The relation between lightning and cosmic rays during ENSO with and without IOD — A statistical study.

The relationship between the number of lightning flashes (NLF) and the cosmic ray flux (CRF) during the period of ENSO (El Niño/La Niña Southern Oscillations) with and without IOD (Indian Ocean Dipole) has been studied for the first time in the region of South/Southeast Asia (8°N–35°N and 60°E–120°E) to the authors' knowledge. Our analysis shows that the relationship is governed by regional meteorology and not by direct solar influence. Unlike on global scale, the data during ENSO are important for this relationship on regional scale. CRF and NLF are in statistically significant relationship only when CRF is significantly correlated with the meteorological parameters. CRF and NLF are significantly correlated during the period of ENSO with IOD (ENSO–IOD) but not during the period of ENSO without IOD (ENSO). The Aerosol Optical Depth (AOD), the positive temperature anomaly (TA) and an increase in TA may be responsible for this relationship during the ENSO–IOD period. On the shorter temporal/spatial scale, meso-scale meteorological parameters are responsible for the negative correlation between the CRF and the NLF. On the other hand, on the longer scale, an amount of Low Level Cloud Fraction (LLCF) is responsible for the positive correlation between the CRF and the NLF. Our partial correlation analysis shows that controlling for the AOD weakens the correlation between the CRF and the NLF but does not affect that between the 12month running means of the same. Thus, aerosols are responsible during the total study period and during the IOD period for enhancing the significant CRF–NLF relationship. Solar radio flux F10.7 cm (SRF10.7) seems to be the main controlling parameter for the stronger relationship. We find that there is a distinct difference in the average magnitude of different solar and meteorological parameters between that during the ENSO period and the ENSO–IOD period which may be attributed to the difference in cloud types and aerosol properties between the two periods. The results of our analysis may be confirmed with longer data sets and more number of IOD events in the future. [ABSTRACT FROM AUTHOR]