Motivation
The ionosphere layer, the upper region of the Earth’s atmosphere, is a layer of electrons created from ionizing the atom and molecules by solar radiation. This layer plays very important role in satellite communications and navigations as well as skywave radio communications because the changes in the electrons density of this layer influences the radio signal propagation. Especially, in the magnetic low-latitude and equatorial regions, the ionosphere is known to be highly variable due to ionospheric disturbances and irregularities such as the spread F events, sporadic E events, maximum usable frequency (MUF) depressions, etc.
Thus, it is very import to continuously monitor the ionosphere’s dynamic occurred at the low-latitude and equatorial regions by analyzing the observed ionospheric parameters such as the critical frequency of F2 layer (foF2), the virtual height of the bottom-side F layer (h’F), the F2-layer peak electron density as well as local geomagnetic K-index for understanding the local ionospheric irregularities and predicting the disturbances. The foF2 parameter and MUF are normally used to specify usable radio signal frequencies in high frequency (HF) band for coastal areas and emergency situation. For the Spread F events, they are used to indicate the ionospheric disturbance which will be important for HF communication and aeronautical navigation. Since the dynamic sin the ionosphere also depends on the solar and geomagnetic activity, it is also important to study the relationship between the ionospheric irregularities and the local K-index, especially derived from the magnetic field measured near the magnetic equator.
Objectives
In this research, we aim to analyze the ionospheric parameters such as foF2, h’F and NmF2 that are derived the data from the ionosonde at Chumphon, Thailand, and local geomagnetic K-index generated based on the data from the magnetometer at Phuket, Thailand. Since Chumphon and Phuket are very close to the magnetic equator, we believe that these parameters are good proxies for studying and prediction the ionospheric irregularities and disturbances. Moreover, we plan to analyze these observed data based on diurnal and seasonal variation as well as during the events of ionospheric and geomagnetic disturbances and then develop a local ionospheric disturbance prediction model using the local observed data as the input parameters based on machine learning. The developed prediction model will be investigated comparing with the International Reference Ionosphere (IRI) model.
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Fig. 1. Comparison of Local K-index from Phuket Observatory (AACGM 1.07°N, 171.15°E) and the global Kp index on (a) a solar disturbed day (March 17, 2019) and (b) a solar quiet day (December 3, 2019).
Figure 1 shows the comparison of local K-index from Phuket and Kp-index values for a disturbed day (March 17, 2019) and a quiet day (December 3, 2019). In the disturbed day, the values of both indices are quite similar, except sun-set time and after sun-set periods. However, the local K-index value is significantly higher than the Kp-index during the quiet days due the local ionospheric phenomenon. We find that the values of the local K-index significantly differ from those of the Kp-index due to the local ionospheric current system such as equatorial electrojet (EEJ).
References:
- Bartels, J., Heck, N. H. & Johnston, H. F., 1939. The three-hour-range index measuring geomagnetic activity. Terrestrial Magnetism and Atmospheric Electricity, 44(4), pp. 411-454.
- Matzka, J. a. S. C. a. Y. Y. a. B. O. a. M. A., 2021. The Geomagnetic Kp Index and Derived Indices of Geomagnetic Activity. Space Weather, 19(5), p. e2020SW002641.
- Stankov, S., Stegen, K. & Warnant, R., 2011. K-type geomagnetic index nowcast with data quality control. Annals of geophysics = Annali di geofisica, 54(3), pp. 285-295.