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Comparison between high-precipitation (HP) years and low-precipitation (LP) years led to our main findings which are as follows: Cyprus lows are instrumental in the cooling of surface and epilimnion water in subtropical Lake Kinneret and in the cooling of eastern Mediterranean surface water. Cyprus lows are responsible for cold weather, rainfall, and for an increase in cloudiness causing a decrease in solar radiation over the eastern Mediterranean and north Israel (including Lake Kinneret). In the daytime, comparison between HP and LP years of Kinneret surface water temperature (SWT) and epilimnion water temperature (WT) showed water cooling of up to 2 °C in HP years. This study was carried out using the 21-year period of satellite and in-situ data: (1) MODIS 1 km × 1 km resolution records of SWT, in (2) shipboard measurements of WT vertical profiles down to a depth of ~40 m (2000–2020). We found that a decrease in solar radiation caused by Cyprus lows (due to an increase in cloudiness) was the main factor contributing to Kinneret water cooling. In winter (December–January) when solar radiation (SR) was minimal, no water cooling was observed: the WT difference between HP and LP years was insignificant. However, in spring (March–April) when SR increased and became the main factor contributing to water heating, water cooling was observed: SWT and epilimnion WT, averaged over the HP years, was lower by ~2 °C and ~1.4 °C, respectively, than SWT and epilimnion WT, averaged over the LP years. Not only was water cooling observed in Lake Kinneret, but also in eastern Mediterranean surface water. Comparison of SWT over the eastern Mediterranean between the same HP and LP years in spring showed SWT cooling by ~1.2 °C. This is evidence of the regional character of the daytime water-cooling phenomenon caused by Cyprus lows. [ABSTRACT FROM AUTHOR]

Despite the long history of investigation of foehn phenomena, there are few studies of the influence of foehn winds on air pollution and none in the Dead Sea valley. For the first time the foehn phenomenon and its effects on local dust pollution, frontal cloudiness and surface solar radiation were analyzed in the Dead Sea valley, as it occurred on 22 March 2013. This was carried out using both numerical simulations and observations. The foehn winds intensified local dust emissions, while the foehn-induced temperature inversion trapped dust particles beneath this inversion. These two factors caused extreme surface dust concentration in the western Dead Sea valley. The dust pollution was transported by west winds eastward, to the central Dead Sea valley, where the speed of these winds sharply decreased. The transported dust was captured by the ascending airflow contributing to the maximum aerosol optical depth (AOD) over the central Dead Sea valley. On the day under study, the maximum surface dust concentration did not coincide with the maximum AOD: this being one of the specific effects of the foehn phenomenon on dust pollution in the Dead Sea valley. Radar data showed a passage of frontal cloudiness through the area of the Dead Sea valley leading to a sharp drop in noon solar radiation. The descending airflow over the downwind side of the Judean Mountains led to the formation of a cloud-free band followed by only the partial recovery of solar radiation because of the extreme dust pollution caused by foehn winds. [ABSTRACT FROM AUTHOR]

The Dead Sea is one of the saltiest bodies of water in the world. Observational evidence has been obtained of unexpected short-term water heating in the 2 m uppermost layer of this hypersaline lake, following a sharp drop in solar radiation under weak winds. This was carried out using Dead Sea buoy measurements. Passing frontal cloudiness mixed with significant dust pollution over the Judean Mountains and the Dead Sea, which occurred on March 22, 2013, led to a dramatic drop in noon solar radiation from 860 W m−2 to 50 W m−2. This drop in solar radiation caused a short-term (1-hour) pronounced temperature rise in the uppermost layer of the sea down to 2 m depth. After the sharp drop in noon solar radiation, in the absence of water mixing, buoy measurements showed that the temperature rise in the uppermost layer of the Dead Sea took place for a shorter time and was more pronounced than the temperature rise under the regular diurnal solar cycle. The water heating could be explained by gravitational instability in the skin-surface layer, when the warm surface water with the increased salinity and density submerged, thereby increasing temperature in the layers below. [ABSTRACT FROM AUTHOR]

The Dead Sea has been drying up over the last four decades: the water level has dropped at the rate of approximately 1 m per year. The Dead Sea drying up is due to the lack of water inflow from the Jordan River and increasing evaporation. A positive feedback loop between the steady shrinking of the Dead Sea and positive sea surface temperature (SST) trends takes place in the Dead Sea (Kishcha et al., 2018). This positive feedback loop together with atmospheric warming causes the following processes: increasing evaporation; an accelerating decrease in Dead Sea water levels; and increasing warming of steadily shrinking Dead Sea surface water. Using observations from Moderate Resolution Imaging Spectroradiometer (MODIS), positive trends were detected in both daytime and nighttime Dead Sea surface temperature (SST) over the period of 2000 – 2016. These positive SST trends were observed in the absence of positive trends in surface solar radiation, measured by the Dead Sea buoy pyranometer. We also show that long-term changes in water mixing in the uppermost layer of the Dead Sea under strong winds could not explain the observed SST trends. Satellite-based SST measurements showed that maximal SST trends of over 0.8 degrees per decade were observed over the north-west and southern sides of the Dead Sea, where shrinking of the Dead Sea water area was pronounced. No noticeable SST trends were observed over the eastern side of the lake, where shrinking of the Dead Sea water area was insignificant. This finding demonstrates correspondence between the positive SST trends and the shrinking of the Dead Sea, indicating a causal link between them. There are two opposite processes taking place in the Dead Sea: sea surface warming and cooling. On the one hand, the positive feedback loop (between the steady shrinking of the Dead Sea and SST trends) and atmospheric warming lead to sea surface warming every year accompanied by a long-term increase in SST. On the other hand, the measured acceleration of the Dead Sea water-level drop suggests a long-term increase in Dead Sea evaporation accompanied by a long-term decrease in SST. During the period under investigation, the total result of these two opposite processes is the statistically significant positive sea surface temperature trends in both daytime (0.6 degrees per decade) and nighttime (0.4 degrees per decade), observed by the MODIS instrument. Our findings of the existence of a positive feedback loop between the positive SST trends and the shrinking of the Dead Sea imply the following significant point: any meteorological, hydrological or geophysical process causing the steady shrinking of the Dead Sea will contribute to positive trends in SST. Our results shed light on continuing hazards to the Dead Sea.Reference: Kishcha P., Pinker R., Gertman I., Starobinets B., Alpert P. (2018). Observations of positive sea surface temperature trends in the steadily shrinking Dead Sea. Nat. Hazards Earth Syst. Sci., 18, 3007-3018, https://doi.org/10.5194/nhess-18-3007-2018. [ABSTRACT FROM AUTHOR]