Long-term changes in the heat island of Prague under different synoptic conditions

Summary The long term changes of the Prague urban heat island are analyzed separately for different groups of synoptic (circulation) types during the 1961–1990 period. The synoptic types are taken from Brádka’s synoptic catalogue, which is in common use in the Czech Republic; and the grouping of types is based on their cyclonicity and directional characteristics. The increase in the heat island intensity is steeper under anticyclonic than cyclonic conditions in all seasons except for spring. The increase in the intensity differs between dominant airflow directions. With only a single exception, the heat island intensification is much larger under the synoptic types with the north to northeast and south to southwest flow than under the other flow directions.     

Prairie tornadoes: Research note

Abstract

The frequency of tornadoes on the Canadian Prairies is a subject of much current debate. The author questions the traditional view that tornado frequency on the Prairies decreases westwards from southern Manitoba. A study of various sources of information on severe thunderstorm events on both sides of the 49th parallel leads to the conclusion that prairie tornadoes often are not isolated singular cases but rather are members of tornado outbreaks. Tornadoes in the northern Great Plains and Prairies are more frequent than has previously been thought, and are likely to be under‐reported compared with those of “tornado alley” in the United States. The Prairie Region can validly be regarded as an outlying section of the North American tornado belt.     

Climate analysis of tornadoes in China

Based on analysis of historical tornado observation data provided by the primary network of national weather stations in China for the period from 1960 to 2009,it is found that most tornadoes in China(85%)occurred over plains.Specifically,large numbers of tornado occurrences are found in the Northeast Plain,the North China Plain,the middle-lower Yangtze Plain,and the Pearl River Delta Plain.A flat underlying surface is conducive to tornado occurrence,while the latitudal variation of tornado occurrence in China is not so obvious.Tornadoes mainly occur in summer,and the highest frequency is in July.Note that the beginning and the time span of tornado outbreaks are different in North and South China.Tornadoes occur during May-September in South China(south of 25°N),June-September in Northeast China(north of 40°N),July-September in the middle-lower Yangtze Plain,and July-August in North China(between25°and 40°N).More than 80%of total tornadoes occurred during the above periods for the specific regions.The 1960s and 1970s have seen about twice the average number of tornadoes(7.5 times per year)compared to the mean for 1960-2009.The most frequent occurrence of tornado was in the early and mid 1960s;there were large fluctuations in the 1970s;and the number of tornadoes in the 1980s approached the 50-yr average.Tornado occurrences gradually decreased in the late 1980s,and an abrupt change with dramatic decrease occurred in 1994.The decrease in the tornado occurrence frequency is consistent with the simultaneous climatic change in the meteorological elements that are favorable for tornado formation.Tornado formation requires large vertical wind shear and sufficient atmospheric moisture content near the ground.Changes in the vertical wind shear at both 0-1 and 0-6 km appear to be one important factor that results in the decrease in tornado formation.The changing tendency of relative humidity also has contributed to the decrease in tornado formation in China.     

A developing inventory of tornadoes in France

The analysis of 304 French tornadoes shows that the most struck areas are the northwestern part of the country, the south and the east. Tornadoes occur mainly in spring and in summer; August is the month when the frequency is maximum. Tornadoes move mainly from southwest to northeast, except in the south where the direction is sometimes south to north. Thirty-six killer tornadoes were listed (12% of the cases); most of them with an intensity greater or equal to F3. The occurrence is approximately 15–20 tornadoes each year in France, and the annual risk probability of significant tornadoes in France is 0.66×10⁻⁵. This value is probably underestimated because all the tornadoes are not listed.     

Parameterisation of surface radiation flux at an Antarctic site

During the Antarctic summer 1994/95 the values of downward and upward flux densities of both solar and terrestrial radiation were recorded at 1200 m for a period of 1 month on the Reeves Nevè Glacier (lat 74°39′S, long 161°35′E), near the Italian base of Terra Nova Bay. The relations proposed by Swinbank [Swinbank, W.C., 1963. Long-wave radiation from clear skies. Q. J. R. Meteorol. Soc. 89, 339–348], Idso and Jackson [Idso, S.B., Jackson, R.D., 1969. Thermal radiation from the atmosphere. J. Geophys. Res. 74, 5397–5403] and Deacon [Deacon, E.L., 1970. The derivation of Swinbank's long-wave radiation formula. Q. J. R. Meteorol. Soc. 96, 313–319] associating the long-wave atmospheric radiation flux only to the air temperature at screen level were tested in extreme Antarctic climatological condition. A relation between the long-wave radiation flux and both screen air temperature and cloud cover fraction in accordance to the height of the cloud base was defined using the Kasten and Czeplak relationship that relates the solar radiation flux and the cloud cover index. The study of the incoming short-wave radiation flux from the clear sky and that reflected by the surrounding snow cover allowed for highlighting the role of surface geometry on the albedo measurements.     

Long-term changes of the surface air temperature in relation to solar inertial motion

The inertial motion of the Sun around the barycentre, or centre of mass, of the Solar System has been employed as the base in searching for possible influence of the Solar System as a whole on climatic processes, especially on the changes in surface air temperature. A basic cycle of about 180–200 years and its higher harmonics up to 30 years have been found in surface air temperature of central Europe since 1753, established from 13 continuous instrumental time series. These periods correspond to the periods of solar inertial motion. In the first half of the 19th century, when the solar motion was chaotic, this temperature was about 0.75°C lower than that in the 20th (1940–50) and the 18th (1760–70) centuries. The mentioned decades of long-term temperature maxima coincide with the central decades of the ordered (trefoil) motion of the Sun. The temperatures in coastal Europe have been found to have slightly different properties, especially on a long-time scale. The periods of 35–45 years are significantly pronounced in the coastal Europe temperature spectrum. The chaotic motion of the Sun in the next decades could decrease both the solar forcing and global surface air temperature.This research was performed with support of the Grant Agency of the Czech Republic, Grant No. 205/93/0417, I. Charvátová: Prognosis of climate development in central Europe.     

Climatic fluctuations in Bohemia from the 16th century until the present

Summary This is paper appraises the possibilities of using written sources of weather information and indirect indicators of the climate of Bohemia. The data are related mainly to the socalled Bohemian vine and hop growing region (the lower reaches of the Ohe River). On the basis of these data climatic fluctuations from the 16th century up to the present are described. Characteristics of climatic types are presented: the continental type (1501–1560, 1681–1750), the oceanic type (1561–1630), and the ambiguous type (1631–1680). On the basis of instrumental observations of the station Prague Klementinum it is possible to describe fluctuations of air temperature since 1771 and fluctuations of precipitation since 1804. These series are the basis material for the analysis of the cyclicity of climatic fluctuations and for the study of possible causes of this cyclicity. The obtained information of the climate of Bohemia since the 16th century for forecasting the climate fluctuations by means of the so-called diagnostic methods, which are based on the method of analogies.With 7 Figures     

Meteorological singularities in the Czech Republic in the period 1961–2002

Summary Based on the mean daily values of air temperature, air pressure, and precipitation totals at 13 climatological stations within the territory of the Czech Republic in the period 1961–2002, a statistical analysis of “meteorological singularities” (i.e., calendar-dependent deviations from the mean annual variation for selected meteorological elements) was performed. At the 13 stations analysed, a total of 45 meteorological singularities (37 singularities in air temperature, 35 in air pressure, and 30 in precipitation) were found. The singularities detected correlate well with cases traditionally recognised in the Czech Republic as well as with the results of analyses performed for Germany. Despite the considerable variability of singularities in time and space, most of them are found across the entire territory of the Czech Republic and can be observed for the most part in all three elements processed. The majority of the singularities detected may be explained on the basis of circulation mechanisms, by relating them to a significantly higher occurrence of certain groups of synoptic situations characterised by anomalous temperature or precipitation effects. Cases of “competition” between singularities, when different singularities may occur on the same calendar day, were found.     

Pollutant concentrations in fog and low cloud water at selected sites of the Czech Republic

In this paper, the basic composition of fog and low cloud water are presented, resulting from the analyses of water samples from 111 fog/cloud events. The samples were collected at five sites located in various regions of the Czech Republic. Two sampling sites are in mountainous regions and three sites represent various urban areas. The mountain stations are located in two regions of the Czech Republic with different industry types. At all the sites, active fog collectors were employed. In the water samples, the conductivity, acidity (pH), cations (H⁺, Na⁺, K⁺, NH₄⁺, Mg²⁺, Ca²⁺) and anions (F⁻, Cl⁻, NO₃⁻, SO₄²⁻) were determined.A mean pH value of about 4.5 was obtained at mountain sites whereas the measurements in urban areas showed mean pH values from 4.9 to 6.4. The mean conductivity values in the samples from the two mountain stations were 137 and 191.5 μS cm⁻¹. The samples from urban sites showed mean values between 127.7 and 654.4 μS cm⁻¹. The maximum concentration means for the three dominant pollutants (expressed by the ratio mountain sites/urban sites) are 32.9/99.6 mg l⁻¹ for NO₃⁻, 32.5/192.9 mg l⁻¹ for SO₄²⁻ and 18.5/52.7 mg l⁻¹ for NH₄⁺. As expected, we found higher ion concentrations in the northern part of the Czech Republic where larger numbers of lignite-burning power plants, chemical factories and opencast lignite mines are located. A decrease in ion concentrations was observed at higher altitude sites, probably reflecting at least in part higher liquid water contents at these locations.     

CLIMATE CHANGE HYDROLOGY AND WATER RESOURCES IMPACT AND ADAPTATION FOR SELECTED RIVER BASINS IN THE CZECH REPUBLIC

The Czech Republic has a northern hemisphere Atlantic-continental type of moderate climate. Mean annual temperature ranges between 1.0 and 9.4 °C (between 8.8 and 18.5 °C in summer and between –6.8 and 0.2 °C in winter). Annual precipitation ranges between 450 mm in dry regions and 1300 mm in mountainous regions of the country. With its 2000 m³ per capita fresh water availability, the Czech Republic is slightly below average. Occasional water shortages do not usually result from general unavailability of water resources but rather from time or space variability of water supply/demand and high degree of water resources exploitation. To study potential impacts of climate change on hydrological system and water resources, four river basins have been selected in the territory of the Czech Republic: the Elbe River at Decin (50761.7 km²), the Zelivka River at Soutice (1188.6 km²), the Upa River at Ceska Skalice (460.7 km²) and the Metuje River at Marsov n. M. (93.9 km²). To simulate potential changes in runoff, three hydrological models have been applied using incremental and GCM (GISS, GFDL and CCCM) scenarios: the BILAN water balance model, the SACRAMENTO (SAC-SMA) conceptual model and the CLIRUN water balance model. The paper reviews methods applied in the study, results of the assessments and concludes with suggestions for possible general adaptation policy options where the preference is for nonstructural measures such as water conservation, efficient water demand management and protection of water resources.     

Tornado climatology of Austria

After several decades of little work, a revised tornado climatology for Austria is presented. Tornadoes seldom form in the alpine areas, however, near the eastern flanks of the Alps, favourable conditions for tornado genesis are found. Whereas in the alpine regions less than 0.3 tornadoes per 10,000 km² a year touch down (averaged for provinces or major parts of a province), we can count 0.9 in the greater Graz area, 1.0 in the greater Linz area and 1.2 tornadoes per 10,000 km² a year in the greater Vienna area, suggesting the existence of so-called tornado alleys. As these regions are the most populated areas of Austria, there is a possible population bias in the dataset. The overall average for Austria is 0.3 tornadoes per 10,000 km² a year.The database consists of 89 tornadoes, one landspout and six waterspouts, with a total of 96 events. The seasonal peak is in July with a maximum probability of tornadoes in the late afternoon and early evening hours. Every fifth tornado occurs in the hour after 5 p.m. The maximum intensity determined for a tornado in Austria was T7 on the TORRO-Scale (F3 on the Fujita-Scale), the most common intensity is T2 on the TORRO-Scale (F1 on the Fujita-Scale).     

Winter tornadoes in Ireland: The case of the Athlone tornado of 12 January 2004

Records to date show that the maximum frequency of tornadoes in Ireland is during the summer months of July and August. However, significant tornadoes have also occurred during the winter months. This study identifies the main characteristics of such events in Ireland and examines one particular case that occurred on 12th January 2004 in the town of Athlone, County Westmeath. It occurred at approximately 2000 UTC, during the hours of darkness. This, together with the severe weather that occurred at the same time, minimised the eyewitness evidence. But site investigations established a recognisable, narrow damage track approximately 4.15 km long and local witness evidence suggests it lasted between 15 and 20 min. The synoptic environment for this event consisted of a cold front that was crossing Ireland from the west. This was in close proximity to a strong jet streak at 300 hPa and an upper level trough with an intense cold pool of air. Overall there was very modest instability. However, both horizontal and vertical wind shear was very marked, at middle levels and, in particular, low levels up to 800 hPa. This appears to have played the major role in the development of a favourable environment for the tornado. Mesoscale detail from radar images suggests that the tornado occurred in a storm cell behind the cold front along a surface boundary between the rear outflow from a storm cell ahead of it and surface winds from the SSW. It is also suggested that low level wind speed shear may have produced a downburst into the flank of the Athlone storm cell and created a bow echo of particularly small space–time dimensions, a mere 11 km long lasting for up to 30 min. The tornado occurred in the northern ‘bookend’ portion of the bow echo. If so, this is the first record of a bow echo tornado for Ireland.     

0808号台风凤凰前部龙卷的环境场和雷达回波分析

用多普勒天气雷达、常规观测和地面加密观测资料对2008年7月29-30日发生在江苏的台风凤凰前部系列龙卷过程进行了详细分析.结果如下:该龙卷发生在台风前部风切变区里,低空较强的垂直风切变、极不稳定的大气层结和深厚的正涡度区,为龙卷的发生提供了热力和动力条件.龙卷回波的反射率因子特征表现为最大反射率因子梯度位于回波的后侧,一般都有弱回波区和后侧入流缺口相伴随.东台龙卷产生于飑线型弓形回波的顶点,具有相对较大的反气旋性切变.高邮龙卷中低层具有弱的气旋性涡旋,宝应龙卷回波的内部环流特征明显,有明显的中气旋结构.在业务工作中,强回波质心高度和垂直累积液态含水量的骤降、径向速度风场中气旋性涡旋的迅速发展是对龙卷的提前警戒很好的参考指标.     

Increasing Growing-Season Length in Illinois during the 20th Century

Using daily minimum air-temperature (T_min) data from the state of Illinois, the dates of spring and fall freezes – and the resulting growing-season length – are examined for trends during theperiod 1906–1997. Of the stations in the Daily Historical Climate Network, mostshow trends toward earlier spring freezes; however, trends in fall freezes are not consistent over the station network. Although the time series are highly variable (noisy), results suggest that the growing-season length in Illinois became roughly one week longer during the 20thcentury. To examine how changing freeze-date statistics relate to changing air-temperature probability distributions, percentiles of T_min formoving 10-year periods were analyzed for trends during the typical times for spring and fall freezes in Illinois (i.e., the months of April and October). The lower portion of the April probability distribution shows substantially larger warming (0.5–0.7 ° C/100 yrs) than the upper portion of the distribution (0.2–0.3 ° C/100 yrs), suggesting that although cold events are warming during April, warm events are not warming as fast. Conversely, the lower portion of the October probability distribution shows modest cooling in T_min (–0.2 ° C/100yrs for the 10th percentile), while middle and upper portions of the distribution show very large rates of cooling (up to –1.5 ° C/100 yrs for the 40th–70th percentiles). Analysis ofthe entire probability distribution provides a more-comprehensive perspective on climatic change than does the traditional focus on central tendency.     

冷涡背景下辽宁龙卷气候特征和环境条件

为了研究冷涡与辽宁龙卷的关系,揭示冷涡背景下辽宁龙卷发生的特征,利用1951—2020年辽宁省龙卷观测和灾情数据以及欧洲中期天气预报中心ERA5大气再分析资料,收集整理冷涡背景下辽宁龙卷个例,对比冷涡背景下EF2—4级(EF2+)和EF0—1级(EF1?)龙卷物理量参数的差异.结果表明:(1)冷涡背景下辽宁龙卷主要出现...     

Relevance of ion-induced nucleation of sulfuric acid and water in the lower troposphere over the boreal forest at northern latitudes

The relevance of ion-induced nucleation of sulfuric acid and water (IINSW) in the troposphere over the boreal forest at northern latitudes is investigated by combining two existing and previously published models (MALTE — model to predict new aerosol formation in the lower troposphere; PARNUC — a parameterized steady-state model of neutral and ion-induced nucleation of sulfuric acid and water for atmospheric conditions). Simulations were performed for 4 days with observed new particle formation at ground level by using input data from the SMEAR II station in Hyytiälä, Finland. The selected days were chosen to cover a wide range of values of the parameters most relevant for IINSW. The results showed that ion-induced nucleation of sulfuric acid and water can contribute up to 15% to the total amount of newly formed particles in the size range of 3–10 nm inside the mixed layer at the Hyytiälä site. The importance of IINSW seemed to increase in the free troposphere above the boundary layer, however, lack of measurements in the vertical structure of the input parameters suggest that the model results are burdened with high uncertainties.     

采用不同背景场的龙卷模拟结果对比分析

采用常规气象观测资料,对2014年5月21日17:40广州市黄埔区九龙镇一次西风带龙卷的环流背景场进行分析,并利用FNL和ERA5再分析资料作为背景场模拟该龙卷过程,研究了不同再分析场对模拟效果的影响,结果表明:对于雷达回波、垂直速度、水平风场及水成物,FNL资料作为初始场对西风带龙卷的模拟优于ERA5资料。FNL再分析资料作为初始场、边界场能有效地模拟出西风带龙卷的超级单体结构。5月21日17:45对流风暴与经典超级单体结构相似,出现了钩状回波特征与入流缺口,其垂直结构上强回波向东倾斜,形成穹窿结构。17:50超级单体钩状回波处有明显的强上升气流与后侧下沉气流,具备生成龙卷的必要条件;从垂直涡度的低层平面发现涡旋特征十分明显,其高度从250m伸展至2km,龙卷有可能发生在从地面一直延伸至2km向西北倾斜的小尺度气旋内。      

On the capability of RegCM to capture extremes in long term regional climate simulation – comparison with the observations for Czech Republic

Summary We analyze daily precipitation and temperature extremes over the Czech Republic in a regional climate simulation for the 40-year period of 1961–2000 carried out with the RegCM3 regional climate model. The model is run at 45 km grid interval and is driven by NCEP/NCAR reanalysis lateral boundary conditions. Comparison with station data shows that the model performs reasonably well in simulating the frequency of daily precipitation events of medium to high intensity as well as the precipitation intensities (return levels) of long return periods, with the exception of mountain stations. While this is attributed mainly to the relatively coarse representation of topography across the area of the Czech Republic, the parameterization of convection can be another reason. The model underestimates daily maximum temperature (especially in the warm seasons) and as a result the occurrence of heat waves (high temperature episodes). The performance of the model improves in the simulation of daily minimum temperature and cold wave events. In order to apply this regional model to the simulation of extreme events over the complex terrain as for Czech Republic we recommend that a higher resolution is used in order to better describe the topography of the Czech Republic and that the daily maximum temperature bias is reduced.     

An estimation of the probable maximum precipitation for river basins in the Czech Republic

The hydro-meteorological evaluation of a flood event in July 1997 (the Odra flood in Central Europe) demonstrated that new procedures to estimate design floods for the reservoir outflow structures in the Czech Republic (CR) were needed. Therefore, the techniques of the estimation of Probable Maximum Precipitation (PMP) were developed in a national research project (1998–2000), and the activity focused on the improvement of the area related PMP estimates was going on within a present national project. In the frame of the evaluation of the next extreme precipitation event in August 2002 (the Labe flood in the CR and Germany), we compared the catchments related precipitation with the PMP estimates. In this paper, an outline of the PMP estimation techniques is given and the use of data from the Czech gauges is described, the aim being the statistical derivation of the point and area PMP estimates for precipitation duration of 1 to 5 days. The use of radar data in assessing the maximized area reduction factor is discussed and the relationship resulting from the radar measurements over the CR territory is presented. An evaluation of the radar-based area rainfall enabled us to transform the point PMP to the area PMP estimate designed for the river basins in CR. In the last part of the paper, the results obtained by comparing the rainfalls in 1997 and 2002 flood events with the PMP estimates are presented. The comparison showed that the maximum area rainfalls over small Czech catchments (the 3rd order river basins) did not exceed 63% of the corresponding PMP values.     

典型强龙卷风暴中的地闪活动特征

闪电活动对于强龙卷天气的发生有一定的指示作用,基于闪电定位资料,结合多普勒天气雷达、探空和ECMWF再分析资料对两次典型强龙卷风暴中地闪的时空演变、雷电流强度及正地闪活动特征进行了统计分析,结果表明:地闪主要发生在组合反射率因子≥30 dBZ的区域内,龙卷发生期间,地闪活动减弱且较为分散。不同龙卷风暴的地闪频次差异较大,这与风暴中上升气流的强度有关;当地闪频次从峰值降至最小值期间,龙卷及地,两次过程中地闪频次峰值分别提前龙卷发生约33 min和28 min。同时,龙卷及地之前,地闪会出现连续多次闪电跃增;龙卷等级越强,正地闪表现越活跃,特征越明显,在江苏盐城阜宁龙卷发生期间,还出现了地闪极性从正地闪主导向负地闪主导的反转;两次龙卷风暴雷电流强度随时间的变化规律并不明显,但均小于历史平均值,地闪发生愈频繁的龙卷风暴,对应的雷电流强度值愈小。