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

Abstract

Abstract: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.

Secondary circulations at a solitary forest surrounded by semi-arid shrubland and their impact on eddy-covariance measurements

“…Multi-site analyses across different ecosystems have shown that energy balance ratios usually range between 0.7 and 0.9 (Wilson et al, 2002;Hendricks-Franssen et al, 2010;Stoy et al, 2013). A potential reason for this is the non-consideration of fluxes carried by (i) turbulent structures with timescales larger than the averaging time of the EC system (Sakai et al, 2001;Turnipseed et al, 2002;Foken et al, 2006;Charuchittipan et al, 2014) or by (ii) secondary circulations that are bound to surface heterogeneities and do not move in space (Lee and Black, 1993;Mahrt, 1998;Hiyama et al, 2007). There are indications that the non-closure of the energy balance is related to the heterogeneity of the surrounding landscape (Mauder et al, 2007a;Panin and Bernhofer, 2008;Stoy et al, 2013), but experimental evidence that secondary circulations are an important transport mechanism in the surface layer is still lacking.…”

Eddy-covariance flux measurements with a weight-shift microlight aircraft

“…Here process studies with airborne platforms provide a valuable link to understand and bridge scale discrepancies (e.g. Bange et al, 2002;Davis et al, 1992;Hiyama et al, 2007;Isaac et al, 2004a). At the same time, fixed-wing aircraft and helicopters are expensive to operate or not applicable in settings such as remote areas beyond the range of an airfield.…”

Effects of soil heat storage and phase shift correction on energy balance closure of paddy fields

“…The most popular is EBR, which has the advantage of giving an overall evaluation of energy balance closure at longer time scales by averaging over random errors in the half-hourly measurements. A disadvantage of EBR is its potential to overlook biases in the half-hourly data, such as the tendency to overestimate positive fluxes during the day and underestimate negative fluxes at night (Wilson et al, 2002;Hiyama et al, 2007). The linear regression coefficients (slope and intercept) are determined from the OLS relationship between half-hourly estimates of the dependent turbulent flux variables against the independently derived available energy, which is technically valid only if there are no random errors in the independent variable (Li et al, 2005).…”