Cirrus Feedback on Interannual Climate Fluctuations
Cirrus clouds are not only important in determining the current climate, but also play an important role in climate change and variability. Analysis of satellite observations shows that the amount and altitude of cirrus clouds (cloud optical depth<3.6, cloud top pressure<440 hPa) increase in response to inter-annual surface warming. Using cirrus cloud radiative kernels, the magnitude of the inter-annual cirrus feedback is estimated to be 0.20±0.21W/m2/°C, which represents an important component of the cloud feedback. Thus, cirrus clouds are likely toact as a positive feedback on inter-annual climate fluctuations, by reducing the earth’s ability to radiate longwave radiation to space in response to planetary surface warming. Most of the cirrus feedback comes from increasing cloud amount in the tropical tropopause layer (TTL) and subtropical upper troposphere.