Synoptic Weather Types Research Articles

Diurnal variation of precipitation frequency in the warm half of the year according to circulation types in Kraków, South Poland

A 117 year series of hourly precipitation data from Krakow, South Poland and the Niedźwiedź classification of synoptic weather types were the basis of a detailed study of diurnal precipitation variation and atmospheric circulation types. The analysis of the relationship between precipitation and circulation types was restricted to the warm half of the year (May–October). During this period precipitation ispredominantly liquid. This paper discusses the role of theCarpathian orographic barrier in the development of the 24 hour precipitation pattern.

Synoptic weather types and morning rush hour nitrogen oxides concentrations during Auckland winters

Synoptic weather types and morning rush hour nitrogen oxides concentrations during Auckland winters

Categorization of cold period weather types in Greece on the basis of the photointerpretation of NOAA/AVHRR imagery

The Advanced Very High Resolution Radiometer (AVHRR) on board the National Oceanic and Atmospheric Administration (NOAA) satellites may be used to detect and monitor prevailing synoptic weather systems and to describe the state of the atmosphere with very good spatial and temporal resolution. In this study, the synoptic weather types which are responsible for severe cold and rainy weather conditions in Greece during the cold period of the year were examined with the use of NOAA/AVHRR satellite images in conjunction with weather charts. An attempt was made to develop a classification scheme for these synoptic weather types on the basis of their tracks and cloud patterns inferred by satellite images. Forty-two visible and thermal infrared AVHRR images were interpreted with emphasis on the analysis of cloud patterns formed in synoptic weather systems in order to relate cloud features in every image to physical processes. Synoptic maps (12:00 UTC) from the European Centre for Medium-Range Weather Forecasts (ECMWF) were used as auxiliary data. The final product was a categorization of the cloud features formed by each of the four prevailing weather types in the area of Greece for the winter rainy period (three Depressional Weather Types and one Mixed Weather Type).

Classification of New Zealand Synoptic Weather Types and Relation to the Southern Oscillation Index

Obliquely rotated T-mode principal component analysis has been applied to the NCEP/NCAR geopotential height reanalysis data for winter months from 1958 to 1996 over the New Zealand region. A new set of ten representative weather types were identified, with two being the most dominant. The temporal characteristics of the ten synoptic weather types were anlayzed in relation to different phases of the Southern Oscillation Index (SOI). While weather type-local meteorology relationships were consistent over time, the frequency of some weather types changed significantly with the SOI phases. In general, and relative to “normal” conditions, the frequency changes in El Nino years tended to be more significant than in La Nina episodes.

Estimation of transboundary air pollution on the basis of synoptic‐scale weather types

AbstractA methodology to estimate annual transboundary atmospheric transport is proposed, taking into account different background meteorological conditions. For this purpose, the 850 hPa synoptic‐scale atmospheric circulation over the area examined was classified on a daily basis into 14 distinct synoptic types, using a database for an extended period of 40 years. The corresponding frequency of appearance of the synoptic types for a normal year was calculated. For selected days representing the synoptic types during this year, the inflow–outflow fluxes of NOx and SO2 were estimated through a balancing box with the aid of a MEMO/TRAPPA modelling system. According to the proposed method, the total inflow–outflow fluxes were calculated using the lateral fluxes for each representative day, being weighted by the annual relative frequency of appearance of the synoptic scale weather types. It was demonstrated that this approach provides similar results to the intensive method based on day‐by‐day calculations. Furthermore, this approach is easier to use, since it is based on the simulations of selected days, and it allows the investigation of the influence of different types of atmospheric circulation on the inflow–outflow budget. Copyright © 2003 Royal Meteorological Society

Weather Observations Across the Southern Andes at 53°S

Regional variations of weather pattern were analyzed along a west-to-east profile across the Southern Andes (53°S), one of the most pronounced climate-divides in the world. For the first time we present a meteorological record from an array of three automatic weather stations (AWS), operated by the authors, for the central part of the climate divide which, together with previously existing Chilean weather stations, complete the transect. These data cover a time period of 3 yr. from October 1999 until September 2002. Air temperatures along the profile are highly correlated. Annual precipitation drops from between 6000 mm and 7000 mm at sea level along the main divide of the mountains to only about 1000 mm at the eastern slopes of the Andes and to as little as 430 mm at Punta Arenas. The variations of rainfall with wind direction and synoptic weather types are markedly different between the central part of the Andes and Punta Arenas. At the center of the climate divide precipitation correlates positively with wind speed from the west, whereas at Punta Arenas, east of the Andes, higher rainfall rates occur with easterly air flow. It is assumed that this reflects the barrier effect of the mountain range of the Andes. The results indicate that in order to make references about present or past climatic variations in Patagonia, it is essential to consider the effect of changes in circulation patterns.

The influence of weather-type and long-range transport on airborne particle concentrations in Edinburgh, UK

This study investigated the influence of regional-scale synoptic weather type and geographical source regions of air masses on two-particle concentration metrics (Black Smoke (BS) and PM 10) in the city of Edinburgh, UK, between 1981 and 1996. Twenty-seven classifications of Jenkinson Daily Weather Types (JWT) were sub-divided into 9 directional categories and 3 vorticity categories, and the influence of JWT category on BS and PM 10 determined. Four-day air mass back-trajectories for 1 July 1995–30 June 1996 were computed and grouped into 8 categories depending on the geographical route followed. Significantly elevated concentrations of BS (median values 2, 5 and 4 μg m −3 greater than median for 1981–1996) and PM 10 (median values 3, 5.5 and 8 μg m −3 greater than median for 1992–1996) were observed for anticyclonic, southerly and south-easterly weather types, respectively. These differences were not identified at conventional levels of significance for BS in 1995–1996. This may reflect a shift in more recent times to lower concentrations of predominantly locally emitted BS less affected by regional scale meteorology. Conversely, significant inter-trajectory category differences were observed for PM 10 during 1995–1996, with highest concentrations associated with Eastern European trajectories and south-easterly weather type categories (11.4 and 10.7 μg m −3 greater than annual means, respectively). The variation in particle concentration across weather-type was a significant proportion of total median particle concentration, and of a magnitude associated with adverse health outcomes. Thus current PM 10 concentrations (and associated health outcomes) in Edinburgh are likely to be significantly influenced by regional-scale meteorology independent of local air quality management areas. Furthermore, changes in long-term trends in distributions of synoptic weather types indicate that future climate change may influence exposure to PM 10 and the PM 10:BS ratio in Edinburgh. Further definition of the relationships between long-range transport and particle concentration will improve classification of human exposure in epidemiological studies.

Weather and emotional state: a search for associations between weather and calls to telephone counseling services.

Previous research has revealed that an emotional response to weather might be indicated by calls to telephone counseling services. We analyzed call frequency from such "hotlines", each serving communities in a major metropolitan area of the United States (Detroit, Washington DC, Dallas and Seattle). The periods examined were all, or parts of, the years 1997 and 1998. Associations with subjectively derived synoptic weather types for all cities except Seattle, as well as with individual weather elements [cloudiness (sky cover), precipitation, windspeed, and interdiurnal temperature change] for all four cities, were investigated. Analysis of variance and t-tests (significance of means) were applied to test the statistical significance of differences. Although statistically significant results were obtained in scattered instances, the total number was within that expected by chance, and there was little in the way of consistency to these associations. One clear exception was the increased call frequency during destructive (severe) weather, when there is obvious concern about the damage done by it.

Diurnal characteristics of heavy precipitation according to weather type at an upland site in Scotland

AbstractThe diurnal characteristics of heavy 3 h and 24 h precipitation events exceeding a certain threshold (o‐called peak‐over‐threshold or POT events) were studied according to synoptic weather type. Hourly precipitation data for 1970–86 from Eskdalemuir, an upland site in southern Scotland, and the (daily) Mayes weather type classification for Scotland were used. Through cluster analysis, the weather types were divided into five groups according to the overall diurnal distribution of precipitation. Subsequently, 272 POTs for each duration were extracted and analysed using circular statistics. The diurnal distributions of the 3 h POTs were found to be significantly non‐uniform for four of the five weather type groups.The 3 h POTs in the group that includes the Cyclonic weather type show a bimodal distribution with early‐morning and afternoon maxima. A bias towards increased temperatures and a shift in the wind direction suggest that early‐morning POTs may be caused mainly by warm fronts. This is consistent with warm fronts providing favourable conditions for orographic enhancement, which occurs predominantly during the early morning. The afternoon maximum may represent cold frontal precipitation enhanced by thermal convection. Because a cyclone passage generally involves a warm front followed by a cold front, 24 h POTs were found to start significantly more often in the first 4 h after midnight than during the rest of the day. Copyright © 2002 Royal Meteorological Society.

Daily wind gust speed probabilities over Switzerland according to three types of synoptic circulation

AbstractThe nowcasting and prediction of strong winds are still far from adequate, using either statistical or numerical modelling approaches. During the last decade, Switzerland has been struck by two extratropical storms, namely the February 1990 storm ‘Vivian’, and the December 1999 storm ‘Lothar’, that caused severe damage to infrastructure and to forests. Although numerical weather prediction models captured in both cases the cyclone tracks on the synoptic scale, the severity of local gusts was not properly predicted over the Swiss territory. To help predicting such phenomena, a combined approach to diagnose the wind gust speeds over Switzerland is described. The diagnostics aim at computing the probability of exceeding a gust speed based on the mean wind in relation to the prevailing synoptic weather type for a limited number of groups of climatological stations distributed throughout Switzerland. Based on 10 years of Swiss station observations, the computation of this probability uses an empirical gust factor that is a function of the daily gust speed, itself a function of the daily mean wind speed. For this period, each day has been categorized into three weather types according to the Schüepp classification. Principal component analysis and cluster analysis are performed in order to group climatological stations having similar characteristics in daily wind gust velocities. The results show that the gust factor provides an accurate method to compute the daily wind gust speeds at each Swiss climatological station for the given period. When combined with the three weather types and group of stations, the proposed diagnostics are an efficient method to predict the distribution of wind gust speeds. The gusts associated with the ‘Vivian’ and ‘Lothar’ storms are then diagnosed for each specific group where more than 85% of the stations responded similarly to their specific group members, which is highly satisfactory in this case. Copyright © 2002 Royal Meteorological Society

Aerosol optical depth measurements by means of a Sun photometer network in Switzerland

Within the Swiss Atmospheric Radiation Monitoring program (CHARM) the Swiss Meteorological Institute ‐ MeteoSwiss operates a network of presently six Sun photometer stations. Aerosol optical depths (AOD) at 368, 500, and 778 nm were determined from measurements of the relative direct solar irradiance, primarily to provide climatological information relevant in particular to climate change studies. The six instruments are located at various sites representative of high and low altitudes at the north and south part of the Alps in areas free from urban pollution in Switzerland. AOD time series of recordings back to 1991 are discussed, when data were first collected at Davos. An important aerosol layer is often present over stations at lower sites, showing seasonal variability and regional differences for the observed tropospheric aerosols. A classification scheme for synoptic weather types was applied to separate the AOD data into groups corresponding to different atmospheric transport conditions. On average, lower AODs are measured within advective weather situations than within convective ones. However, at the high Alpine sites such a classification is incomplete for AOD characterization due to orographically induced vertical motion. Monthly averaged values of AOD at 500 nm ranged from 0.05 during winter up to 0.3 in summer. The scale height of the aerosol optical depth is found to be 1–2 km depending on season. The high mountain sites are more suitable to the study stratospheric aerosols, for example, the change of the aerosol content and of its size distribution due to Mount Pinatubo eruption was clearly identified at Davos. In 1996 the aerosol optical depth returned to pre‐Pinatubo values. Minimum AODs of ≈0.004–0.007 measured at 500 nm in 1997 are in good agreement with widely reported aerosol optical depth measurements of the stratospheric background aerosols. Besides the Pinatubo‐affected period aerosol characterization by means of the Angström power law exhibits on average a mean wavelength exponent of 1.3–1.8. A climatology of the AOD data obtained between 1994 and 2000 in both space and time has been established.

Climatology of near‐surface wind patterns over Switzerland

AbstractOver complex, mountainous terrain the near‐surface winds can form intricate patterns as large‐scale winds and locally forced wind systems interplay. Switzerland, with its mountainous topography and dense meteorological network of 115 automated surface stations, ideally serves as a study area for such wind system interactions. Applying an automated classification scheme to the wind data of one single year (1995), 16 distinct near‐surface flow patterns were found. These patterns also show characteristic distributions in magnitude and areal extent of temperature, global radiation and precipitation. An 18‐year climatology of flow patterns was created with an identification method for fewer stations. This allowed the determination of annual and diurnal variations in the frequencies of occurrence of the different flow patterns, revealing pronounced daytime and night‐time classes characterized by thermally forced winds. Transition probabilities between the flow patterns were computed as well. The relationship between the near‐surface wind patterns and the synoptic flow situation was investigated with a comparison with synoptic weather types defined for the Alpine region. The results show clear but not unequivocal interdependencies between the synoptic weather type and the near‐surface flow pattern. Copyright © 2001 Royal Meteorological Society

A climatology of regional background ozone at different elevations in Switzerland (1992–1998)

The ozone records of several monitoring stations in Switzerland from 1992 to 1998 are investigated with respect to the variability observed during regional background conditions, i.e. conditions with little detectable local or regional-scale influences as evident by NO x and CO concentrations. The sites cover different altitudes between 490 and 3600 m asl. They are characteristic of near-surface conditions, the top of the planetary boundary layer or residual layer, the complex atmosphere in an alpine valley, and the free troposphere. The results reveal a distinctly different ozone variability (diurnal cycles, seasonal cycles, trends) during regional background conditions compared to all days. The estimated annual average ozone concentration under these conditions is between 33 and 50 ppb, dependent on altitude, with a spring maximum and an autumn/winter minimum. Differences in background ozone are found depending on the synoptic weather type. For all sites a positive ozone trend is calculated for background conditions that is larger than for all data. For the latter, the trends appear to be stronger positive for the last 7 years than for the last 11 years.

Winter synoptic weather types in Catalonia (NE Spain) and their linkage with minimum temperature anomalies

Winter synoptic weather types in Catalonia (NE Spain) and their linkage with minimum temperature anomalies

Winter synoptic weather types in Catalonia (NE Spain) and their linkage with minimum temperature anomalies

An objective classification of winter synoptic weather types in Catalonia (NE Spain) is obtained by means of the principal component analysis of daily variables followed by cluster analysis based on Average Linkage and K-Means methods. The period analysed includes days belonging to December, January and February, from 1976 to 1980. The data list consists of thermal, pressure, cloud cover, humidity, wind and precipitation values recorded at four different stations in Catalonia. The classification includes 14 clusters which accurately explain the winter synoptic variety of the country. All cluster features are discussed in detail and a study concerning transitions between these clusters is presented. Three groups (1, 3 and 7) are related to high pressure weather types, clusters 4, 5 and 8 to cold sectors of mid-latitude depressions and clusters 2 and 9 can be associated with cyclonic conditions with western circulation. The weather types related to extended precipitation are included in clusters 6 and 10 which are linked to eastern surface circulation. The obtained classification is then applied in a study concerning daily minimum temperature anomalies. The spatial distribution of these anomalies are analysed for each significant weather type. The clusters related to widely extended frost risk are finally identified (groups 4, 8 and 14).

Prediction of carbon monoxide acute air pollution episodes. Model formulation and first application in Lombardy

This paper describes a method to forecast the exceedance probability of a fixed threshold for a certain air pollutant concentration. This general approach has been applied in the case of carbon monoxide on 35 traffic monitoring stations in the Lombardy Region. The implemented model has been called FOREPOLL (Forecast Pollution). The model structure, consisting in three basic modules (the deterministic, the stochastic and the Bayesian one), has been thought to be adjustable to different stations of an air quality network and to various pollutants. Forepoll uses the last biennium data set of the station in exam (pollutants and micrometeorological parameters) as a moving learning time and also needs the forecasted synoptic weather type. In the first module the daily maxima of the hourly measured pollutant concentrations are checked in order to eliminate some known physical dependencies, such as the temperature dependence of the emissions. Then the data are divided into subgroups depending on the weather type and in each group fitted by a different Weibull distribution. To provide a first a priori exceedance probability, this distribution is daily rebuilt by taking into account the forecasted parameters. In the last module this probability is enhanced or reduced using simple, experience based, bayesian rules providing the a posteriori exceedance probability. Model validation trials have been carried out on a year of CO forecasted concentrations in different air quality stations; the first results are quite good particularly for the metropolitan areas, because the model seems to work better in case of stronger and more diffuse pollution.

Climatology of Regional Flow Patterns around Basel

Recently a method has been developed to classify local-scale flow patterns from the wind measurements at a dense network of stations. It was found that in the area around Basel twelve characteristic near-surface flow patterns occur. However, as the dense network of stations was running for one year only during the MISTRAL field experiment, no reliable climatology of the flow patterns can be inferred from these data. Mainly the annual cycle is not well determined from a single year of observations. As there exist several routinely operated meteorological stations with longer data records in and near the area discussed, a method was searched to identify the local flow patterns from the wind observations at these few permanent stations. A linear discriminant analysis turned out to be the best method. Based on wind data from 11 stations which were simultaneously in operation during 1990-1995, a six-year climatology of the flow patterns could be obtained and compared to synoptic weather types. Although there are relations to existing synoptic classes there is no unique correspondence between them and the flow patterns.

Aerosol transport to the high Alpine sites Jungfraujoch (3454 m asl) and Colle Gnifetti (4452 m asl)

Atmospheric transport processes, relevant to high Alpine sites, were deduced from 2 sets of aerosol records: a 9-year record from the Jungfraujoch (3454 m) on the northern side of the Swiss Alps and a 2.5-year record from Colle Gnifetti (4452 m) on the southern side. A classification scheme for synoptic weather types was applied to separate the aerosol data into groups corresponding to different atmospheric transport conditions. For both sites, vertical aerosol transport by thermally driven convection, acting between late spring and late summer, was found to be the dominant transport process. In summer, the thermally driven aerosol transport to both sites caused an increase of the seasonally averaged aerosol concentration between 0800 and 1800 local standard time by a factor of two. Under anticyclonic conditions, when subsidence on a synoptic scale is present, the thermally driven aerosol transport is most pronounced. Therefore, the aerosol determining thermal transport takes place within a synoptic scale vertical motion of opposite direction. Under cyclonic conditions, when lifting on a synoptic scale is present, the thermally driven aerosol transport is nearly absent. In winter, thermally driven convection does not contribute to the aerosol concentrations at both sites. Nevertheless, also in winter statistically significant differences in aerosol concentration were found between cyclonic and anticyclonic weather conditions, which can be attributed to the vertical transport acting on the synoptic scale. These differences in aerosol concentration were small compared to the corresponding differences in summer. Within the weather types, which are dominated by horizontal advection in the Alpine region, the aerosol concentrations are more diffcult to interpret with respect to the effective transport process.

A comparison of anticyclone and trough influences on the vertical distribution of ozone and meteorological conditions during SAFARI‐92

The vertical distribution of ozone recorded over northern Namibia during SAFARI‐92 is examined as a function of prevailing atmospheric circulation. Two dominant synoptic weather types, namely, anticyclonic flow and flow associated with a westerly trough, are identified and composite ozone profiles produced for each weather type. In both cases an elevated, enriched ozone layer (9–12 km), where ozone concentrations exceed 80 ppbv on average, and 100–120 ppbv on individual days, is present. Under anticyclonic conditions, ozone increases steadily from surface values of around 40 ppbv to about 60–80 ppbv throughout the troposphere. In contrast, the westerly trough is characterized by a midtropospheric (4–8 km) ozone minimum, where values are 20 ppbv lower. This gives rise to a double ozone maximum in the troposphere. The elevated, enriched layer is thought to be a pervasive layer equatorward of 20°S and to result from biomass burning.

A Simple Method for Spatial Interpolation of the Wind in Complex Terrain

Abstract The topographical elevation difference is proposed as a new variable for spatial interpolation of the sparse surface wind measurements to a finer mesh in a complex terrain area. The most used method for the initialization of diagnostic wind field models is based on the inverse-distance-squared weighted averaging interpolation technique regardless of the topographical elevation. Analysis of experimental data obtained from six meteorological towers deployed at several heights on the slopes along a valley in the South of Spain has shown a good correlation between wind speed and elevation above valley bottom. The efficiency of the inverse absolute elevation difference and the inverse distance squared as averaging weights for interpolation of the wind vector at several locations is checked; this is done for two meteorological synoptic weather types: strong synoptic winds, and thermal low over the Iberian Peninsula. For the latter weather type, the formation of nocturnal thermal inversion and the drainage flows are taken into account. Wind fields in the valley resulting from the two interpolation methods are compared. The elevation difference between meteorological station and grid point seems to be an important variable to be included in the wind field initialization process, that is, interpolation of the wind vector to a grid, when complex terrain areas are considered.