Empirical orthogonal analysis of temperature and vertical velocity in lake Shira

Abstract

The empirical orthogonal functions method is widely used for the study of the hydrophysical characteristics in meteorology and oceanography, for example for the analysis of ocean surface currents in the North Carolina and the distribution of horizontal velocities in the Shira Lake. This method is also applied to study the distribution temperatures with depth in the Pacific Ocean and to analyze sea surface temperature in the Western North Atlantic. The empirical orthogonal functions method gives us an optimal modal decomposition of the data and allows us to identify particular modes with relevant physical processors. The empirical orthogonal functions analysis used in this study was performed to measure temperature and vertical velocity in Lake Shira (Southern Siberia, Russia) in the summer of 2014 and 2015. The measurements of currents were recorded using Acoustic Doppler Current Profilers 600 kHz and 1200 kHz at two points. The measurements of temperature were recorded by termistor sensors distributing with depth at ten locations. The first and second empirical orthogonal modes for temperature account for 70-90 % of the total energy. They were used to identify the periods of summer heating and the location of the thermocline. The first mode for surface temperature accounts for about 96 % of the total energy and corresponds to surface temperature gradients. The first mode for vertical velocities accounts for about 10 % of the total energy and the analysis of the corresponding modal coefficient makes it possible to determine the periods when water moves up or down vertically.