The development of local circulations around the Lena River and their effect on tower-observed energy imbalance

Horizontal wind speed and vertical wind speed fluctuation data obtained from aircraft during the GEWEX Asian Monsoon Experiment-Siberia (GAME-Siberia) project revealed the development of a local circulation in the atmospheric boundary layer (ABL) near the Lena River, Siberia. Horizontal wind speed distributions showed regions where wind direction was opposite that of the synoptically dominant wind flow. Horizontal wind speed distributions and horizontally averaged vertical wind speed fluctuations with a 4-km cut-off distance were used to derive air stream vectors. The vectors showed the development of local circulations only over the upwind side of the Lena River on some days. Criteria for local circulation detection are suggested. Tower-based energy imbalances were observed at two flux-tower sites. Turbulent heat fluxes were underestimated relative to the available energy when mean downward flow dominated at the flux tower. This tower-observed energy imbalance might be related to the development of local circulations near the Lena River.