Do transient cosmic ray decrease cause changes in the global cloud cover ?

Abstract

It has often been speculated that the atmospheric cloud cover might be affected by the flux of cosmic rays incident on the earth’s atmosphere. The basis for this speculation is that cosmic rays (which are essentially charged particles incident on the Earth) can act as cloud condensation nuclei. It is well known that the cosmic ray flux is a sensitive function of the solar activity. Eruptions in the solar corona, called coronal mass ejections (CME) cause transient dips in the cosmic ray intensity observed at the earth, called Forbush decreases (FD). In this work, we investigate if FD events can be correlated with changes in the global cloud cover. We use the high energy cosmic ray data from the GRAPES 3 experiment operated by the Tata Institute of Fundamental Research (TIFR) at Ooty, India and look for correlations with global cloud properties such as Ice and Liquid cloud effective radius, Optical thickness, Water path in addition to Cloud fraction and the precipitation rate. While some of the correlations are suggestive, we conclude that it is difficult to claim an unambiguous causal link between cosmic rays and global cloud cover based on an overall examination of all the data.