Location: Darwin, Australia
Date: January 1989
The cumulonimbus cloud is what we commonly call a thunderstorm, characterized by rumbling thunder and electrifying displays of light. These storms can be isolated or as part of a larger group of storms, at times bringing periods of heavy rain followed by longer periods of lighter persistent rainfall. Radar is one tool to look inside the clouds to study the formation of rainfall, and instruments are also available to measure the electricity in clouds. Put these together and an understanding of how processes in the storm lead to lightning production in a variety of storm types and sizes can be investigated.
Darwin, Australia is a great location to study this range of storms, especially during the wet, monsoon season when there are both intense individual storms and large clusters of storms (what we refer to as mesoscale convective systems). While there have been several scientific studies in the region, these pictures are from one particular project in 1989 called The Down Under Doppler and Electricity Experiment, or DUNDEE for short (clever name for a project in Australia, right?). Using radars (the protective radome of the MIT radar can be seen in the second photo), surface and upper-air measurements, and instruments to measure electrical activity, this study allowed for valuable insight into the characteristics of these various storms, how they relate to environmental conditions, and the relationship between lightning and microphysical processes inside the storm (such as formation of ice, collision of ice, rainfall production, etc.). This diagram shows where the lightning sensors were located during this project (courtesy of Rutledge, S.A., E.R. Williams, and T.D. Keenan, 1992: The Down Under Doppler and Electricity Experiment (DUNDEE): Overview and preliminary results.Bull. Amer. Meteor. Soc., 73, 3-16):
There are many types of lightning, from the cloud-to-ground (CG) strokes seen in the first photo to the intra-cloud (IC) lightning that appears to be crawling across the cloud. Collisions of smaller ice crystals and large, precipitation-sized ice (such as graupel and hail) lead to charge separations in the cloud. The discharge of electricity can occur between different layers of charge within the cloud, between the cloud and the ground, between different clouds, and between the cloud and the air. Always seeking the path of least resistance, many step leaders can be seen in addition to the main stroke, creating an incredible display of light.