Year: 2020
Type: article
Abstract: Context. One of the main discoveries from the first two orbits of Parker Solar Probe (PSP) was the presence of magnetic switchbacks, whose deflections dominated the magnetic field measurements. Determining their shape and size could provide evidence of their origin, which is still unclear. Previous work with a single solar wind stream has indicated that these are long, thin structures although the direction of their major axis could not be determined. Aims. We investigate if this long, thin nature extends to other solar wind streams, while determining the direction along which the switchbacks within a stream were aligned. We try to understand how the size and orientation of the switchbacks, along with the flow velocity and spacecraft trajectory, combine to produce the observed structure durations for past and future orbits. Methods. The direction at which the spacecraft cuts through each switchback depended on the relative velocity of the plasma to the spacecraft and the alignment direction for that stream. We searched for the alignment direction that produced a combination of a spacecraft cutting direction and switchback duration that was most consistent with long, thin structures. The expected form of a long, thin structure was fitted to the results of the best alignment direction, which determined the width and aspect ratio of the switchbacks for that stream. Results. We find that switchbacks consistently demonstrate a non-radial alignment in the same sense as the Parker spiral field, but not the background flow direction within each stream. This alignment direction varied between streams. The switchbacks had a mean width of 50 000 km, with an aspect ratio of the order of 10. Conclusions. We conclude that switchbacks are not aligned along the background flow direction, but instead aligned along the local Parker spiral, perhaps suggesting that they propagate along the magnetic field. Since the observed switchback duration depends on how the spacecraft cuts through the structure, the duration alone cannot be used to determine the size or influence of an individual event. For future PSP orbits, a larger spacecraft transverse component combined with more radially aligned switchbacks will lead to long duration switchbacks becoming less common.
Source: Astronomy and Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Awards: G178474015, Space and planetary physics 2019-2022, G246295646, WE PROPOSE TO OBTAIN NEW MEASUREMENTS OF THE SUN'S MAGNETIC FIELD (HELIOSPHERIC MAGNETIC FIELD HMF) INTERIOR TO THE EARTH'S ORBIT BY TRACING THE TRAJECTORIES OF TYPE III SOLAR RADIO BURSTS USING THE TIME DELAY OF ARRIVAL (TDOA) METHOD. THE MAIN OBJECTIVES ARE: (1) TO EVALUATE THE ACCURACY AND IDENTIFY COMPLICATING EFFECTS IN THE TDOA METHOD AND MAKE USE OF THE COMPUTATIONAL SIMPLICITY OF THE METHOD TO AUTOMATE ANALYSIS OF A GIVEN RADIO BURST EVENT. (2) UTILIZE THE EVALUATED AND AUTOMATED METHOD TO OBTAIN A CATALOG OF TRACES OF FIELD LINES OVER A PERIOD OF TIME WHICH SAMPLES A LARGE PORTION OF A SOLAR CYCLE AND USE THIS TO DETERMINE NEW STATISTICAL INFORMATION ABOUT THE HMF GEOMETRY AND PROVIDE NEW INPUT DATA FOR HELIOSPHERIC MODELS TO IMPROVE SPACE WEATHER FORECASTING. (3) EXTEND THE METHOD TO USE WITH DATA FROM THE FUTURE HELIOSPHERIC MISSIONS: NASA'S PARKER SOLAR PROBE AND ESA'S SOLAR ORBITER TO PERFORM FULL 3D MEASUREMENTS OF THE HMF AND PROBE IT'S GEOMETRY ABOVE AND BELOW THE PLANE OF EARTH'S ORBIT. USE WILL ALSO BE MADE OF THE NASA-SELECTED CUBESAT MISSION: CUBESAT RADIO INTERFEROMETRY EXPERIMENT TO IMPROVE PRECISION OF FIELD LINE TRACING. THE METHOD TO BE EVALUATED USES THE FINITE PROPAGATION TIME OF RADIO SIGNALS IN SPACE WHICH LEADS TO A TIME DELAY IN THEIR DETECTION AT DIFFERENT SPACECRAFT DEPENDING ON THE SOURCE POSITION. COMBINING OBSERVATIONS FROM AT LEAST 3 SPACECRAFT ALLOWS CONFINEMENT OF THE SOURCE TO A UNIQUE POINT IN THE ECLIPTIC PLANE. PERFORMING THIS ANALYSIS ON OBSERVATIONS OF TYPE III BURSTS AT DIFFERENT FREQUENCIES ALLOWS US TO TRACE THE TRAJECTORY OF THE BURST AS IT TRAVELS OUT FROM THE SUN. THESE TYPE III BURSTS FOLLOW THE LOCAL MAGNETIC FIELD AND SO TRACE OUT THE FIELD LINE AS THEY PROPAGATE. TO EVALUATE THIS METHOD WILL REQUIRE CONSIDERATION OF THE SPACECRAFT MEASUREMENT CADENCE AND FREQUENCY RESOLUTION AND IDENTIFICATION OF PROPAGATION EFFECTS SUCH AS REFRACTION OR REFLECTION (THEJAPPA AND MACDOWALL 2010 2011). COMPARISONS WILL BE MADE WITH RESULTS OBTAINED FROM THE COMPLEMENTARY AND MORE ESTABLISHED METHOD OF RADIO DIRECTION FINDING. THIS WILL ALLOW AN INDEPENDENT CHECK OF THE LOCALIZATION OBTAINED WITH THE NEW METHOD AND QUANTIFY THE DISCREPANCY OBSERVED DUE TO PROPAGATION EFFECTS. THIS WORK DIRECTLY ADDRESSES THE NASA SMD HELIOPHYSICS OBJECTIVES TO 'ADVANCE OUR UNDERSTANDING OF THE CONNECTIONS THAT LINK THE SUN THE EARTH [AND THE] PLANETARY SPACE ENVIRONMENTS' AND THE STATED OBJECTIVE IN THE 2014 NASA STRATEGIC PLAN TO 'UNDERSTAND THE SUN AND ITS INTERACTIONS WITH EARTH'. THIS IS BECAUSE THIS WORK WILL INVESTIGATE AND PURSUE A ROUTE TO OBTAINING MORE INFORMATION ABOUT THE SOLAR MAGNETIC FIELD WHICH CHANNELS ENERGY AND SPACE WEATHER IN THE INTERPLANETARY MEDIUM. THROUGH OBTAINING A SAMPLE OF FIELD LINE TRACES OVER A LARGE PERIOD OF TIME AND SPACE STATISTICAL INFERENCES ABOUT THE MAGNETIC FIELD GEOMETRY INTERIOR TO THE EARTH'S ORBIT CAN BE INVESTIGATED AND STRONG CONSTRAINTS FOR HELIOSPHERIC MODELING CAN BE IMPOSED TO IMPROVE THEIR PREDICTIVE POWER FOR SPACE WEATHER FORECASTING., G5597996807, G5687480117, G5966779717, STFC Imperial Physics 2015 DTP
OpenAlex ID: W3093615366