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"Alpert, Pinhas"
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Factor Separation in the Atmosphere : Applications and Future Prospects
\"Modeling atmospheric processes in order to forecast the weather or future climate change is an extremely complex and computationally intensive undertaking. One of the main difficulties is that there are a huge number of factors that need to be taken into account, some of which are still poorly understood. The Factor Separation (FS) method is a computational procedure that helps deal with these nonlinear factors. In recent years many scientists have applied FS methodology to a range of modeling problems, including paleoclimatology, limnology, regional climate change, rainfall analysis, cloud modeling, pollution, crop growth, and other forecasting applications. This book is the first to describe the fundamentals of the method, and to bring together its many applications in the atmospheric sciences. The main audience is researchers and graduate students using the FS method, but it is also of interest to advanced students, researchers, and professionals across the atmospheric sciences\"-- Provided by publisher.
Book
Multi-factor analysis of DTR variability over Israel in the sea/desert border
The contributions of twelve independent factors/variables to the magnitude of the local diurnal temperature range (DTR) in Israel were examined, and five to seven were found to contribute significantly. Israel was chosen due to its complex terrain with several climatic zones and proximity to the Mediterranean Sea. The seven sites for this study represent different terrains, from mountainous with a Mediterranean climate to desert. Each site had 6 years of data available. Stepwise analysis was performed in order to determine the contribution of each factor/variable at each site. The linear correlations between the DTR and each factor were calculated. These were carried out at each site for the whole year and for each season, separately. Relative humidity was found to have the largest DTR contribution at all sites, for 3 seasons, except summer at shoreline sites and in Jerusalem. The daily cloud cover and the wind speed had small contributions in most sites. The magnitude of the DTR was found to vary largely with location and to be considerably smaller in the seashore sites than those inland.
Journal Article
High-Resolution Humidity Observations Based on Commercial Microwave Links (CML) Data—Case of Tel Aviv Metropolitan Area
The humidity in the atmosphere plays a crucial role in a wide range of atmospheric processes determined by the water-vapor concentration in the air. The accuracy of weather forecasts is largely dictated by the humidity field measured at low atmospheric levels. At the near-surface level, the absolute humidity variations can be large due to the variability of land cover (LC). Cities are one of the primary LCs which have a substantial impact on the humidity field. Large urban areas are expanding, causing a significant change in the near-surface humidity field. Current measurement tools, however, do not satisfactorily assess the cities’ effects on the humidity field. This paper presents an innovative method for high-resolution humidity measurements based on the cellular network. Here, the humidity field around Tel Aviv was retrieved from the cellular network during the summer of 2017. The results show a well-noticed impact of the city and other LC types on the humidity field over the Tel Aviv metropolitan area. The method presented here can offer an improved description of the humidity field at the city-canopy level and therefore provide a better assessment of the urban/LC effects on the environment, atmospheric modeling, and particularly on clouds/rain development.
Journal Article
Absence of Surface Water Temperature Trends in Lake Kinneret despite Present Atmospheric Warming: Comparisons with Dead Sea Trends
This study was carried out using Moderate Resolution Imaging Spectroradiometer (MODIS) 1 km × 1 km resolution records on board Terra and Aqua satellites and in-situ measurements during the period (2003–2019). In spite of the presence of increasing atmospheric warming, in summer when evaporation is maximal, in fresh-water Lake Kinneret, satellite data revealed the absence of surface water temperature (SWT) trends. The absence of SWT trends in the presence of increasing atmospheric warming is an indication of the influence of increasing evaporation on SWT trends. The increasing water cooling, due to the above-mentioned increasing evaporation, compensated for increasing heating of surface water by regional atmospheric warming, resulting in the absence of SWT trends. In contrast to fresh-water Lake Kinneret, in the hypersaline Dead Sea, located ~100 km apart, MODIS records showed an increasing trend of 0.8 °C decade−1 in summer SWT during the same study period. The presence of increasing SWT trends in the presence of increasing atmospheric warming is an indication of the absence of steadily increasing evaporation in the Dead Sea. This is supported by a constant drop in Dead Sea water level at the rate of ~1 m/year from year to year during the last 25-year period (1995–2020). In summer, in contrast to satellite measurements, in-situ measurements of near-surface water temperature in Lake Kinneret showed an increasing trend of 0.7 °C decade−1.
Journal Article
The dynamics of cyclones in the twentyfirst century: the Eastern Mediterranean as an example
The Mediterranean region is projected to be significantly affected by climate change through warming and drying. The Eastern Mediterranean (EM) is particularly vulnerable since the bulk of the precipitation in the region is associated with a specific circulation pattern, known as Cyprus Low (CL). Here, we study the influence of increased greenhouse gases on the average properties and dynamics of CLs, using a regional semi-objective synoptic classification. The classification is applied to NCEP/NCAR reanalysis data for the present day (1986–2005) as well as to eight CMIP5 models for the present day and for the end of the century (2081–2100; RCP8.5). This is complemented by a dynamical systems analysis, which is used to investigate changes in the dynamics and intrinsic predictability of the CLs. Finally, a statistical downscaling algorithm, based on past analogues, is applied to eighteen rain stations over Israel, and is used to project precipitation changes associated with CLs. Significant changes in CL properties are found under climate change. The models project an increase in CL meridional pressure gradient (0.5–1.5 hPa/1000 km), which results primarily from a strong increase in the pressure over the southern part of the study region. Our results further point to a decrease in CL frequency (− 35%, as already noted in an earlier study) and persistence (− 8%). Furthermore, the daily precipitation associated with CL occurrences over Israel for 2081–2100 is projected to significantly reduce (− 26%). The projected drying over the EM can be partitioned between a decrease in CL frequency (~ 137 mm year−1) and a reduction in CL-driven daily precipitation (~ 67 mm year−1). The models further indicate that CLs will be less predictable in the future.
Journal Article
Challenges in Diurnal Humidity Analysis from Cellular Microwave Links (CML) over Germany
Near-surface humidity is a crucial variable in many atmospheric processes, mostly related to the development of clouds and rain. The humidity at the height of a few tens of meters above ground level is highly influenced by surface characteristics. Measuring the near-surface humidity at high resolution, where most of the humidity’s sinks and sources are found, is a challenging task using classical tools. A novel approach for measuring the humidity is based on commercial microwave links (CML), which provide a large part of the cellular networks backhaul. This study focuses on employing humidity measurements with high spatio–temporal resolution in Germany. One major goal is to assess the errors and the environmental influence by comparing the CML-derived humidity to in-situ humidity measurements at weather stations and reanalysis (COSMO-Rea6) products. The method of retrieving humidity from the CML has been improved as compared to previous studies due to the use of new data at high temporal resolution. The results show a similar correlation on average and generally good agreement between both the CML retrievals and the reanalysis, and 32 weather stations near Siegen, West Germany (CML—0.84, Rea6—0.85). Higher correlations are observed for CML-derived humidity during the daytime (0.85), especially between 9–17 LT (0.87) and a maximum at 12 LT (0.90). During the night, the correlations are lower on average (0.81), with a minimum at 3 LT (0.74). These results are discussed with attention to the diurnal boundary layer (BL) height variation which has a strong effect on the BL humidity temporal profile. Further metrics including root mean square errors, mean values and standard deviations, were also calculated.
Journal Article
Dust Dry Deposition over Israel
Similar quasiperiodic year-to-year variations of dust dry deposition (DDD) with a two–three-year period were found over Israel and north-east Africa. This phenomenon of quasiperiodic interannual variations of DDD has not been discussed in previous publications. Moreover, similar seasonal variations of DDD were found over both Israel and north-east Africa, characterized by significant dust deposition in spring and a decrease in DDD from spring to autumn. These findings indicate the existence of the same causal factors for interannual and seasonal variations of DDD over the two regions, such as similar surface winds created by Mediterranean cyclones. Daily runs of the Dust REgional Atmospheric Model (DREAM) at Tel Aviv University from 2006 to 2019 were used to investigate the main features of the spatio-temporal distribution of dust dry deposition in the eastern Mediterranean, with a focus on Israel. DREAM showed that, on average, during the 14-year study period, in the winter, spring, and summer months, the spatial distribution of monthly-accumulated DDD over Israel was non-uniform with the maximum of DDD over southern Israel. In the autumn months, DREAM showed an increase in DDD over northern Israel, resulting in an almost uniform DDD pattern. The knowledge of DDD spatio-temporal distribution is helpful for understanding the negative effects of DDD on the performance of solar panels and on insulator flashover in the Israel power electric network.
Journal Article
Mediterranean water cycle changes: transition to drier 21st century conditions in observations and CMIP3 simulations
We use CMIP3 multi-model simulations to show how individual hydroclimatic changes will concur to determine even greater alterations of 21st century Mediterranean water cycle characteristics, with contrasting behavior over land and sea. By 2070–2099, the average of the models predicts a 20% decrease in land surface water availability and a 24% increase in the loss of fresh water over the Mediterranean Sea due to precipitation reduction and warming-enhanced evaporation, with a remarkably high consensus among analyzed models. The projected decrease in river runoff from the surrounding land will further exacerbate the increase in Mediterranean Sea fresh water deficit. 20th century simulations indicate that the ‘transition’ toward drier conditions has already started to occur and has accelerated around the turn of the century towards the larger rates projected for the 21st century. These tendencies are supported by observational evidence of century-long negative trends in regionally averaged precipitation, PDSI and discharge from numerous rivers; and are consistent with reported increases in Mediterranean sea water salinity.
Journal Article
Dew is a major factor affecting vegetation water use efficiency rather than a source of water in the eastern Mediterranean area
The purpose here is to reexamine the ecological importance of dew in arid and semiarid regions with a focus on the eastern Mediterranean area. This reevaluation is of particular importance under the controversial perspective that dew is insufficient as a source of water for plants but is sufficient to promote the spread of plant diseases. Adana, Turkey, was selected as an appropriate semiarid test ground with well‐documented meteorological data and a newly developed photosynthesis and transpiration rate monitor (PTM), which was used to detect the response of transpiration and photosynthesis to the presence of dew on the leaves. A convolution theoretical model was used to simulate no‐dew days; simultaneously, PTM measurements were used to obtain actual situations with dew. Contrary to expectations, we detected separate, early peaks of photosynthesis and late peaks of transpiration, leading to an average ratio of about 2:1 units of water use efficiency (WUE) for dew‐affected versus no‐dew conditions. The impressive performance of the dew‐affected WUE was explained by a synergy between (1) low transpiration during dew‐affected morning hours and (2) high CO2 gradient toward the canopy. The first resulted from dew formation that created a humid environment in the near vicinity of the leaf followed by a low leaf to air vapor pressure deficit, which minimized transpiration. The second resulted from night respiration that induced a high CO2 gradient from the air toward the canopy. This synergy resulted in intensive carbon intake at a low water cost and explained the ecological importance of dew.
Journal Article
Spatial Non-Uniformity of Surface Temperature of the Dead Sea and Adjacent Land Areas
Pronounced spatial non-uniformity has been obtained of daytime sea surface temperature (SST) of the Dead Sea and of land surface temperature (LST) over areas adjacent to the Dead Sea. This non-uniformity was observed in the summer months, under uniform solar radiation. Our findings are based on Moderate Resolution Imaging Spectroradiometer (MODIS) data (2002–2016) on board the Terra and Aqua satellites. MODIS data showed that, on average for the 15-year study period, daytime SST over the eastern part of the lake (Te) exceeded by 5 °C that over the western part (Tw). This SST non-uniformity (observed in the absence of surface heat flow from land to sea at the eastern side) was accompanied by spatial non-uniform distribution of land surface temperature (LST) over areas adjacent to the Dead Sea. Specifically, LST over areas adjacent to the eastern side exceeded by 10 °C that over areas adjacent to the western side. Our findings of spatial non-uniformity of SST/LST based on MODIS data were supported by Meteosat Second Generation LST records. Regional atmospheric warming led to a decrease in spatial non-uniformity of SST during the study period. Temperature difference between Te and Tw steadily decreased at the rate of 0.32 °C decade−1, based on MODIS/Terra data, and 0.54 °C decade−1, based on MODIS/Aqua data. Our simulations of monthly skin temperature distribution over the Dead Sea by the Weather Forecast and Research (WRF) model contradict satellite observations. The application to modeling of the observed SST/LST spatial non-uniformity will advance our knowledge of atmospheric dynamics over hypersaline lakes.
Journal Article