Amaya Castro

Analysis of hailstone size distributions from a hailpad network

Abstract In the province of Leon, a network of 250 hailpads has been installed in an area of 1000 km 2 . After the individual calibration of every plate, the dents are measured by a manual method which stores data in files that can be analyzed by computer. Once the hailstones are classified according to their size, difficulties may arise when fitting linearly this distribution to a function of the type log N = log N 0 - β x , where N is the number of hailstones in the size class x . A discussion is presented on the universal validity of parameters N 0 and β, on the problem of empty classes (to which it is impossible to apply logarithms), and on the discrimination of the smallest hail classes when making such a fitting. In conclusion, statistical methods are proposed for fitting the exponential or gamma distribution. The latter of these distributions assumes the former as a particular case and offers a better fit to the experimental data.

Radiative forcing of haze during a forest fire in Spain

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.

CAPE values and hailstorms on northwestern Spain

A study has been carried out in Leon (in the northwest of the Iberian Peninsula) on atmospheric convection during summer periods, by analyzing the values of the Convective Available Potential Energy (CAPE) around 07:00 UTC. The project analyzed the data provided by a network of voluntary observers, a hailpad network, and a meteorological station on a sample of 224 days. The CAPE values found were not high: they never reached 2000 J/kg, not even on hail days, i.e. on days with high convective activity. These values are much lower than the ones measured in convective situations in tropical regions, but they are within the usual values found in Europe. The same happens with the wet bulb potential temperature measured in Leon. The frequency distribution of the CAPE values shows a clear prevalence of very low or zero values. The group of days with the lowest CAPE value is that which included days with no storm. The mean value increases on storm days, and it is even higher for the days with recorded hailfalls. All these differences are significantly marked. Nevertheless, the differences across the years are not significant enough to be able to speak of an influence of the climatic change on the CAPE. The correlation of the CAPE with some of the variables previously used for hail forecasts was analyzed, and the correlation found was higher for the lifted index. The possible use of the CAPE as a thunderstorm and hailstorm forecasting method was considered. The results were encouraging, especially for hail forecasting, although the CAPE should not be used as the only variable, but combined with other parameters. Moreover, the relationships between the CAPE and the wet bulb potential temperature and between the CAPE and the physical parameters of the hailstones were also analyzed. A relationship was observed with the parameters of the hailstone size distribution. Nonetheless, these results are provisional, and they should be confirmed by analyzing a more representative sample. With a more detailed analysis of these and other relationships, the present forecast model used by the Laboratory for Atmospheric Physics at the University of Leon is expected to be greatly improved by including the CAPE in this model.

Noteworthy C-band radar parameters of storms on hail days in northwestern Spain

Abstract The data provided by a meteorological C-band radar have been employed in order to analyze the behavior of 224 storms that occurred on hail days in the provinces of Leon and Zamora, in the northwest of Spain. A network of more than 700 voluntary observers supplied the necessary information to distinguish hailstorms from storms that did not produce hail precipitation. The observers also reported the size of the hailstones found. Among the variables studied are the maximum reflectivity factors, the vertical developments, and the motion speed of the storm for hailstorms as well as for storms with no hail. The altitude at which the precipitation processes take place inside the storm cell and its average lifetime are the variables that determine the subsequent evolution of hailstorms and no-hail storms in the same day. Furthermore, these variables have been analyzed taking into account the type of storm: unicellular, multicellular or supercellular. Finally, a correlation between the characteristics of the storms and the size of the hailstones registered simultaneously on the ground has been searched for using the RHI detected on the radar exactly at the time of the precipitation.

The influence of melting on hailstone size distribution

AbstractThe physical properties of hailstones registered by a hailpad network (size distribution, mass,kinetic energy) are essential data for the establishment of a regional hail climatology. Nevertheless,when comparing these data to the same properties of hailstones inside the cloud, the melting processmust be taken into account. This paper presents a brief theoretical study of the changes effected onhailstone size distribution due to the melting process. The paper is based on previous studies dealingwith the melting of hailstones before they reach the ground. The aim is to analyze the influence ofthis melting process on hailstone size distribution. An initial melting simulation was carried out inorder to achieve this aim. Despite the common assumption that hailstone size distribution on theground is exponential, it was found that when the in-cloud size distribution is exponential, on theground, there are fewer small hailstones than what would be expected in an exponential distribution.The data registered by the hailpad network in Leo´n (Spain) for 1 year were used to estimate thesize of every hailstone before the melting process. The results show that the hailstone sizedistribution simulated inside the cloud resembles more closely an exponential distribution than thehailstones on the ground.The type of hailstone size distribution inside the cloud will be the starting point for calculating thehailstone size distribution on the ground. Several equations describing the melting processes are usedtocalculate anew probability densityfunction thatinitiallycorresponds to anexponential distributionthat undergoes a partial melting process. The result is a function that is not monotonously decreasinglike the exponential function, but rather a function that has a peak for a given size. This new functionfits better the data found than the exponential function and actually resembles the gamma function.D 2003 Elsevier B.V. All rights reserved.

Indoor aerosol size distributions in a gymnasium

In this study, an indoor/outdoor monitoring program was carried out in a gymnasium at the University of Leon, Spain. The main goal was a characterization of aerosol size distributions in a university gymnasium under different conditions and sports activities (with and without magnesia alba) and the study of the mass fraction deposited in each of the parts of the respiratory tract. The aerosol particles were measured in 31 discrete channels (size ranges) using a laser spectrometer probe. Aerosol size distributions were studied under different conditions: i) before sports activities, ii) activities without using magnesia alba, iii) activities using magnesia alba, iv) cleaning procedures, and v) outdoors. The aerosol refractive index and density indoors were estimated from the aerosol composition: 1.577-0.003i and 2.055 g cm(-3), respectively. Using the estimated density, the mass concentration was calculated, and the evolution of PM1, PM2.5 and PM10 for different activities was assessed. The quality of the air in the gymnasium was strongly influenced by the use of magnesia alba (MgCO3) and the number of gymnasts who were training. Due to the climbing chalk and the constant process of resuspension, average PM10 concentrations of over 440 μg m(-3) were reached. The maximum daily concentrations ranged from 500 to 900 μg m(-3). Particle size determines the place in the respiratory tract where the deposition occurs. For this reason, the inhalable, thoracic, tracheobronchial and respirable fractions were assessed for healthy adults and high risk people, according to international standards. The estimations show that, for healthy adults, up to 300 μg m(-3) can be retained by the trachea and bronchi, and 130 μg m(-3) may reach the alveolar region. The different physical activities and the attendance rates in the sports facility have a significant influence on the concentration and size distributions observed.

Concentration of ice nuclei in continental and maritime air masses in León (Spain)

Among the objectives of the Plan de Actuacion de Lucha Antigranizo, (PALA, Hail Suppression Activity Plan), is the on-going analysis of the mechanisms operating during the formation of storms. There is a relationship between the processes at work in the interior of cloud masses and the concentration of natural ice nuclei (IN) at ground level. Through the rigorous analysis of 954 measurements made with an isothermal cloud chamber, it has been possible to establish that a dependence exists between the background concentration of IN and the type of air mass. The work shows that the concentration of IN in the samples analyzed in Leon was, on average, higher for continental than for maritime air masses, with a substantial presence of continental air masses originating from the Sahara desert. Furthermore, from the analysis of 4-day back trajectories, it has been observed that slow-moving maritime air masses gradually become altered during their passage over the peninsula, which causes an increase in the number of active IN.

A logistic regression model applied to short term forecast of hail risk

Abstract In areas where high-quality agricultural products are grown that are also highly susceptible to hailfall damage, short-term forecasting is a prerequisite, in order to evaluate the risk of hail falling. In cases such as this, where a relationship exists between a response variable and one or more explanatory variables, and the outcome variable is also binary (risk/no risk) the multiple Logistic Regression Model is a good tool to use. A collection of 15 independent meteorological variables was obtained from a sample of 229 days. The determination of risk/no risk situations was based on the meteorological information supplied by a dense network of over 500 observation points, distributed across an area of more than 6,500 km2.

Statistical comparison of the properties of thunderstorms in different areas around the Ebro-Valley (Spain)

Abstract It has been attempted to determine whether the orography of the area where storm formation takes place has an effect on the behaviour of storms. This may enable us to improve whatever seeding action is planned. The results, obtained from an area located in the northeast of the Iberian Peninsula, namely, the Middle Ebro Valley, show different storm behaviour. The following parameters are taken into account: area of formation, distance covered, trajectory velocity, maximum reflectivity and the height of the point of maximum reflectivity. It has also been observed how storms with different internal structure, unicellular or multicellular, are affected by orography. These present the greatest changes in distance covered and velocity. Moreover, we have observed that the majority of the supercellular storms occur in the geographical area of the Cordillera Iberica.

Nitrogen oxides and ozone in Portugal: trends and ozone estimation in an urban and a rural site.

This study provides an analysis of the spatial distribution and trends of NO, NO2 and O3 concentrations in Portugal between 1995 and 2010. Furthermore, an estimation model for daily ozone concentrations was developed for an urban and a rural site. NO concentration showed a significant decreasing trend in most urban stations. A decreasing trend in NO2 is only observed in the stations with less influence from emissions of primary NO2. Several stations showed a significant upward trend in O3 as a result of the decrease in the NO/NO2 ratio. In the northern rural region, ozone showed a strong correlation with wind direction, highlighting the importance of long-range transport. In the urban site, most of the variance is explained by the NO2/NOX ratio. The results obtained by the ozone estimation model in the urban site fit 2013 observed data. In the rural site, the estimated ozone during extreme events agrees with observed concentration.