Enhanced Cooling Efficiency of Urban Trees on Hotter Summer Days in 70 Cities of China

Increasing the urban tree cover percentage(TCP) is widely recognized as an efficient way to mitigate the urban heat island effect. The cooling efficiency of urban trees can be either enhanced or attenuated on hotter days, depending on the physiological response of urban trees to rising ambient temperature. However, the response of urban trees' cooling efficiency to rising urban temperature remains poorly quantified for China's cities. In this study, we quantify the response of urban trees' cooling efficiency to rising urban temperature at noontime [~1330 LT(local time), LT=UTC+8] in 17summers(June, July, and August) from 2003–19 in 70 economically developed cities of China based on satellite observations. The results show that urban trees have stronger cooling efficiency with increasing temperature, suggesting additional cooling benefits provided by urban trees on hotter days. The enhanced cooling efficiency values of urban trees range from 0.002 to 0.055℃ %-1 per 1℃ increase in temperature across the selected cities, with larger values for the lowTCP-level cities. The response is also regulated by background temperature and precipitation, as the additional cooling benefit tends to be larger in warmer and wetter cities at the same TCP level. The positive response of urban trees' cooling efficiency to rising urban temperature is explained mainly by the stronger evapotranspiration of urban trees on hotter days.These results have important implications for alleviating urban heat risk by utilizing urban trees, particularly considering that extreme hot days are becoming more frequent in cities under global warming.

Seasonal Prediction of Extreme High-Temperature Days in Southwestern China Based on the Physical Precursors

Extreme high temperatures frequently occur in southwestern China,significantly impacting the local ecological system and economic development.However,accurate prediction of extreme high-temperature days(EHDs)in this region is still an unresolved challenge.Based on the spatiotemporal characteristics of EHDs over China,a domain-averaged EHD index over southwestern China(SWC-EHDs)during April-May is defined.The simultaneous dynamic and thermodynamic fields associated with the increased SWC-EHDs are a local upper-level anticyclonic(high-pressure)anomaly and wavy geopotential height anomaly patterns over Eurasia.In tracing the origins of the lower boundary anomalies,two physically meaningful precursors are detected for SWC-EHDs.They are the tripolar SST change tendency from December-January to February-March in the northern Atlantic and the February-March mean snow depth in central Asia.Using these two selected predictors,a physics-based empirical model prediction was applied to the training period of 1961–2005 to obtain a skillful prediction of the EHDs index,attaining a correlation coefficient of 0.76 in the independent prediction period(2006–19),suggesting that 58%of the total SWC-EHDs variability is predictable.This study provides an estimate for the lower bound of the seasonal predictability of EHDs as well as for the hydrological drought over southwestern China.

Impacts of Sea Surface Temperature on the Interannual Variability of Winter Haze Days in Guangdong Province

The impact of sea surface temperature(SST)on winter haze in Guangdong province(WHDGD)was analyzed on the interannual scale.It was pointed out that the northern Indian Ocean and the northwest Pacific SST play a leading role in the variation of WHDGD.Cold(warm)SST anomalies over the northern Indian Ocean and the Northwest Pacific stimulate the eastward propagation of cold(warm)Kelvin waves through the Gill forced response,causing Ekman convergence(divergence)in the western Pacific,inducing abnormal cyclonic(anticyclonic)circulation.It excites the positive(negative)Western Pacific teleconnection pattern(WP),which results in the temperature and the precipitation decrease(increase)in Guangdong and forms the meteorological variables conditions that are conducive(not conducive)to the formation of haze.ENSO has an asymmetric influence on WHDGD.In El Niño(La Niña)winters,there are strong(weak)coordinated variations between the northern Indian Ocean,the northwest Pacific,and the eastern Pacific,which stimulate the negative(positive)phase of WP teleconnection.In El Niño winters,the enhanced moisture is attributed to the joint effects of the horizontal advection from the surrounding ocean,vertical advection from the moisture convergence,and the increased atmospheric apparent moisture sink(Q2)from soil evaporation.The weakening of the atmospheric apparent heat source(Q1)in the upper layer is not conducive to the formation of inversion stratification.In contrast,in La Niña winters,the reduced moisture is attributed to the reduced upward water vapor transport and Q2 loss.Due to the Q1 increase in the upper layer,the temperature inversion forms and suppresses the diffusion of haze.

Load-forecasting method for IES based on LSTM and dynamic similar days with multi-features

To fully exploit the rich characteristic variation laws of an integrated energy system(IES)and further improve the short-term load-forecasting accuracy,a load-forecasting method is proposed for an IES based on LSTM and dynamic similar days with multi-features.Feature expansion was performed to construct a comprehensive load day covering the load and meteorological information with coarse and fine time granularity,far and near time periods.The Gaussian mixture model(GMM)was used to divide the scene of the comprehensive load day,and gray correlation analysis was used to match the scene with the coarse time granularity characteristics of the day to be forecasted.Five typical days with the highest correlation with the day to be predicted in the scene were selected to construct a“dynamic similar day”by weighting.The key features of adjacent days and dynamic similar days were used to forecast multi-loads with fine time granularity using LSTM.Comparing the static features as input and the selection method of similar days based on non-extended single features,the effectiveness of the proposed prediction method was verified.

Effect of Temperature on Frost-Free Days and Length of Crop Growing Season across Southern Ontario

Climate change has an impact on various climatic variables. In this study our focus is mainly on temperature characteristics of climate parameter. In temperate and humid regions like southern Ontario, the effect of climate change on Frost-free days in winter is distinctive. The average annual temperature is going upward but the extreme increase is in the winter temperature. Winter average temperature is going up by about 2˚C. However, extreme daily minimum temperature is going up by more than 3˚C. This climate effect has a great impact on the nature of precipitation and length of frost-free days. The snowfall over winter months is decreasing and the rainfall is increasing. However, the number of frost-free days during late fall months, early winter months, late winter months and early spring months are increasing. This result reveals an increase in length of the growing season. This research focuses on the effect of change in climatic variables on Frost-free days in Southern Ontario. Therefore, special attention should be given to the effect of change in climate Frost-free conditions on length of crop growing in winter season for potential investigation.

Interannual Variation and Statistical Prediction of Summer Dry and Hot Days in South China from 1970 to 2018

The frequent occurrence of dry and hot(DH)days in South China in summer has a negative impact on social development and human health.This study explored the variation characteristics of DH days and the possible reasons for this knotty problem.The findings revealed a notable increase in the number of DH days across most stations,indicating a significant upward trend.Additionally,DH events were observed to occur frequently.The number of DH days increased during 1970-1990,decreased from 1991 to 1997,and stayed stable after 1997.The key climate factors affecting the interannual variability of the number of DH days were the Indian Ocean Basin warming(IOBW)in spring and the East Asian Summer Monsoon(EASM).Compared with the negative phase of IOBW,in the positive phase of IOBW,500 hPa and 850 hPa geopotential height enhanced,the West Pacific subtropical high strengthened and extended abnormally to the west,more solar radiation reached the surface,surface outgoing longwave radiation increased,and there was an anomalous anticyclone in eastern South China.The atmospheric circulation characteristics of the positive and negative phases of ESAM were opposite to those of IOBW,and the abnormal circulation of the positive(negative)phases of ESAM was unfavorable(favorable)for the increase in the number of DH days.A long-term prediction model for the number of summer DH days was established using multiple linear regression,incorporating the key climate factors.The correlation coefficient between the observed and predicted number of DH days was 0.65,and the root-mean-square error was 2.8.In addition,independent forecasts for 2019 showed a deviation of just 1 day.The results of the independent recovery test confirmed the stability of the model,providing evidence that climatic factors did have an impact on DH days in South China.

Causes and Effects of Stillbirths on Days Open and Cow Herd Survival in Holstein Friesian Cows

The aim of this retrospective study was to investigate the causes and the effects of stillbirth on the number of days open and cow herd survival in subsequent lactation of Holstein Friesian cows. A total of 1371 calvings from research dairy farm were used. Stillbirth in calves was defined as the death of a fetus before or during calving at full term (≥270 days of gestation) or within 24 hours after calving. During the period from January 2006 to December 2017 a percent of 95.04% of the calvings were with live calves, and 4.96% of the calvings were stillbirths. The major causes of stillbirth identified were: calving difficulty, parity of the cows, and sex of the calves at calving. A five point scale was used to assess calving difficulties, and numbers 1, 2 and 3 were considered unassisted calvings and number 4 and 5 as assisted. The twin calvings were not taken into account. Days open were measured as days from first calving to conception, and cow herd survival from first calving to culling or death. Trend test and multivariate data analysis were used. The findings revealed that primiparous cows were at higher risk of having stillbirths compared with multiparous cows. Cows that were at calving male calves were at higher risk of having stillbirths compared with cows that had female calves at calving. Also, cows with assisted calving were at higher risk of having stillbirths compared with cows with unassisted calvings. Cows with stillbirths had a increase mean of days open with 32 days. Cow herd survival was better in the cows with live calves at calving compared with the cows that had stillbirth at calvings.

Causes of a Heavy Snowfall Process in Eastern Yunnan in 2022

Based on NCEP/NCAR reanalysis data, Micaps data and ground observation data, the physical characteristics of a heavy snowfall process in eastern Yunnan from January 31 to February 3, 2022 were analyzed. The results show that the circulation background of the heavy snowfall process was "north-ridge and south-trough" type, and the cold air accumulated in the deep East Asian transverse trough. The cold advection behind the trough moved southwards into eastern Yunnan under the movement of the transverse trough. The establishment of upper and lower air jet provided abundant water vapor, and the snowfall area coincided with the strong water vapor convergence area. The strong cold center near the ground was maintained, and the cold air moved southwards. As a result, the cold pad was lasting and deep, and the ground temperature was 0 ℃ or below, which was conducive to snow accumulation on the ground. Seen from the spatial distribution of pseudo-equivalent potential temperature, the low layer always had certain warm and wet conditions during the heavy snowfall, which was conducive to the establishment of unstable energy. The snowfall occurred near the θ se steep area and the warm and wet unstable area. The vertical distribution of temperature had a good indication of precipitation form. The upper layer was controlled by strong cold advection, while the middle and lower troposphere was controlled by warm advection, and there was a warm inversion layer, which was conducive to the transformation of ice crystals into snowflakes, so that ice crystals fell to the ground in the form of snowflakes.

Snowfall Shift and Precipitation Variability over Sikkim Himalaya Attributed to Elevation-Dependent Warming

Sikkim Himalaya hosts critical water resources such as glacial,rain,and snow-fed springs and lakes.Climate change is adversely affecting these resources in various ways,and elevation-dependent warming is prominent among them.This study is a discussion of the elevation-dependent warming(EDW),snowfall shift,and precipitation variability over Sikkim Himalaya using a high-resolution ERA5-land dataset.Furthermore,the findings show that the Sikkim Himalaya region is experiencing a warming trend from south to north.The majority of the Sikkim Himalayan region shows a declining trend in snowfall.A positive advancement in snowfall trend(at a rate of 1 mm per decade)has been noticed above 4500 meters.The S/P ratio indicates a shift in snowfall patterns,moving from lower elevations to much higher regions.This suggests that snowfall has also transitioned from Lachung and Lachen(3600 m)to higher elevated areas.Moreover,the seasonal shifting of snowfall in the recent decade is seen from January-March(JFM)to February-April(FMA).Subsequently,the preceding 21 years are being marked by a significant spatiotemporal change in temperature,precipitation,and snowfall.The potent negative correlation coefficient between temperature and snowfall(–0.9),temperature and S/P ratio(–0.5)suggested the changing nature of snowfall from solid to liquid,which further resulted in increased lower elevation precipitation.The entire Sikkim region is transitioning from a cold-dry to a warm-wet weather pattern.In the climate change scenario,a drop in the S/P ratio with altitude will continue to explain the rise in temperature over mountainous regions.

2022年初5次降雪过程分析和预报着眼点

本文采用ECMWF(European Centre for Medium-Range Weather Forecasts)细网格和NCEP(National Centers for Environmental Prediction)模式数据、NCEP 1°×1°再分析资料、降雪加密观测和常规资料,对2022年初的5次降雪过程进行对比分析,发现5次降雪过程均为雨转雪过程,且持续时间相对较短,平原为雨夹雪或小雪到中雪,山区中到大雪,局部暴雪,数值模式预报的积雪深度与实况相差甚远;大尺度环流形势为500 hPa中低纬南支槽或弱波动配合700 hPa上的暖湿气流和中低层冷空气,造成边界层浅薄的冷垫上温度骤降而在短时间内形成降雪;相较于平原地区,高山区上空温度层结与最大上升运动中心的配置,有利于降雪粒子较长时间维持在有利于枝状雪花的形成区域,且高山区云底云水含量显著偏低、整层温度足够低,故高山区更利于暴雪的形成。

气候变暖对吉林省降雪量与新增雪深关系的影响

降雪量和积雪深度的关系是降雪预报及水文气候模拟中的重要参数。本文利用吉林省50个站点1961—2021年的降水量、积雪深度、气温、风速和天气现象等气象观测资料,分析了降雪量和新增积雪深度的关系及主要气候影响因子。结果表明,在中等及以上强度的降雪过程中,吉林省新增积雪深度(D)与降雪量(S)的比值(深量比,Rds)平均为0.96 cm·mm^(-1);该比值存在空间差异,呈西部小东部大的分布特征,且存在明显的月际、年际和年代际变化特征,其中月际变化呈现不对称的抛物线型,12月和1月为大值时段;近60年来Rds呈减小趋势,变化速率为-0.01 cm·mm^(-1)·(10a)^(-1);降雪日Rds与气温呈明显反相关关系,其中在-12~0℃的温度区间,Rds随气温上升呈明显减小趋势。气候变暖、降水量增加和风速的减小是降雪过程中降雪量与新增雪深关系年代际变化的直接原因。揭示降雪量和新增雪深的关系对于认识东北亚中高纬度降雪积雪特征及其成因具有重要意义。

青年职场“Gap day”现象探究

青年职场“Gap day”现象引起了社会的广泛关注和热烈讨论。青年职场“Gap day”现象的典型特征是:通过语言上的拼贴与再造,表达部分职业青年的困顿疲倦情绪;通过行为上的放空与逃离,排解青年在工作中积攒的情绪和压力;通过价值上的戏谑与自嘲,赋予青年的短暂休息以正向意义。青年职场“Gap day”现象的深层原因是:青年在高压生存环境中的“弹性姿态”、在加速社会运行中的“精神逃离”和在社会时钟齿轮下的“自我审视”。对青年职场“Gap day”现象的有效治理,既要着眼于青年发展,运用公共政策实现青年发展的普遍性诉求,又要立足于青年就业,采取切实措施促进青年实现高质量充分就业。

2012—2019年昌吉冬季降雪日变化特征分析

利用2012-2019年冬季昌吉回族自治州(简称“昌吉州”)11个国家级台站逐时降水资料,运用常规统计方法,对昌吉州冬季降雪日变化特征进行分析。结果表明:昌吉州冬季降雪量空间分布与海拔高度呈正相关,与纬度呈显著的负相关,降雪强度与纬度关系密切。昌吉州逐时累积降雪量呈双峰型分布,主峰出现在17时,次峰出现在08时;西部呈三峰型特征,主次峰值分别出现在17、14、08时;东部呈准单峰单谷型,峰值发生在19时,谷值出现在13时。昌吉州冬季降水以短时降水事件为主,对冬季降水量贡献为64%,12 h以上长持续性降水事件发生概率很小,仅在部分台站偶有发生。西部和东部冬季降水日循环与降水持续性关系较密切,其中持续3~4 h降水事件对西部和东部冬季降水量贡献最大,随着持续时间的延长对降水量的贡献变小。

CMIP6耦合模式对青藏高原积雪的未来预估

基于第六次国际耦合模式比较计划(CMIP6)的历史模拟试验以及情景预估试验数据,分析了21世纪中(2035—2064年)、后期(2070—2099年)青藏高原积雪相对于参考期(1985—2014年)的变化。结果表明:相对于参考期,21世纪中、后期青藏高原平均年积雪日数、平均积雪期均表现为减少,减少幅度总体随着人为辐射强迫的增加而加大;除低强迫情景外,21世纪后期的减少幅度均大于21世纪中期;空间上总体表现为青藏高原东南部的减少幅度大于西北部。21世纪中、后期青藏高原积雪初日均表现为推迟、积雪终日均表现为提前,积雪初日推迟天数是积雪终日提前天数的1.5~2.0倍;人为辐射强迫越高,积雪初(终)日推迟(提前)天数越多;相同情景下21世纪后期积雪初(终)日推迟(提前)天数均多于21世纪中期。降雪(气温)与年积雪日数呈正(负)相关;随着人为辐射强迫的增加,降雪对年积雪日数的相对贡献率总体呈增加趋势;空间特征表现为降雪(气温)对青藏高原南部和北部(东部和西部)的年积雪日数的相对贡献更大。7—12月降雪的减少幅度大于1—6月,这可能是积雪初日推迟天数多于积雪终日提前天数的重要原因。不同情景下青藏高原未来积雪变化差异明显,由此可见,控制温室气体排放对减缓未来青藏高原积雪的减少速率至关重要。

2024年初两次雨雪冰冻天气过程对公路通行影响的对比分析

2024年1月31日-2月5日、2月18-25日我国先后出现两次大范围雨雪冰冻天气过程(分别简称0131"过程和"0218"过程),两次过程具有相态复杂、雨雪量大、影响范围广、持续时间长等特点。利用全国2430个国家气象站观测数据以及交通流量和公路阻断信息,对比分析了两次雨雪冰冻天气过程对公路通行的影响;同时,选取降雪量、冻雨、积雪深度、地面温度、地面结冰作为影响公路通行的气象指标,构建冰雪天气指数,探讨冰雪天气强度与公路通行影响的关系。结果表明:两次过程发生于春节前后人口流动高峰期,"0218"过程影响范围更广,造成交通流量的降低幅度总体高于"0131"过程;两次过程中陕西、山西、河南、湖北、湖南以及贵州6省公路通行受积雪或结冰影响严重,路段封闭段次多,但影响程度存在地区差异,其中山西、河南、湖北、湖南"0131"过程影响更重,陕西、贵州"0218"过程影响更重;两次过程中冰雪天气指数强度与公路阻断影响度的变化趋势一致,与交通流量变化率呈反比,反映出冰雪天气指数对于冰雪天气下的公路交通影响研判具有良好指示意义。

2023年3月河南省一次极端暴雪和雷电天气成因分析

选用自动气象站、双偏振雷达、风廓线雷达和ERA5再分析等资料,分析2023年3月16日河南省一次极端暴雪和雷电天气成因。结果表明:此次极端暴雪过程主要天气系统为低槽、切变线、急流以及东北冷涡。冷涡配合-39℃冷中心稳定维持,其后部冷空气持续南下,850 hPa以下形成深厚冷垫,中高层西南暖湿气流沿冷垫爬升,形成河南省典型的降雪天气类型“天南地北型”。此次强降雪区位于整层大气可降水量大于20 mm区域的北部与700 hPa强辐合中心重叠的区域,河南中西部地形的抬升作用利于此极端降雪天气发生。冷平流与其次级环流共同作用,使局地气温骤降,导致降水相态转换较预期提前,以致多站降雪量或积雪深度超历史极值。双偏振雷达零滞后相关系数产品(CC)为相态转换监测提供了重要参考。850 hPa以下大气温度均低于0℃,且2 m气温降至1℃左右,可作为降雪预报指标。辐合切变及锋面次级环流有利于高架雷暴天气出现,20 dBz回波高度超过-20℃层高度可作为产生雷暴的关键指标。

2024年2月初河南一次罕见雨雪冰冻过程诊断分析

2024年1月31日-2月5日河南出现了一次罕见的雨雪冰冻天气,表现为持续时间长、累积雨雪量大、积雪深、温度低、降水相态复杂等特点。利用国家气象站和双偏振雷达观测数据以及ERA5再分析资料,对本次过程的极端性及降水相态演变、雨雪冰冻成因进行了诊断分析,结果表明:(1)过程期间有5个国家气象站最大积雪深度达到或突破2月历史同期极值,多站最高气温达到或刷新2月上旬历史同期最小值;单日至少有68.3%的国家气象站出现降水,单站最长连续降水近29h。(2)大尺度环流系统稳定维持是本次过程发生发展的重要原因之一;对流层低层强冷空气持续入侵不仅起到动力抬升作用,也为雨雪冰冻天气提供了持续降温条件;异常强盛的偏南气流为本次过程提供了充足的水汽和动量,同时也增强了不稳定层结。(3)使用单一特性层温度来判识降水相态依据不足,应根据整层大气层结温度来预判可能出现的降水相态,当整层大气温度均低于0℃时降水相态为纯雪,若存在温度高于0℃的融化层或云体由过冷却水滴组成时,将出现混合型降水相态。(4)双偏振雷达的相关系数和差分反射率产品对区分雨夹雪和纯雪有较好的指示意义,当相关系数接近1、差分反射率为-1~0dB时,为纯雪;当相关系数小于1、差分反射率大于1dB时,为雨夹雪。

2024年春运期两次极端雨雪冰冻天气过程对比分析

2024年1月31日-2月6日和2月19-25日,我国先后出现两次大范围持续性低温雨雪冰冻天气过程(分别简称过程1和过程2),对春运造成严重影响。利用多源观测和ERA5再分析资料对两次过程进行对比,重点分析了南方地区雨雪天气强度及冻雨和降水相态差异的原因。结果表明:(1)两次过程的累计降水量均有一定极端性,并伴有复杂的降水相态变化,冻雨强度和范围为2009年以来最大;过程1冻雨强度和积雪深度大于过程2,过程2冻雨范围、降水和对流强度大于过程1。(2)两次过程均发生在高空槽与低层冷空气共同作用的环流背景下,南支槽前和西太平洋副热带高压外围的西南急流稳定维持且较常年显著偏强,为两次极端雨雪冰冻天气过程提供了持续而充沛的水汽条件;暖湿气流在冷垫上的爬升以及低层风场的水平辐合是产生雨雪天气的重要动力机制,逆温层和融化层的稳定维持是出现冻雨及降水相态反复变化的关键原因。(3)两次过程不同点主要在于,过程1冻结层内温度多在-4~0℃,高于过程2,相对而言更有利于形成冻雨;逆温区狭长且少动,冻雨影响范围集中,强度大;过程2副热带高压更偏西偏北,有利于西南暖湿急流加强和北推,同时强寒潮导致冷垫较强,冷暖交汇有利于上升运动发展和降水增强;过程2融化层维持时间更长,云水含量较高,但冻结层内温度低,更有利于出现冰粒或湿雪。

青藏高原雪水比例时空变化特征

为厘清青藏高原地区不同相态降水及其变化规律,本文基于第三极地区长时间序列(1979—2020年)高分辨率(1/30°,日)地面气象要素驱动数据集,采用基于表面高程和气象条件的雨雪识别方法,识别了青藏高原地区的降雨和降雪,分析了青藏高原雪水比例(SPR)的分布特征和时空演变规律。结果表明:①SPR空间分布差异显著,西高东低;②SPR整体呈下降趋势,平均以1.11%/(10 a)的速率显著降低;③冷、暖季均呈现降雨增加、降雪减少、SPR降低趋势,但暖季的变化速率和显著性高于冷季;④高原东西部降雪量在冷、暖季相当,高原中部以暖季降雪为主,高原暖季降雨量约占全年的90%,高原大部分地区暖季降雪占全年降雪的比例呈下降趋势(-0.29%/(10 a))。研究结果有望为区域气候变化和水科学研究提供科学依据。

青藏高原冬季降雪特征及相关环流分析

利用1961-2020年青藏高原降雪观测资料和大气再分析数据,分析了高原冬季降雪特征及其关键环流系统。结果表明:高原冬季降雪空间分布不均,表现为西北少、东南多,同时降雪年际振荡和年代际变化特征明显,1988年发生由偏少向偏多的转折。青藏高原冬季降雪一致偏多时,中高纬呈现类似欧亚南部型(Southern Eurasian,SEA)遥相关的正位相特征,即欧洲西南部、阿拉伯海、东北亚上空位势高度场为显著正异常,中东地区、青藏高原上空为显著负异常,经分析发现,SEA正位相时中东急流增强,高原南部上升运动明显,高原东北部和西南侧出现水汽显著辐合区,为青藏高原冬季降雪异常偏多提供有利条件。与此同时,北大西洋涛动(North Atlantic Oscillation,NAO)正(负)位相时有利于青藏高原降雪偏多(少),NAO主要通过SEA型遥相关和中东急流等环流系统来调控高原冬季降雪。