skip to main content


Search for: All records

Award ID contains: 1732209

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract

    This paper uses a regional simulation of plasma convective instability in the postsunset equatorial ionosphere together with a global atmosphere/ionosphere/plasmasphere GCM (WAM‐IPE) to forecast irregularities associated with equatorial spreadF(ESF) for 1–2 hr after sunset. First, the regional simulation is initialized and forced using ionosphere state parameters derived from campaign data from the Jicamarca Radio Observatory and from empirical models. The irregularities produced by these simulations are found to be quantitatively similar to those observed. Next, the aforementioned state parameters are replaced with parameters from WAM‐IPE, and the resulting departures between the simulated and observed irregularities are noted. In one of five cases, the forecast failed to accurately predict ESF irregularities due to the late reversal of the zonal thermospheric winds. In four of five cases, significant differences between the observed and predicted prereversal enhancement (PRE) of the background vertical drifts resulted in degraded forecast accuracy. This highlights the need for improved PRE forecasting in the global‐scale model.

     
    more » « less
  2. Abstract

    We present measurements of the equatorial topside ionosphere above Jicamarca made during extremely low solar flux conditions during the deep solar minimum of 2019–2020. Measurements were made in October, 2019, February, 2020, and September, 2020. The main features observed are a large and extended decrease in noontime temperatures unlike that seen in studies at moderate solar flux levels, predawn ionospheric heating as early as 0300 LT, large day‐to‐day variability in the O+/H+transition height, and negligible helium ion concentration at all altitudes. Data from the Ion Velocity Meter (IVM) instrument onboard the Ionospheric Connection Explorer (ICON) and the Topside Ionospheric Plasma Monitor (SSIES) onboard the Defense Meteorological Satellite Program (DMSP) satellites are used to assess agreement with ISR data and assist with the analysis of the predawn heating phenomena. We also analyze the data in light of the SAMI2‐PE model which shows less agreement with the data than at higher solar flux. The main areas of discrepancy with the data are outlined, such as the absence of significant predawn heating, less pronounced decreases in noontime temperatures, and much higher O+fractions at high altitudes, particularly in September. Finally, a sensitivity analysis of the model to various forcing agents such as neutral winds, plasma drifts, solar flux, and heat flow is performed. A discussion is presented on bridging the discrepancies in future model runs. Novel techniques of clutter removal and noise power bias correction are introduced and described in the appendices.

     
    more » « less
  3. Abstract

    Data from a network of high‐frequency (HF) beacons deployed in Peru are used to estimate the regional ionospheric electron density in a volume. Pseudorange, accumulated carrier phase, and signal power measurements for each of the 36 ray paths provided by the network at a 1 min cadence are incorporated in the estimates. Additional data from the Jicamarca incoherent scatter radar, the Jicamarca sounder, and GPS receivers can also be incorporated. The electron density model is estimated as the solution to a global optimization problem that uses ray tracing in the forward model. The electron density is parametrized in terms of B‐splines in the horizontal direction and generalized Chapman functions or related functions in the vertical. Variational sensitivity analysis has been added to the method to allow for the utilization of the signal power observable which gives additional information about the morphology of the bottomside F region as well as absorption including absorption in the D and E regions. The goal of the effort is to provide contextual information for improving numerical forecasts of plasma interchange instabilities in the postsunset F region ionosphere associated with equatorial spread F (ESF). Data from two ESF campaigns are presented. In one experiment, the HF data revealed the presence of a large‐scale bottomside deformation that seems to have led to instability under otherwise inauspicious conditions. In another experiment, gradual variations in HF signal power were found to be related to the varying shape of the bottomside F layer.

     
    more » « less
  4. Abstract

    Radar and sounding rocket observations of plasma irregularities in theF‐region ionosphere acquired on 19 June 2019 during NASA experiment Too WINDY on Kwajalein Atoll are presented. The experiment was conducted near local midnight during a period of low solar flux and quiet geomagnetic conditions. Plasma density irregularities were seen by the rocket and also in the incoherent scatter radar data to emerge and persist mainly in the topside. Density irregularities in the bottomside remained very small by comparison throughout the observations. Zonal plasma drifts measured by the rocket were highly structured in the topside. Patches of coherent scatter entrained in the large‐scale topside density irregularities appeared to propagate slowly westward in a narrow flow channel detected by the rocket. Broadband ELF emissions were also detected in the topside. Some of the characteristics of the topside irregularities are typical of postsunset equatorialF‐region irregularities observed frequently by coherent scatter radars, and some of the common features in the coherent scatter database are reviewed. Two scenarios that have been proposed to account for postmidnight spreadFare tested computationally. One involves unseasonably large background zonal electric fields, and the other involves forcing from below by neutral waves and turbulence. Neither scenario appears to be able to account for the Too WINDY observations and the preponderance of topside irregularities without bottomside precursors in particular.

     
    more » « less
  5. Abstract

    We argue that combining a high‐power, large‐aperture radar transmitter with several large‐aperture receiving arrays to make a geospace radar—a radar capable of probing near‐Earth space from the upper troposphere through to the solar corona—would transform geospace research. We review the emergence of incoherent scatter radar in the 1960s as an agent that unified early, pioneering research in geospace in a common theoretical, experimental, and instrumental framework, and we suggest that a geospace radar would have a similar effect on future developments in space weather research. We then discuss recent developments in radio‐array technology that could be exploited in the development of a geospace radar with new or substantially improved capabilities compared to the radars in use presently. A number of applications for a geospace radar with the new and improved capabilities are reviewed including studies of meteor echoes, mesospheric and stratospheric turbulence, ionospheric flows, plasmaspheric and ionospheric irregularities, and reflection from the solar corona and coronal mass ejections. We conclude with a summary of technical requirements.

     
    more » « less
  6. Abstract

    Inverse methods involving compressive sensing are tested in the application of two‐dimensional aperture‐synthesis imaging of radar backscatter from field‐aligned plasma density irregularities in the ionosphere. We consider basis pursuit denoising, implemented with the fast iterative shrinkage thresholding algorithm, and orthogonal matching pursuit (OMP) with a wavelet basis in the evaluation. These methods are compared with two more conventional optimization methods rooted in entropy maximization (MaxENT) and adaptive beamforming (linearly constrained minimum variance or often “Capon's Method.”) Synthetic data corresponding to an extended ionospheric radar target are considered. We find that MaxENT outperforms the other methods in terms of its ability to recover imagery of an extended target with broad dynamic range. Fast iterative shrinkage thresholding algorithm performs reasonably well but does not reproduce the full dynamic range of the target. It is also the most computationally expensive of the methods tested. OMP is very fast computationally but prone to a high degree of clutter in this application. We also point out that the formulation of MaxENT used here is very similar to OMP in some respects, the difference being that the former reconstructs the logarithm of the image rather than the image itself from basis vectors extracted from the observation matrix. MaxENT could in that regard be considered a form of compressive sensing.

     
    more » « less
  7. This paper discusses the relationship between planning and discovery in science using examples drawn from equatorial aeronomy in general and research at the Jicamarca Radio Observatory in particular. The examples reveal a pattern of discoveries taking place despite rather than because of careful planning. 
    more » « less
  8. null (Ed.)