Detection of F-region electron density irregularities using incoherent-scatter radar

Detection of F-region electron density irregularities using incoherent-scatter radar

Gudivada, Krishna Prasad

Date: 2014-08

Type: Thesisms

Table of Contents: Chapter 1. Introduction -- 1.1. Overview of the Ionosphere -- 1.2. Impact of Electron Density Irregularities on Navigation Systems and SAR Imaging -- 1.3. Historical Review and Objective of Thesis -- Chapter 2. Incoherent scatter radar -- 2.1. Introduction -- 2.2. Determination of Electron Density -- 2.3. Basic Experiment Design and Estimation of Line-of-sight Velocity -- 2.4. Determination of Ion Vector Velocities -- Chapter 3. Experimental approach -- 3.1. Introduction -- 3.2. AMISR System Description -- 3.3. Description of Experiments -- 3.4. Determination of Ionization Blob Scale Sizes -- Chapter 4. Observations of electron density irregularities using the poker flat incoherent scatter radar -- 4.1. Introduction -- 4.2. Results -- 4.2.1. August 28th, 2011 -- 4.2.2. August 31st, 2011 -- 4.2.3. March 9th, 2012 -- 4.2.4. March 25th, 2012 -- 4.2.5. October 9th, 2012 -- 4.2.6. October 12th, 2012 -- 4.2.7. October 19th, 2012 -- 4.2.8. November 4th, 2012 -- 4.3. Discussion -- Chapter 5. Conclusions and future work -- 5.1. Conclusions -- 5.2. Future Work.

Abstract:

Incoherent-scatter radar data from Poker Flat, Alaska has been used to determine size distributions of electron density structures in the evening time sector of the auroral zone. At high latitudes ionospheric plasma typically moves east-west with speeds of several hundred meters per second. Density irregularities that rapidly move through the radar beam are therefore observed as time-varying power fluctuations. The new phased array radar used for this study has been operated with several antenna directions with successive pulses transmitted in each direction. It is therefore possible to observe plasma Doppler velocities in multiple directions and determine the vector direction of the plasma motion. This near-simultaneous observation of the plasma velocity in conjunction with the electron density height profile data enable a new technique to determine the scale sizes of electron density fluctuations that move horizontally through the radar beam. The study focuses on the collision-less F-region ionosphere where the plasma drift is approximately constant with altitude. The experimental technique limits the range of scale sizes that may be studied to relatively large-scale sizes (i.e. greater than few tens of km). Results show that during magnetically disturbed conditions (Kp ≥ 4) when westward plasma velocities are relatively high (500-1000 m/s) the scale sizes of irregularities (often called plasma blobs) are in the range of 100-300 km and predominantly originate from the polar cap and are transported over long distances (~1000 km) due to the long chemical recombination times (30-90 minutes). Some irregularities are caused by local auroral particle precipitation and have been identified with associated electron temperature enhancements. For cases of low magnetic activity (Kp ≤ 1), when the radar is located in a region of low plasma velocities (100-500 m/s) well south of the auroral oval (essentially a mid-latitude type ionosphere), the density distribution is always biased strongly toward small-scale sizes (less than 50 km).