Cooling by Cyprus Lows of Surface and Epilimnion Water in Subtropical Lake Kinneret in Rainy Seasons

Abstract

Cyprus lows are the main reason for precipitation over Lake Kinneret during the rainy season (December–May): these lows are centered over the Mediterranean Island of Cyprus. Cyprus lows are responsible for cold weather conditions when westerly winds transport cold moist air from the eastern Mediterranean into north Israel (including Lake Kinneret). Such cold weather conditions, accompanied by rainfall and a decrease in solar radiation (due to an increase in cloudiness over the lake), could cause cooling of Kinneret and eastern Mediterranean water temperature (WT) in rainy seasons.However, in the Eastern Mediterranean and in Lake Kinneret, surface water temperature is increasing by ~1.5 oC over the last 40 years. Moreover, climate model predictions showed a reduction by one third in the appearance of Cyprus lows by the end of the 21st century. This suggests a reduction in cooling by Cyprus lows of water in the Eastern Mediterranean and in Lake Kinneret. Therefore, a comprehensive investigation of the influence of Cyprus lows on water temperature in subtropical Lake Kinneret and the Eastern Mediterranean is environmentally important.Comparisons, conducted on a monthly basis, 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 (Kishcha et al., 2022). In particular, comparison between HP and LP years of Kinneret surface water temperature (SWT) and epilimnion water temperature (WT) have shown water cooling of up to 2 °C in HP years, in the daytime. 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, and (2) shipboard measurements of WT vertical profiles down to a depth of 40 m (2000–2020). We found that the decrease in solar radiation (caused by Cyprus lows due to an increase in cloudiness) was the main factor contributing to Kinneret water cooling. In spring (March–April), 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. This was when SR increased and became the main factor contributing to water heating. In situ shipboard measurements of WT at a depth of 1 m and 5 m, at five monitoring sites within Lake Kinneret, showed similar patterns of the WT difference between HP and LP years. This is evidence that cooling by Cyprus lows of Kinneret water was evenly distributed within the lake. Water cooling by Cyprus lows was also observed in eastern Mediterranean surface water. In particular, in the spring months (March–April), Mediterranean SST averaged over the same HP years was lower by ~1.2 oC than that averaged over LP years. This is evidence of the regional character of the water-cooling phenomenon caused by Cyprus lows.Reference:Kishcha et al. (2022).  Remote Sensing 2022, 14, 4709. https://doi.org/10.3390/rs14194709