Abstract: The number of particles and their size distributions were measured in a rural area, during the summer, using a PCASP-X. The aim
was to study the influence of wildfires on particle size distributions. The comparative studies carried out reveal an average increase
of around ten times in the number of particles in the fine mode, especially in sizes between 0.10 and 0.14 μm, where the increase
is of nearly 20 times. An analysis carried out at three different points in time—before, during, and after the passing of the smoke
plume from the wildfires—shows that the mean geometric diameter of the fine mode in the measurements affected by the fire is
smaller than the one obtained in the measurements carried out immediately before and after (0.14 μm) and presents average values
of 0.11 μm.
Abstract: The measurement of the physical characteristics of hailstones reaching the ground is usually carried out by means of hailpads, on which the impact of hailstones leaves dents. Hailstone dents provide information about parameters, such as the number N of hailstones, their size M, and their kinetic energy E. In the case of intense hailfalls, however, the dents often overlap and the final measurement may not be totally reliable. This paper presents a computerized simulation with the aim of assessing measurement errors caused by dent overlap. The simulated dents represent several random hailfalls with both exponential size distributions and monodispersed size distributions. The simulated hailpads were measured following the procedure employed in the case of hailpads exposed to authentic hailfalls, and it was thus possible to assess the error due to dent overlap. The results show that dent overlap makes it impossible to measure all the dents, which means that in a real hailfall the number of hailstones registered will often be lower than the number of hailstones that actually hit the ground (up to 25% may go undetected). Consequently, the energy and mass of the hailstones are also underestimated (they may be up to 50% higher than the values registered on a hailpad). The maximum size registered, however, does not depend on the degree of overlapping and neither does the slope parameter λ of the exponential distribution, except when λ takes higher values. Finally, the authors suggest a heuristic correction of the data obtained by real hailpads based on the results of the simulations. An example is provided that applies these corrections to the 228 hailfalls registered by the Italian hailpad network over a period of 10 yr. The results show that, on average, the correction applied because of overlapping increases the number of hailstones in 3.2%, the mass in 1.9%, and the energy in 5.4%. However, there are cases in which these corrections reached much higher values of up to 6.9% in N and M, and up to 25.2% in E. It is therefore advisable to correct dent overlap before carrying out a regional climatic study of hail, since this study would certainly be affected by the errors accumulated by all the hailpads.
Abstract: This paper studies the influence of the North Atlantic Oscillation (NAO) on monthly, seasonal and annual precipitation regimes in continental Spain. The data used for this study include the monthly rain series of 325 meteorological stations distributed homogeneously over the study zone, and the monthly NAO indices from 1961 to 1998. A total of 5525 rain series were employed for the analysis. Simple and multiple linear correlations were established between these variables in different combinations. The main aim was to check whether monthly, seasonal or annual precipitation data could be predicted using earlier precipitation data and the NAO index. The geographical areas where the stations have shown a statistically significant correlation have been represented on maps. The results differ depending on the correlation, but, in general, the best results have been found in the fall and winter months. Finally, a practical application of the method was carried out in the Ebro Valley and it was observed that the combination of the NAO index for spring and summer and the precipitation registered in those two seasons may be useful to forecast rain in the fall.
Abstract: Annual, seasonal and monthly rainfall trends from 1961 to 2006 period were analysed in this study by
applying various statistical tools to data from 553 Spanish weather stations. The magnitude of the trends was derived
from the slopes of the regression lines using the least squares method, while the statistical significance was determined
using the non-parametric Mann-Kendall test. Geostatistical interpolation techniques were applied to generate rainfall trend
surfaces. Combining classic trends tests and spatially interpolated precipitation permits the spatio-temporal visualization of
detected trends. Updated trends reveal that rainfall is generally decreasing in January, February, March, April, and June.
Around 61, 44 and 12% of the whole territory is evidencing significant negative trends in February, June and March,
respectively. Significant precipitation decreases are also noted in more than 28% of Spain in summer and winter. On the
contrary, rainfall is significantly increasing in October in more than 21% of Spain and areas mainly located in north-western
areas. May, August, September and autumn also show significant positive trends in the period 1961–2006, although the
percentages are lower than for negative trends. Finally, the annual precipitation is significantly decreasing in 11% of the
territory.
Abstract: A number of controlled combustions have been carried out in the laboratory using samples of oats and barley straw
collected in Spain in order to establish the characteristic particle spectra of these emissions. In addition, chemical compounds
such as CO2, NO2 and NO and gravimetric variations have been registered during the combustion processes. For each
combustible the burning phase has also been defined. Burning barley generates a higher number of particles in the fine mode
(with a diameter of less than 0.5 μm) than oats (74% vs. 59%). The distributions of particles emitted during the flaming phase
have been characterized, as well as during the previous and subsequent phases. The average geometric diameter reached its
maximum during the flaming phase, with 0.53 ± 0.10 μm and 0.44 ± 0.04 μm for oats and barley, respectively. After the
flaming phase, oat straw generates coarser particles than barley.
Abstract: The present paper describes the procedures used to measure and compute the kinetic energy and various other rainfall characteristics as well as the concurrent splash erosion rates in a recently terraced forest plantation in Soutelo, north-central Portugal, from May to September 2007. This involved the use of an optical disdrometer, a standard automated rain gauge and two types of splash erosion measurement devices (i.e. 10 cups and 10 funnels). In the computation of the kinetic energy, the raindrops exceeding a specific threshold size were considered to not have a spherical shape. Without this correction for the shape of the bigger raindrops, the kinetic energy can be overestimated by 50% of its real value. A meteorological analysis indicated that four weather types with a western component produced more precipitation and kinetic energy, and, thus, a higher erosive power. The relationship between splash erosion and various rainfall characteristics set was analyzed in an exploratory manner, since the splash data only concern nine sampling periods. It showed well-defined relationships of increasing splash erosion with, amongst others, increasing total rainfall as well as total kinetic energy but these relationships require further analysis using additional data. The splash erosion figures obtained with the two types of devices showed a strong agreement but appeared to corroborate that the funnels are a more effective design than the cups. (c) 2009 Elsevier B.V. All rights reserved.
Abstract: This study was carried out in the region of Castile and Leon, Spain, from 1980 to 1998 and analyzes the relationship between the number of monthly deaths caused by cardiovascular, respiratory and digestive diseases and three meteorological variables: temperature, pressure and humidity. One of the innovations in this study is the application of principal component analysis in a way that differs from its usual application: one single series representing the whole region was constructed for each meteorological variable from the series of eight weather stations. Annual and seasonal mortality trends were also studied. Cardiovascular diseases are the leading cause of death in Castile and Leon. The mortality related to cardiovascular, respiratory and digestive systems shows a statistically significant rising trend across the study period (an annual increase of 6, 16 and 4‰, respectively). The pressure at which mortality is lowest is approximately the same for all causes of death (about 915 hPa), but temperature values vary greatly (16.8–19.7°C for the mean, 10.9–18.1°C for the minimum, and 24.1–27.2°C for the maximum temperature). The most comfortable temperatures for patients with cardiovascular diseases (16.8°C) are apparently lower than those for patients with respiratory diseases (18.1°C), which are, in turn, lower than in the case of diseases of the digestive system (19.7°C). Finally, the optimal humidity for patients with respiratory diseases is the lowest (24%) among the diseases, and the highest (51%) corresponds to diseases of the digestive system, while the optimal relative humidity for the cardiovascular system is 45%.
Abstract: The damage caused to property by hail mainly depends on the size of the hailstones. This paper explores the possibility of forecasting the maximum hailstone size registered on a particular day using sounding data. The data employed for the study are those provided by hail events registered over an 11-year period in the hailpad network in the plain of Friuli-Venezia-Giulia, in Italy. As for the description of the atmosphere, the most common weather variables (stability indices, layer thickness, kinetic variables, temperatures, etc.) were obtained from the daily sounding carried out at Udine, a city almost in the middle of the Friulian plain. Only the days with sounding data and with dents on the hailpads were considered for the study: a minimum of 10 dents per plate was established as the lower threshold. The final sample that fulfilled these conditions included 313 days. A detailed study was carried out on the relationship between the weather variables before the hail event and daily data on hail size. The results show that the variable that relates best to hail size is the drop in surface pressure in the 12 h immediately prior to the hail event, as well as the lifted index. Principal component analysis was applied to the weather variables. The first eight principal components were used together with the drop in pressure to establish a linear forecast model. The result improves considerably when the smaller hailstones are not considered, with sizes smaller than 10 or 15 mm. (c) 2009 Elsevier B.V. All rights reserved.
Abstract: This study describes winter precipitation chemistry data (2002-2006) from a remote regional background EMEP station located at Viznar (Granada, Spain). The rainwater samples collected were analyzed for pH, major ion concentrations and conductivity. Wet-only precipitation chemistry was dominated by Ca2+, SO42- and Cl- and the station did not have an acid rain problem (pH lies between 5.8 and 7.4). The samples were classified into nine groups of origin considering the back-trajectory and the chemical composition of the precipitation due to its meteorological origin. Saharan air masses at 1500 m and 3000 m a.g.l. seem to have an important influence on chemical rain composition. Among the marine air masses, the Mediterranean air mass carries the smallest amount of contaminants. Important correlations have been found between acidic anions (SO42- and NO3-) and crustal-derived cations (Mg2+, Ca2+, and K+), suggesting the absorption of acid elements contained in aerosols, such as sulfuric acid and nitric acid, and the subsequent reaction with alkaline components rich in carbonate materials contained in particulate matter. Principal Component Factor Analysis was used in order to provide quantitative insights into the sources of specific chemical components in precipitation. Enrichment factors relative to soil and seawater have also been calculated. Although both Mg2+ and K+ have a crustal origin, a certain marine contribution is also observed. (c) 2010 Elsevier B.V. All rights reserved.
Abstract: Intense fires occurred in northwestern Spain on 6 September 2000, filling a valley with smoke haze. Aerosol size distribution measurements were performed during 1 day with a thermal inversion, so the aging process of the smoke aerosol could be closely monitored. In 3.5 h, the fine aerosol increased up to 0.06 μm in the geometric median diameter of the fine mode. This aging process enhanced the scattering ability of aerosols. On the basis of several hypotheses on the data obtained, shortwave radiative forcing at surface level, at top level, and in the atmosphere was estimated: instantaneous surface forcing reached up to between −80.4 and −67.4 W/m2, top of the atmosphere (TOA) instantaneous forcing reached up to between −23.4 and +4.9 W/m2, and instantaneous atmosphere forcing reached up to between +44.2 and +85.3 W/m2. The study reveals not only the absorption of solar radiation in the atmosphere by smoke aerosols but also an aerosol-induced case study, where TOA cooling forcing shifts to warming for specific aerosol single scattering albedo. The daily mean heating rate of the smoke haze was estimated at 5.9 ± 0.6 K/d.
Abstract: Precipitation and continuous particle number size distributions have been measured using a passive cavity aerosol spectrometer probe PCASP-X, in an urban environment: the city of Leon, Spain. Five rain events have been analyzed in detail, none of which registered very intense precipitation, ranging from 2.5 mm to 14.7 mm, with a maximum rain intensity of 5.6 mm/h. The study focuses on the influence of precipitation in aerosol size distributions before, during and after a rain event. Washout effects have been observed during rain events with intensities of over 3.2 +/- 1.5 mm/h, resulting in a decrease of 20% in the number of particles detected, the decrease affecting large and small particles alike. However, if the rain intensity is about 0.6 mm/h or lower, the result is a considerable increase in the number of aerosols measured up to 89% more - with an increase in the number of particles smaller than 1.3 mu m and a decrease in the number of particles larger than 1.3 mu m. It may be the case that during very weak rain intensity the probe does not discriminate adequately between aerosols and small precipitating droplets or the extremely small droplets that remain in suspension in the atmosphere. In consequence, it will be argued that measurements taken during very weak rain events (with an intensity of less than 0.6 mm/h), such as drizzle or dense fog, should be treated separately or not be considered. The performance of the accumulation and coarse modes has also been studied, as well as the count median diameters (CMDs) before, during and after the rain event. (c) 2010 Elsevier B.V. All rights reserved.
Abstract: dimensionless. Consequently, measurements in dBZ depend on the units used to measure Z. This study, in contrast, suggests an expression of the type 10 log10 (Z/Z0). An adequate selection of the constant Z0 (10-18 m3) will produce a redefinition that will not affect the measurements that have already been carried out and published up to now, since the result in dBZ will remain unchanged. A physical meaning has been searched for Z0 in relation with parameters typical for rain. It could be considered as an indicator of the minimum daily precipitation, but this cannot be extrapolated to all types of precipitation. However, it may be affirmed that for a specific distribution of hydrometeor sizes, Z0 provides a physical reference in terms of the number and volume of raindrops.
Abstract: This paper presents the physical characteristics of the precipitation of the rainiest day in 2006 in Leon, Spain. The aim is to analyze the situation of the atmosphere during a period of 24 h using different techniques (synoptic situation, satellite imagery, sounding balloons, and radar imagery) to determine the causes of this extreme precipitation event. The relationship between the atmospheric conditions and the characteristics of the precipitation (measured with a rain gauge and with a disdrometer) has also been studied. The precipitation was observed to be of the stratiform, type during the whole day, except for two episodes of convective precipitation, which have been analyzed in greater detail. The analysis of the Z-R relation (Z= 139.6R(1.34)) confirms the existence of a mixture of different types of precipitation during the day, and about half of the volume was of convective origin. The radar images were compared with precipitation data registered at surface level. The radar reflectivities have been found to coincide with the ones estimated by the disdrometer. In addition, the drop size distribution of the precipitation registered was studied in the case of the two convective events, and compared with the distribution during the rest of the day. Assuming an exponential distribution, the parameters of the distribution were calculated and it was found that the values were slightly lower in the two convective episodes (lambda = 2.22 and 2.73 mm(-1)), which implies that the drops were larger during these episodes. (C) 2008 Elsevier B.V. All rights reserved.
Abstract: This paper reports on the behaviour of Alnus glutinosa (alder) pollen grains in the atmosphere of Ponferrada (León, NW Spain) from 1995 to 2006. The study, which sought to determine the effects of various weather-related parameters on Alnus pollen counts, was performed using a volumetric method. The main pollination period for this taxon is January-February. Alder pollen is one of the eight major airborne pollen allergens found in the study area. An analysis was made of the correlation between pollen counts and major weather-related parameters over each period. In general, the strongest positive correlation was with temperature, particularly maximum temperature. During each period, peak pollen counts occurred when the maximum temperature fell within the range 9º degrees C-14º degrees C. Finally, multivariate analysis showed that the parameter exerting the greatest influence was temperature, a finding confirmed by Spearman correlation tests. Principal components analysis suggested that periods with high pollen counts were characterised by high maximum temperature, low rainfall and an absolute humidity of around 6 g m(-3). Use of this type of analysis in conjunction with other methods is essential for obtaining an accurate record of pollen-count variations over a given period.
Abstract: This paper is an overview of hailpad research from its origin until today using as a search criterion the bibliographic references on the subject in the Web of Science database (ISI). The search was carried out on 1st September 2008. Among the more than 3.10(7) scientific documents included in the Science Citation Index Expanded (SCI-EXPANDED) from 1945 to the present, the search engine identified 41 containing the word "hailpad*" (the asterisk is a wildcard for any letter or group of letters). The results have been analyzed according to various criteria: countries with hailpad networks or studies on hailpads; date of the first article; evolution of the number of articles per decade; concepts studied and research lines followed in each article; and finally, a bibliometric analysis of the journals where these articles have been published. It was found that 70% of the articles on hailpads were published in 2 journals: Journal of Applied Meteorology and Atmospheric Research. These two journals also concentrate most of the citations. The number of articles on hailpads and the documents that cite them have grown steadily, and it is expected to grow still further in the present decade if we take into account the trends found. (C) 2008 Elsevier B.V. All rights reserved.
Abstract: The parameter lambda of an exponential distribution with a probability density function f(x) = lambda exp (-lambda x) may be calculated in different ways. The analysis carried out in this paper confirms the difference existing between the value of this parameter when it is calculated by means of the moments method using all the data and the value obtained when the data used have previously been classified into groups. This difference must be taken into account if the aim is to compare the parameter in two or more distributions. The present study develops a theoretical calculation of the error introduced when classifying the data into groups, and a correction is put forward. This error depends on the size of the group used and on the value of lambda itself. Finally, the equations obtained have been applied to one particular case study: hailstone size distributions provided by the hailpad network installed in Italy. The data corroborate the validity of the results and the usefulness of the correction suggested for the value of lambda when it is calculated from a classification into hailstone size groups. (C) 2008 Elsevier B.V. All rights reserved.
Abstract: Ambient PM10 and PM2.5 aerosols were monitored in Toulouse from March 2004 to February 2005 (Extensive Observed Period (EOP)) as part of the research project CAPITOUL (Canopy and Aerosol Particles Interaction in TOulouse Urban Layer). Concentrations of 8 major ions (Na+, NH4+, K+, Mg+2, Ca+2, Cl-, NO3, SO42), 15 metal elements (Al, Ba, Cd, Ce, Cr, Cu, Fe, La, Mn, Ni, Pb, Sr, Th, Ti, Zn), and carbonaceous aerosols [TC, POM and EC (total carbon, organic carbon and elemental carbon, respectively)] were measured in a total of 52 samples of each size. Inter-seasonal variations were analyzed. Weekly PM2.5 and PM 10 total mass concentrations (major ions + carbon + metal elements) were 4.4-18.0 mu m(-3) and 6.5-23.5 mu g m(-3), with an annual average concentration of 11.0 +/- 3.6 mu g m(-3) and 13.2 + 4.3 mu g m(-3), respectively. The highest concentration for sulfate was found in summer and fall, whereas the highest NO3- concentration was observed in winter. This study is strengthened by Kruskal-Wallis and Mann-Whitney statistical tests. On average, carbonaceous species constitute between 49% and 75% of the monthly concentration registered, POM concentration always remaining higher (ratio more than 51%) than EC in both size ranges. The average OC/EC ratios were 2.70 +/- 0.81 and 2.70 +/- 0.60 for PM2.5 and PM10, re-spectively. Secondary organic carbon concentrations were significantly higher in the warmer seasons reaching in summer average ratios of 65.9% and 64.5% of the total OC concentration for PM2.5 and PM10, respectively. Secondary organic carbon was produced in the fine fraction of the aerosol. Metal elements analysis and enrichment factor calculations show that traffic emissions were the major influence on the chemical composition of the urban aerosol. A receptor modeling study was conducted using Principal Component Factor Analysis followed by multi-linear regression analysis in order to provide quantitative insights into the sources of specific chemical components in PM10.
Abstract: This paper is a comparative study between the two most common hailpad calibration systems: one annual calibration of a whole consignment of material, and the individual calibration of each plate after a hailfall. Individual calibration attempts to minimize errors due to differences in sensitivity to the impact of hailstones between plates from the same consignment, or due to differences in the inking process before the actual measurement. The comparison was carried out using calibration data from the past few years in the hailpad network in south-western France, and data from an individual calibration process on material provided by the hailpad network in Lleida (Spain). The same type of material was used in the two cases. The results confirm that the error in measuring hailstone sizes is smaller in the case of an individual calibration of hailpads than when one single calibration process was carried out for a whole consignment. The former is approximately 80% of the latter. However, this error could have been higher if it had not been the same person carrying out the single calibration process and the measuring of the dents: it has been found that differences in the inking process may account for up to 20% of the error in the case of small hailstones. Calibration errors affecting other variables, e.g. energy or parameter of the exponential size distribution are generally higher (5% and 18%, respectively) than errors due to the spatial variability of the hailstones. However, the calibration method does not influence the maximum size, since the relative error attributed to the spatial variability is about 8 times the calibration error. In conclusion, if errors in determining energy or parameter are to be reduced to a minimum, it is highly advisable to be consistent in applying the measuring procedure (if possible with the same person carrying out the measurements all the time), and even to use individual calibration on each plate, always bearing in mind that technicians have to be trained appropriately in order to achieve the highest possible degree of uniformity. (c) 2006 Elsevier B.V. All rights reserved.
Abstract: The present paper is an analysis of mean maximum and minimum temperatures carried out on monthly, seasonal and annual time-scales examining the data collected at 171 meteorological stations over a region in the North West of Spain (Castilla y Leon) for the period 1961-1997. Various statistical tools were used to detect and describe significant trends in these data. The magnitude of the trends was derived from the slopes of the regression lines using the least squares method, and the statistical significance was determined by means of the non-parametric Mann-Kendall test. The pattern obtained is quite similar for mean maximum and minimum temperatures with increases in all months of the year, and in the annual series. The seasonal series corresponding to winter and summer also followed this same pattern. Spring and autumn were found to be more irregular. Because maximum temperature increased at a higher rate than minimum temperature in this period, an increase in the annual diurnal temperature range (DTR) was observed. The correlation between the North Atlantic Oscillation (NAO) and the regional maximum and minimum temperatures and DTR series for the period 1961-1997 have also be studied in this paper.
Abstract: Long-range transport of gases and aerosols depends on vertical and horizontal air shifts: studies on atmospheric transport have to be based on the meteorological conditions of the environment. The aim of this paper is to review the physical principles on which meteorological models are based, and to make an exhaustive inventory of the main models used for the prognosis and diagnosis of air masses and a list of the long-range transport models associated to them. URL addresses are provided for all of these models to allow the reader to check their usefulness. A practical application is included with reference to trajectories followed by air masses that reach the Iberian Peninsula at various altitudes, depending on the synoptic meteorological situation. Further examples describe air masses entering Europe with desert dust from Africa. This dust may eventually develop into freezing nuclei and form hailstones in summer storms.
Abstract: This paper reports the results of the analysis of annual mean temperature and precipitation series front 171 rneteorological stations distributed over Castile and Leon [Castilla y Leon in Spanish] in Spain on monthly, seasonal and annual time-scales for a 37-year study period (1961-1997). Various statistical tools were used to detect and characterize significant changes in these series. The magnitude of the trends was derived front the slopes of the regression lines using the least squares, method, and the statistical significance was determined by means of nonparametric tests. Positive trends of about 0.33 degreesC in the annual mean temperature were found for the whole period. Mean temperatures increased in spring and winter. the winter trend being statistically significant. The months of December and March also showed significant trends. Decreases in rainfall were found for three seasons (winter, spring and autumn), with statistically significant trends in March. Summer precipitation showed slight increases over the 37-year period. On this basis, die authors consider that the increase in summer precipitation and the decrease in the range of average temperatures between the wannest and the coldest months of the year (continentality), point towards a trend to a more oceanic climate in Castile and Leon. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: Exponential distributions of the type N = N-0 exp(-lambda t) occur with a high frequency in a wide range of scientific disciplines. This paper argues against a widely spread method for calculating the A parameter in this distribution. When the In function is applied to both members, the equation of a straight line in t is obtained, which may be fit by means of linear regression. However, the paper illustrates that this is equivalent to a least squares fit with a weight function that assigns more importance to the higher values of t. It is argued that the method of maximum likelihood should be applied, because it takes into account all of the data equally. An iterative method for determining A is proposed, based on the method of moments for cases in which only a truncated distribution is available.
