actually result in increased extreme rainfall in the region, whose climate is characterized by distinct dry and wet seasons. Using hourly and daily gauge observations, rainfall intensity changes since 1971 are examined for a network of 142 locations in the region. From the analysis, dry season changes are negligible but wet season changes exhibit a significantly strong downward trend [−2.4% (10 yr)−1], particularly during the past 15 years [−17.7% (10 yr)−1]. However, the intensity of events during the wettest of 5% hours appears to steadily increase during the whole period [1.4% (10 yr)−1], tying in with government statistical reports of recent droughts and flooding. If the opposing trends are a consequence of a warming climate, it is reasonable to expect the contradictory trend to continue with an enhanced risk of flash flooding in coming decades in the region concerned.
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    Impacts of Anthropogenic Forcings and El Niño on Chinese Extreme Temperatures
    DOI: 10.1007/s00376-018-7258-8
    Abstract   ( 32 ) PDF (1878KB) (7)
    This study investigates the potential influences of anthropogenic forcings and natural variability on the risk of summer extreme temperatures over China. We use three multi-thousand-member ensemble simulations with different forcings (with or without anthropogenic greenhouse gases and aerosol emissions) to evaluate the human impact, and with sea surface temperature patterns from three different years around the El Niño--Southern Oscillation (ENSO) 2015/16 event (years 2014, 2015 and 2016) to evaluate the impact of natural variability. A generalized extreme value (GEV) distribution is used to fit the ensemble results. Based on these model results, we find that, during the peak of ENSO (2015), daytime extreme temperatures are smaller over the central China region compared to a normal year (2014). During 2016, the risk of nighttime extreme temperatures is largely increased over the eastern coastal region. Both anomalies are of the same magnitude as the anthropogenic influence. Thus, ENSO can amplify or counterbalance (at a regional and annual scale) anthropogenic effects on extreme summer temperatures over China. Changes are mainly due to changes in the GEV location parameter. Thus, anomalies are due to a shift in the distributions and not to a change in temperature variability.
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    Assessment and Assimilation of FY-3 Humidity Sounders and Imager in the UK Met Office Global Model
    Fabien CARMINATI, Brett CANDY, William BELL, Nigel ATKINSON
    DOI: 10.1007/s00376-018-7266-8
    Abstract   ( 12 ) PDF (1767KB) (4)
    China’s FengYun 3 (FY-3) polar orbiting satellites are set to become an important source of observational data for numerical weather prediction (NWP), atmospheric reanalyses, and climate monitoring studies over the next two decades. As part of the Climate Science for Service Partnership China (CSSP China) program, FY-3B Microwave Humidity Sounder 1 (MWHS-1) and FY-3C MWHS-2 observations have been thoroughly assessed and prepared for operational assimilation. This represents the first time observations from China’s polar orbiting satellites have been used in the UK’s global NWP model. Since 2016, continuous data quality monitoring has shown occasional bias changes found to be correlated to changes in the energy supply scheme regulating the platform heating system and other transient anomalies. Nonetheless, MWHS-1 and MWHS-2 significantly contribute to the 24-h forecast error reduction by 0.3% and 0.6%, respectively, and the combination of both instruments is shown to improve the fit to the model background of independent sounders by up to 1%. The observations from the Microwave Radiation Imager (MWRI) also are a potentially significant source of benefits for NWP models, but a solar-dependent bias observed in the instrument half-orbits has prevented their assimilation. This paper presents the bases of a correction scheme developed at the Met Office for the purpose of a future assimilation of MWRI data.
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    Indian Ocean SST modes and Their Impacts as Simulated in BCC_CSM1.1(m) and HadGEM3
    Bo LU, Hong-Li REN, Rosie EADE, Martin ANDREWS
    DOI: 10.1007/s00376-018-7279-3
    Abstract   ( 29 ) PDF (3238KB) (10)
    The sea surface temperature anomalies (SSTAs) in the tropical Indian Ocean (TIO) show two dominant modes at interannual time scales, referred to as the Indian Ocean basin mode (IOBM) and dipole mode (IOD). Recent studies have shown that the IOBM and IOD not only affect the local climate, but also induce remarkable influences in East Asia via teleconnections. In this study, we assess simulations of the IOBM and IOD, as well as their teleconnections, using the operational seasonal prediction models from the Met Office (HadGEM3) and Beijing Climate Center [BCC_CSM1.1(m)]. It is demonstrated that the spatial patterns and seasonal cycles are generally reproduced by the control simulations of BCC_CSM1.1(m) and HadGEM3, although spectra biases exist. The relationship between the TIO SSTA and El Niño is successfully simulated by both models, including the persistent IOBM warming following El Niño and the IOD–El Niño interactions. BCC_CSM1.1(m) and HadGEM3 are capable of simulating the observed local impact of the IOBM, such as the strengthening of the South Asian high. The influences of the IOBM on Yangtze River rainfall are also captured well by both models, although this teleconnection is slightly weaker in BCC_CSM1.1(m) due to the underestimation of the northwestern Pacific subtropical high. The local effect of the IOD on East African rainfall is reproduced by both models. However, the remote control of the IOD on rainfall over southwestern China is not clear in either model. It is shown that the realistic simulations of TIO SST modes and their teleconnections give rise to the source of skillful seasonal predictions over China.
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    Further-Adjusted Long-Term Temperature Series in China Based on MASH
    Zhen LI, Zhongwei YAN, Lijuan CAO, Phil D. JONES
    DOI: 10.1007/s00376-018-7280-x
    Abstract   ( 34 ) PDF (2301KB) (6)
    A set of homogenized monthly mean surface air temperature (SAT) series at 32 stations in China back to the 19th century had previously been developed based on the RHtest method by Cao et al, but some inhomogeneities remained in the dataset. The present study produces a further-adjusted and updated dataset based on the Multiple Analysis of Series for Homogenization (MASH) method. The MASH procedure detects 33 monthly temperature records as erroneous outliers and 152 meaningful break points in the monthly SAT series since 1924 at 28 stations. The inhomogeneous parts are then adjusted relative to the latest homogeneous part of the series. The new data show significant warming trends during 1924--2016 at all the stations, ranging from 0.48 to 3.57°C (100 yr)−1, with a regional mean trend of 1.65°C (100 yr)−1; whereas, the previous results ranged from a slight cooling at two stations to considerable warming, up to 4.5°C (100 yr)−1. It is suggested that the further-adjusted data are a better representation of the large-scale pattern of climate change in the region for the past century. The new data are available online at http://www.dx.doi.org/10.11922/sciencedb.516.
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    Changes in the Proportion of Precipitation Occurring as Rain in Northern Canada during Spring--Summer from 1979--2015
    Wei HAN, Cunde XIAO, Tingfeng DOU, Minghu DING
    DOI: 10.1007/s00376-018-7226-3
    Abstract   ( 25 ) PDF (2396KB) (11)
    Changes in the form of precipitation have a considerable impact on the Arctic cryosphere and ecological system by influencing the energy balance and surface runoff. In this study, station observations and ERA-Interim data were used to analyze changes in the rainfall to precipitation ratio (RPR) in northern Canada during the spring--summer season (March--July) from 1979--2015. Our results indicate that ERA-Interim describes the spring--summer variations and trends in temperature and the RPR well. Both the spring--summer mean temperature [0.4°C--1°C (10 yr)−1] and the RPR [2%--6% (10 yr)−1] increased significantly in the Canadian Arctic Archipelago from 1979--2015. Moreover, we suggest that, aside from the contribution of climate warming, the North Atlantic Oscillation is probably another key factor influencing temporal and spatial differences in the RPR over northern Canada.
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    On Northern Hemisphere Wave Patterns Associated with Winter Rainfall Events in China
    Claudia Christine STEPHAN, Yan Ho NG, Nicholas P. KLINGAMAN
    DOI: 10.1007/s00376-018-7267-7
    Abstract   ( 46 ) PDF (4068KB) (11)
    During extended winter (November–April), 43% of the intraseasonal rainfall variability in China is explained by three spatial patterns of temporally coherent rainfall. These patterns were identified with empirical orthogonal teleconnection (EOT) analysis of observed 1982–2007 pentad rainfall anomalies and connected to midlatitude disturbances. However, examination of individual strong EOT events shows that there is substantial inter-event variability in their dynamical evolution, which implies that precursor patterns found in regressions cannot serve as useful predictors. To understand the physical nature and origins of the extratropical precursors, the EOT technique is applied to six simulations of the Met Office Unified Model at horizontal resolutions of 200–40 km, with and without air–sea coupling. All simulations reproduce the observed precursor patterns in regressions, indicating robust underlying dynamical processes. Further investigation into the dynamics associated with observed patterns shows that Rossby wave dynamics can explain the large inter-event variability. The results suggest that the apparently slowly evolving or quasi-stationary waves in regression analysis are a statistical amalgamation of more rapidly propagating waves with a variety of origins and properties.
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    Climate Change of 4°C Global Warming Above Pre-industrial Levels
    Xiaoxin WANG, Dabang JIANG, Xianmei LANG
    DOI: 10.1007/s00376-018-7160-4
    Abstract   ( 382 ) PDF (3105KB) (119)
    Using a set of numerical experiments from 39 CMIP5 climate models, we project the emergence time for 4°C global warming with respect to pre-industrial levels and associated climate changes under the RCP8.5 greenhouse gas concentration scenario. Results show that, according to the 39 models, the median year in which 4°C global warming will occur is 2084. Based on the median results of models that project a 4°C global warming by 2100, land areas will generally exhibit stronger warming than the oceans annually and seasonally, and the strongest enhancement occurs in the Arctic, with the exception of the summer season. Change signals for temperature go outside its natural internal variabilities globally, and the signal-to-noise ratio averages 9.6 for the annual mean and ranges from 6.3 to 7.2 for the seasonal mean over the globe, with the greatest values appearing at low latitudes because of low noise. Decreased precipitation generally occurs in the subtropics, whilst increased precipitation mainly appears at high latitudes. The precipitation changes in most of the high latitudes are greater than the background variability, and the global mean signal-to-noise ratio is 0.5 and ranges from 0.2 to 0.4 for the annual and seasonal means, respectively. Attention should be paid to limiting global warming to 1.5°C, in which case temperature and precipitation will experience a far more moderate change than the natural internal variability. Large inter-model disagreement appears at high latitudes for temperature changes and at mid and low latitudes for precipitation changes. Overall, the inter-model consistency is better for temperature than for precipitation.
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    Assessment of Two Two-stream Radiative Transfer Schemes in a Climate Model
    Quan YANG, Feng ZHANG, Jiangnan LI, Kun WU, Yining SHI, Yiran PENG
    DOI: 10.1007/s00376-018-7302-8
    Abstract   ( 20 ) PDF (2274KB) (13)
    The accuracies of the two-stream discrete-ordinate-method (DOM) and Eddington approximation schemes are systematically compared in an offline single-column model and in a general circulation model (GCM). It is found that the two-stream DOM produces more accurate results for the heating rate, upward radiative flux and downward radiative flux under clear-sky conditions in single-column model, and the Eddington approximation is more accurate under all-sky conditions. An experiment using satellite data as the real cloud properties confirms the superiority of the Eddington approximation under cloudy-sky conditions. Experiments using the GCM of the Beijing Climate Center (BCC_AGCM2.0.1) show that, compared to the two-stream DOM, the Eddington approximation can enhance the fraction of low cloud, and this increased cloud fraction can affect the differences in radiative fluxes between the two two-stream schemes. This study suggests that the most suitable approach in GCMs is to use the two-steam DOM for clear-sky conditions and the Eddington approximation for all-sky conditions.
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