The effect of solar activity on the Doppler and multipath spread of HF signals received over paths oriented along the midlatitude trough

A J Stocker,E M Warrington

doi:10.1029/2010rs004482

Abstract

Measurements of the Doppler and delay spread associated with HF signals propagating along an oblique (1440 km) path tangential to the midlatitude ionospheric trough are presented for sunspot maximum and minimum. During the day, Doppler spread is independent of solar activity, but for winter and equinoctial nights, it is very much higher at sunspot maximum. The delay spread is also generally higher at sunspot maximum for all seasons and times of day. For sunspot minimum, measurements from a second, longer path (1800 km) are also presented. The observed Doppler and delay spreads are similar for both paths. Finally, a novel method of more accurately deriving the delay spread defined by the International Telecommunication Union (i.e., the largest delay spread including all modes that have a peak power within a user‐defined threshold of that of the strongest mode) from Voice of America coverage analysis program (VOACAP) predictions is presented. For the first time, the predicted values are compared with the measured delay spreads and, while there is generally good agreement at sunspot minimum, the agreement at sunspot maximum tends to be poor because the behavior of the high‐order ionospheric modes (e.g., 3F2) is not well predicted by VOACAP.

Highlights

[2] The midlatitude or subauroral trough is a region of the ionosphere of a few degrees in latitudinal extent where the electron density is reduced [Rodger et al, 1992]
[4] In this paper, we present experimental observations of delay and Doppler spreads together with predictions of delay spreads for three situations
April 2010 minimum aTime of flight measurements from August to December 2006 are unreliable, so delay spreads from this period are not included in the results presented below

Summary

Introduction

[2] The midlatitude or subauroral trough is a region of the ionosphere of a few degrees in latitudinal extent where the electron density (and the critical frequency and the maximum usable frequency) is reduced [Rodger et al, 1992]. For this example, taking the median SNR values results in an IMPS of 1.03 ms, while properly including the SNR probability distribution functions results in a median IMPS of 0 ms and a mean IMPS of 0.42 ms (with a standard deviation of 0.55 ms). The way the power profile with delay time was determined was changed, second weak modes were removed from the calculation of CMPS (see above), and third a small error in the calculation of the Doppler spread was corrected.

16 NL06 543

Findings

14.36 VOA Observed