Ionospheric Piercing Point. 60º. 50º. 40º. Ionosphere. 30º. 12 hr. 18 hr. 0 hr. 6 hr. 12 hr. Earth Surface. h m. Local Time. Sub-ionospheric Point. High Resolution GPS-TEC Gradients in the Northern Hemisphere Ionospheric Trough.
High Resolution GPS-TEC Gradients in the Northern Hemisphere Ionospheric Trough
Continuous Operational Reference Station (CORS) network in New Jersey (see map) is a network of GPS stations that provide continuous dual frequency (fL1, fL2) measurements. Modeling the altitude dependency of electron density by a Chapman profile yield estimate of TEC. A recent GPS acquisition at Jenny Jump (NJJJ), NJIT’s experimental station equipped with magnetometer and other imaging instruments, should add new insights on ionospheric trough dynamics and related variables of space weather research.
The intent of this work is to integrate GPS observations at NJJJ with the NJ CORS GPS network to produce high spatial and temporal TEC maps. These GPS-derived TEC maps, in turn, will provide new high resolution data to search for short wavelength gradients in the mid-latitude ionospheric trough.
Major factors that determine TEC are intensity of solar activity, season, position, altitude, etc. Previous studies suggest that strong latitudinal gradients are associated with the ionospheric trough. However, the physical mechanisms of the trough formation include complex interconnected physical processes that are not well studied. Integrating NJJJ with the NJ CORS network may further our knowledge on small scale structure and related dynamic processes.
Geomagnetic storm indicators are indices such as Kp, Dst, and AE. Values for the Dst parameter ranges from low positive values for quiet times to high negative values to indicate storm activity. Figures below show solar activity for January and February of 2009 as derived from the Dst parameter. No storms were reported for 2009.
Laramie V. Potts
New Jersey Institute of Technology
Department of Engineering Technology
Newark, NJ 07102-1982 (firstname.lastname@example.org)
Ionospheric modeling using dual frequency geospatial mapping (Satellite Altimetry) and satellite-based positioning (GPS) data is the focus of extensive research in space weather systems . The poorly understood complex dynamics of ionospheric irregularities and external field variability over the mid-latitude regions are not well explored due to limitations of empirical models. The limited accuracy in predicting ionospheric effects presents significant problems affecting communication, remote sensing, surveillance, navigation and climate change research. However, currently available space geodetic sensors can facilitate substantial improvements on modeling ionospheric Total Electron Content (TEC) from various ground- and space-based observations . These observations include the GPS derived Global Ionosphere Maps (GIMs) generated by the mapping of the slant radar signals (L-band) from satellite (20,000 km) to the global ground receiver station network at each receivers’ zenith direction , LEO’s (400 km -1300 km, in the F and H ionosphere regions) carrying GPS receivers, and EnviSat (750 km) dual-frequency altimeter observations. Comparison with high spatial and temporal resolution GPSTEC from CONUS and CORS network is expected to provide new insight on short wavelength variability in the mid-latitude ionospheric trough. The Figure below is an example of the low resolution GPSTEC over most of North America
Latitudinal Profile of Ionospheric TEC from Altimetry
Data and Models
Nadir ionosphere delay over oceans and large lakes is measured by dual- frequency altimeters. Dual frequency altimeters such as Envisat, carrying a Ku-band (13.575 GHz) ad S-band (3.2 GHz) altimeter at 800 km, measures the fluctuations in TEC between the satellite and the earth’s surface to remove ionospheric influence and obtain a better estimate of altitude. Measured height at a given frequency hf is given by :
The transient location of the ionospheric trough is dependent on season, time, and geomagnetic activity as represented by Kp index. Experimental GPS TEC data was used to develop the trough location. The model is represented by a Fourier expansion of degree 2 as;
with A = 40250.
TEC obtained from altitudes (ranges) from two frequencies hKu and hs as:
to be determined
GPSTEC is calculated using a mapping function (Figure below) to estimate vertical TEC (VTEC) using group path lengths from two frequencies (L1=1.575GHz and L2=1.2276 GHz)
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