Daniel Berdichevsky

Origin of coronal and interplanetary shocks: A new look with Wind spacecraft data

We have investigated type II radio bursts in the solar corona using data from ground-based radio telescopes (>18 MHz) and from the Radio and Plasma Wave experiment (WAVES) on board the WIND spacecraft (<14 MHz). The wavelength range of the WAVES experiment includes the 2- to 14-MHz band, previously unobserved from space. We found that all 34 coronal type II bursts observed over a period of 18 months (November 1, 1994, to April 30, 1996), decayed within a few solar radii and did not propagate into the interplanetary medium. On the other hand, most of the accompanying type III radio bursts observed by the ground-based instruments were observed to continue into the interplanetary medium as the electron beams propagated freely along open magnetic field lines. Over the same period of time, other instruments on board the WIND spacecraft detected about 18 interplanetary shock candidates, which seem to be unrelated to the coronal type II bursts. This result confirms the idea that the coronal and interplanetary shocks are two different populations and are of independent origin. We reexamine the data and conclusions of Gosling et al. [1976], Munro et al. [1979], and Sheeley et al. [1984] and find that their data are consistent with our result that the coronal type II bursts are due to flares. We also briefly discuss the implications of our result to the modeling studies of interplanetary shocks based on input from coronal type II radio bursts.

Interplanetary fast shocks and associated drivers observed through the 23rd solar minimum by Wind over its first 2.5 years

A list of the interplanetary shocks observed by Wind from its launch (in Nov 1994) to May 1997 is presented. The magnetohydrodynamic nature of the shocks is investigated, and the associated shock parameters and their uncertainties are accurately computed using two techniques. These are: 1) a combination of the “preaveraged” magnetic-coplanarity, velocity-coplanarity, and the Abraham-Schrauner-mixed methods, and 2) the Vinas and Scudder [1986] technique for solving the nonlinear least squares Rankine-Hugoniot equations. Within acceptable limits these two techniques generally gave the same results, with some exceptions. The reasons for the exceptions are discussed. The mean strength and rate of occurrence of the shocks appear to correlate with the solar cycle. Both showed a decrease in 1996 coincident with the time of the lowest ultraviolet solar radiance, indicative of solar minimum and the beginning of solar cycle 23. Eighteen shocks appeared to be associated with corotating interaction regions (CIRs). The shock normal distribution showed a mean direction peaking in the ecliptic plane and with a longitude of ∼ 200° (GSE coordinates). Another 16 shocks were determined to be driven by solar transients, including magnetic clouds. These had a broader distribution of normal directions than those of the CIR cases with a mean direction close to the Sun-Eart line. Eight shocks of unknown origin had normal orientations far off the ecliptic plane. No shock propagated with longitude ϕn ≥ 220±10°, i.e. against the average Parker spiral direction. Examination of the obliquity angle θBn (i.e., between the shock normal and the upstream interplanetary magnetic field) for the full set of shocks revealed that about 58% were quasi-perpendicular, and about 32% of the shocks oblique, and the rest quasi-parallel. Small uncertainty in the estimated angle θBn was obtained for about 10 shocks with magnetosonic Mach numbers between 1 and 2.

Solar-cycle variation of low density solar wind during more than three solar cycles

The May, 1999 low density (< 1 cm -3 ) solar wind interval is one of a series of intervals of low density solar wind which have been detected since in-situ, near-Earth observations began. Examining the NSSDC OMNI database since 1965, covering solar Cycles 20-23, we show that such intervals, which are also periods of unusually low mass flux and low dynamic pressure, occur most frequently around sunspot maximum and are rarer at solar minimum. The occurrence rate of low-density plasma may be higher in weaker sunspot cycles (Cycle 20 and the current Cycle 23). Around two-thirds of periods with densities < 1 cm -3 are associated with transient solar wind structures, in particular with ejecta and post-shock flows. The majority of other events are associated with corotating streams. The May 1999 event is unusual because it is not associated with an ejecta or stream. A similar period was observed in July-August 1979.

High‐velocity tails on the velocity distribution of solar wind ions

Recent observations of the solar wind using the SWICS instrument on the Ulysses spacecraft have shown the presence of high-velocity [open quotes]tails[close quotes] on the velocity distribution of protons. Similar features have also been observed on the velocity distributions of helium and oxygen ions. Of the order of 1% of the solar wind density is involved in these tails, which are approximately exponential in shape and persist to V = V[sub B] + 10V[sub th] or beyond, where V[sub B] is the bulk velocity and V[sub th] the thermal velocity of the solar wind. This paper contains a preliminary description of the phenomenon. It is clear that it is ultimately connected with the passage of interplanetary shocks past the spacecraft and that particle acceleration at oblique shocks is involved. 21 refs., 6 figs., 2 tabs.

A statistical study of interplanetary shocks and pressure pulses internal to magnetic clouds

[1] We have examined Wind field and plasma data over the time period from November of 1994 through August of 2003 to find cases of interplanetary shocks and pressure pulses internal to magnetic clouds for which we could determine accurate shock normal directions. We have found eight cases in 82 clouds, so these shocks and pressure pulses occurred in approximately 10% of the Wind magnetic clouds. Of the eight cases, six were forward shocks and two were pressure pulses. The internal shocks and pressure pulses tend to occur in the latter half of the clouds, i.e., timewise, about two-thirds of the way through. In every case the magnetic field change is highly compressive at the shock showing little or no change (<10°) in angle during or after the magnitude jump. These shocks and pressure pulses internal to magnetic clouds appear to be associated with outline asymmetric halo coronal mass ejections of greater than average speed which may imply an interaction between an earlier, slower halo CME and a later, faster, off-center CME driving a strong shock, but other interpretations are possible and they are discussed.

Correction to “Major geomagnetic storms (Dst ≤ −100 nT) generated by corotating interaction regions”

[1] In the paper ‘‘Major geomagnetic storms (Dst 100 nT) generated by corotating interaction regions’’ by I. G. Richardson et al. (Journal of Geophysical Research, 111, A07S09, doi:10.1029/2005JA011476, 2006), there are several typographical errors. In Figures 1, 2, 3, 4, and 7, the y component of the solar wind electric field (Ey) is plotted with the incorrect sign. Signed values of Ey referred to in the text and given in Table 1 also have the incorrect sign. As stated in the second paragraph of section 2, the ‘‘Ey’’ panel shows the value of VxBz. However, this is equal to Ey, not Ey (assuming that VxBz VzBx in the solar wind). JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, A12105, doi:10.1029/2007JA012332, 2007 Click Here for Full Article

Solar‐Heliospheric‐Magnetospheric Observations on March 23–April 26, 2001: Similarities to Observations in April 1979

We discuss the similarities and differences of two intervals of extreme interplanetary solar wind conditions, separated almost precisely by two solar cycles, in April 1979 and March–April 2001. The similarities extend to various data‐sets: Energetic particles, solar wind plasma and interplanetary magnetic field. In April 1979 observations were made by three spacecraft covering a wide longitudinal range (∼ 70°) in the heliosphere. Data are presented from Helios 2, located 28° East of the Sun‐Earth line at ∼ 2/3 AU, and from near the Earth. Observations of the 2001 interval are from Wind. We examine the geomagnetic activity during each interval.

Concerning the Helium-to-Hydrogen Number Density Ratio in Very Slow Ejecta and Winds near Solar Minimum†

Near the solar minimum the average value of the helium-to-proton number density ratio is a strong function of speed. The average ratios for both solar ejecta and ambient winds obey approximately the same relation with speed. At the lowest speeds, the ratio takes on small values near and below 0.01. Here winds and ejecta with very slow speeds ( ≲ 310 km/s) are examined. STEREO and Wind spacecraft data are employed that were obtained from 2007 to 2010. This was during the prolonged solar activity minimum between cycles 23 and 24. Case event and statistical studies are made with 12 very slow ejecta. The helium-to-proton ratio in very slow ejecta relative to the ratio for very slow winds of comparable speed averaged in an inclusive one-year period is 1.06. The ejecta and ambient slow winds have, then, nearly the same concentrations on average. The values did not approach 0 with decreasing speed and are shown to deviate from a predicted form. A survey of potential solar sources of very slow ejecta and other inferences based on interplanetary data found a strong correspondence with active regions and a dependence of the properties of very slow ejecta with the solar cycle.

Correction to “A statistical study of interplanetary shocks and pressure pulses internal to magnetic clouds”

[1] In the paper ‘‘A statistical study of interplanetary shocks and pressure pulses internal to magnetic clouds’’ by Michael R. Collier, Ronald P. Lepping, and Daniel B. Berdichevsky (Journal of Geophysical Research, 112, A06102, doi:10.1029/2006JA011714, 2007), there were several misprints in the text and tables. The corrected text and Table 2 appear below. [2] The section headings following section 5 are incorrect. They are reproduced correctly here.

Long-distance Correlations of Interplanetary Parameters: A Case Study with HELIOS

In recent work, promising agreement has been obtained between measured indices of geomagnetic activity (Dst, and cross‐polar cap potential) and their predicted values using interplanetary input from probes in the inner heliosphere (∼0.7 AU) when the probe was close to, (5), and even substantially displaced from, (4), the Earth‐Sun line. Implicit in this agreement is a good correlation of, at least, the basic temporal profiles of the major interplanetary parameters at the two observing sites. In this work we discuss a case study using Helios 1 and 2 data when the spacecraft are lined ‐ up and separated by an almost constant radial distance of 0.2 AU. In the period studied, the interplanetary medium consists of a fast stream being trailed by a magnetic cloud in a slower flow. Good correlation is found between the plasma and field observations at the two sites. Two lag times, reflecting the two types of major structures in the interval chosen, are determined. Evidence of evolutionary processes are briefly discussed. Spectral analysis confirms the results obtained from time series analysis.