1951—2018年汕头汛期暴雨变化趋势及与ENSO的关系

根据汕头气象站1951—2018年汛期逐日雨量资料,采用滤波、线性倾向计算、趋势系数计算、相关分析等方法,分析该站汛期暴雨的变化趋势及与ENSO事件的关系。结果表明:汕头市近68年来的前汛期暴雨日数没有显著的上升或下降趋势,后汛期自20世纪90年代以后有轻微下降趋势;前汛期雨量有波动下降趋势;前、后汛期最大日雨量变化呈波动下降趋势;后汛期最大日雨量在La Nina时期呈减少趋势。     

Synoptic Typing and Its Application for Evaluating Climatic Impact on Air Quality in Urumqi

An automated procedure employing principal-component analysis and a two-stage cluster analysis was developed to classify the synoptic meteorological conditions prevailing over Urumqi, one of the most heavily polluted cities in the world. Six clusters representing different circulation patterns and air-mass characteristics were classified using surface- and upper-meteorological variables during the heating period from 2001 to 2008, and the relationships between synoptic clusters and air quality were evaluated. The heaviest air-pollution episodes occurred when Urumqi was in either an extremely cold, strong anticyclone or at the front of a migrating cyclone, both with light winds, wet surface air, and relatively dry upper air. Moderate pollution was seen when Urumqi was in the pre-cold/cold frontal passages with lower temperatures and light winds or moderate anticyclone with relatively warmer, drier air. When Urumqi was at the front of a migrating anticyclone or in a weak anticyclone with moderate winds and most warm, dry air, or in the cold/post-cold frontal passages with relatively strongly northerly airflows and precipitation, relatively good air quality could be seen. These results suggest that air pollution in Urumqi is very closely related to the synoptic meteorological conditions, which provides an important basis for not only the prediction and control of urban air-quality problems here but also for the analysis of the differential impacts of weather and pollution on human morbidity.     

Thunder Events in China: 1980-2008

Using data collected at 517 weather stations in contiguous China over the period 1980-2008,characteristics of thunder events have been investigated.These characteristics include geographical distribution,interdecadal variation,annual variation,and seasonal variation.The areas with the highest frequencies of thunder events are located in the central Tibetan Plateau,Yunnan,Guangxi,and Guangdong.The annual number of thunder days increases from northern to southern China.But the frequency of thunder events over mountains and plateaus is much higher than the frequency of events over plains in the same latitude.The interdecadal variation of events shows that the frequency of thunder occurrences was highest during the 1980s,decreased during the 1990s,and increased slightly afterwards.Thunder occurrences vary with the season,northward in May and retreating southward in September.     

IMPACTS OF CUMULUS PARAMETERIZATION AND RESOLUTION ON THE MJO SIMULATION

Madden-Julian Oscillations (MJO) in six integrations using an AGCM with different cumulus parameterization schemes and resolutions are examined to investigate their impacts on the MJO simulation. Results suggest that the MJO simulation can be affected by both resolution and cumulus parameterization, though the latter, which determines the fundamental ability of the AGCM in simulating the MJO and the characteristics of the simulated MJO, is more crucial than the former. Model resolution can substantially affect the simulated MJO in certain aspects. Increasing resolution cannot improve the simulated MJO substantially, but can significantly modulate the detailed character of the simulated MJO; meanwhile, the impacts of resolution are dependent on the cumulus parameterization, determining the basic features of the MJO. Changes in the resolution do not alter the nature of the simulated MJO but rather regulate the simulation itself, which is constrained by cumulus parameterization schemes. Therefore, the vertical resolution needs to be increased simultaneously. The vertical profile of diabatic heating may be a crucial factor that is responsible for these different modeling results. To a large extent, it is determined by the cumulus parameterization scheme used.     

The importance of moisture distribution for the growth and energetics of mid-latitude systems

A primitive equation model is used to study the sensitivity of baroclinic wave life cycles to the initial latitude-height distribution of humidity. Diabatic heating is parametrized only as a consequence of condensation in regions of large-scale ascent. Experiments are performed in which the initial relative humidity is a simple function of model level, and in some cases latitude bands are specified which are initially relatively dry. It is found that the presence of moisture can either increase or decrease the peak eddy kinetic energy of the developing wave, depending on the initial moisture distribution. A relative abundance of moisture at mid-latitudes tends to weaken the wave, while a relative abundance at low latitudes tends to strengthen it. This sensitivity exists because competing processes are at work. These processes are described in terms of energy box diagnostics. The most realistic case lies on the cusp of this sensitivity. Further physical parametrizations are then added, including surface fluxes and upright moist convection. These have the effect of increasing wave amplitude, but the sensitivity to initial conditions of relative humidity remains. Finally, control and doubled CO₂ life cycles are performed, with initial conditions taken from the time-mean zonal-mean output of equilibrium GCM experiments. The attenuation of the wave resulting from reduced baroclinicity is more pronounced than any effect due to changes in initial moisture.     

Update of a Footprint-Based Approach for the Characterisation of Complex Measurement Sites

Horizontal heterogeneity can significantly affect the flux data quality at monitoring sites in complex terrain. In heterogeneous conditions, the adoption of the eddy-covariance technique is contraindicated by the lack of horizontal homogeneity and presence of advective conditions. In addition, uncertainty concerning the sources or sinks influencing a measurement compromises the data interpretation. The consideration of the spatial context of a measurement, defined by a footprint analysis, can therefore provide an important tool for data quality assessment. This study presents an update of an existing footprint-based quality evaluation concept for flux measurement sites in complex terrain. The most significant modifications in the present version are the use of a forward Lagrangian stochastic trajectory model for the determination of the spatial context of the measurements, and the determination of effective roughness lengths with a flux aggregation model in a pre-processing step. Detailed terrain data gathered by remote sensing methods are included. This approach determines spatial structures in the quality of flux data for varying meteorological conditions. The results help to identify terrain influences affecting the quality of flux data, such as dominating obstacles upwind of the site, or slopes biasing the wind field, so that the most suitable footprint regions for the collection of high-quality datasets can be identified. Additionally, the approach can be used to evaluate the performance of a coordinate rotation procedure, and to check to what extent the measured fluxes are representative for a target land-use type.     

Exploring fog as a supplementary water source in Namibia

Namibia is an arid country where many rural and urban centres depend on ephemeral rivers for their water supply. These water sources are, however, limited and display seasonal salinisation. Fog occurs along the coast and extends for some distance inland, and it could be used as a source of drinking water. Data on groundwater salinisation and fog deposition were collected at villages of the indigenous communities and at the Gobabeb Training and Research Centre (GTRC) in the Central Namib Desert. Fog collection experiments were done with Standard Fog Collectors (SFCs) and 1-m² fog collectors made from the Raschel mesh that is used in SFCs from 1996 onwards. The results indicate that fog occurs throughout the year and that it has low major ion concentrations (chemical composition). The period of high fog deposition coincides with that of high groundwater salinity and would suit mixing of the two waters to provide water of good drinking quality to people in these areas. In conclusion, fog is a viable source of water in the Namib and could supplement traditional sources in rural settlements and perhaps also in urban water supply schemes in this region as in other parts of the world where it is used as a source of drinking water.

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Six years of dew observations in the Negev Desert, Israel

Dew measurements taken at the desert site of Sede Boker for nearly 6 years are analysed. The instrument used is a Hiltner-type dew balance. Several parameters describing various aspects of dew formation are discussed. The total monthly amount of dew and the distribution of the number of dew nights per month shows two maxima (in September and in December–January) and two minima (in April and November). The average dew deposit per dew night behaves differently: the most striking feature of this quantity is the appearance of distinct summer and winter regimes, with the winter having more dew per dew night. With respect to the total monthly dew hours, the year appears to be divided in half: first, the 6 months from August to January, with an average of 145 h per month, and second, the 6 months from February to June, with 80 h per month. The average duration of dew per dew night appears to follow very closely the length of the night: there is a clear maximum of dew duration in December (9·7 h) and a clear minimum in July (5·5 h). Finally, the rate of dew accumulation is found to have a distinct dry season regime and a winter, rainy season regime.     

盆地气象学及其一些概念

就盆地气象学的某些问题进行了讨论。     

Atmosphere,Weather, and Baseball: How Much Farther Do Baseballs Really Fly at Denver's Coors Field?

This article tests the widely held assumption that batted baseballs travel 10 percent farther in Denver than in major‐league ballparks at sea level. An analysis of (1) National League fly‐ball‐distance data for 1995–1998, (2) the micrometeorology of Coors Field, and (3) weather dynamics along the Colorado front range shows that the assumed elevation enhancement of fly‐ball distance has been greatly overestimated due to prevailing weather conditions in downtown Denver. We conclude that the record number of home runs at Coors Field must be attributed as much to the personnel of the Colorado Rockies team and the effects of mile‐high elevation on the act of pitching a baseball as to the effect of low air density on fly‐ball distance.