Energetics of interannual temperature variability

Abstract

Energetics of interannual temperature variability in the years 1980-2016 is studied using two reanalysis data sets. Monthly temperature anomalies are decomposed to contributions from the net surface energy flux, atmospheric energy convergence minus storage (CONV), and processes that affect the top-of-the-atmosphere radiation balance. The analysis reveals a strong compensation between the net surface heat flux and CONV over the ice-free oceans, with the former driving the temperature variability over the tropical oceans and the latter at higher latitudes. CONV also makes a dominant contribution to temperature anomalies in the winter hemisphere extratopical continents. During the summer half-year and in the tropics, however, variations in cloudiness dominate the temperature variability over land, while the contribution of CONV is modest or even negative. The latter reflects the diffusion-like behaviour of short-term atmospheric variability, which acts to spread out the local, to a large extent cloud-induced temperature anomalies to larger areas. The ERA-Interim and MERRA2 reanalyses largely agree on the general energy budget features of interannual temperature variability, although substantial quantitative differences occur in some of the individual terms.

Evolution of observed and modelled temperatures in Finland in 1901–2018 and potential dynamical reasons for the differences

“…Wintertime temperature conditions are likewise affected by ice conditions in the nearby Baltic Sea and snow cover through their albedo and thermal insulation capacity (Vavrus, 2007). Correspondingly, summer temperatures are influenced by soil moisture through the latent heat flux of evapotranspiration (Seneviratne et al ., 2010) and cloudiness (Räisänen, 2019b). These factors partly explain the coincidence of a high SLP and temperature in summer (Figure 2), since anticyclonic weather conditions tend to be clear and dry.…”

The summer 2018 heatwave in Finland

“…This heatwave was therefore most likely driven by an increase in incoming solar radiation allowed by unusually clear skies (cf. Räisänen, , who found that variations in the short‐wave cloud forcing – i.e. how clouds affect the amount of solar radiation reaching the surface – drive much of the temperature variability in mid‐latitude land areas in summer).…”

The extremely warm summer of 2018 in Sweden – set in a historical context

“…This is important, as extended periods with warm conditions have a stronger impact on human health as well as on other parts of nature than a single heat day (e.g. Oudin Åström et al, 2013;Rasmont and Iserbyt, 2012). Figure 4d shows the time series for max_conWarmD where the thin coloured lines represent the single ensemble members, the bold lines represent the ensemble means, and the horizontal dotted black line indicates the max_conWarmD value of 2018 as calculated from E-OBS.…”

“…Heatwaves are also reported to have impacted Sweden prior to 2018 in terms of an increased mortality rate among people (e.g. Oudin Åström et al, 2013), ecological consequences (Rasmont and Iserbyt, 2012), and in connection with air pollution episodes (Struzewska and Kaminski, 2008).…”