A three-dimensional (3-D) hydrodynamic model based on Princeton Ocean Model (POM) and a one-dimensional (1-D) lake model are applied to simulate the thermal structure and circulations of Lake Nam Co (LNC), the second largest lake in Tibet. Results show that POM can well reproduce the seasonal and synoptic variations of the in-situ observed vertical temperature profile, and the spatial distribution of satellite estimated lake surface temperature during May-December 2013. However, without considering the water and energy exchanges related to the lake hydrodynamics, the 1-D model exhibits much more evident biases in the lake thermal evolution. These shortages of the 1-D lake model solutions emphasize that the complex temperature-current interactions must be accounted for investigating the thermodynamics in large lakes over Tibet. From both observation and hydrodynamic simulations, LNC is identified to experience the springtime overturning, warm stratified phase during early-June to mid-November, autumnal overturning, and weak inverse stratified phase since mid-December. The two overturning processes last for about one month and are both related to the thermal bar development, which is controlled by the density-driven convection associated with the radiative heating (surface cooling) in spring (autumn). During the warm stratified phase, the eastern shallow basin is mainly characterized by anticyclonic circulation and bowl-shaped thermocline, while the central deep basin is featured by a cyclonic gyre (eastward currents) and dome-shaped (bowl-shaped) thermocline with the enhancement (weakness) of thermal stratification. The lake circulation during December is basically dominated by a single strong cyclonic gyre in the main lake basin.

Remotely sensed solar-induced fluorescence (SIF) has emerged as a novel approach for terrestrial vegetation monitoring. The in situ continuous optical remote sensing tool in conjunction with concurrent eddy covariance (EC) flux measurements provides a new opportunity to advance terrestrial ecosystem science. Here we introduce a network of ground-based SIF observations at flux tower sites across the mainland China referred as ChinaSpec. Until now, it consists of 15 tower sites including 5 cropland sites, 4 grassland sites, 4 forest sites and 2 wetland sites. At each of these sites, an automated spectroscopy system was deployed to collect continuous super-high resolution spectra for high-frequency SIF retrievals in synergy with EC flux measurements. The goal of ChinaSpec is to provide ground SIF measurements and promote the collaborations between optical remote sensing and EC flux communities in China. We present here the details of instrument specifications, data collection and processing procedures, data sharing and utilization protocols, and future plans. Furthermore, we show the examples how ground SIF observations can be used to track vegetation photosynthesis from diurnal to seasonal scales, to assist in the validation of fluorescence models and satellite SIF products (e.g., from OCO-2, TanSat and TROPOMI) with the measurements from these sites since 2016. This network of SIF observations could improve our understanding of the controls on the biosphere-atmosphere carbon exchange and enable the improvement of carbon flux predictions. This SIF network will also help integrate ground SIF measurements with EC flux networks which will advance ecosystem and carbon cycle researches globally.