Can convective precipitation variability be deduced from the variability in CAPE and CIN? An analysis of global CAPE and CIN variability in present and future climates
The variability of convective precipitation is relevant for its prediction on short and long time
scales. On short time scales severe weather events are vital for weather forecasting, on long time
scales convection anomalies affect wetness and droughts. Since convective precipitation requires
parameterisation in numerical models, CAPE (convective available potential energy) and CIN
(convective inhibition) are applied to estimate trends and long-term memory. Their variability is
determined in present-day climate (ECMWF reanalysis: 6 hourly during 1979-2001 in T106 trun-
cation; ECHAM5/MPI-OM, 20C simulation: 6 hourly during 1902-2001 in T63 truncation) and a
possible warmer future scenario (ECHAM5/MPI-OM, A1B scenario: 6 hourly during 2002-2101
in T63 truncation).
Future changes in CAPE and CIN reveal similar changes for small, mean and large values. A
global pattern is found of increasing values in CAPE and CIN over most regions of the conti-
nents and northern hemispheric ocean basins, while decreasing values are found over the Southern
Ocean. This pattern changes towards mostly positive trends if CAPE is analysed for large CIN
occurring simultaneously. In contrast, the original pattern remains similar if CAPE is investigated
for small CIN.
Temperature and humidity, which form the basis of CAPE and CIN, show almost entirely higher
values in the future. Decreasing values in CAPE and CIN correlate with large scale patterns like
the North Atlantic Oscillation (NAO), El Ni
̃
no/Southern Oscillation (ENSO) and the Southern
Annular Mode (SAM). Furthermore, a southward shift of the descending branch of the southern
hemisphere Hadley Cell in a warmer climate decreases CAPE further.
The correlations of CAPE with the above named teleconnections influence the distribution of
global memory on long time scales. The influence of ENSO on the memory in CAPE and CIN
intensifies in a warmer climate with regards to spread and frequency. Furthermore, the impact
of the NAO on CAPE also spreads in terms of location, while the frequency remains similar in a
warmer climate. In contrast, the regions where SAM influences CAPE decrease due to declining
values of the SAM index. Additional analyses with an ECHAM5 simulation and climatological
sea surface temperature reveal that the variability of the ocean has a stronger influence on CAPE
than on CIN