Estimation of the IC to CG Ratio Using JEM-GLIMS and
Ground-basedLightning Network Data
Abstract
The occurrence ratio of intracloud (IC) to cloud-to-ground (CG)
discharges, which is denoted by -ratio, is the crucial parameter for the
studies on the climatological differences of thunderstorm structures and
the quantitative evaluation of lightning contributions to the global
electric circuit. However, the latitudinal, regional, and seasonal
dependences of -ratio are not fully clarified. Therefore, using optical
data obtained by the JEM-GLIMS mission, we distinguished the lightning
discharge type, , IC, positive CG (+CG), and negative CG (-CG)
discharges, and statistically estimated the Z-ratio. We analyzed 8354
JEM-GLIMS lightning events and succeeded in identifying 4431 IC
discharges, 597 +CG discharges, and 3326 -CG discharges. From this
result, we calculated the -ratio and estimated its latitudinal,
regional, and seasonal dependences. It is found that the -ratio is
slightly higher over the continental area than the oceanic area. In
addition, the average -ratio in the local summer season is higher than
that in the local winter season. The clear latitudinal dependence of the
-ratio is also found, which is generally comparable to the results shown
in the previous studies. The estimated -ratio varies from 2.9 - 0.19
from the equator to 50º latitude, and the global mean value is 1.6. The
regional dependence of -ratio derived from this study can be combined
with the CG lightning data provided by the ground-based lightning
detection networks to estimate the occurrence number of IC discharges.
It will greatly contribute to a more accurate estimation of the total
lightning currents in the global electric circuit.