Description: Extreme climate events and their impacts are currently arising as a critical feature of climate change. Paleoclimate studies are essential for understanding global environmental change and predicting extreme’s trends as the paleo-studies determine the factors that caused changes in the climate. Many studies have suggested that the mid-Pliocene and last interglacial (LIG) can be potentially used as an analogue for the future climates, but the extreme climate events are often missing in these studies. This thesis aims to show whether the LIG and mid-Pliocene are considered as analogues for the future of two extreme climate indices, including summer days index and heavy precipitation index. The MPI-ESM and COSMOS are employed to simulate the LIG, mid-Pliocene, pre-industrial, and future climates. First, the anomalies of temperature, precipitation, and selected indices are plotted for the simulations with respect to PI. In general, the summer days and heavy precipitation patterns are similar to the temperature and precipitation patterns, respectively. The probability density functions of climate variables and extreme indices in the centre of North America and Africa, the south of Africa, and Malaysia, clearly show that the increases in the average temperature and precipitation result in a growth in the corresponding extreme index. Comparing the anomaly plots for different simulations, the LIG can be only considered as analogue for future of summer days index in the northern-hemisphere regions such as the centre of North America. The mid-Pliocene not only is a good analogue for the summer days at the global scale but also can be used regionally for the prediction of heavy precipitation events. Due to the different characteristics of models employed in this project, there are some discrepancies in the results of similar simulations produced by MPI-ESM and COSMOS.

Description: Low-level mixed-phase clouds (MPCs) are common in the Arctic. Both local and large-scale phenomena influence the properties and lifetime of MPCs. Arctic fjords are characterized by complex terrain and large variations in surface properties. Yet, not many studies have investigated the impact of local boundary layer dynamics and their relative importance on MPCs in the fjord environment. In this work, we used a combination of ground-based remote sensing instruments, surface meteorological observations, radiosoundings, and reanalysis data to study persistent low-level MPCs at Ny-Ålesund, Svalbard, for a 2.5-year period. Methods to identify the cloud regime, surface coupling, and regional and local wind patterns were developed. We found that persistent low-level MPCs were most common with westerly winds, and the westerly clouds had a higher mean liquid (42 g m−2) and ice water path (16 g m−2) compared to those with easterly winds. The increased height and rarity of persistent MPCs with easterly free-tropospheric winds suggest the island and its orography have an influence on the studied clouds. Seasonal variation in the liquid water path was found to be minimal, although the occurrence of persistent MPCs, their height, and their ice water path all showed notable seasonal dependency. Most of the studied MPCs were decoupled from the surface (63 %–82 % of the time). The coupled clouds had 41 % higher liquid water path than the fully decoupled ones. Local winds in the fjord were related to the frequency of surface coupling, and we propose that katabatic winds from the glaciers in the vicinity of the station may cause clouds to decouple. We concluded that while the regional to large-scale wind direction was important for the persistent MPC occurrence and properties, the local-scale phenomena (local wind patterns in the fjord and surface coupling) also had an influence. Moreover, this suggests that local boundary layer processes should be described in models in order to present low-level MPC properties accurately.