J. A. Gonzalez-Esparza

Interplanetary Shock Waves: Ulysses Observations in and Out of the Ecliptic Plane

Between its launch in October 1990 and the end of 1993, approximately 160 fast collisionless shock waves were observed in the solar wind by the Ulysses space probe. During the in-ecliptic part of the mission, to February 1992, the observed shock waves were first caused mainly by solar transient events following the solar maximum and the reorganisation of the large scale coronal fields. With the decay in solar activity, relatively stable Corotating Interaction Regions (CIRs) were observed betwen 3 and 5.4 AU, each associated with at least one forward-reverse shock pair. During the out-of-ecliptic phase of the orbit, from February 1992 onwards, CIRs and shock pairs associated with them continued to dominate the observations. From July 1992, Ulysses encountered the fast solar wind flow from the newly developed southern polar coronal hole, and from May 1993 remained in the unipolar magnetic region associated with this coronal hole. At latitudes beyond 30°, CIRs were associated almost exclusively with reverse shocks only. A comprehensive list of shock waves identified in the magnetic field and solar wind plasma data from Ulysses is given in Table 1. The principal characteristics were determined mainly from the magnetic field data. General considerations concerning the determination of shock characteristics are outlined in the Introduction.

Interplanetary Shock Waves and Large-Scale Structures: Ulysses' Observations in and out of the Ecliptic Plane

We present a study of 153 fast shock waves and their relation to other large-scale features in the solar wind : corotating interaction regions (CIRs), interplanetary counterparts of coronal mass ejections (ICMEs), and the magnetic sector structure, observed by Ulysses from October 1990 to the south solar polar pass in the summer of 1994. This is a comprehensive statistical study of interplanetary shock waves and their possible causes between 1 and 5.4 AU, in particular, out of the ecliptic. We identify six different heliographic intervals with distinct dynamic characteristics and shock wave populations (transient and corotating shocks). We present maps of large-scale features, which provide a general context to studies of particular events observed by Ulysses and a comparison of Ulysses observations with results from other missions. From our analysis of the associations between interplanetary shocks and their possible causes we find that the strongest in-ecliptic shock waves were leading CIRs about 4-5 AU. The strongest out-of-ecliptic shock waves were attributed to diverse causes at about 20° south. We observed many quasi-parallel (θ Bn < 45°) corotating shocks ; in fact, most of the corotating reverse shocks detected during the in-ecliptic trajectory were quasi-parallel. The correlation between transient forward shocks and ICMEs (ejecta signatures) is similar to previous results within 1 AU : during the in-ecliptic trajectory Ulysses detected 25 ICMEs and 31 transient forward shocks, 13 of which were associated with ICMEs. The out-of-ecliptic results show an analogous correlation. After the Jupiter flyby we observed a significant number of nonrecurrent reverse shocks that do not show any association with ICMEs. This type of shock, instead of being driven by supermagnetosonic plasma clouds, might be produced by a different mechanism.

A Numerical Study on the Evolution of CMEs and Shocks in the Interplanetary Medium

We studied the evolution in the solar wind of four CMEs detected by SOHO‐LASCO which were associated with ICMEs and interplanetary (IP) shocks detected afterward by Wind at 1 AU. The study is based on a 1‐D hydrodynamic single fluid model using the ZEUS code. These simple numerical simulations of CME like pulses illuminate several aspects of the heliocentric evolution of the ICME front and its associated IP shock and we were able to reproduce some characteristics of the IP shocks and ICMEs inferred from the two‐point measurements from spacecraft. The simulation shows that ICMEs and IP shocks follow different evolutions in the interplanetary medium both having phases of about constant speed propagation followed by an exponential deceleration with heliocentric distance. IP shocks always propagate faster than their associated ICME drivers and the former began to decelerate well before the IP shock. The results indicate that, in general, although an IP shock is driven by its ICME in the inner heliosphere in m...

Radial evolution of ejecta characteristics and transient shocks: Ulysses in‐ecliptic observations

During its travel to Jupiter, Ulysses detected 25 ejecta and 32 transient forward shocks (TFS), and in the first 3 months after the Jupiter flyby Ulysses detected 9 ejecta and 5 TFS. Half of these ejecta (17) were associated with TFS. We identified the ejecta using bidirectional streaming of suprathermal electrons accompanied by other plasma cloud signatures. This data set of 34 ejecta at low latitudes (±10°) complements previous statistical studies of ejecta and TFS within 1 AU and allows us to study their heliocentric evolution from 1 to 5.4 AU. We used solar wind plasma data to analyze dynamic aspects of these events. In general, ejecta associated with TFS and ejecta without shocks had similar characteristics. However, ejecta associated with TFS had fronts propagating faster than the ambient solar wind, while ejecta not associated with shocks had fronts propagating at about the same speed as the ambient solar wind. The ejecta radial width did not present a clear statistical tendency to expand with heliocentric distance, and the ejecta mean flux density did not decrease more quickly than the square of the distance from the Sun. These two results might suggest that the rate of expansion of ejecta from 1 to 5 AU is less than the rate of expansion within 1 AU. However, a limitation of this analysis is the ambiguity of comparing ejecta parameters that can vary depending on different aspects and with heliocentric distance. Only about 40% of the ejecta associated with TFS had leading edges propagating supermagnetosonically with respect to the ambient solar wind. Ejecta with large radial widths were faster than small ejecta. Stronger TFS (higher Mach numbers) were followed by larger ejecta.

The wavelet transform function to analyze interplanetary scintillation observations

Interplanetary scintillation (IPS) observations are useful to remotely sense the inner heliosphere. We present a new technique to analyze IPS observations using a wavelet transform (WT) function. This technique allows us to derive, in a straightforward way, a simple method to obtain the scintillation index (m). We tested this WT technique to analyze IPS observations obtained by the Solar-Terrestrial Environment Laboratory (STEL) radio telescope. The analysis of the m index of the radio source 3C48 detected by STEL over the year 2012 shows the expected decrease with solar elongation reported in previous studies. The WT technique has a great potential for future solar wind studies using IPS observations from contemporary radio telescopes.

Mexican Space Weather Service (SCIESMEX)

Legislative modifications of the General Civil Protection Law in Mexico in 2014 included specific references to space hazards and space weather phenomena. The legislation is consistent with United Nations promotion of international engagement and cooperation on space weather awareness, studies and monitoring. These internal and external conditions motivated the creation of a space weather service in Mexico. The Mexican Space Weather Service (SCiESMEX in Spanish) (www.sciesmex.unam.mx) was initiated in October 2014 and is operated by the Institute of Geophysics at the Universidad Nacional Autonoma de Mexico (UNAM). SCiESMEX became a Regional Warning Center of the International Space Environment Services (ISES) in June 2015. We present the characteristics of the service, some products and the initial actions for developing a space weather strategy in Mexico. The service operates a computing infrastructure including a web application, data repository and a high-performance computing server to run numerical models. SCiESMEX uses data of the ground-based instrumental network of the National Space Weather Laboratory (LANCE), covering solar radio burst emissions, solar wind and interplanetary disturbances (by interplanetary scintillation observations), geomagnetic measurements, and analysis of the total electron content (TEC) of the ionosphere (by employing data from local networks of GPS receiver stations).

Propagation of CMEs in the interplanetary medium: Numerical and analytical results

Abstract We study the propagation of coronal mass ejections (CMES) from near the Sun to 1 AU by comparing results from two different models: a 1-D, hydrodynamic, single-fluid, numerical model (Gonzalez-Esparza et al., 2003a) and an analytical model to study the dynamical evolution of supersonic velocitys fluctuations at the base of the solar wind applied to the propagation of CMES (Canto et al., 2002). Both models predict that a fast CME moves initially in the inner heliosphere with a quasi-constant velocity (which has an intermediate value between the initial CME velocity and the ambient solar wind velocity ahead) until a ‘critical distance’ at which the CME velocity begins to decelerate approaching to the ambient solar wind velocity. This critical distance depends on the characteristics of the CME (initial velocity, density and temperature) as well as of the ambient solar wind. Given typical parameters based on observations, this critical distance can vary from 0.3 to beyond 1 AU from the Sun. These results explain the radial evolution of the velocity of fast CMEs in the inner heliosphere inferred from interplanetary scintillation (IPS) observations (Manoharan et al., 2001, 2003, Tokumaru et al., 2003). On the other hand, the numerical results show that a fast CME and its associated interplanetary (IP) shock follow different heliocentric evolutions: the IP shock always propagates faster than its CME driver and the latter begins to decelerate well before the shock.

Dynamic evolution of interplanetary shock waves driven by CMEs

We present a study about the propagation of interplanetary shock waves driven by super magnetosonic coronal mass ejections (CMEs). The discussion focuses on a model which describes the dynamic relationship between the CME and its driven shock and the way to approximate the trajectory of shocks based on those relationships, from near the Sun to 1 AU. We apply the model to the analysis of a case study in which our calculations show quantitative and qualitative agreements with different kinds of data. We discuss the importance of solar wind and CME initial conditions on the shock wave evolution.

Calculating travel times and arrival speeds of CMEs to Earth: An analytic tool for space weather forecasting

Coronal mass ejections (CME) are one of the most important phenomena derived from solar activity that potentially perturbs space weather of Earth. In this work we present a semi-empirical arrival-forecasting tool for Earth-directed halo CMEs. This tool combines the piston-shock model and an empirical relationship to estimate in-situ arrivals of halo CMEs. The empirical relationship uses the initial conditions of CMEs to calculate the value of free parameter of piston-shock model, parameter which is closely related with the initial inertia of CMEs. Such a value will let the model to simultaneously approximate the travel time and arrival speed of CMEs (i.e. CME arrivals). We test the forecasting capabilities of our model and its empirical relationship by calculating the arrivals of 40 halo CMEs detected during the period of 1995-2015. Our results indicate that, together, the piston-shock model and its empirical relationship approximate CME arrivals with average errors of 7h for travel times, and 100 km s−1 for arrival speeds. Our results show that our model is suitable for arrival forecasting of isolated events propagating through quiet interplanetary medium.

Observations of Low‐Latitude Red Aurora in Mexico During the 1859 Carrington Geomagnetic Storm

On 1 September 1859, occurred one of the most intense geomagnetic storm that has been documented in recent history. This storm is known as the Carrington Event. On the morning September 1st at arou...