An equilibrium cloud-resolving modeling study of diurnal variation of tropical rainfall

The diurnal variation of tropical rainfall is examined through the analysis of an equilibrium cloud-resolving model experiment. Model domain mean rain rate is defined as a product of rain intensity and fractional rainfall coverage. The diurnal variation of the mean rain rate is associated with that of fractional rainfall coverage because the diurnal variation of rain intensity is significantly weakened through the decrease in rainfall in early morning hours. The decrease in rainfall corresponds to the reduction in secondary circulations through the barotropic conversion from the perturbation kinetic energy to the mean kinetic energy under the imposed negative vertical gradient of westerly winds. The fractional rainfall coverage shows the diurnal signal with the maximum in the early morning hours primarily due to nocturnal infrared radiative cooling.     

Would different methodologies for assessing carbon leakage exposure lead to different risk levels? A case study of the Brazilian industry

Energy-intensive industries play an important role in low-carbon development, being particularly exposed to climate policies. Concern over possible carbon leakage in this sector poses a major challenge for designing effective carbon pricing instruments (CPI). Different methodologies for assessing carbon leakage exposure are currently used by different jurisdictions, each of them based on different approaches and indicators. This paper aims to analyse the extent to which the use of different methodologies leads to different results in terms of exposure to the risk of carbon leakage, using the Brazilian industry sector as a case study. Results indicate that carbon leakage exposure is an expected outcome of eventual CPI implementation in Brazilian industry. However, results vary according to the chosen methodology, so the definition of the criteria is paramount for assessing sectoral exposure to the risk of carbon leakage.

Key policy insights

• Despite increasing discussion about the implementation of carbon pricing on the Brazilian industrial sector, the evaluation of carbon leakage risks is still neglected.

• Assessments of the risk of carbon leakage are directly related to the indicators and criteria used by each methodology. Thus, a given subsector may present different levels of exposure to carbon leakage depending on the methodological choice.

• More than a purely technical discussion, the methodological definition of carbon leakage risk is a political discussion – it can be well-conducted, leading to the success of a CPI, or even sabotaged, by implicitly subsidizing energy-intensive industries.

     

南京市近地层湍流结构及输送特征研究

本文利用"城市生物气溶胶研究”中的超声风温仪观测资料,对南京市近地层大气的湍流强度、相关系数、速度谱及通量输送等进行研究,得到南京市近地层湍流结构及输送特征的一些结论.     

春季北方气旋活动的气候特征及与气温和降水的关系

利用1948-2002年NCEP／NCAR再分析逐日海平面气压资料以及中国160站的降水和气温资料，分析了春季北方气旋活动频数和强度的时空变化特征，以及两者与中国降水和气温的相关关系。结果表明：春季北方气旋活动频繁，存在明显的两个高值中心，分别位于蒙古国的中部和我国东北北部地区。春季北方气旋活动频数和强度均存在明显的年际和年代际变化。伴随着一次全球性的年代际气候跃变，20世纪70年代中后期无论是频数还是强度均出现了显著的突变。春季北方气旋活动频数主要对我国北方地区的降水和气温有一定影响，活动频数多(少)年，我国华北大部、新疆北部降水偏少(多)；北疆地区气温回升(下降)，甘、宁、陕、内部分地区偏冷(暖)。80-90年代春季北方气旋活动频数的偏少，强度的减弱，导致我国北方地区沙尘暴次数比70年代减少.     

The Impact Cooling of the Storm-Induced SST on Hurricane Intensity

The effects of storm-induced sea surface temperature （SST） cooling on hurricane intensity are investigated using a 5-day cloud-resolving simulation of Hurricane Bonnie （1998）. Two sensitivity simulations are performed in which the storm-induced cooling is either ignored or shifted close to the modeled storm track. Results show marked sensitivity of the model-simulated storm intensity to the magnitude and relative position with respect to the hurricane track. It is shown that incorporation of the storm-induced cooling, with an average value of 1.3℃, causes a 25-hPa weakening of the hurricane, which is about 20 hPa per 1℃ change in SST. Shifting the SST cooling close to the storm track generates the weakest storm, accounting for about 47% reduction in the storm intensity. It is found that the storm intensity changes are well correlated with the air-sea temperature difference. The results have important implications for the use of coupled hurricane-ocean models for numerical prediction of tropical cyclones.     

Trends in graded precipitation in China from 1961 to 2000

Daily precipitation rates observed at 576 stations in China from 1961 to 2000 were classified into six grades of intensity, including trace （no amount）, slight （≤ 1 mm d^-1）, small, large, heavy, and very heavy. The last four grades together constitute the so called effective precipitation （〉 1 mm d^-1）. The spatial distribution and temporal trend of the graded precipitation days are examined. A decreasing trend in trace precipitation days is observed for the whole of China, except at several sites in the south of the middle section of the Yangtze River, while a decreasing trend in slight precipitation days only appears in eastern China. The decreasing trend and interannual variability of trace precipitation days is consistent with the warming trend and corresponding temperature variability in China for the same period, indicating a possible role played by increased surface air temperature in cloud formation processes. For the effective precipitation days, a decreasing trend is observed along the Yellow River valley and for the middle reaches of the Yangtze River and Southwest China, while an increasing trend is found for Xinjiang, the eastern Tibetan Plateau, Northeast China and Southeast China. The decreasing trend of effective precipitation days for the middle- lower Yellow River valley and the increasing trend for the lower Yangtze River valley are most likely linked to anomalous monsoon circulation in East China. The most important contributor to the trend in effective precipitation depends upon the region concerned.     

Influence of Sea Surface Temperature on the Predictability of Idealized Tropical Cyclone Intensity

The role of sea surface temperature (SST) forcing in the development and predictability of tropical cyclone (TC) intensity is examined using a large set of idealized numerical experiments in the Weather Research and Forecasting (WRF) model. The results indicate that the onset time of rapid intensification of TC gradually decreases, and the peak intensity of TC gradually increases, with the increased magnitude of SST. The predictability limits of the maximum 10 m wind speed (MWS) and minimum sea level pressure (MSLP) are ~72 and ~84 hours, respectively. Comparisons of the analyses of variance for different simulation time confirm that the MWS and MSLP have strong signal-to-noise ratios (SNR) from 0-72 hours and a marked decrease beyond 72 hours. For the horizontal and vertical structures of wind speed, noticeable decreases in the magnitude of SNR can be seen as the simulation time increases, similar to that of the SLP or perturbation pressure. These results indicate that the SST as an external forcing signal plays an important role in TC intensity for up to 72 hours, and it is significantly weakened if the simulation time exceeds the predictability limits of TC intensity.     

2013年南疆2场罕见暴雨落区和强度的对比分析

2013年5月26～28日和6月15～18日南疆连续出现了2场罕见的暴雨过程,利用常规地面和高空探测资料、NCEP/NCAR每日4时次 1°×1°再分析资料和欧洲ECWMF 0.25°×0.25°细网格数值预报产品,对比分析了这2场暴雨的落区和强度差异的成因。2场暴雨均在有利的环流背景下产生,较强暴雨的高空环流经向度更大、中亚低槽与北支槽打通并南伸更南,低层700hPa以下水汽输送较中高层更为重要,日常预报更应注重低层的水汽输入。对比暴雨强度,低层水汽输送越强(更多水汽路径、更多边界的水汽输入、更强水汽通量和水汽输入量)、低层水汽输送时间越长、低层切变线持续时间长且伸展至中高层,暴雨强度均可能更强。中尺度切变线和涌线在暴雨落区预报中具有一定的指示意义。     

天津地区一次对流性降水过程雨滴谱特征分析

激光雨滴谱仪是天津人影部门近年新引入的探测设备,它对降水过程的即时监测具有重要意义。本文基于LPM-THIES激光雨滴谱仪探测资料,对天津地区2015年7月19日的对流性降水过程进行了分析。研究显示:雨滴谱仪和翻斗雨量计所获取的逐时降水其变化趋势存在一致性,但雨滴谱仪获得的累积雨量要偏大;降水过程的时空差异性大,不同测站雨强差异明显,4站降水粒子平均直径介于0.40~0.64mm,且2.0mm以下的降水粒子占到了粒子总数的95%以上;降水时段的雨强与雷达反射率的起伏变化十分明显,雨滴数浓度基本上处于103量级;蓟县站3个时次的瞬时谱均呈现单峰型分布,且峰值位于0.5mm附近。     

NUMERICAL SIMULATION STUDY ON THE RAPID INTENSIFICATION OF TYPHOON HAIKUI (1211) OFF THE SHORE OF CHINA

Forecasting the rapid intensification of tropical cyclones over offshore areas remains difficult. In this article, the Weather Research and Forecast (WRF) model was used to study the rapid intensification of Typhoon Haikui (1211) off the shore of China. After successful simulation of the intensity change and track of the typhoon, the model output was further analyzed to determine the mechanism of the rapid change in intensity. The results indicated that a remarkable increase in low-level moisture transportation toward the inner core, favorable large-scale background field with low-level convergence, and high-level divergence played key roles in the rapid intensification of Typhoon Haikui in which high-level divergence could be used as an indicator for the rapid intensity change of Typhoon Haikui approximately 6 h in advance. An analysis of the typhoon structure revealed that Typhoon Haikui was structurally symmetric during the rapid intensification and the range of the eyewall was small in the low level but extended outward in the high level. In addition, the vertically ascending motion, the radial and tangential along wind speeds increased with increasing typhoon intensity, especially during the process of rapid intensification. Furthermore, the intensity of the warm core of the typhoon increased during the intensification process with the warm core extending outward and toward the lower layer. All of the above structural changes contributed to the maintenance and development of typhoon intensity.