Response of the Ionosphere to Thunderstorms

A key tool in our investigation of the coupled Sun-Earth system is computer simulations or numerical models. Typically these models cover an altitude ranging from the Earth surface to several hundred kilometers. This range includes the troposphere, where everyday (or terrestrial) weather occurs, middle atmosphere with ozone heating in the stratosphere and cooling in the mesosphere, and the upper atmosphere where the temperature profile increases with altitude, also known as the thermosphere and ionosphere.

A recent study carried out by HAO scientist Hanli Liu, in collaboration with S. Vadas from Northwest Research Associates, Inc. (NWRA), showcases how terrestrial weather phenomena such as thunderstorms can drive large-scale disturbances in the ionosphere and thermosphere. The coupling between the lower atmosphere and the thermosphere-ionosphere takes place through gravity waves. Gravity waves are naturally occurring phenomena that happen in fluids in the presence of gravity. A common form of gravity waves is the waves seen on the ocean driven by the wind. Tidal variations are another form of gravity waves and they are seen both in bodies of water and throughout the atmosphere. Gravity wave perturbations can also be created by the collection of large thunderstorm activity, referred to by meteorologists as deep convection. In the tropical regions, deep convection is more than a typical afternoon thunderstorm and can extend over vast regions.

AIM Highlight- neutral density at the bottom of the F region of the ionosphere

Figure 6: Relative changes in the neutral density at the bottom of the F region of the ionosphere during a 6-hour peroid of strong thunderstorms that occurred over Brazil on the evening of October 1, 2005.

Adapted from [Vadas and Liu, 2013], Figure 6 shows the TIME-GCM simulations driven by reconstructions of the lower atmosphere during a deep convection event that happened on the evening of October 1, 2005. A few hours after the thunderstorm, a decrease of the thermospheric density at 250 km is seen over western Brazil. There is a corresponding increase in density over eastern Brazil and the Atlantic Ocean. Even after the deep convection had ended, the enhancements continued to move eastward. By analyzing the simulation results, the scientists were able to determine that the forces resulting from the dissipation of the gravity waves propagating up from the troposphere were responsible for the large-scale changes in thermospheric and ionospheric density as observed. In addition to these large-scale density enhancements, a series of secondary gravity waves was seen in the thermosphere. The effects of these secondary waves on the large-scale ionosphere structures are studied in a companion paper [Liu and Vadas, 2013] in which they found that these waves change the wind dynamo and transport in the ionosphere. Such ionospheric perturbations can affect radio wave propagation, satellite communications, and acquisition of Global Positioning System (GPS) signals.

This work was supported by funding from the NSF #M0856145 and award number NWRA-10-S-135.

Reference:

Liu, H.-L., and S. L. Vadas (2013), Large-scale ionospheric disturbances due to the dissipation of convectively-generated gravity waves over Brazil, J. Geophys. Res., 118(5), 2419–2427, doi:10.1002/jgra.50244.

Vadas, S. L., and H.-L. Liu (2013), Numerical modeling of the large-scale neutral and plasma responses to the body forces created by the dissipation of gravity waves from 6 h of deep convection in Brazil, J. Geophys. Res., 118(5), 2593–2617, doi:10.1002/jgra.50249.