Climate Science Applications (detailed) The major culmination of ACRE activities is the 20CR reanalysis system conceived and run by the Earth Systems Research Laboratory (CIRES, University of Colorado) with the support of the Earth System Research Laboratory (ESRL, of NOAA). Using relatively sparse input of surface pressure data, much provided and facilitated by ACRE and its partners, the system recreates a rich 4D global dynamical reconstruction of historical weather events. Climate scientists can use this output to analyse in detail a range of climate phenomenon. Below is a representative sample of this research work made possible by ACRE and 20CR. A greater range of scientific research that relied on 20CR is available here and here : Land surface temperatures Confirmation of global warming Even though 20CR does not assimilate surface temperature observations, Compo et al. (2013) were able to confirm the robustness of previous conclusions regarding global warming. 20CR only uses synoptic barometric pressure, monthly sea surface temperature, and monthly sea- ice concentration to reproduce up to 56 realisations of annual variations and centennial trends in the land air temperature data sets. It’s output confirming global warming without using land surface temperature records, is free of any possible inconsistencies in such data that have been proposed previously by climate change sceptics Hemispheric to regional surface temperature variations Yu et al. (2014) focused on decadal modulations of Northern Hemisphere winter land surface air temperatures and atmospheric circulation, while Richard et al. (2012) examined mid to high latitude changes in Southern Hemisphere land surface air temperatures. More regionally, Soon et al. (2011) focused on variations in land surface air temperatures in China, Vose et al. (2012) examined trends in US land surface air temperatures using observed and various reanalyses, while Turco et al. (2012) looked at Spanish instrumental and downscaled 20CR output. Precipitation Regional Zhang et al. (2012) focusing on southern Africa, used 8 global reanalyses to study African monthly-mean precipitation and compared their outputs to the gridded precipitation dataset from the Climate Research Unit (CRU) at the University of East Anglia. They found that: “the preferential reanalysis for investigating the climate variability over southern Africa is 20CRv2 that furthermore spans the longest time period, hence permitting the most precise investigations of interannual to decadal variability”. Sub Regional A pilot project was initiated by the Met Office PRECIS group using their regional climate modelling system to downscale 20CR to study the rainfall associated with the 1894 River Thames/Southern England flooding event (Brugge, 1994). The study aimed to simulate the precipitation drivers of the 1894 flooding of the River Thames. It demonstrated that the downscaled member 37 of the 56 ensemble member output from 20CR provides the best representation of the precipitation conditions over the most heavily impacted regions of the UK. As noted previously, the PRECIS team are now downscaling 20CR to provide a high resolution baseline of UK droughts from 1850-2014 under the MaRUIS Project (Managing the Risks, Impacts and Uncertainties of drought and water Scarcity) Storms 20CR contributed to the analysis of an 1888 blizzard and a 1925 tornado in the US, and storms in the UK in both the 19th and 20th centuries. Wave Heights A number of researchers have used 20CR to reanalyse wave heights and storm surges. They came to the conclusion that the data in the model is incomplete, pointing to the need for more Old World data recovery, digitisation and assimilation into 20CR model, activities championed by ACRE. Heat Waves and cold spells 20CR contributed to the analyses of likely causes of a recent heatwave in Russia and causes of ice sheet melting in Greenland. Ouzeau et al. (2011) used 20CR to establish the uniqueness of the European cold winter of 2009-2010. A weather regime analysis showed that the frequency of the negative North Atlantic Oscillation was unprecedented since the winter of 1939–1940, which was then used as a dynamical analogue of the winter of 2009–2010 to demonstrate that the latter might have been much colder without the background global warming observed during the twentieth century. They further used 20CR products to highlight the relevance of the stratosphere for understanding, if not predicting, such anomalous winter seasons. Floods and Droughts A number of studies have used 20CR to analyse historic floods and droughts in Europe and North America up to 150 years ago. They also examined the synoptic, interannual, decadal and multi- decadal conditions underlying them. El Niño Southern Oscillation Studies using 20CR and other reanalyses have looked to improve understanding of ENSO dynamics. They re-examined ENSO events to determine their connection with other climate anomalies including ocean winds, sea subsurface temperatures, SW Pacific rainfall and global drought. A study of the 1877-1878 El Niño, and the conditions leading up to and following it, using 20CR is in under development. Global warming hiatus In a draft of work led by Li Qingxiang (China Met. Admin., Beijing), a comparison was made between surface air temperature trends from 20CR and observed trends over China. For 1961-2012, 20CR produced year-round warming, as observed. For the global warming “hiatus” period 1998-2012, 20CR reproduced cooling over China in winter, in agreement with observations, with little change in summer. As 20CR does not use air temperature data or aerosol forcings, it was concluded that the winter cooling must have come from the atmospheric circulation, i.e. an increase in winds from the north responding to the assimilated atmospheric pressure data. Other Historical events Tambora Eruption and the ‘Year without a Summer’ (1815-1817) Reaching very far back into climate history, this is a reanalysis of the period around the Tambora volcanic eruption using 20CRv2c, but with climatological SST and sea-ice, and no stratospheric aerosols. Imperial Trans-Antarctic Expedition (1914–17) The Imperial Trans-Antarctic Expedition led by Sir Ernest Shackleton, failed to reach its exploration objectives, but it did allow groups of scientists to spend many months in the Antarctic, where they made careful observations of the weather. Though the expedition records have not been published or systematically analysed, they provide the data required for a reanalysis of the Antarctic weather 1914-1916.