The influence of mesoscale convective systems on the isotopic composition of precipitation: the case of Tomsk city
G.V. Simonova1, A.N. Markelova1, P.M. Nagorskiy1, K.N. Pustovalov1,2, M.V. Oglezneva1, A.E. Davydkina1,3
1Institute of Monitoring of Climatic and Ecological Systems of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Russia
2National Research Tomsk State University, Tomsk, Russia
3National Research Tomsk Polytechnic University, Tomsk, Russia
Keywords: precipitation, mesoscale convective system, hydrogen and oxygen stable isotopes, dD, d18O
Abstract
The isotopic composition of precipitation is a hydrological tracer of convective processes and is often used to reconstruct paleoclimate. Therefore, it is interesting to consider how the isotopic composition of precipitation changes during the passage of mesoscale convective systems (MCS). Variations in the isotopic composition of oxygen (δ18О) and hydrogen (δD) in precipitation during the passage of MCS over Tomsk in 2016-2021 were studied. It was found that δ18О values varied from -14.98 to +0.03‰ with an average of -9.9 ± 3.2‰ and δD values varied from -99.2 to -16.71‰ with an average of -65.1 ± 22.3‰ in MCS precipitation. The relationship between δ18О and δD is described by the equation δD = 5.45d18O - 11 ( R 2 = 0.62). The values of the regression coefficients show the predominant effect of evaporative fractionation on the formation of the isotopic composition of precipitation. Relatively high isotope ratios corresponded to disorganized convection, and lower isotope ratios characterized the isotopic composition as the MCS area increased. Based on the analysis of back air mass trajectories with the use of the indices of convective instability and satellite sounding and WWLLN network data, regions-sources of moisture for MCS precipitation were detected: the underlying surface and shallow water bodies of the steppe zone in the south of Western Siberia and Northern Kazakhstan. The results of the study can be useful for simulating convection in climate models, as well as for better understanding isotope variations in different paleoarchives for regions with convective activity.
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