How Extreme Apparitions of the Volcanic and Anthropogenic South East
Asian Aerosol Plume Trigger and Sustain El Niño Events. First
Attribution and Mechanism using data from the Last Millennium Ensemble,
Large Ensemble, MERRA-2 Reanalysis, four Satellites and the Global
Volcanism Program.
- Keith Alan Potts
Abstract
Volcanic aerosols over south east Asia have always been the trigger and
sustaining cause of ENSO events. In recent decades this natural plume
has been augmented by the anthropogenic plume which has intensified ENSO
events especially in SON. Data from the Last Millennium Ensemble (13,972
months), and Large Ensemble (3,012 months) demonstrate this connection
with three ENSO indices and aerosol data derived from the same datasets
correlating at 1.00 (LME), 0.97 and 0.99 magnitude (segmented and
averaged). ENSO events are the dominant mode of variability in the
global climate responsible for Australian, Indian and Indonesian
droughts, American floods and increased global temperatures.
Understanding the mechanism which enables aerosols over SE Asia and only
over SE Asia to create ENSO events is crucial to understanding the
global climate. I show that the South East Asian aerosol Plume causes
ENSO events by: reflecting/absorbing solar radiation which warms the
upper troposphere; and reducing surface radiation which cools the
surface under the plume. This inversion reduces convection in the region
thereby suppressing the Walker Circulation and the Trade Winds which
causes the SST to rise in the central Pacific Ocean and creates
convection there. This further weakens/reverses the Walker Circulation
driving the climate into an ENSO state which is maintained until the
aerosols dissipate and the climate system relaxes into a non-ENSO state.
Measured aerosol data from four NASA satellites, estimates of volcanic
tephra from the Global Volcanism Program (GVP) for over 100 years and
the NASA MERRA-2 reanalysis dataset all confirm this analysis.