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Deriving the precise true height electron density profile from the measured ionosonde virtual heights is quite a challenging problem. Recently, Ankita and Tulasi Ram (2023, https://doi.org/10.1029/2023RS007808) presented a new method, Iterative Gradient Correction (IGC) method, for true height analysis that uses HF radio wave propagation path computations to reconstruct the true height profile. Through iterative corrections on electron density gradients between successive points, the IGC method minimizes errors below a specified tolerance at each point and reconstructs a complete electron density profile. The derived profiles from the IGC method are found to be accurate when compared with Incoherent Scatter Radar and Global Navigation Satellite System—Radio Occultation observations. To facilitate true height analysis by IGC method for a wider user community, a MATLAB‐based software has been developed and is outlined in this report. The software can be installed on any Windows platform and is designed with a user‐friendly interface for easy and efficient application by the users. It can analyze multiple scaled ionograms in a single run and outputs the real height profiles in ASCII format. Further, the software also captures important ionospheric parameters such as the base altitudes and peak frequencies of E‐ and F‐layers (e.g., hE, hF, foE, and foF2) etc., from the computed true height profiles and tabulates in a separate output file for the ready use. The software also provides the option for extrapolation of true height profile into top‐side ionosphere up to a user‐specified height and reconstructs the complete vertical electron density profile. Key Points: A new software with user‐friendly interface is developed for true height analysis of ionograms using Iterative Gradient Correction methodIt can compute multiple true height profiles in one run with an option to extrapolate into top‐side ionosphere up to a user‐specified heightIt also captures the important ionospheric parameters such as hE, hF, foE, foF2, etc., for ready use in research/practical applications [ABSTRACT FROM AUTHOR]

Inversion of precise true height electron density profile from the measured virtual heights by the Ionosonde is a quite challenging and ill‐posed problem. In this paper, we present a new method to compute the true height profiles from ionograms that relies on computing the propagation path of radio waves with time. This method does not use predefined polynomial functions to fit the vertical electron density distribution; hence, it is free from fitting errors. Instead, this method implements iterative corrections in the electron density gradient between the successive points and progressively reconstructs the true height profile. This Iterative Gradient Correction (IGC) method assures minimizing the error to below a tolerance limit at all sampled points on the ionogram. The true height profiles derived from this method exhibit better accuracy than those derived from the widely used POLynomial ANalysis, particularly, at cusp and F2‐peak regions. Further, the IGC method gives the best results at higher sampling resolutions of ionograms and is less sensitive to scaling errors. Plain Language Summary: The ionosphere is an ionized layer of Earth's upper atmosphere that reflects the incident HF (high frequency) radio waves back to the ground. This property of the ionosphere is used to establish radio communications over far distances beyond the horizon. Monitoring the electron density in the ionosphere is essential, as the changes in the ionospheric electron density distribution can significantly impact these communication systems. Ionosonde is one such classical instrument that is widely used to measure the vertical electron density distribution of the ionosphere. However, like any radar, Ionosonde assumes the radio waves travel with the speed of light, which is not true in the case of ionosphere. This assumption gives rise to higher estimates of reflection heights by the ionosphere known as virtual heights that are far from reality. In this paper, we present a new method that computes the actual path of radio waves with respect to time in the ionospheres and computes the true height electron density distribution from the measured virtual heights by the Ionosonde. This method, besides scientific research, would have potential applications in Skywave communications, over‐the‐horizon target detection and ranging applications. Key Points: A new method to derive the true height profiles from ionograms that relies on computing the propagation path of radio waves with timeProgressively constructs the true height profile by iteratively correcting the gradient between successive points until the error is <±1 kmThe Iterative Gradient Correction method gives more accurate results at the cusp and F2‐peak regions and is less sensitive to scaling errors compared to POLynomial ANalysis [ABSTRACT FROM AUTHOR]

The plasma density distribution in the equatorial and low latitude ionosphere can often be severely disturbed during active space weather events that can have paramount impacts on the long‐distance high frequency (HF) radio wave (Skywave) communications through the ionosphere. On the St. Patrick's Day storm of 17 March 2015, a deep depletion of plasma with more than two orders of magnitude was observed over a narrow longitudinal sector near the sunset terminator. The controlled SAMI2 (Sami2 is Another Model of the Ionosphere) simulations indicate that a large equatorial vertical drift around sunset terminator can produce such a deep electron density depletion and strong reinforcement of equatorial ionization anomaly. The impacts of these ionospheric density disturbances on the Skywave communication systems have been investigated using an HF propagation simulator that solves the propagation path of radio waves under given background ionospheric conditions. The results clearly demonstrate that the usable HF spectrum for Skywave communications is reduced by more than 50% over the region of depletion. Further, large areas of skip zones, where the Skywave signals are not receivable, are produced due to low ionospheric densities over this region. This study can have important applications in the planning and operation of Skywave systems during the active space weather periods. Plain Language Summary: Earth's ionosphere acts as a mirror in space that reflects back the radio waves to the ground and facilitates Radio communication links over very far distances beyond the horizon. However, the ionosphere which is primarily produced via photo‐ionization by solar radiations can often be greatly disturbed due to highly energetic events on the sun such as solar flares, Coronal Mass Ejection, etc., and the resultant changes in the Earth's near space. These ionospheric disturbances can have significant impacts on the usable radio wave spectrum and ground coverage area of reception for Skywave communication systems. This study investigates a unique event of deep ionospheric density depletion that occurred during the geomagnetic storm and its impacts on Skywave systems over equatorial and low latitude regions. This study provides important insights about the space weather impacts on long‐distance radio communications and can have potential applications in the planning and operation of Skywave communication systems. Key Points: A deep electron density depletion occurred over a narrow longitude sector near sunset terminator due to large equatorial vertical driftThe depletion caused severe limitations on the usable high frequency spectrum of Skywave communication systems by reducing the maximum usable frequency by more than 50%The depletion also resulted in a wide area of skip zones over equatorial regions where Skywave communication signals cannot be received [ABSTRACT FROM AUTHOR]

The assumption of spherical uniformity while the retrieval of electron density profiles from the Global Navigation Satellite Systems-Radio Occultation (GNSS-RO) observations is often violated and introduces significant errors in the retrieved electron density profile data. This paper presents an improved Abel-inversion technique by incorporating the horizontal gradients in the ionosphere, which are routinely derived from the Artificial Neural Network (ANN) based background NmF2 (peak electron density of F2-layer) model (ANNC2) assimilated with near real-time Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (FORMOSAT-7/COSMIC-2) NmF2 data. The ANNC2-aided Abel inversion is then implemented for more accurate retrieval of electron density profiles from COSMIC-2 in real-time. It is found that the ANNC2-aided inversion has improved the electron density values around the F2-region and below, which yields a clear separation between two anomaly crests. Further, the ANNC2-aided Abel inversion had significantly reduced the artificial plasma caves beneath the equatorial ionization anomaly crests. Furthermore, COSMIC-2 NmF2 observations obtained from both classical and the ANNC2-aided Abel inversion are compared with the ground-based Digisonde data and found that the ANNC2-aided inversion gives the better results. This study provides some new insights on the aided Abel inversion technique assisted by ANN models for the real-time correction of Abel retrieved electron density profiles. [ABSTRACT FROM AUTHOR]

The existence of an additional stratification in the daytime equatorial ionospheric F region (the F3 layer) was known since the 1940s. However, its characteristics and the underlying physical mechanism have been uncovered only recently. In this paper, we present and discuss the F3 layer characteristics observed by six ionosondes distributed over equatorial and low latitudes (−20° to +25° dip latitudes) in the Brazilian longitude sector during the strongest geomagnetic storm (DstMin = −223 nT) of solar cycle 24, the St. Patrick's Day storm of 17 March 2015. Two eastward prompt penetration electric field (PPEF) events, as seen in equatorial electrojet, occurred during the main phase of the storm on 17 March 2015, a strong one (~100 nT) at around ~1200 UT and a weak one (~50 nT) at around ~1725 UT. Local time variations in the F3 layer occurrence and ionospheric base height (h′F), peak height (hmF), and peak electron density (Nmax) are investigated. Notably, the F3 layer occurred at all six locations, more distinctly during the stronger PPEF event. The large latitudinal extend in the occurrence of the F3 layer in opposite hemispheres (−20° to +25° dip latitudes) covering the equatorial ionization anomaly crests observed for the first time is interpreted in terms of the combined effect of the super plasma fountain generated by the eastward PPEF and storm time equatorward neutral wind. Key Points: F3 layer occurred over a large latitudinal extent from 20°S to 25°N dip latitudes during 17 March 2015 storm‐induced PPEF phasesThe PPEF‐generated superfountain led to the F3 layer occurrence earlier at the equator and later at higher latitudes in both hemispheresF3 layer was more distinct and stronger and lasted longer in the Northern Hemisphere due to the storm time asymmetric equatorward neutral winds [ABSTRACT FROM AUTHOR]

Abstract Various ionospheric vertical scale heights (VSH) including, the Chapman (H m), VSH at upper ionosphere (VSH UP) and 500 km (VSH 500) derived using COSMIC radio occultation (RO) retrieved electron density profiles during a complete solar cycle (2006–2016) are presented in this research. VSH show distinct latitudinal variations and solar-activity dependencies. VSH follow the geomagnetic equator with a longitudinal structure irrespective of the season and year, although mid and high latitudes show higher values and irregular variations in low (2006–2010) and moderate-to-high (2011–2016) sunspot years during the daytime hours (1300 LT-1500 LT). The longitudinal structure of VSH 500 appears only in moderate-to-high sunspot years, which is an important observation reported for the first time in this communication. Diurnal variations of Hm at equatorial latitudes show higher values starting from ∼0400 LT to ∼2300 LT with a post-sunset peak. However, an absence of the post-sunset peak is seen in VSH UP and VSH 500 which is probably due to the altitudinal gradients of vertical drifts that increase (decrease) below (above) the F-layer peak during evening pre-reversal enhancements. The reduced drifts above the F-layer peak thereby, suppresses the post-sunset peak in VSH. Concurrent and large-scale structures in VSH 500 and VSH UP at mid and high latitudes in summer hemispheres during June and December solstice seasons are reported for the first time, which occurred possibly due to the long-duration exposure to the Sun's strong radiation during summer seasons. A one-to-one correlation exists between the Chapman scale heights and peak height of the F 2 layer (hmF 2) at equatorial latitudes in different seasons, while moderate correlation is seen between them away from the equatorial latitudes. These presented scale heights at a global scale are very significant, particularly, for future empirical modeling studies and the long-term availability of COSMIC RO retrieved electron density profiles allowed us to present these scale heights. Highlights • Vertical scale heights during one complete solar cycle (2006–2016) are presented. • A substantial longitudinal structure is evident in the equatorial regions. Absence of a post-sunset peak in VSH UP and VSH 500 is an interesting observational finding. • Concurrent and large-scale structures found in VSH 500 and VSH UP in summer hemispheres during June and December solstice. • A significant (moderate) correlation is found between hmF 2 and H m at (away from) equatorial latitudes. [ABSTRACT FROM AUTHOR]

The vertical E × B drift is very important parameter as its day to day variability has great influence on the variability in the low latitude F-region ion and electron density distributions. The measurements of vertical ion velocity from the first Republic of China Satellite (ROCSAT-1) provide a unique data base for the development of possible relationship between vertical E × B drifts and ground based magnetometer observation. An attempt has been made to derive quantitative relationship between F-region vertical E × B drifts measured by ROCSAT-1 (600 km) and ground measured equatorial electrojet for the solar maximum period 2001–2003 for Indian and Japanese sectors. The results consistently indicate existence of linear relationship between the measured vertical E × B drifts at topside F-region and EEJ for both the sectors, with a moderate to high correlation coefficients. The linear relationship between ROCSAT-1 measured E × B drifts and EEJ for Indian and Japanese sectors has been compared with a similar relationship with Jicamarca Unattended Long-term Ionosphere Atmosphere Radar (JULIA) measured E × B drifts (150 km echos) and EEJ strength from Peruvian sector during 2003. It has been found that ROCSAT-1 measured E × B drifts shows linear relationship with EEJ, however, exhibits a larger scatter unlike JULIA radar observed E × B drifts. This may be attributed to the large height difference as ROCSAT-1 measures E × B drifts at 600 km altitude and the EEJ is E-region (110 km) phenomenon. [ABSTRACT FROM AUTHOR]