## 1 Introduction  
Frost events, defined by temperatures falling below freezing during the growing season, rank among the most critical extreme climate events on Earth [1, 2, 3]. These events can hinder plant growth, decrease carbon uptake [4, 5], and disrupt nutrient cycling [6], leading to significant changes in the structure and function of terrestrial ecosystem. Numerous studies have examined the spatial and temporal distribution of late spring frost events [1, 2, 3, 7, 1] and their impact on various ecosystems. While frost impact in North America [8, 9], on boreal ecosystems [5, 10], and on deciduous European forests [11, 12] are well-documented,there is a notable gap in research on frost events during the growing season and at seasonal scales in cold regions. Several studies indicate that frost is a critical environmental factor in such areas [13]. Therefore, understanding frost events and assessing their effects on alpine ecosystems is vital for predicting future terrestrial carbon balance and informing effective frost mitigation strategies. Given the increasing frequency of extreme weather events globally, climate change has altered the timing of developmental stages in most plants. The extent of frost damage largely depends on the plant's developmental phase at the time of the event [14]. Studying frost events can significantly enhance our understanding of frost dynamics at both seasonal and annual scales on a regional level [10; 11]. Moreover, vegetation has evolved various strategies to mitigate frost damage in response to seasonal frost events [10; 11]. Research indicates that earlier bud bursts in spring, caused by shifting climates, heighten the risk of frost damage to plants [5; 8]. Despite alpine vegetation's adaptations to harsh environments [15], frost events in spring remain a significant threat. In contrast, summer frost events, though less extreme in terms of temperature, showcase the remarkable resilience of alpine vegetation to frost [15; 16]. Autumn frost events, however, can accelerate or induce early senescence, leading to premature death of plant tissue before nutrient resorption is complete, which in turn can reduce summer crop yields in the next year [17]. Understanding the varying responses of alpine vegetation to frost events across different seasons offers valuable insights for agriculture and animal husbandry. Satellite-based vegetation indicators offer an opportunity to quantify the impacts of extreme climate events on ecosystems at the regional scale [18; 19; 20; 21]. Traditional vegetation indices (VIs) primarily reflect vegetation greenness (or structure) [22], while recent advancements in solar-induced chlorophyll fluorescence (SIF) products provide a promising approach [23] for monitoring vegetation photosynthesis on a regional scale [20; 24]. SIF, emitted from photosystem I (PSI) and photosystem II (PSII), is characterized by two peaks centered in the red and far-red spectral regions [25]. As SIF captures environmental information, it plays a critical role in monitoring vegetation photosynthesis under extreme climate conditions [26]. SIF is considered a direct indicator of the functional status of actual plant photosynthesis [27], providing information on the biochemical, physiological, and metabolic functions of a plant, as well as the amount of absorbed PAR (APAR) [28; 29]. The NDVI represents the greenness or structure of the canopy, while the SIF represents actual photosynthesis [30]. GOSIF offers a long time series and high resolution, making it highly useful for exploring vegetation photosynthesis responses to climate change [31]. In this study, a combination of NDVI and SIF is employed to analyze spatial-temporal variations and compare vegetation responses to frost events across different temporal scales. The Third Pole region experiences freezing temperatures even during the growing season, leading to potential frost events with ecological and economic consequences [7].