Observation and simulation of lake‐air heat and water transfer processes in a high‐altitude shallow lake on the Tibetan Plateau

Abstract

Lakes are an important part of the landscape on the Tibetan Plateau. Most of the Plateau lakes' area has been expanding in recent years, but lake‐atmosphere energy and water interaction is poorly understood because of a lack of observational data and adequate modeling systems. Based on the eddy covariance observation over a high‐altitude shallow and small lake (the small Nam Co Lake) during an ice‐free period from 10 April to 30 August 2012, this study analyzes the lake‐air heat and water vapor turbulent transfer processes and evaluates two popular lake‐air exchange models: a bulk aerodynamic transfer model (B model) and a multilayer model (M model). Our main results are as follows: (1) observations show that the bulk transfer coefficient (CE) and roughness length (zoq) for water are higher than those for heat (CH and z0h), especially under low wind speed; (2) both models underestimate turbulent fluxes due to inaccurate values of the Charnock coefficient (α) and the roughness Reynolds number (Rr) which are both important parameters for calculating the roughness length for momentum (z0m) over water; (3) α within a reasonable range of 0.013–0.035 for rough flow and Rr for smooth flow (Rr = 0.11) are 0.031 and 0.54, respectively, by our observation. The wave pattern of shorter wavelength gives a larger z0m in the small and shallow lake; and (4) the B model and the M model gave consistent results, and both models are more suitable for simulation of turbulent flux exchange after z0m optimization.

Airlake boundary layer and performance of a simple lake parameterization scheme over the Tibetan highlands

“…The monthly mean temperature difference peaked in November when the monthly H was the highest. The phenomenon with the higher daily mean T s compared with T a was also observed over a small lake next to the large Nam Co Lake in the observation period from April to September 2012 (Wang et al, 2015). Among lakes in other regions of the world, the lake surface persistently warmer than the air was observed in tropical and subtropical lakes.…”

“…In lowlands, the long-lasting unstable boundary layer is more typical for tropical and subtropical lakes (Verburg and Antenucci, 2010) than for temperate and boreal lakes with strong seasonality (Long et al, 2007;Rouse et al, 2008), and implies strong effects on the energy transport from the lake surface. On the TP, a persistently unstable atmosphere has been observed over Ngoring Lake during the most part of the ice-free period , as well as over a small lake nearby Nam Co Lake (Wang et al, 2015). Wang et al (2015) analysed data from a single year, while study combined observations from two subsequent summers that started in the middle of June, missed the early open-water period immediately after the ice-off and only show the daily mean characteristics.…”

“…On the TP, a persistently unstable atmosphere has been observed over Ngoring Lake during the most part of the ice-free period , as well as over a small lake nearby Nam Co Lake (Wang et al, 2015). Wang et al (2015) analysed data from a single year, while study combined observations from two subsequent summers that started in the middle of June, missed the early open-water period immediately after the ice-off and only show the daily mean characteristics. The study of Verburg and Antenucci (2010) on Lake Tanganyika demonstrated that an unstable atmosphere could increase the annual mean latent heat flux (LE) to 13 % and the sensible heat flux (H) loss to 18 % compared to the condition with the assumed neutral atmospheric boundary layer.…”

“…A set of lake models has previously been validated over lowland lakes within the Lake Model Intercomparison Project (Stepanenko et al, 2010(Stepanenko et al, , 2014Thiery et al, 2014b), demonstrating good ability of the models to simulate mixing processes and temperature distribution. Only a few lake models Wang et al, 2015) have been applied into high-altitude areas, but these models did not dynamically forecast the lake temperature, and the observed lake temperature was input and employed in the simulation .…”

Quantifying Surface Energy Fluxes and Evaporation over a Significant Expanding Endorheic Lake in the Central Tibetan Plateau

“…Li et al (2015) analyzed two-year surface energy budgets during the ice-free period over Lake Ngoring in the northeast of the TP. Wang et al (2015) observed and modeled the interactions between a lake and the air during the summer over a small and shallow lake in the Nam Co basin of the central TP. Moreover, remote-sensing-based investigations have suggested that most lakes in the central TP have experienced significant expansions in area and increases in water level during the past few decades Wang et al 2013;.…”