Increasing free-air 0°C isotherm height in Southwest China from 1960 to 2010

Based on the radiosonde data observed at 14 stations in Southwest China from 1960 to 2010, as well as the corresponding surface air temperature, the long-term change of free-air 0°C isotherm height in Southwest China and the relationships between surface air temperature and 0°C isotherm height are discussed. The results indicated that the spatial distribution of 0°C isotherm height is generally related with latitude, but the huge massif or plateau may complicate the latitude pattern. The two main regimes influencing the spatial patterns of 0°C isotherm height in Southwest China are latitude and huge massif. The annual 0°C isotherm height has increased by 35 m per decade in the recent decades, which is statistically significant at the 0.001 level. Generally, the increasing trend can be examined for each seasonal series, especially in winter (53 m per decade). The diversity of trend magnitudes for annual and seasonal series can also be detected at a spatial view, but generally 0°C isotherm height correlated well with surface air temperature.