ALBERT

Description: The water temperature characteristics of the Lena River at basin outlet during the summer season (June–September) are considered. The analysis is based on a long-term data series covering the period from the beginning of observation (1936) to the present time (2012) at Kusur (Kyusyur) gauging station and complementary data at several stations downstream and one station upstream. These additional data are rarely used, but their analysis is important for understanding processes in the basin outlet area. The differences between the stream surface temperatures at Kusur station and 200 km downstream to the north at Habarova (Khabarova) station have almost always been an anomalously large and negative for the considered period since the beginning of observation during open water season from July to September. The description of this difference and its analysis are presented. To sort the problem out, we consider the observational data in terms of the hydrology and morphology of the Lena River delta and main channel area and apply statistical and deterministic modelling approaches. The inability of water temperature observational data at Kusur station to represent the mean cross-sectional temperature is addressed. The analysis of the water temperature trends at the Kusur and Habarova stations is also presented.

Description: The Lena River is one of the largest rivers in the Arctic and has the largest delta. Given the large territory of the Lena Delta, the direct measurements are by far insufficient, calling for a modeling approach. However, most of the models, which include the Laptev Sea shelf zone, do not resolve the Lena Delta and as a consequence lose information about Lena river stream changes using input data with insufficient quality. In the current work we present the hydrodynamics model for the Lena Delta region and full baroclinic model for the Laptev Sea shelf area. The available hydrological information in the Lena Delta was collected, analyzed and used for the model verification. The developed hydrodynamics model provides the first necessary step for the further modeling efforts in the area. It also gives an input for the larger scale models resolving hydrodynamics of more than twenty main Lena River freshwater channels with switched-on wetting/drying option. Additionally the Lena Plume dynamics in the Lena Delta region of the Laptev Sea are explored by us in simulations performed with the FVCOM (Finite Volume Coastal Ocean Model). The impact of winds and tides on the Lena plume propagation is analysed based on simulations for the summer season of 2008 and also on idealized experiments. For that period, the simulated distributions of temperature and salinity agree well with the observations, including the thick-ness and border position of the buoyant plume. The model simulates the most energetic semi-diurnal and diurnal tidal constituents. The amplitudes and phases of the tidal components at the open boundary were derived from AOTIM5 and TPXO7.1 with corrections. These corrections noticeably improve the agreement of the modelled tidal maps with available tide gauge data.

Description: The goal of the current work is to analyze the available data on the water temperature of the Lena River at the basin outlet in the summer ice-free period (June–September). The analysis is based on a long-term data series covering the period from the beginning of observations to the present time at Kyusyur gauging station and complementary data at several stations downstream and one station upstream. These complementary data are rarely used, but their analysis is important for understanding processes in the basin outlet area. The differences between the stream surface temperatures at Kyusyur station and Yu. A Khabarova station 200 km downstream to the north have almost always been anomalously large and negative during open water season from July to September since the beginning of observations. The warming of the water downstream from Kyusyur raises questions because it cannot be explained by the heat exchange with the atmosphere. The analysis of factors that may be responsible for it is a major focus of this paper. We discuss whether the water temperature observations at Kyusyur station represent the mean stream temperature and show that they fail to represent the mean cross-sectional value but reflect thermal variability of the Lena River at this position. We carry out numerical experiments to verify this hypothesis and to explain the mentioned difference.

Description: A large number of observations available for the Laptev Sea shelf zone suggests significant changes both in climatology and ecosystem over the last seventy years. The Lena River plays one of the key roles in these processes. The scientists from Melnikov Permafrost Institute have shown that increasing of the Lena water temperature in a flood period led to strong coastal erosion in the Lena Delta region and thus to changes in chemical water composition. Some shifts are observed in time of the onset of daily discharge peak. As a result the changes are also observed in food webs. The large amount of observations in the considered area has been collected. On this stage somehow possible to get a complex picture about the dynamics in the region. However the output from any modeling efforts directly depends on the quality and detail of input data. For the models, especially ecosystem models, which do not resolve the Delta, one of the key points of success is accurate distribution of total freshwater runoff in the mouth area and also setting of precise temperature profiles. The main goal of our work is modeling of mean daily temperature of the water in the main freshwater channels near the mouth area depending on atmospheric conditions. The necessary accuracy of desired values requires the bringing observational data in frame of hydrology and morphology for the Lena River delta and main stream area including data about permafrost conditions under the river bed. The work includes analysis of temperature regimes for the lower reaches of the Lena River in the summer period, identification of its main factors and estimation of stratification in the main freshwater channels near the mouth. Also the work contains assessment of statistical and deterministic approaches to stream temperature modeling depending on atmospheric conditions in the region and considering the unique characteristics of the Lena River.