DATE2022-05-30 13:40:11
TITLEA Factor Separation Study of the Effect of Synoptic‐Scale Wind, Atmospheric Moisture and of Their Synergy on the Diurnal Temperature Range During the Israeli Summer
AUTHORSMaaian Rotstein (1) ,Pinhas Alpert (1) ,Dorita Rostkier-edelstein (2)
  1. 1) Tel-aviv University, Tel-aviv (Israel) ,2) The Hebrew University, Jerusalem (Israel)
ABSTRACTGlobal mean temperatures are the most widely used and accepted meteorological variable for investigating climate change, however, they alone do not capture the complexity of the processes leading to the observed increasing trend. One of the clearest examples of this is the observed decrease in the global mean diurnal temperature range (DTR), defined as the difference between daytime maximum and night-time minimum temperatures (Tmax and Tmin, respectively). Regionally, DTR trends exhibit large variations. Despite the abundance of studies on DTR, the factors contributing to the observed trends remain poorly understood, highlighting the problem in identification of the physical causes. Water vapor is one of the most important greenhouse gases in the atmosphere, resulting in increased surface temperatures (i.e., 2 m temperatures). The relative increase in Tmax and Tmin will determine whether the DTR increases or decreases, and to what extent. In Israel, a statistical analysis conducted by Barkan et al. (2019) based on observations found that relative humidity was strongly correlated to DTR magnitude, across all studied locations and seasons. Winds are known to influence the DTR in a number of ways. Diurnal variations in wind direction can affect the DTR through advection of different air masses; an example of this is the sea breeze, which transports cool and humid air from the sea inland during the day, thereby reducing Tmax. Wind speeds can affect surface sensible and latent heat fluxes, thereby changing surface temperatures. Variations between day and night will lead to differences in DTR. Strong nocturnal winds can increase mixing in the lower atmosphere, with air temperatures higher above. This mixing of air can increase Tmin and thus reduce DTR. We conducted a factor separation analysis investigate the impact of atmospheric moisture, synoptic‐scale winds, and their synergy on the DTR during the Israeli summer. The Weather Research and Forecasting (WRF) Single Column Model was run for summer representative days, at four locations in Israel. In almost all cases, the contribution of the factors and of their synergy to the DTR was dominated by their contribution to Tmin. The largest contribution resulted from atmospheric moisture, reducing the DTR. The contribution of synoptic‐scale winds showed more variability, with significant differences in both magnitude and sign on different days. The sign of the effect on Tmin depended on the relative direction and magnitude of the nocturnal synoptic‐scale wind with respect to the local wind, which in turn determined the effect on the low‐level jet (LLJ) and vertical mixing. The contribution from synergy between the two factors depended on the effect of moisture on the LLJ and on the effect of the synoptic‐scale winds on moisture advection in or out of the atmospheric column. All cases were classified into groups depending on the sign of contributions of the single factors and of their synergy when analyzing the DTR observed trends. These results highlight the importance of the synoptic wind, of its synergy with atmospheric moisture and of the feedback mechanisms. Significant changes in both studied single factors, atmospheric moisture and synoptic-scale winds, are projected in future climate scenarios. The methodology exploited in this research can be further applied under future atmospheric conditions. Such numerical experiments can be conducted by modifying the present atmospheric variables used in our study according to future climate predictions. References Rotstein, M., Alpert, P., & Rostkier-Edelstein, D. (2021). A factor separation study of the effect of synoptic-scale wind, atmospheric moisture and of their synergy on the diurnal temperature range during the Israeli summer. Journal of Geophysical Research: Atmospheres,126, e2021JD034923 Barkan, J., Shafir, H., & Alpert, P. (2019). Multi-Factor analysis of DTR variability over Israel in the sea/desert border. Theoretical and Applied Climatology, 139, 287–295.