Anomalous lightning activity over Metropolitan Region of S(a)o Paulo due to urban effects

摘要

The city of S(a)o Paulo, one of the largest urban areas of the world, presented a significant enhancement in the number of negative cloud-ground (CG) lightning and a decrease of the percentage of positive CG lightning compared to its surroundings. Strong evidences indicate that this anomalous behavior is a result of the urban effect on S(a)o Paulo. In order to understand this relationship in details, parameters such as (1) the cloud base height, which is related to the lightning activity due to its direct relation to the convective available potential energy (CAPE); (2) the particulate matter (PM10), that works as condensation nuclei (CN) and can affect the microphysical processes of the clouds; (3) the CG lightning data provided by the Brazilian lightning detection network over the S(a)o Paulo urban area for a 6-year period (1999 to 2004) were analyzed and compared to each other. Annual and monthly variations of these parameters were studied, as well as the CG lightning activity during weekends, when a decrease of the PM10 concentration (pollution) is expected. The statistical results had shown a relationship between the number of negative cloud-ground (CG) lightning and PM10 (pollution), evidencing the decrease of the number of CG lightning followed by the decrease of the PM10.