Comparison between IRI and preliminary Swarm Langmuir probe measurements during the St. Patrick storm period

Alessio Pignalberi,Igino Coco,Paola De Michelis,Roberta Tozzi,Michael Pezzopane

doi:10.1186/s40623-016-0466-5

Abstract

Preliminary Swarm Langmuir probe measurements recorded during March 2015, a period of time including the St. Patrick storm, are considered. Specifically, six time periods are identified: two quiet periods before the onset of the storm, two periods including the main phase of the storm, and two periods during the recovery phase of the storm. Swarm electron density values are then compared with the corresponding output given by the International Reference Ionosphere (IRI) model, according to its three different options for modelling the topside ionosphere. Since the Swarm electron density measurements are still undergoing a thorough validation, a comparison with IRI in terms of absolute values would have not been appropriate. Hence, the similarity of trends embedded in the Swarm and IRI time series is investigated in terms of Pearson correlation coefficient. The analysis shows that the electron density representations made by Swarm and IRI are different for both quiet and disturbed periods, independently of the chosen topside model option. Main differences between trends modelled by IRI and those observed by Swarm emerge, especially at equatorial latitudes, and at northern high latitudes, during the main and recovery phases of the storm. Moreover, very low values of electron density, even lower than 2 × 104 cm−3, were simultaneously recorded in the evening sector by Swarm satellites at equatorial latitudes during quiet periods, and at magnetic latitudes of about ±60° during disturbed periods. The obtained results are an example of the capability of Swarm data to generate an additional valuable dataset to properly model the topside ionosphere.

Highlights

At the end of 2013, the European Space Agency (ESA) launched the three-satellite Swarm constellation
Before getting to the hearth of the discussion of results, we want to draw the attention to the fact that each time we talk generically about Swarm, we refer to all satellites (Swarm A, B, and C), and each time we talk about Swarm A, due to their proximity, we are implicitly talking about Swarm C
Concerning the period P1, for the morning sector (Fig. 5), the equatorial band shows for both International Reference Ionosphere (IRI) and Swarm the same usual pattern characterized by a maximum of electron density along the magnetic equator (e.g., Balan and Bailey 1995)

Summary

Introduction

At the end of 2013, the European Space Agency (ESA) launched the three-satellite Swarm constellation. Two [Alpha (A) and Charlie (C)] are orbiting the Earth side-by-side at the same altitude of about 460 km, while the third [Bravo (B)] is flying about 60 km above They are all equipped with identical instruments consisting of high-resolution sensors for measurements of both geomagnetic and electric fields, as well as plasma density. We are interested mainly in the measurements made by the electric field instrument (EFI) comprising two thermal ion imagers (TIIs) and two Langmuir probes (LPs). The former measures the three-dimensional ion distribution, the latter the spacecraft potential, plasma density, and electron temperature, both at 2 Hz rate. Some details on the complex structure of this storm can be found in Kamide and Kusano (2015) and Cherniak et al (2015)

Methods

Results

Conclusion