 To this day, the prediction of space weather effects near the Earth suffers from a fundamental problem: The radial propagation speed of "halo" CMEs (ie CMEs pointed along the Sun-Earth-line that are known to be the main drivers of space weather disturbances) towards the Earth cannot be measured directly because of the unfavorable geometry From inspecting many limb CMEs observed by the LASCO coronagraphs on SOHO we found that there is usually a good correlation between the radial speed and the lateral expansion speed Vexp of CME clouds This latter quantity can also be determined for earthward-pointed halo CMEs Thus, Vexp may serve as a proxy for the otherwise inaccessible radial speed of halo CMEs We studied this connection using data from both ends: solar data and interplanetary data obtained near the Earth, for a period from January 1997 to 15 April 2001 The data were primarily provided by the LASCO coronagraphs, plus additional information from the EIT instrument on SOHO Solar wind data from the plasma instruments on the SOHO, ACE and Wind spacecraft were used to identify the arrivals of ICME signatures Here, we use "ICME" as a generic term for all CME effects in interplanetary space, thus comprising not only ejecta themselves but also shocks as well Among 181 front side or limb full or partial halo CMEs recorded by LASCO, on the one hand, and 187 ICME events registered near the Earth, on the other hand, we found 91 cases where CMEs were uniquely associated with ICME signatures in front of the Earth Eighty ICMEs were associated with a shock, and for 75 of them both the halo expansion speed Vexp and the travel time Ttr of the shock could be determined The function Ttr=203-2077*ln (Vexp) fits the data best This empirical formula can be used for predicting further ICME arrivals, with a 95% error margin of about one day Note, though, that in 15% of comparable cases, a full or partial halo CME does not cause any ICME signature at Earth at all; every fourth partial halo CME and every sixth limb halo CME does not hit the Earth (false alarms) Furthermore, every fifth transient shock or ICME or isolated geomagnetic storm is not caused by an identifiable partial or full halo CME on the front side (missing alarms)

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The association of coronal mass ejections with their effects near the Earth

We present the “Drag-Based Model” (DBM) of heliospheric propagation of interplanetary coronal mass ejections (ICMEs). The DBM is based on the hypothesis that the driving Lorentz force, which launches a CME, ceases in the upper corona and that beyond a certain distance the dynamics becomes governed solely by the interaction of the ICME and the ambient solar wind. In particular, we consider the option where the drag acceleration has a quadratic dependence on the ICME relative speed, which is expected in a collisionless environment, where the drag is caused primarily by emission of magnetohydrodynamic (MHD) waves. In this paper we present the simplest version of DBM, where the equation of motion can be solved analytically, providing explicit solutions for the Sun–Earth ICME transit time and impact speed. This offers easy handling and straightforward application to real-time space-weather forecasting. Beside presenting the model itself, we perform an analysis of DBM performances, applying a statistical and case-study approach, which provides insight into the advantages and drawbacks of DBM. Finally, we present a public, DBM-based, online forecast tool.

Propagation of Interplanetary Coronal Mass Ejections: The Drag-Based Model

The dual frequency radio signals of the Global Positioning System (GPS) allow measurements of the total number of electrons, called total electron content (TEC), along a ray path from GPS satellite to receiver. We have developed a new technique to construct two-dimensional maps of absolute TEC over Japan by using GPS data from more than 1000 GPS receivers. A least squares fitting procedure is used to remove instrumental biases inherent in the GPS satellite and receiver. Two-dimensional maps of absolute vertical TEC are derived with time resolution of 30 seconds and spatial resolution of 0.15° × 0.15° in latitude and longitude. Our method is validated in two ways. First, TECs along ray paths from the GPS satellites are simulated using a model for electron contents based on the IRI-95 model. It is found that TEC from our method is underestimated by less than 3 TECU. Then, estimated vertical GPS TEC is compared with ionospheric TEC that is calculated from simultaneous electron density profile obtained with the MU radar. Diurnal and day-to-day variation of the GPS TEC follows the TEC behavior derived from MU radar observation but the GPS TEC is 2 TECU larger than the MU radar TEC on average. This difference can be attributed to the plasmaspheric electron content along the GPS ray path. This method is also applied to GPS data during a magnetic storm of September 25, 1998. An intense TEC enhancement, probably caused by a northward expansion of the equatorial anomaly, was observed in the southern part of Japan in the evening during the main phase of the storm.

A new technique for mapping of total electron content using GPS network in Japan

Knowledge of the radial evolution of the coronal mass ejection (CME) is important for the understanding of its arrival at the near-Earth space and of its interaction with the disturbed/ambient solar wind in the course of its travel to 1 AU and further. In this paper, the radial evolution of 30 large CMEs (angular width > 150∘, i.e., halo and partial halo CMEs) has been investigated between the Sun and the Earth using (i) the white-light images of the near-Sun region from the Large Angle Spectroscopic Coronagraph (LASCO) onboard SOHO mission and (ii) the interplanetary scintillation (IPS) images of the inner heliosphere obtained from the Ooty Radio Telescope (ORT). In the LASCO field of view at heliocentric distances R≤30 solar radii (R
 ⊙), these CMEs cover an order of magnitude range of initial speeds, V
 CME≈260–2600 km s−1. Following results have been obtained from the speed evolution of these CMEs in the Sun–Earth distance range: (1) the speed profile of the CME shows dependence on its initial speed; (2) the propagation of the CME goes through continuous changes, which depend on the interaction of the CME with the surrounding solar wind encountered on the way; (3) the radial-speed profiles obtained by combining the LASCO and IPS images yield the factual view of the propagation of CMEs in the inner heliosphere and transit times and speeds at 1 AU computed from these profiles are in good agreement with the actual measurements; (4) the mean travel time curve for different initial speeds and the shape of the radial-speed profiles suggest that up to a distance of ∼80 R
 ⊙, the internal energy of the CME (or the expansion of the CME) dominates and however, at larger distances, the CME's interaction with the solar wind controls the propagation; (5) most of the CMEs tend to attain the speed of the ambient flow at 1 AU or further out of the Earth's orbit. The results of this study are useful to quantify the drag force imposed on a CME by the interaction with the ambient solar wind and it is essential in modeling the CME propagation. This study also has a great importance in understanding the prediction of CME-associated space weather at the near-Earth environment.

Evolution of Coronal Mass Ejections in the Inner Heliosphere: A Study using White-light and Scintillation Images

The physics governing the propagation of solar coronal mass ejections (CMEs), an important cause of bad space weather on Earth, is poorly understood. The authors model a CME's three-dimensional propagation and determine accurate arrival times near the Earth's surface.

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Propagation of an Earth-directed coronal mass ejection in three dimensions

[1] Recently, an empirical model of the acceleration/deceleration of coronal mass ejections (CMEs) as they propagate through the solar wind was developed using near-Sun (coronagraphic) and near-Earth (in situ) observations [Gopalswamy et al., 2000, 2001a]. This model states and quantifies the fact that slow CMEs are accelerated and fast CMEs are decelerated toward the ambient solar wind speed (∼400 km/s). In this work we study the propagation of CMEs from near the Sun (0.083 AU) to 1 AU using numerical simulations and compare the results with those of the empirical model. This is a parametric study of CME-like disturbances in the solar wind using a one-dimensional, hydrodynamic single-fluid model. Simulated CMEs are propagated through a variable ambient solar wind and their 1 AU characteristics are derived to compare with observations and the empirical CME arrival model. We were able to reproduce the general characteristics of the prediction model and to obtain reasonable agreement with two-point measurements from spacecraft. Our results also show that the dynamical evolution of fast CMEs has three phases: (1) an abrupt and strong deceleration just after their injection against the ambient wind, which ceases before 0.1 AU, followed by (2) a constant speed propagation until about 0.45 AU, and, finally, (3) a gradual and small deceleration that continues beyond 1 AU. The results show that it is somewhat difficult to predict the arrival time of slow CMEs (Vcme 1000 km/s) has a smaller dispersion so the prediction can be more accurate.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JA009186

A numerical study on the acceleration and transit time of coronal mass ejections in the interplanetary medium

Review on space weather in Latin America. 2. The research networks ready for space weather

We report advances in the construction of a 64x64 (4096) full wavelength dipole antenna array, which will operate at 140 MHz, occupying 10 000 square meters (70 m x 140 m) to carry out interplanetary scintillation (IPS) observations. This will be a dedicated radio array of nearly 1000 well known radio sources which is being built in the state of Michoacan 350 km north-west from Mexico City, lat. 19°48’ N, long. 101°41’ W and 1964 m above sea level. The Mexican Array Radio Telescope (MEXART) will have similar characteristics to the MRAO array in Cambridge, but with significant advantages such as a better electronic system, higher operation frequency, state of the art back end, and location at intermediate geomagnetic latitudes (29°). The MEXART project consists of two phases. In the first phase, we built a prototype radio array near Mexico City, which contained all the basic antenna elements of the final array but covering a smaller area (1000 square meters) and operating with a 4x4 Butler matrix. In the second phase we are building the final array in Michoacan with technical assistance by NCRA-TIFR in India. MEXART will be the only IPS station in the American continent and will be part of a global network of IPS observatories combining measurements with ORT in India and the STEL IPS systems in Japan. Combining data from these IPS observatories will provide important information for solar wind studies and in particular for solar activity associated storms and ionospheric disturbances. We expect to initiate IPS observations by early 2003.

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The MEXART interplanetary scintillation array in Mexico

[1] We performed an event-by-event study of 47 geomagnetic storms (GSs) that occurred during the ascending phase of solar cycle 23. All the GSs are associated with the passage of a shock and an interplanetary coronal mass ejection (ICME). For each event, we identified the section in the interplanetary (IP) medium causing the GS (the sheath behind the shock, the main body of the ICME or the combination of both). On average, the most intense GSs are caused by sheaths, followed by sheath-ICME combinations and by ICMEs. We obtained the correlation coefficients between the intensity of each GS (minimum Dst) and several solar wind parameters. We found that the well-known correlation between the GS intensity and the solar wind convected electric field, Ey, stands for the GSs caused by ICMEs (CC = −0.88) and sheath-ICME combinations (CC = −0.95), but it is very low for the GSs caused by sheaths (CC = −0.44). In contrast, we found a very good correlation between the GSs caused by sheaths and the total convected electric field (ΣEy) (CC = −0.89). On the other hand, we estimated the total perpendicular pressure (Pt) for each IP event associated with the GSs and identified the three different types of Pt profiles. The most intense GSs are related with IP events with Pt = 1, but moderate and less intense storms are associated with the three Pt profiles. The correlations between the Dst and the solar wind parameters results that the CCs decrease significantly for IP events having a Pt profile of 3.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2010JA015471

J. Americo Gonzalez-Esparza

Papers

A numerical study on the acceleration and transit time of coronal mass ejections in the interplanetary medium

Review on space weather in Latin America. 2. The research networks ready for space weather

The MEXART interplanetary scintillation array in Mexico

Geomagnetic storms caused by shocks and ICMEs

Review on space weather in Latin America. 3. Development of space weather forecasting centers