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Simulating the ice phenology of deep alpine lakes is important and challenging in coupled atmosphere-lake models. In this study, the Weather Research and Forecasting (WRF) model, coupled with two lake models, the fresh-water lake model (WRF-FLake) and the default lake model (WRF-Lake), was applied to lake Nam Co, a typical deep alpine lake located in the centre of the Tibetan Plateau, to simulate its lake ice phenology. Due to the large errors in simulating lake ice phenology, related key parameters and parameterizations were improved in the coupled model based on observations and physics-based schemes. By improving the momentum, hydraulic and thermal roughness length parameterizations, both the WRF-FLake and the WRF-Lake models reasonably simulated the lake freeze-up date. By improving the key parameters associated with shortwave radiation transfer process when lake ice exists, both models generally simulated the lake break-up date well. Compared with WRF-Lake without improvements, the coupled model with both revised lake models significantly improved the simulation of lake ice phenology. However, there were still considerable errors in simulating the spatial patterns of freeze-up and break-up dates, implying that significant challenges in simulating the lake ice phenology still exist in representing some important model physics, including lake physics such as grid-scale water circulation, and atmospheric processes such as snowfall and surface snow dynamics. Therefore, this work can provide valuable new implications for advancing lake ice phenology simulations in coupled models and the improved model also has practical application prospects in weather and climate forecasts. [ABSTRACT FROM AUTHOR]

Understanding cloud distribution over lakes is crucial to determine input radiation and precipitation for lake thermal and water balance processes. Based on Himawari‐8 satellite observation and Weather Research and Forecasting model results, this study examines the influences of lakes on daytime cloud cover during warm seasons over the Tibetan Plateau (TP), which is home to thousands of lakes. Observation shows the existence of cloud holes and narrow cloud rings around the lakes, that is, fewer clouds over the lakes and more clouds along the shoreline, which has rarely been reported and is considered typical to TP by comparison with lakes outside of TP. The threshold size of lakes that can produce the shoreline cloud ring is identified to be about 300 km2, as a conservative estimate. We further highlight the importance of atmosphere advection/background wind in the formation of lake‐associated clouds. Lake breeze forms under weak background winds and the downdraft branch inhibits cloud formation over the lakes; while the updraft branch causes convection to form clouds over lakeshores. However, strong background winds do not favor lake breeze formation, changing cloud distribution over the lakes. Fewer clouds are also found in the downwind regions, and this influence is at a distance comparable to the lake scale. Due to fewer clouds over lakes, shortwave radiation is significantly larger (∼100 W/m2) and longwave radiation is smaller (∼a few W/m2) than that of the further land region. Therefore, the above observational facts provide a new perspective to advance the understanding of lake‐air interactions. Plain Language Summary: There are lots of lakes over the Tibetan Plateau (TP), but the influence of these lakes on cloud during warm seasons remain unclear. Satellite data shows the existence of cloud holes and narrow cloud rings around the lakes, that is, fewer clouds over the lakes and more clouds along the shoreline, which has rarely been reported before. Simulation results demonstrate that the lake breeze accounts for this phenomenon: air descends over the lake, which inhibits cloud formation, while ascending branch over the shoreline favors cloud formation. Lakes over 300 km2 can yield these cloud influences, so this area is thought as the threshold area that lakes can have influence on atmosphere. Clouds in the downwind regions are also fewer under the influence of background wind, and this influencing distance is almost equal to the lake scale itself. Due to less block by clouds, solar radiation is much higher over the lake than surrounding land, but downward longwave radiation is a little lower because of less emission from the cloud bottom, resulting an increase of net radiation in total at the lake surface. The conclusions of this study can help understand energy and hydrology processes of lakes better over the TP. Key Points: Evident "cloud holes" and "cloud rings" are found for lakes over the Tibetan Plateau, which are mainly induced by lake breezeClouds in the downwind regions are also fewer due to atmosphere advection; this distance is almost equal to the size of the lake itselfFewer clouds over the lake increase the net radiation mainly due to much higher downward shortwave radiation [ABSTRACT FROM AUTHOR]

The alpine lakes widely distributed over the Tibetan Plateau (TP) are not only highly sensitive to climate but also regulate the regional climate. However, the lack of TP alpine lake observations limits the understanding of the lake‐atmosphere interactions. Here, we show the relative importance of parameterizing lake surface and internal thermal processes in describing the lake energy budget and lake‐atmosphere interactions. Based on the in situ observations at Lake Nam Co, a large and deep lake in the TP, we employed the coupled Weather Research and Forecasting with lake (WRF‐Lake) model to clarify their relative roles. Results show that the original model produces cold biases and too early timing of lake freeze onset. The adjustments of parameterizations of lake internal (temperature of maximum water density, extinction coefficient) and lake surface (roughness length) processes significantly improve the ability of the WRF‐Lake in simulating the lake thermal features and the freeze onset timing. The different parameterizations of lake internal thermal processes affect the onset timing of lake freeze mainly by altering the release of turbulent heat fluxes in summer, but the adjustments of lake surface roughness lengths change the turbulent heat fluxes during the unfrozen season from summer through early winter. Accordingly, the simulated lake freeze onset is much more sensitive to the surface roughness length schemes than to the internal thermal processes schemes. As the lake‐atmosphere interactions are very sensitive to the lake freeze onset, our results are critical for understanding and simulating the impact of TP lakes on the regional climate. Key Points: Simulated lake temperature profile and freeze onset timing are closer to observations with improved parameterizations in coupled Weather Research and Forecasting with lakeCompared to the lake internal thermal processes, the surface roughness length scheme (ROU) is the key to control lake freeze onset timingAdjustments of lake surface ROU notably delay the freeze onset by reducing turbulent heat fluxes during unfrozen season [ABSTRACT FROM AUTHOR]

As a region that is highly sensitive to global climate change, the Tibetan Plateau (TP) experiences an intra‐seasonal soil water deficient due to the reduced precipitation during the South Asia monsoon (SAM) breaks. Few studies have investigated the impact of SAM breaks on TP ecological processes, although a number of studies have explored the effects of inter‐annual and decadal climate variability. In this study, the response of vegetation activity to SAM breaks was investigated. The data used are: (1) soil moisture from in situ, satellite remote sensing and data assimilation; and (2) the normalized difference vegetation index (NDVI) and solar‐induced chlorophyll fluorescence (SIF). We found that in the SAM break‐impacted region, which is distributed in the central‐eastern part of TP, photosynthesis become more active during SAM breaks. And temporal variability in the photosynthesis of this region is controlled mainly by solar radiation variability and has little sensitivity to soil moisture. We adopted a diagnostic process‐based modeling approach to examine the causes of enhanced plant activity during SAM breaks on the central‐eastern TP. Our analysis indicates that more carbon assimilated by photosynthesis in the reduced precipitation is stimulated by increases in solar radiation absorbed and temperature. This study highlights the importance of sub‐seasonal climate variability for characterizing the relationship between vegetation and climate. Key Points: South Asia monsoon (SAM) breaks occur almost every year impacting a wide area on the central‐eastern Tibetan Plateau (roughly east of 92°E)The carbon assimilation becomes more active during SAM breaksThe increase in solar radiation absorbed boosts grass productivity during SAM break on the central‐eastern Tibetan Plateau [ABSTRACT FROM AUTHOR]