Asymmetries of the lag between air temperature and insolation in gauge observations and reanalyses over China

Abstract

The annual cycle of near-surface air temperature should receive more attention in climate studies because it is especially important to crop growth and to human comfort. The phase of the annual temperature cycle generally lags behind that of insolation due to the time required for the Earth's surface to absorb the energy from solar radiation and then warm the near-surface air. This study decomposes the daily maximum, minimum, and mean air temperatures using Fourier transforms and examines the lag in number of days between the phases of temperature and insolation. It was found that the lags between air temperature and insolation were asymmetrical during the summer and winter seasons. The mean summer lags were 30.8, 32.4, and 30.6 days from gauge observations over China, which were longer than the 21.0, 21.5, and 16.7 days of winter lags for daily maximum, minimum, and mean temperature respectively. Spatially, these lags showed wider climatological and interannual variability in southern than in northern areas because higher atmospheric water vapor content and greater cloud cover caused a longer response time of air temperature to solar radiation. Decreasing variations were derived for the winter lag, at about −1.11 days/decade, −0.68 days/decade, and − 0.78 days/decade for the maximum, minimum, and mean temperature respectively. Currently, reanalysis data can accurately simulate the climatological, long-term, and interannual variability of the summer and winter lags over most of the study area, except for southwestern China, although they have negative biases in characterizing the annual cycle.