Recent changes in Phoenix,Arizona summertime diurnal precipitation patterns

Summary Summertime diurnal precipitation patterns for Phoenix, Arizona are analyzed for the period 1954 through 1985. Although the mean precipitation amounts and frequencies for the entire summer monsoon season have not shown any significant effects from the rapidly developing urban heat island, diurnal patterns have displayed substantial changes in the recent period of explosive population growth. During the most recent 16 years, late afternoon and evening storms have become more frequent and produce greater rainfall totals. Sharp declines are noted in the frequency of rain events between midnight and noon; especially large drops occur in the rainfall amounts between 9.00 and 12.00 MST. These findings appear to be consistent with several mechanisms proposed to explain the unusual diurnal character of the summertime rainfall in the Phoenix, Arizona area.

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Zusammenfassung In der vorliegenden Arbeit wird der sommerliche Tagesgang des Niederschlags für Phönix, Arizona, analysiert.Obwohl keine signifikante Beeinflussung der durchschnittlichen Niederschlagsmengen und -häufigkeiten über die gesamte Sommermonsunzeit durch die rasch anwachsende städtische Wärmeinsel zu verzeichnen ist, weisen die Tagesgänge in der jüngsten Zeit explosiven Bevölkerungswachstums substantielle Veränderungen auf. In den vergangenen 16 Jahren sind Unwetter spätnachmittags und abends häufiger geworden und führten zu einer größeren Niederschlagssumme. Eine starke Abnahme der Regenfälle zwischen Mitternacht und Mittag ist zu verzeichnen; bei Regenfällen zwischen 9.00 und 12.00 MST ist der Rückgang besonders deutlich.Wie sich zeigt, stehen diese Beobachtungen im Einklang mit einigen Mechanismen, die zur Erklärung der ungewöhnlichen Tagesverteilung der sommerlichen Regenfälle über Phönix, Arizona, angeführt werden.

     

An anthropogenic signal in Phoenix, Arizona winter precipitation

Many other investigators have shown pronounced weekly cycles in atmospheric composition, particularly in large urban settings. A substantial body of literature shows that the varying concentrations of fine atmospheric aerosols (particulate matter (PM)_2.5) impact precipitation processes; generally, higher concentrations of these aerosols tend to depress winter precipitation especially in short-lived, shallow, and orographic clouds. Phoenix, Arizona has a large population relying heavily on motor vehicles as the primary means of transportation. This results in a strong weekly cycle of PM_2.5 concentrations with a maximum on Wednesday and Thursday and a distinctive minimum on the weekend. To determine any influence on rainfall, we analyze daily precipitation records from 291 stations in the Phoenix area and find a strong weekly cycle in winter precipitation frequencies with maximum values on Sunday and minimum values on Thursday. The weekly cycle in precipitation frequency strengthens slightly moving eastward (downwind) across the metropolitan area as well as with increasing proximity to the metropolitan area. These results strongly suggest that human activity is influencing winter precipitation primarily by the suppressing effect of PM_2.5.     

南京地区2013年12月重霾污染事件成因分析

利用2013年12月在南京地区针对气溶胶化学成分及其前体物进行的一个月的强化观测资料,结果发现,期间观测到了两次严重的灰霾污染事件（事件1和事件2）,其PM_2.5的平均浓度分别达到267和150μg/m³。事件1过程中,气团主要起源于长三角及南京地区,天气系统稳定,混合层低矮,空气相对湿热,气溶胶多来自于前体物集聚后的二次转化;事件2过程中,来自华北地区的污染物长距离传输则有显著贡献。事件1中的化学转化机制较为复杂,白天的气相均相氧化以及夜间的非均相或液相转化均对硫酸盐和硝酸盐的二次形成有所贡献;而事件2中则主要为白天均相氧化机制,夜间的化学转化过程不明显。     

Recent changes in dry spell and extreme rainfall events in Ethiopia

Summary This paper assesses recent changes in extremes of seasonal rainfall in Ethiopia based on daily rainfall data for 11 key stations over the period 1965–2002. The seasons considered are Kiremt (‘main rains’, June–September) and Belg (‘small rains’, February/March–May). The Mann-Kendall and linear regression trend tests show decreasing trends in the Kiremt and the Belg extreme intensity and maximum consecutive 5-day rains over eastern, southwestern and southern parts of Ethiopia whereas no trends are found in the remaining part of Ethiopia. In general, no trends are found in the yearly maximum length of Kiremt and Belg dry spells (days with rainfall below 1 mm) over Ethiopia.     

The recent characteristics of Asian dust and haze events in Seoul, Korea

Summary The study on the characteristics of aerosol in Seoul during springtime from 1998 to 2003 is performed by the size-resolved number concentrations of aerosol. Asian dust events occur in spring most frequently, but it has been often observed in wintertime since 1999. Since 2000, the number of Asian dust days has been increasing, and the intensity has been more severe until 2002. However, there were only 3 dust days in Seoul during the spring of 2003, since the synoptic cyclone was relatively not intense enough to rise and transport dust to Korean peninsula, and the air stream was usually tiled to north of Korean peninsula. In addition, the precipitation was relatively plentiful and the air temperature was cold enough not to keep dry soil condition.Haze is the suspended particles in the air, reducing visibility by scattering light, and it is often a mixture of aerosols and photochemical smog. Dry particles with diameters of the order of 0.1µm, are small enough to scatter short wavelengths of light. Haze occurs well in winter and spring, and severe haze is observed in the afternoon. The occurrence frequency of haze has been decreasing since 2000 except in May of 2003.During Asian dust events from 1998 to 2003, the number concentration of aerosol with diameters from 0.3µm to 0.5µm decreases notably, but that larger than 1µm increases rapidly. On the other hand, for the haze events the number concentration from 0.3µm to 0.5µm increases notably, but that larger than 1µm decreases.     

Recent changes in the precipitation-driving processes over the southern tropical Andes/western Amazon

Climate Dynamics - Analyzing December–February (DJF) precipitation in the southern tropical Andes—STA ($$12^{\circ }\,\hbox {S}$$–$$20^{\circ }\,\hbox {S}$$; > 3000...     

Recent changes in precipitation extremes in the Heihe River basin,Northwest China

Changes in rainfall extremes pose a serious and additional threat to water resources planning and management, natural and artificial oasis stability, and sustainable development in the fragile ecosystems of arid inland river basins. In this study, the trend and temporal variation of extreme precipitation are analyzed using daily precipitation datasets at 11 stations over the arid inland Heihe River basin in Northwest China from 1960 to 2011. Eight indices of extreme precipitation are studied. The results show statistically significant and large-magnitude increasing and decreasing trends for most indices, primarily in the Qilian Mountains and eastern Hexi Corridor. More frequent and intense rainfall extremes have occurred in the southern part of the desert area than in the northern portion. In general, the temporal variation in precipitation extremes has changed throughout the basin. Wet day precipitation and heavy precipitation days show statistically significant linear increasing trends and step changes in the Qilian Mountains and Hexi Corridor. Consecutive dry days have decreased obviously in the region in most years after approximately the late 1980s, but meanwhile very long dry spells have increased, especially in the Hexi Corridor. The probability density function indicates that very long wet spells have increased in the Qilian Mountains. The East Asian summer monsoon index and western Pacific subtropical high intensity index possess strong and significant negative and positive correlations with rainfall extremes, respectively. Changes in land surface characteristics and the increase in water vapor in the wet season have also contributed to the changes in precipitation extremes over the river basin.     

Recent changes of precipitation in Gansu,Northwest China: An index-based analysis

Theoretical and Applied Climatology - Monitoring variations in precipitation is important in detecting regional climate change and studying the hydrological cycle. An understanding of its dynamic...     

喀拉海和巴伦支海海冰对中高纬异常纬向环流暨中国东部重霾天气形成的作用

采用1981年1月—2017年2月国家气象信息中心雾、霾数据集资料、同期NCEP/NCAR再分析资料以及哈德来中心的海冰资料,分析了秋冬季喀拉海和巴伦支海海冰变化与东亚冬季风暨中国东部冬季雾和霾日数变化特征之间的关系。研究结果表明,喀拉海和巴伦支海海冰对亚洲区中高纬纬向环流有重要影响,秋季海冰异常偏少是冬季亚洲区中高纬异常纬向环流形成的诱因之一。该地区秋季海冰偏少年,冬季亚洲中高纬地区纬向环流异常偏强,东亚大槽偏弱,影响我国东部地区的东亚冬季风减弱,这为大气污染物在水平方向上的聚集提供了有利条件,同时在海冰偏少年,对流层从中层向下均为正温度距平,与地表温差减小,不利于对流发展,使得大气的状况变得更加稳定,不利于大气污染物在垂直方向上的扩散,水平和垂直方向上的共同作用导致中国东部地区易发生霾天气过程。虽然喀拉海和巴伦支海海冰是影响中国东部地区冬季霾过程发生的重要因子之一,但其对冬季中国东部雾天气发生日数多寡的影响并不显著。亚洲区纬向环流指数相比经向环流指数更能反映中国东部地区冬季雾-霾日数的变化,冬季亚洲中高纬纬向环流越强,中国东部地区雾-霾日数越多。     

Global changes in extreme events: regional and seasonal dimension

This study systematically analyzes the complete IPCC AR4 (CMIP3) ensemble of GCM simulations with respect to changes in extreme event characteristics at the end of the 21st century compared to present-day conditions. It complements previous studies by investigating a more comprehensive database and considering seasonal changes beside the annual time scale. Confirming previous studies, the agreement between the GCMs is generally high for temperature-related extremes, indicating increases of warm day occurrences and heatwave lengths, and decreases of cold extremes. However, we identify issues with the choice of indices used to quantify heatwave lengths, which do overall not affect the sign of the changes, but strongly impact the magnitude and patterns of projected changes in heatwave characteristics. Projected changes in precipitation and dryness extremes are more ambiguous than those in temperature extremes, despite some robust features, such as increasing dryness over the Mediterranean and increasing heavy precipitation over the Northern high latitudes. We also find that the assessment of projected changes in dryness depends on the index choice, and that models show less agreement regarding changes in soil moisture than in the commonly used ‘consecutive dry days’ index, which is based on precipitation data only. Finally an analysis of the scaling of changes of extreme temperature quantiles with global, regional and seasonal warming shows that much of the extreme quantile changes are due to a seasonal scaling of the regional annual-mean warming. This emphasizes the importance of the seasonal time scale also for extremes. Changes in extreme quantiles of temperature on land scale with changes in global annual mean temperature by a factor of more than 2 in some regions and seasons, implying large changes in extremes in several countries, even for the commonly discussed global 2°C-warming target.     

Recent changes in sea level and their possible causes

A new analysis of ‘global’ sea level has been made that largely avoids space/time bias of previous works. A coherent pattern of increasing relative sea level (RSL) was found to exist on average at all stations analyzed between 1903–1969. Subject to considerable assumption, the rate of RSL increase associated with this pattern was 15 cm/century. A similar analysis of the period 1930–1975 again showed RSL increasing on average everywhere but in the western half of the North Pacific Ocean. Decrease of RSL in this area was substantiated by hydrographic data. Thus in recent years the concept of a ‘global’ sea level rise is not supported. The temporal behavior of thenear global signals from both time periods was well approximated by a simple linear trend. There was no evidence of a more rapid rise in RSL in recent years. Potential causes of the above RSL change were investigated. Changes in the position of the earth's axis of rotation support the idea that the RSL change was due to approximately equal melting of Greenland/Antarctica. Changes in the length of day only marginally support this idea. However, other attractive geophysical explanations for variations in both these astronomical parameters exist. Observed change in sea surface temperature (SST), if representative of reasonable changes in vertical thermal structure, could give the observed RSL change. However, the SST data are likely biased instrumentally toward increasing trend. Also, thermal expansion of the oceans would not significantly affect the rotational parameters although changes in these parameters could be due to non-RSL related processes. Changes in ocean circulation and/or subsidence along all the coastal margins simultaneously seem unlikely causes of the observed change in RSL. In summary, it is not possible at this time to explain reliably the apparent increase in RSL.     

安徽省不同等级雾和重度霾时空分布特征及地面气象条件比较

雾和霾都是低能见度天气,生成条件相似。利用安徽78个地面站逐时观测资料,基于雾、霾发生物理条件,建立了不同等级雾日和重度霾日的观测诊断方法,重建了不同等级雾和重度霾的时序资料。根据各站强浓雾发生的同步性,将安徽分为5个雾、霾分布特征不同的区域,探讨了各区域不同等级雾及重度霾出现时地面气象条件的异同。结果表明:（1）安徽省强浓雾主要是辐射雾。强浓雾、浓雾和大雾空间分布形势大体一致,淮河以北东、西部和江南都属于强浓雾高发区,但各地强浓雾的时、空分布特征和影响系统不同;重度霾有明显的北多、南少、山区最少的分布特征。（2）强浓雾年变化呈双峰型分布,峰值在1月和4月,日变化为单峰型,峰值在06时;而重度霾年变化为单峰型,峰值在1月,日变化为双峰型。（3）在强浓雾的高发时段（02—08时）,强浓雾时降温幅度最大,比重度霾平均高1℃,风速显著偏低,超过75%的样本风速低于1.5 m/s,且无明显主导风向;而重度霾时,风速比雾时明显要大,个别区域有超过75%的样本风速大于1.5 m/s,且以西北风到东北风为主。说明重度霾能否演变为强浓雾的关键地面气象因子是风速、风向和降温幅度。      

Recent changes in the spatio-temporal characteristics of monsoon intraseasonal oscillations

Theoretical and Applied Climatology - Monsoon intraseasonal oscillations (MISOs) define a significant proportion of intraseasonal variability of the Indian summer monsoon. In the backdrop of...     

我国西北降水变化趋势和预估

利用观测资料、GPCC再分析资料和第六次耦合模式比较计划（CMIP6）模拟结果,研究了我国西北地区近几十年及未来降水变化趋势。结果表明,1979—2019年我国西北干旱半干旱区降水在全年各季节均有显著增加,其中秋季增加最多。CMIP6模拟结果显示,随着全球变暖,我国西北地区降水在2015—2100年将继续增加。至21世纪末,在SSP2-4.5和SSP5-8.5情景下,我国西北地区年平均降水量将分别增加约13.7%（37 mm）和25.8%（78 mm),其中降水量增加最多的季节分别为夏季和春季。考虑到西北地区蒸发量也将随全球变暖而增加,模式平均的结果显示西北地区年平均净降水量在两种情景下的增幅分别约1.4%和4.9%,表明我国西北地区未来气候呈现显著的变湿趋势。进一步分析表明,西北地区未来降水增加可能与局地大气低层位势高度降低和上升运动加强有关。