The paper presents the latest version of the International Reference Ionosphere model (IRI-2016) describing the most important changes and improvements that were included with this version and discussing their impact on the IRI predictions of ionospheric parameters. IRI-2016 includes two new model options for the F2 peak height hmF2 and a better representation of topside ion densities at very low and high solar activities. In addition, a number of smaller changes were made concerning the use of solar indices and the speedup of the computer program. We also review the latest developments toward a Real-Time IRI. The goal is to progress from predicting climatology to describing the real-time weather conditions in the ionosphere.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016SW001593

International Reference Ionosphere 2016: From ionospheric climate to real‐time weather predictions

The International Reference Ionosphere (IRI) project was established jointly by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI) in the late sixties with the goal to develop an international standard for the specification of plasma parameters in the Earth’s ionosphere. COSPAR needed such a specification for the evaluation of environmental effects on spacecraft and experiments in space, and URSI for radiowave propagation studies and applications. At the request of COSPAR and URSI, IRI was developed as a data-based model to avoid the uncertainty of theory-based models which are only as good as the evolving theoretical understanding. Being based on most of the available and reliable observations of the ionospheric plasma from the ground and from space, IRI describes monthly averages of electron density, electron temperature, ion temperature, ion composition, and several additional parameters in the altitude range from 60 km to 2000 km. A working group of about 50 international ionospheric experts is in charge of developing and improving the IRI model. Over time as new data became available and new modeling techniques emerged, steadily improved editions of the IRI model have been published. This paper gives a brief history of the IRI project and describes the latest version of the model, IRI-2012. It also briefly discusses efforts to develop a real-time IRI model. The IRI homepage is at http://IRImodel.org.

/pdf/the-international-reference-ionosphere-2012-a-model-of-1o61n09tjl.pdf

The International Reference Ionosphere 2012 – a model of international collaboration

The international reference ionosphere (IRI) is the internationally recognized and recommended standard for the specification of plasma parameters in Earth’s ionosphere. It describes monthly averages of electron density, electron temperature, ion temperature, ion composition, and several additional parameters in the altitude range from 60 to 1,500 km. A joint working group of the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI) is in charge of developing and improving the IRI model. As requested by COSPAR and URSI, IRI is an empirical model being based on most of the available and reliable data sources for the ionospheric plasma. The paper describes the latest version of the model and reviews efforts towards future improvements, including the development of new global models for the F2 peak density and height, and a new approach to describe the electron density in the topside and plasmasphere. Our emphasis will be on the electron density because it is the IRI parameter most relevant to geodetic techniques and studies. Annual IRI meetings are the main venue for the discussion of IRI activities, future improvements, and additions to the model. A new special IRI task force activity is focusing on the development of a real-time IRI (RT-IRI) by combining data assimilation techniques with the IRI model. A first RT-IRI task force meeting was held in 2009 in Colorado Springs. We will review the outcome of this meeting and the plans for the future. The IRI homepage is at http://www.IRI.gsfc.nasa.gov.

/pdf/the-international-reference-ionosphere-today-and-in-the-1qc6wam8da.pdf

The international reference ionosphere today and in the future

Space weather refers to dynamic conditions on the Sun and in the space environment of the Earth, which are often driven by solar eruptions and their subsequent interplanetary disturbances. It has been unclear how an extreme space weather storm forms and how severe it can be. Here we report and investigate an extreme event with multi-point remote-sensing and in situ observations. The formation of the extreme storm showed striking novel features. We suggest that the in-transit interaction between two closely launched coronal mass ejections resulted in the extreme enhancement of the ejecta magnetic field observed near 1 AU at STEREO A. The fast transit to STEREO A (in only 18.6 h), or the unusually weak deceleration of the event, was caused by the preconditioning of the upstream solar wind by an earlier solar eruption. These results provide a new view crucial to solar physics and space weather as to how an extreme space weather event can arise from a combination of solar eruptions.

Observations of an extreme storm in interplanetary space caused by successive coronal mass ejections

A survey of military applications of wireless sensor networks

Extreme space weather: impacts on engineered systems and infrastructure

During the total solar eclipse observed in Europe on August 11, 1999, measurements were made of the amplitude and phase of four VLF transmitters in the frequency range 16–24 kHz Five receiver sites were set up, and significant variations in phase and amplitude are reported for 17 paths, more than any previously during an eclipse Distances from transmitter to receiver ranged from 90 to 14,510 km, although the majority were 10,000 km Negative phase changes were observed on most paths, independent of path length Although there was significant variation from path to path, the typical changes observed were ∼3 dB and ∼50° The changes observed were modeled using the Long Wave Propagation Capability waveguide code Maximum eclipse effects occurred when the Wait inverse scale height parameter β was 05 km−1 and the effective ionospheric height parameter H′ was 79 km, compared with β=043 km−1 and H′=71 km for normal daytime conditions The resulting changes in modeled amplitude and phase show good agreement with the majority of the observations The modeling undertaken provides an interpretation of why previous estimates of height change during eclipses have shown such a range of values A D region gas-chemistry model was compared with electron concentration estimates inferred from the observations made during the solar eclipse Quiet-day H′ and β parameters were used to define the initial ionospheric profile The gas-chemistry model was then driven only by eclipse-related solar radiation levels The calculated electron concentration values at 77 km altitude throughout the period of the solar eclipse show good agreement with the values determined from observations at all times, which suggests that a linear variation in electron production rate with solar ionizing radiation is reasonable At times of minimum electron concentration the chemical model predicts that the D region profile would be parameterized by the same β and H′ as the LWPC model values, and rocket profiles, during totality and can be considered a validation of the chemical processes defined within the model

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000RS002395

Total solar eclipse effects on VLF signals: Observations and modeling

[1] Data assimilation processes aim to combine measurement data with background models in an optimal way. In anticipation of the availability of global radio occultation (RO) measurements, a computationally practical data assimilation technique for combining RO data with background ionospheric models has been implemented, and simulations have been conducted to assess the utility of the technique. In simulations where tomographic images provide the truth data and the Parameterized Ionospheric Model (PIM) provides the background, a fourfold decrease in the electron density error at 300 km altitude was achieved. A global assimilation simulation has also been conducted using the International Reference Ionosphere as the truth data. For a constellation of eight RO satellites, a factor of four decrease in the vertical total electron content RMS error has been demonstrated. The same simulation also results in a factor of three decrease in the NmF2 RMS error and a halving of the hmF2 RMS error.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002RS002819

Assimilation of radio occultation measurements into background ionospheric models

Measurements of Doppler spread, multipath spread, and signal-to-noise ratio have been made on four high-latitude high-frequency (HF) communications paths. The measurement system and analysis techniques are outlined, and an analysis of the data pertinent to the design of robust HF data modems is presented. A summary of the spreads that are exceeded for 5% of time is presented for each path. Doppler spreads range from 2 to 55 Hz, while multipath spreads range from 1 to 11 ms. Physical interpretations of the data are made, and the data are related to the measured performance characteristics of an HF data modem to estimate the modem availability on the paths considered. When there is mode support, availabilities range from 64% to 100% for a signal-to-noise ratio of 0 dB, although the data indicate that the availabilities can generally be increased by optimizing frequency selection.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97RS02206

Measurements of Doppler and multipath spread on oblique high‐latitude HF paths and their use in characterizing data modem performance

Results of ionospheric drift measurements with a Digisonde 256 digital ionospheric sounder located at Qaanaaq, Greenland (87°N, corrected geomagnetic latitude), are presented. Digisonde drift data have been related to the interplanetary magnetic field (IMF) measured by the IMP 8 satellite for 32 days during 1986, 1987, and 1988. Extremely good statistical agreement between these measurements and convection directions derived from satellite instrumentation is demonstrated when the IMF z component is negative. For Bz negative and By negative the daily average convection direction is centered on −12° (anticlockwise) from the antisunward direction. When Bz is negative but By is positive, the convection direction is centered on +36°. These directions differ by 3° and 9°, respectively, from the models of Heppner and Maynard (1987). The variation about these values is ∼ ±20°. The excellent agreement between the Digisonde measurements and models derived from satellite measurements demonstrates the utility of the Digisonde for making ground-based measurements of the convection direction in the polar cap F region when Bz is south. The convection directions under conditions of positive Bz have also been examined, and we have measured three types of temporal variation in azimuth, namely, an ordered and slowly (OS) varying change in direction, an ordered and quickly (OQ) varying change in direction, and disordered (D) variations in direction. The latter are believed to result from a breakdown of the analysis technique due to velocity shears in the vicinity of polar cap arcs, and we estimate that they account for ∼25% of the measurements when Bz > 0. When Bz is positive and By is negative, our small subset of OS measurements supports the distorted two-cell model of Heppner and Maynard (1987). The remainder of the measurements show no well-defined daily average convection direction or diurnal variation. Likewise for Bz positive and By positive, no well-defined convection direction can be discerned, nor can any diurnal variation. The existence of OQ variations when Bz > 0 suggests that meaningful average statistical convection patterns may be much harder to synthesize than similar patterns when Bz < 0.

Paul S. Cannon

Papers

Extreme space weather: impacts on engineered systems and infrastructure

Total solar eclipse effects on VLF signals: Observations and modeling

Assimilation of radio occultation measurements into background ionospheric models

Measurements of Doppler and multipath spread on oblique high‐latitude HF paths and their use in characterizing data modem performance

Response of the polar cap F region convection direction to changes in the interplanetary magnetic field: Digisonde measurements in northern Greenland