Towards the establishment of a reliable proxy for the reactive surface area of smectite

Reactive surface area is one of the key parameters for studying the kinetics of mineral dissolution. The common practice in experimental kinetics is to normalize the dissolution rate to the surface area measured by the BET method. The relationship between BET surface area and the reactive surface area is not trivial in minerals such as smectites, which possess both internal and external surface areas, and in which the dissolution is controlled by the chemical attack on the edge surface. The present study examines two proxies for the reactive surface area of the Clay Mineral Society reference smectite SAz-1: BET surface area and the edge surface area measured using AFM.Since smectites are very microporous, their BET surface area is strongly influenced by the degassing procedure. It is demonstrated that outgassing the smectite powder at 135°C in a 15 mL min⁻¹ N₂ gas flow for at least 24 hours minimizes contribution from micropores to less than 11% of the BET surface area.Following dissolution experiments in solutions with a low electrolyte concentration, the BET surface area increased from 34 ± 2 m² g⁻¹ in raw SAz-1 to 127 ± 13 m² g⁻¹ in SAz-1 sample recovered from dissolution experiments. This increase in BET surface area is explained by a decrease in the average size of the smectite aggregates, and by an increase in microporosity due to the depletion in the major interlayer cation, i.e., Ca²⁺. As the BET surface area of the raw smectite sample includes considerably less microporosity compared to the BET surface area of the smectite recovered from dissolution experiments, the former is a better approximation of the external surface area of the dried sample powder.AFM measurements show that there is no correlation between the specific external surface area of the sample and its specific edge surface area. This observation is explained by the platy morphology of the smectite particle in which the specific external surface area depends linearly on the height reciprocal, whereas the specific edge surface area is independent of the particles height and depends linearly on the sum of the reciprocals of the length of the axes. Therefore, there is no reason to expect a correlation between the BET and the edge surface area. Our results show that the edge surface area (4.9 ± 0.7 m² g⁻¹) of the smectite particles cannot be predicted based on its external surface area (136 ± 20 m² g⁻¹). Therefore, the BET surface area cannot serve as a proxy for the reactive surface area. We suggest using AFM measurements of the specific edge surface area as an alternative proxy for the reactive surface area of smectite.     

Automatic estimation of olive tree dendrometric parameters based on airborne laser scanning data using alpha-shape and principal component analysis

The aim of this study is to present an automatic approach for olive tree dendrometric parameter estimation from airborne laser scanning (ALS) data. The proposed method is based on a unique combination of the alpha-shape algorithm applied to normalized point cloud and principal component analysis. A key issue of the alpha-shape algorithm is to define the α parameter, as it directly affects the crown delineation results. We propose to adjust this parameter based on a group of representative trees in an orchard for which the classical field measurements were performed. The best value of the α parameter is one whose correlation coefficient of dendrometric parameters between field measurements and estimated values is the highest. We determined crown diameters as principal components of ALS points representing a delineated crown. The method was applied to a test area of an olive orchard in Spain. The tree dendrometric parameters estimated from ALS data were compared with field measurements to assess the quality of the developed approach. We found the method to be equally good or even superior to previously investigated semi-automatic methods. The average error is 19% for tree height, 53% for crown base height, and 13% and 9% for the length of the longer diameter and perpendicular diameter, respectively.     

Atmospheric factors governing winter thunderstorms in the coastal region of the eastern Mediterranean

The factors controlling lightning activity over central Israel and the adjacent Mediterranean Sea were studied. Potential predictors were correlated at 12-h intervals with total number of flashes. Since during the winter season lightning is generated in this region by Cyprus Lows, the data includes 283 observations on days in which this system prevailed for December to February, which covered four winters. The average lightning rate was 26.8 h^-1, with a high standard deviation of 55.2 h^-1. The total number of flashes at night exceeded the daytime number by 35%, in agreement with previous studies. The CAPE values were on the order of hundreds of J kg^-1. A statistical linear multi-regression model was developed for the number of lightning flashes based on 35 atmospheric variables. The correlation between the modeled and the observed number of lightning flashes was 0.67, and 0.81 for the logarithm of the number of lightning flashes (log-lightning). This suggests that the lightning intensity responds exponentially to its governing factors. A linear multi-regression stepwise model for the log-lightning selected seven predictors as significant and yielded a correlation of 0.74. This model was validated by three holdout and three leave-one-out validation experiments. The composition and hierarchy of the significant predictors reflect the dominance of the thermodynamic factors, in particular instability, in determining lightning activity. Though thunderstorms are local or meso-scale phenomena, the synoptic-scale atmospheric variables were found to be powerful predictors for their intensity.     

Winter synoptic-scale variability over the Mediterranean Basin under future climate conditions as simulated by the ECHAM5

Changes of the winter climate in the Mediterranean Basin (MB) for future A2 conditions are investigated for the period 2071–2100 and compared with the control period 1961–1990. The analysis is based on time-slice simulations of the latest version of the ECHAM model. First, the control simulation is evaluated with reanalysis data. The emphasis is given to synoptic and large-scale features and their variability in the MB. The model is found to be capable of reproducing the main features of the MB and southern Europe in the winter season. Second, the A2 simulation is compared with the control simulation, revealing considerable changes of the synoptic variability. Focusing on the synoptic spatio-temporal scale aims to unfold the dynamic background of the climatic changes. The Mediterranean cyclones, which are individually detected and tracked, decrease by 10% in the Western Mediterranean (WM) whereas no significant change is found in the Eastern Mediterranean. The cyclone intensity is slightly reduced in the entire region. To understand these changes, the underlying dynamical background is analyzed. It is found that changes in baroclinicity, static stability, transformation from eddy kinetic energy to kinetic energy of the mean flow and stationary wave activity are significant in particular in the WM and the coastline of North Africa. The reduction of cyclonic activity severely impacts the precipitation mainly in the southern part of the WM.     

Rainfall uncertainty in the Mediterranean: Intraseasonal rainfall distribution

The rainfall distribution within the rainy season has crucial implications on a variety of disciplines. According to one approach of analyzing the intraseasonal rainfall distribution, it is essential to examine the date of different accumulated percentage (DAP hereafter), as presented in Paz and Kutiel (Isr J Earth Sci 52:47–63, 2003). The present study identifies various intraseasonal temporal distributions of rainfall, in 41 stations within the Mediterranean basin. Furthermore, classifications of these distributions according to their time, yield, and length are presented. The accumulated percentage was calculated for each Julian day for every available year in all stations. A correlation matrix between every possible pair of years, in each station, was calculated, and a cluster analysis (average linkage method) was performed. Finally, the averages of the entire dataset and the average of every cluster were compared in order to classify the clusters by using three parameters: timing represented by DAP_{(25%, 50%, 75%)} annual rainfall total and the rainy season length (RSL). Between 2 and 5 different types of clusters, with various probabilities, were defined for every station. Out of 132 overall clusters, which were found in 41 stations, the most frequent type (cluster 1) was the median in all three parameters. There were 16 clusters identified as short in their RSL, and 18 were identified as having a long classification. There were 19 dry clusters, and only eight were identified as wet. As for the parameter of timing, 39 clusters were classified as early and 38 as late. One conclusion of this study was that the probability of a dry year is higher than a wet one, and likewise, the probability of a long year is higher than of a short one.     

Easterly Wind Storms over Israel

Summary Continental wind storms are common along the Mediterranean coast. Along the northern coast they are mostly cold, similar to the Bora or the Mistral, and along the southern coast they are mostly warm, e.g., the Ghibli or the Shirocco. At the eastern Mediterranean basin and the Levant region, these storms are intermittently warm and cold during the same season and often even during the same event. Quasi-stationary systems, as well as moving disturbances, are the cause of such wind storms. Accordingly, the resulting weather conditions may be extremely converse due to the characteristics of the advected airmass. Specific regions in Israel, sensitive to easterly storms, are influenced by these wind storms for about 10% of the year (e.g., the westerly slopes of the mountains and valleys with west-east orientation). The frequency, however, of widespread storms covering the entire region is only approximately 1.4% of the entire year. These wind storms are therefore classified in the present study according to their climatological and synoptic characteristics; indicating that the dominant synoptic situation is the Red-Sea trough and the warm advections. These storms appear only from October-May and are most frequent during the cold season. The diurnal course is characterized by a strengthening in the morning hours and a weakening at noon and in the afternoon hours, due to the opposing effect of the westerly sea breeze, suppressing the easterly winds and the effect of katabatic winds. Nevertheless, synoptic conditions may contribute to this tendency as well. Accordingly, a significant increase in the frequencies of easterly storms, in relation to distance from the seashore has been identified. Although most of the stormy days are with westerly winds, the easterly wind storms has vast environmental implications, creating damage especially to agriculture and occasionally also to property and life; coastal flooding, potential air pollution, intensifying of forest fires and occasionally dust and sand storms. Received September 9, 1996 Revised March 6, 1997     

Fire Weather in Israel — Synoptic Climatological Analysis

The study examines the synoptic situations and weather conditions under which occurred Israel's largest forest fires between the years 1987–1995. Annual rainfall and maximum temperature were found to have a positive correlation with both the size of the burnt area and the frequency of fires. A negative correlation was found for the relative humidity at 12 UTC for the same parameters. The fire season in Israel starts in May and ends in November, the peak months being May, June and July. No large fires were observed during the rainy season, December–February, despite the relatively low precipitation characterizing the region. Atmospheric disturbances as well as quasi-stationary systems were found to be favorable for the development of forest fires in Israel: the North African (‘Sharav’) cyclone and the Red Sea trough, which are common during spring and autumn. These systems carry hot, dry air from the deserts and are responsible for 55% of the burnt area from major forest fires in Israel and up to 33% of the major forest fires. Sixty-five percent of the forest fires occurred during the summer all of them under the quasi-stationary system of the Persian Gulf trough. These fires did not spread as widely as those that occurred under the North African cyclone and the Red Sea trough systems. The role of weather in the propagation of fire is exemplified in the case study of the ‘Sha'ar ha Gai’ fire of July 1995 — the biggest forest fire in the history of Israel (1300 ha). This revised version was published online in July 2006 with corrections to the Cover Date.     

The contribution of moisture to heat stress in a period of global warming: the case of the Mediterranean

This study deals with potential changes in the relative humidity associated with global warming and their implications on heat stress along the coastal region of the Mediterranean in the summer season. It is based on the assumption that the regional warming will enhance the lower-level stability due to the thermal inertia of the sea with respect to its overlying air. The enhanced stability implies more effective trapping of the near surface moisture, and as a result—further increase of the relative humidity. The marine boundary layer over the Mediterranean is modeled. The central feature of the model is the marine inversion capping the marine moist air, which intensity is positively correlated with the stability. Simple calculations indicate that if the temperature increases, while the stability remains unchanged, the near-surface relative humidity would not be affected. But, an increase in the stability would result in an increase in the near-surface relative humidity. This prediction is validated through observed trends of the respective fields, using the NCEP/NCAR reanalysis data and soundings from the eastern Mediterranean. The results are consistent in indicating an increase in the near-surface temperature, the lower-level stability and the relative humidity over the eastern part of the Mediterranean, but not in its western part. The results for the eastern Mediterranean support the expectation for an aggravation of heat stress beyond that imparted by the temperature rise.