Electric field measurements above mesoscale convective systems

We show that electric field discontinuities occur above the stratiform clouds associated with mesoscale convective systems. Above cloud top, 12 discontinuities were observed at altitudes between 10 and 16 km. The field changes of the discontinuities ranged from -1.1 to -4.0 kV m(-1). The data suggest that the electric field discontinuities were caused by coincident, positive, cloud-to-ground lightning flashes. The coincident ground flashes included both single and multiple return stroke flashes, with first-stroke peak currents between 20 and 154 kA, We modeled the electric field change that would occur if lightning discharged a horizontally extensive positive charge layer within the stratiform cloud, In the model, disks with charge densities of 1 and 3 nC m(-3), a thickness of 400 m, and diameters ranging from 20 to 200 km were discharged and produced field changes similar to the observed above-cloud field discontinuities. Our results support the idea that sprites may be initiated by above-cloud field changes caused by positive cloud-to-ground lightning flashes that discharge a horizontally extensive charge region in the stratiform cloud of a mesoscale convective system. During the time between the electric field discontinuities the electric field above the stratiform clouds was -0.5 to -1.0 kV m(-1) this field may be important in the global electrical circuit because the stratiform clouds have large horizontal extents (similar to 10(4) km(2)).