Towards a better understanding of the global electric circuit and thunderstorm trends utilizing satellite and ground-based measurements

Date

2022-12

Authors

Lavigne, Thomas

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Abstract

The Global Electric Circuit (GEC) of the atmosphere is a naturally occurring phenomenon in which the Earth’s atmosphere acts as a leaky capacitor between the Ionosphere and the Earth’s surface. Primarily due to the constant presence of thunderstorms and electrified clouds around the globe, the leaky capacitor is continually recharged by the upward storm current produced above thunderstorms and electrified clouds. The balance between the fair-weather return current which drains the circuit, and the input from the upward storm current creates the stable Earth’s electrical system known as the GEC. Under the changing climate, it is anticipated the GEC would vary accordingly. To understand the changes of global thunderstorms, a novel approach at observing thunderstorm trends is conducted by combining a 43-year ground station thunder day dataset with shorter-term satellite optical flash data from the Tropical Rainfall Measuring Mission-Lightning Imaging Sensor (TRMM-LIS). A regional relationship between the thunder day occurrence and the lightning flash density as well as thunderstorm population is conducted in each global 5oxo5 grid. In many regions of the globe such as Argentina, China, and the Maritime Continent, a statistically significant agreement (r-value >0.8) is present between the simultaneous 16-year trends of all three explored variables. This indicates that in these regions, the thunder day recordings statistically represent the flash density and number of thunderstorm events. However, in other regions of the globe, the long-term changes of thunder day occurrence and flash density are not well correlated, or even negatively correlated, indicating the regional nature of the relationship between the two variables. With the understanding that thunderstorm activity is indeed changing over the course of the past several decades, it emphasizes the importance of monitoring the GEC, which is directly tied to the variations of global electrified clouds. Here, a novel method is introduced to determine fair-weather time periods and monitor this global component of the vertical electric field (Ez) at two sites separated by over 6,000 km (Barrow, AK, and Corpus Christi TX). With the use of a Micro-Pulse Lidar (MPL) backscattering coefficient, as well as other meteorological information, a definition of 5-minute averaged -50 V/m to -300 V/m electric fields, with 5-minute averaged standard deviations of less than 25 V/m is selected as criteria to define fair-weather periods. Using this method, agreement is found between the composited diurnal variation of fair-weather Ez between the two sites on the hourly, monthly, and yearly timescales. Recent studies also suggest that it is possible that the GEC may also have notable influences on the local cloud properties in the polar region. To validate these findings, the variations of the fair-weather Ez measured in Barrow, AK are compared to numerous local cloud, precipitation, and radiation properties during the polar night. Comparisons between the averaged diurnal variations of fair-weather Ez, and cloud thickness, maximum column backscatter, and precipitation particle counts show correlated diurnal variability. During the time periods with a stronger fair weather Ez, clouds bases tend to be higher, clouds are thicker, have a larger column backscatter, and produce more precipitating particles at the surface. Furthermore, a slight diurnal variability in the polar night surface temperature was found to be highly correlated (r=0.87) to the longwave downwelling irradiance, indicating that the characteristics of these persistent layered clouds act as the primary driver of diurnal surface temperature variability during the polar night in Barrow, AK. The feedback nature of the GEC system illustrates the global connectivity of the system, with the aggregate of localized electrified clouds around the globe driving the magnitude of the fair-weather return current, which in turn may influence the properties of localized clouds, such as the persistent layered clouds during the polar night in Barrow, AK.

Description

A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Coastal and Marine Systems Science.

Keywords

arctic clouds, atmospheric electricity, electric field, global electric circuit, lightning, thunder-day

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