On fourier-analysis of geomagnetic pulsations pc-1, “two-fold” and “three-fold” pulsations pc-1 and fundamental frequencies of the magnetospheric cavity—I

The paper gives the results of detailed studies of the frequency spectra $\text{S}{}_{\mathrm{s}}\text{(?)}$ of the chain of the wave packets F_s(t) of geomagnetic pulsations PC-1 recorded at the Novolazarevskaya station. The bulk of the energy of F_s(t) is concentrated in the vicinity of the central frequencies $\text{?}{}_{\mathrm{s0}}$ of spectra—the carrier frequencies of the signals. The velocity $\text{V}{}_0\text{≌ 6.10}{}^3\text{km s}{}^{\mathrm{?1}}$ of the flux of protons generating these signals correspond to them. The spectra of the signals have oscillations—“satellites” irregularly distributed in frequency. These satellites, as the authors believe, testify to the presence of the individual groups of protons of low concentration whose velocities vary within 10³–10⁴ km s^?1.Their energy is only of the order of 10^?2–10^?3 of the energy of the main proton flux. Clearly pronounced maxima on double and triple frequencies $\text{? = 2?}{}_{\mathrm{s0}}\text{and}\text{3?}{}_{\mathrm{s0}}$ are detected. They show that the generation of pulsations PC-1 is accompanied by the generation on the overtones of wave packets called in this paper “two-fold” and “three-fold” pulsations PC-1. Intensive symmetrical satellites of a modulation character have been discovered on frequencies $\text{?}{}^{\mathrm{\pm }}{}_{\mathrm{sK}}$. Frequency differences $\text{Δ?}{}_{\mathrm{sK}}{}^{\mathrm{\pm }}\text{=}\text{¦?}{}_{\mathrm{s0}}\text{? ?}{}_{\mathrm{sK}}{}^{\mathrm{\pm }}\text{¦}\text{= (0.011,0.022}\text{and}\text{0.035)}\text{Hz}$ correspond to them. The authors believe that the values of Δ?^±_sK are resonance frequencies of the magnetospheric cavity in which geomagnetic pulsations PC-1 are generated. It is established that the values of Δ?^±_sK coincide closely with the carrier frequencies of geomagnetic pulsations PC-3 and PC-4 generated in the magnetosphere. This leads to the conclusion that the resonance oscillations of the magnetospheric cavity are their source. Thus, the generation of geomagnetic pulsations of different types and resonance oscillations in the magnetosphere are integrated into a unified process. The importance of the results obtained and the necessity to check further their trustworthiness and universality, using experimental data gathered in different conditions, is stressed.     

A double-resolution transient RCM climate change simulation experiment for near-coastal eastern zone of the Eastern Mediterranean region

A double-resolution regional experiment on hydrodynamic simulation of climate over the eastern Mediterranean (EM) region was performed using an International Center for Theoretical Physics, Trieste RegCM3 model. The RegCM3 was driven from the lateral boundaries by the data from the ECHAM5/MPI-OM global climate simulation performed at the MPI-M, Hamburg and based on the A1B IPCC scenario of greenhouse gases emission. Two simulation runs for the time period 1960-2060, employing spatial resolutions of 50?km/14?L and 25?km/18?L, are realized. Time variations of the differences in the space distributions of simulated climate parameters are analyzed to evaluate the role of smaller scale effects. Both least-square linear and non-linear trends of several characteristics of the EM climate are evaluated in the study. One of the key findings with regard to linear trends is a notable and statistically significant precipitation drop over the near coastal EM zone during December-February and September-November. Statistically significant positive air temperature trends are projected over the entire EM region during the four seasons. Also projected are increases in air temperature extremes and the relative contribution of convective processes in the Southern Mediterranean coastal zone (ECM) region. A notable sensitivity of projected larger-scale climate change signals to smaller-scale effects is also demonstrated.     

Decadal trends of main Eurasian oscillations and the Eastern Mediterranean precipitation

Summary ?The role of the two main European low-frequency oscillations – the East Atlantic/West Russian (EA/WR) and the North Atlantic Oscillation (NAO), in controlling the precipitation in the Eastern Mediterranean region is investigated based on the NCEP/NCAR reanalysis and the Israeli precipitation data for 1958–1998. The data on the EA/WR and NAO indices, received from the NCEP Climate Prediction Center, are also adapted. Composite mean sea level and precipitation anomaly patterns are constructed and analyzed. In addition to the widely investigated positive NAO trend, another, also positive EA/WR trend characterized atmospheric developments during the period. During NAO positive months, the EA/WR-associated positive SLP anomaly areas were shifted from the east Atlantic to southwest Europe. The areas were shifted to the north during the NAO-negative months and were located over central and northern Europe. This demonstrates that the use of fixed pressure NAO patterns may be not the optimum way to understand climate variability. Analysis of the NAO, EA/WR patterns, as well as that of their decadal trends, demonstrated a relationship between the main European oscillations and the EM precipitation. The results allow explanation of the observed reduction of the north Israeli precipitation by the EA/WR positive trend during the period. Received April 5, 2001; Revised February 14, 2002     

Interaction of topography and tropospheric flow — A possible generator for the Red Sea Trough?

Summary Numerical investigation of the nature of one of the most typical Eastern Mediterranean atmospheric circulation phenomena — the Red Sea Trough is undertaken. The role of interaction of typical atmospheric flow systems with the local topography of the North African region is analyzed with the help of idealized numerical simulations employing the Penn State and the National Center for Atmospheric Research (NCAR) MM4 modeling system. The simulations are designed, based on results of a climatological evaluation of the 250 hPa wind field. Idealized initial data sets corresponding to typical transient and winter period positions of the upper tropospheric westerly jet stream are constructed. The data for the analysis are from the National Center for Environmental Prediction (NCEP) 25 y (1965–1989) objective analysis archive. It was found that the primary factor in the Red Sea trough generation is the interaction of the mid-tropospheric westerlies with the terrain in the area of the Red Sea.With 5 Figures     

Some assessments of the potential 2 × CO2 climatic effects on water balance components in the eastern mediterranean

General circulation model (GCM) coarse evaluations of the climatological impact in the Eastern Mediterranean due to global doubling of the atmospheric CO₂ concentration were used as input for apreliminary estimation of modifications in local processes affecting the water balance in this region. It is suggested that: (i) in the 2 × CO₂ climate theaverage regional change of precipitation associated with typical mid-winter cyclonic systems is relatively small, however, it is associated with redistribution of the regional rainfall; (ii) in the elevated terrain in the northern part of the region, daytime snowmelt due to warm air advection may be enhanced, as much as 2.8 cm per day; and (iii) transpiration in the coastal area of the Eastern Mediterranean may increase by ~ 13% of its current level in the summer and somewhat more in the winter.     

An evaluation of the role of hurricane Olga (2001) in an extreme rainy event in Israel using dynamic tropopause maps

Summary During the period from end of November to early December 2001, a sequence of extremely intense synoptic developments occurred over the area from the Atlantic to Mediterranean. These included the formation of hurricane Olga, an intensification of the Icelandic Low, strengthening of the subtropical westerly jet stream (STJ) over North Africa, formation of the Red Sea Trough (RST) and Cyprus Low cyclones, which resulted in torrential rains in Israel on December 4–5. The evolution of the synoptic processes over a large area from the Atlantic to Western Europe and the Mediterranean region during November 25–December 2 is investigated here with the help of dynamic tropopause patterns calculated based on reanalysis data. It is shown that the chain of extreme weather events was triggered by the acceleration of a coherent tropopause disturbance (CTD) over the Labrador Sea. Two branches of the process may be distinguished, southern and northern. The southern one was associated with the transformation of a tropical storm into hurricane Olga, strengthening of the STJ and eventually the formation of the RST cyclone. The RST contributed to the intensification of the transport of moist air masses from equatorial Africa to the Mediterranean region. The northern branch was determined by an eastward drift of the CTD, moist air mass transport from the area of the hurricane to the North Atlantic and the European-Mediterranean region, strengthening of the Icelandic Low and formation of an upper troposphere potential vorticity-streamer system over western Scandinavia. Displacement of the streamer to the Mediterranean region and its interaction with the RST system played a major role in the development of the powerful Cyprus Low cyclone over the northeastern Mediterranean region.     

Temporal and Spatial Trends of Temperature Patterns in Israel

Summary  Daily maximum and minimum temperatures from 40 stations in Israel were analyzed to detect long-term trends and changes in temporal and spatial distribution patterns during the second half of the 20th Century. The trend analysis, reveals a rather complex changing pattern, with a significant decreasing trend of both the daily maximum and minimum temperature, during the cool season, and an increasing trend during the warm season. On an annual basis, there seems to be almost no temporal trends in minimum and maximum temperatures since the changes in winter and summer show an opposite tendencey. Received November 30, 1998 Revised May 27, 1999     

The combined use of three different approaches to obtain the best estimate of meso-β surface winds over complex terrain

Three approaches for estimating meso-β (Δx=5–10 km) surface winds over complex terrain are applied to obtain best estimates of typical summertime surface flow in Israel, based on a detailed 3-D model, a one-level sigma model and a dense network of surface wind observations. A scheme for combining the three approaches is outlined and illustrated through two examples showing how the approaches complement each other. It is suggested that such a man-machine combination is best for estimation of surface winds over complex terrain.     

Reply to comment by Ben-Zvi,A., D. Rosenfeld and A. Givati on the paper: Levin,Z., N. Halfon and P. Alpert, “Reassessment of rain experiments and operations in Israel including synoptic considerations,” Atmos. Res. 97, 513–525. DOI: 10.1016/j.atmosres.2010.06.011

Levin et al. (2010; hereafter LHA) (Levin, Z., Halfon, N., Alpert, P., 2010. Reassessment of rain experiments and operations in Israel including synoptic considerations. Atmos. Res. 97, 513–525. DOI:10.1016/j.atmosres.2010.06.011.), reanalyzed the results of the operational seeding in northern Israel between 1975 and 2007 and the preceding Israel 2 cloud seeding experiment (1969–1975) and concluded that there is no net increase in precipitation over the target areas. Our analysis revealed that a synoptic bias during Israel 2 is one of the reasons for the apparent positive effect of seeding in the northern target area and the negative effect in the southern area both of which disappeared in the following experiment in the south (Israel 3; 1975–1995) and the operational seeding in the north.Ben-Zvi et al. (2010;hereafter BRG) criticized our paper primarily on the ground that we did not consider the positive results of Israel 1 experiment (1960–1967). It should be noted that in Israel 1 different seeding lines were used from those in both Israel 2 and the operational period. In addition, its raw data is not accessible anymore for reanalysis. Furthermore, Israel 2 had been designed as a confirmatory cross-over experiment to Israel 1 and failed to reproduce its promising results with double ratio (DR) of ~ 1.00, namely, zero rainfall enhancements. The same DR values were also found in Israel 3 and in the operational seeding. Therefore, because of the differences in the two experiments, the lack of access to the raw data and the disappointing results of the confirmatory experiment, we decided to concentrate our analysis on the more recent seeding activities.The attempt by BRG to explain the reduction of the DR to ~ 1.00 in the operational seeding period by the suppression due to pollution have been disproved by Alpert et al., 2008, Alpert et al., 2009 and also fail to explain the sharp decline of the target/control ratio right at the beginning of the operational seeding period when the lucky draw in this area came to its end (see LHA).