R. P. Lepping

Goddard Space Flight Center

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ÁS

Á. Szabó

Pázmány Péter Catholic University

L. F. Burlaga

Davidson College

S. Kokubun

Sendai Nishitaga National Hospital

Chin‐Chun Wu

United States Naval Research Laboratory

D. B. Berdichevsky

Consejo Nacional de Investigaciones Científicas y Técnicas

K. W. Ogilvie

Goddard Space Flight Center

R. P. Lin

Shandong University

N. F. Ness

University of Delaware

J. A. Slavin

University of Michigan–Ann Arbor

C. J. Farrugia

University of New Hampshire

Cooperative Institutions

Goddard Space Flight Center

192

Johns Hopkins University Applied Physics Laboratory

University of California, Berkeley

Planetary Science Institute

University of California, Los Angeles

Heliophysics

Los Alamos National Laboratory

University of New Hampshire

Southwest Research Institute

Johns Hopkins University

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A comparison between the geoeffectiveness of north‐south and south‐north magnetic clouds and an associated prediction

Space Weather (2017)

Chin‐Chun Wu R. P. Lepping D. B. Berdichevsky K. Liou

Abstract Using 1995–2015 Wind in situ solar wind plasma and magnetic field data, 217 magnetic clouds (MCs) were identified. The following pertinent results were found: (i) 120 MCs were N‐S type (northward → southward, magnetic field, B rotated from northward to southward), and 97 MCs are S‐N type. (ii) S‐N MC S‐N dominated N‐S MC N‐S in the periods of 1995–1999, 2001–2002, and 2014–2015. In contrast, N‐S MC N‐S dominated S‐N MC S‐N in the periods of 2000 and 2003–2013. (iii) The averages of storm intensity (< Dst min >) were −69, −57, and −84 nT for “all 217 MCs,” “120 N‐S MCs,” and “97 S‐N MCs” types, respectively. (iv) Confirmed with observations, MC type depends on the phase of the magnetic solar cycle. Hence, on average, the S‐N types trigger more severe storms (i.e., Dst min < −100 nT). Also, from 1995 to 2009, the percentage of N‐S types of MCs keeps increasing and the percentage of S‐N types decreasing. The percentage of S‐N MCs starts increasing in the interval of 2010–2015. Therefore, we expect to see a predominance of the S‐N types of MC for the coming few years. This means on average that more severe geomagnetic storms are expected in the near future. This is an interesting solar wind feature and is going to be stressed in its application to “space weather predictions.”

Space Weather

10.1002/2016sw001520

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Citations (6)

Correlation of changes in the outer‐zone relativistic‐electron population with upstream solar wind and magnetic field measurements

Geophysical Research Letters (1997)

J. B. Blake D. N. Baker N. E. Turner K. W. Ogilvie R. P. Lepping

A study has been made of the correlation of the population of relativistic electrons in the outer‐zone magnetosphere with the properties of the solar wind (speed, density, magnetic field) during a solar minimum period. The study is based upon observations made in the Spring of 1995 with sensors aboard 1994‐026 and WIND. It is found that a large relativistic electron enhancement depends upon a substantial solar‐wind speed increase associated with precursor solar‐wind density enhancement, and, in particular, upon a southward turning of the interplanetary magnetic field.

Heliospheric current sheet

10.1029/97gl00859

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Citations (181)

Estimated errors in magnetic cloud model fit parameters with force‐free cylindrically symmetric assumptions

Journal of Geophysical Research Atmospheres (2003)

R. P. Lepping D. B. Berdichevsky Timothy Ferguson

This paper briefly reviews our earlier study done on estimated errors in various output fit parameters resulting from a specific force‐free interplanetary magnetic cloud model [ Lepping et al. , 1990 ], applied to randomly noised‐up fields of simulated clouds, and shows that such random noise simulation studies are inadequate. It then proceeds to carry out an error study of the same model output parameters on the basis of more realistic input magnetic field noise sets derived from actual clouds observed in WIND data over the years 1995 to 1998. In this part of the study, 1824 “noised‐up” simulated clouds are produced for use in the same force‐free cloud model to study the spread in values for each of 7 model parameters, plus associated quantities, as a function of noise level. Four noise levels are used with RMSs of 0.5, 2.0 (typical level), 3.0, and 4.0 nT per field component of input bias‐free fluctuation fields. These are based on manipulation of difference fields from 19 actual magnetic clouds, where a difference field is defined as the vector difference between the observational field and that from the original model fit for each actual cloud. The averages and RMSs of 240 output (model fit) parameter distributions are produced and discussed. The study determines how the model fit parameters, and especially their distributions, vary as a function of various input noise levels and of the resulting least squares values for various exact input parameters, such as the cloud's axial attitude and the closest approach distance of the spacecraft. Practical goals were to better understand the fit program's limitations and to provide a prescription for estimating future errors in specific magnetic cloud (and probably magnetotail flux rope) fittings. The degree of symmetry in the model solution is used along with to judge the quality of the fit.

10.1029/2002ja009657

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Citations (49)

Observations at Mercury encounter by the plasma science experiment on Mariner 10

Science (1974)

N. F. Ness K. W. Behannon R. P. Lepping Y. C. Whang Kenneth H. Schatten

Mercury

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Citations (7)

Upstream waves at Uranus

Journal of Geophysical Research Atmospheres (1990)

C. T. Russell R. P. Lepping C. W. Smith

Since the Mach number of the solar wind increases with increasing heliocentric distance, the ratio of thermal to magnetic pressure, or beta, of the Uranian magnetosheath is expected to be much higher than in the terrestrial magnetosheath. Consistent with this expectation the magnetosheath is observed to be extremely turbulent, and we may expect many particles to leak back upstream into the solar wind and/or be scattered from the bow shock. In accord with the expected presence of backstreaming particles, waves of the type associated with terrestrial backstreaming particles are seen outbound along the trajectory of Voyager in the pre‐shock solar wind with frequencies close to 10 −3 Hz. The wave frequency is close to that expected for upstream waves based on measurements closer to the Sun. Upstream from the bow shock the magnetic field was found to be much weaker than expected from observations in the inner solar system. The cause of this depression is unlikely to be the upstream particles; rather the cause is probably intrinsic to the solar wind such as reconnection across the heliospheric current sheet.

Magnetosheath

Uranus

Bow wave

Heliospheric current sheet

10.1029/ja095ia03p02273

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Citations (43)

Statistical and superposed epoch study of dipolarization events using data from Wind perigee passes

Annales Geophysicae (2005)

K. Sigsbee J. A. Slavin R. P. Lepping Á. Szabó M. Øieroset

Abstract. From 1995 to 2000, the Wind spacecraft spent over 500h in the magnetotail, much of it within ~2x104km of the predicted location of the neutral sheet. Wind passed through the near magnetotail at distances of -15 RE<X GSM<-6 RE on 35 occasions. Another 10 passes took place at distances of -30 RE<X GSM<-15 RE. We identified 65 dipolarization events in the Wind magnetic field data set between Y GSM~-16 and +16 RE based upon our requirements that the magnetic field inclination had to change by more than 15°, the maximum inclination angle had to be greater than 20°, and the inclination angle had to increase by a factor of at least 1.5. Most of the dipolarization events occurred in the pre-midnight region of the magnetotail and were accompanied by earthward flows with speeds greater than 100km/s. The properties of the dipolarization events did not depend upon the Y GSM position. However, they did vary with the distance to the neutral sheet. Isolated dipolarization events, defined as occurring more than 20min apart, were characterized by a decrease in Bx GSM and BTOTAL, and an increase in Bz GSM and the magnetic field inclination. Dipolarizations that occurred as part of a series of small dipolarizations spaced less than 20min apart were characterized by a transient increase in Bz GSM and the magnetic field inclination, but no significant change in Bx GSM and BTOTAL. The events consisting of a series of small dipolarizations occurred predominantly near midnight. We interpret these results in terms of two different modes of magnetotail convection: 1) a classical substorm pattern featuring storage of magnetic energy in the tail lobes which is explosively released at onset, and 2) a directly driven process.

GSM

10.5194/angeo-23-831-2005

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Citations (16)

On the origin and configuration of the 20 March 2003 interplanetary shock and magnetic cloud at 1 AU

Journal of Geophysical Research Atmospheres (2005)

D. B. Berdichevsky I. G. Richardson R. P. Lepping S. F. Martin

On 20 March 2003, a forward shock was observed in the near‐Earth solar wind, followed 8 hours later by an interplanetary magnetic cloud (IMC), in a configuration having several uncommon features: Both were parts of a 38‐hour interval containing transient solar outflows that occurred in an extended high‐speed stream from a Y‐shaped extension of the south polar coronal hole. (In contrast, IMCs, and ejecta in general, were rarely observed within high‐speed streams at low heliolatitudes during cycle 23.) The most likely solar source for the IMC is AR 10314, located at S15°, just above the “fork” of the Y‐shaped coronal hole. Several solar flares occurred in this active region on 17–18 March, as well as a succession of four coronal mass ejections (CMEs). Velocity considerations narrow the most likely source of the 38‐hour interval of activity to two CMEs on 17 March 2003 associated with solar flares at W33° and W39°. The IMC axis had a north‐south orientation, which is unusual for IMCs during this solar cycle. Its left‐handedness implies an association with a left‐skewed coronal arcade, which is less common in the Southern Hemisphere. Considering the shock observed ahead of the IMC, we conclude based on orientation and ram pressure arguments that this shock was not driven by the IMC, as might be presumed, but was the flank of an unrelated shock that overtook the IMC approximately halfway between Sun and Earth, heating the plasma and accelerating particles within the IMC. The CME associated with the X‐class flare, at 1208 UT on 18 March in AR 10314 appears to be the solar source for this shock.

Coronal cloud

Coronal hole

Magnetic cloud

Corona (planetary geology)

Solar cycle 22

10.1029/2004ja010662

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Citations (17)

Flux rope structures in the magnetotail: Comparison between Wind/Geotail observations and global simulations

Journal of Geophysical Research Atmospheres (1998)

R. M. Winglee S. Kokubun R. P. Lin R. P. Lepping

On December 11, 1994, Geotail observed several reconnection (negative B z ) events at a position 30–40 R E down the tail over a 24 hour period. This period is also interesting because the solar wind conditions were well monitored by Wind, which was only about 20 R E in front of the bow shock, and because IMP 8 was at nearly the same x value as Geotail, but at high latitudes. Global fluid simulations that incorporate higher‐order corrections to Ohm's law are used to produce a three dimensional picture of the reconnection site in conjunction with the Geotail data. It is shown that many of the negative B z events have appreciable core magnetic fields, which in the modeling appear to form around 20 R E about 10 min earlier than observed by Geotail. The predicted time of the formation coincides approximately with increased ionospheric activity observed by the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) magnetometer chain. The flux ropes also appear to be highly localized (2–4 R E ), particularly in x and z when they are first created. In addition, they have a distinctive bipolar core magnetic field, but the probability that a spacecraft observes a unidirectional or bipolar signature is highly dependent on the position of the center of the current sheet relative to the spacecraft. Bipolar signatures are predicted to be most easily seen when the spacecraft is near the center of the current sheet, while unidirectional signatures are most likely to be observed at more distant encounters.

Current sheet

Plasma sheet

10.1029/97ja02415

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Citations (30)

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

Journal of Geophysical Research Atmospheres (2000)

D. B. Berdichevsky Á. Szabó R. P. Lepping A. F. Viñas F. Mariani

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 Viñas 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 ϕ n ≥ 220±10°, i.e. against the average Parker spiral direction. Examination of the obliquity angle θ Bn (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 θ Bn was obtained for about 10 shocks with magnetosonic Mach numbers between 1 and 2.

Ecliptic

Longitude

Heliosphere

10.1029/1999ja000367

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Citations (100)

The ionospheric signatures of flux transfer events and solar wind dynamic pressure changes

Journal of Geophysical Research Atmospheres (1990)

M. Lockwood S. W. H. Cowley P. E. Sandholt R. P. Lepping

The generation of flow and current vortices in the dayside auroral ionosphere has been predicted for two processes ocurring at the dayside magnetopause. The first of these mechanisms is time‐dependent magnetic reconnection, in “flux transfer events” (FTEs); the second is the action of solar wind dynamic pressure changes. The ionospheric flow signature of an FTE should be a twin vortex, with the mean flow velocity in the central region of the pattern equal to the velocity of the pattern as a whole. On the other hand, a pulse of enhanced or reduced dynamic pressure is also expected to produce a twin vortex, but with the central plasma flow being generally different in speed from, and almost orthogonal to, the motion of the whole pattern. In this paper, we make use of this distinction to discuss recent observations of vortical flow patterns in the dayside auroral ionosphere in terms of one or other of the proposed mechanisms. We conclude that some of the observations reported are consistent only with the predicted signature of FTEs. We then evaluate the dimensions of the open flux tubes required to explain some recent simultaneous radar and auroral observations and infer that they are typically 300 km in north–south extent but up to 2000 km in longitudinal extent (i.e., roughly 5 hours of MLT). Hence these observations suggest that recent theories of FTEs which invoke time‐varying reconnection at an elongated neutral line may be correct. We also present some simultaneous observations of the interplanetary magnetic field (IMF) and solar wind dynamic pressure (observed using the IMP8 satellite) and the ionospheric flow (observed using the EISCAT radar) which are also only consistent with the FTE model. We estimate that for continuously southward IMF (<B z > ≈ 5 nT) these FTEs contribute about 30 kV to the mean total transpolar voltage (∼30%).

Dynamic pressure

10.1029/ja095ia10p17113

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Citations (151)