Study of daytime vertical E × B drift velocities inferred from ground-based magnetometer observations of ΔH, at low latitudes under geomagnetically disturbed conditions

Abstract

In this study, 30 storm sudden commencement (SSC) events during the period 2001–2007 for which daytime vertical E×B drift velocities from JULIA radar, Jicamarca (geographic latitude 11.91°S, geographic longitude 283.11°E, 0.81°N dip latitude), Peru and ΔH component of geomagnetic field measured as the difference between the magnitudes of the horizontal (H) components between two magnetometers deployed at two different locations Jicamarca (geographic latitude 11.91°S, geographic longitude 283.11°E, 0.81°N dip latitude) and Piura (geographic latitude 5.21°S, geographic longitude 279.41°E, 6.81°N dip latitude), in Peru, were considered. It is observed that a positive correlation exists between peak value of daytime vertical E×B drift velocity and peak value of ΔH for the three consecutive days of SSC. A qualitative analysis made after selecting the peak values of daytime vertical E×B drift velocity and ΔH showed that 57% of the events have daytime vertical E×B drift velocity peak in the magnitude range 20–30m/s and 63% of the events have ΔH peak in the range 80–100nT. The maximum probable (45%) range of time of occurrence of peak value for both vertical E×B drift velocity and ΔH during the daytime hours were found to be the same, i.e., 10:00–12:00 LT. A strong positive correlation was also found to exist between the daytime vertical E×B drift velocity and ΔH for all the three consecutive days of SSC, for all the events considered. To establish a quantitative relationship between day time vertical E×B drift velocity and ΔH, linear and polynomial (order 2 and 3) regression analysis (Least Square Method (LSM)) were carried out, considering the fully disturbed day after the commencement of the storm as ‘disturbed period’ for the SSC events selected for analysis. The formulae indicating the relationship between daytime vertical E×B drift velocity and ΔH, for the ‘disturbed periods’, obtained through the regression analysis were verified using the JULIA radar observed E×B drift velocity for 3 selected events. Root Mean Square (RMS) error analysis carried out for each case suggest that polynomial regression (order 3) analysis provides a better agreement with the observations from among the linear, polynomial (order 2 and 3) analysis.