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McKenzie, David E.

Publications and source records attributed to McKenzie, David E..

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Center-to-Limb Variation of the Polarization of Mg II H & K Lines as Measured by CLASP2

Who cares? Magnetograms in the upper chromosphere are needed for accurate magnetic coronal extrapolations. The CLASP2 sounding rocket took spatially resolved spectropolarimetric data of Mg II h & k in the upper chromosphere, that can be used as a pathfinder to routine magnetograms. This work: Preliminary results of the center-to-limb variation (CLV) of the linear polarization in the quiet sun. We compare the signals to recent theoretical calculations of the expected polarization which include PRD, J-state interference, and magneto-optical effects.

Rachmeler, Laurel↗
NASA NTRS2012

Complex Dynamic Flows in Solar Flare Sheet Structures

Observations of high-energy emission from solar flares often reveal the presence of large sheet-like structures, sometimes extending over a space comparable to the Sun's radius. Given that these structures are found between a departing coronal mass ejection and the post-eruption flare arcade, it is natural to associate the structure with a current sheet; though the relationship is unclear. Moreover, recent high-resolution observations have begun to reveal that the motions in this region are highly complex, including reconnection outflows, oscillations, and apparent wakes and eddies. We present a detailed first look at the complicated dynamics within this supra-arcade plasma, and consider implications for the interrelationship between the plasma and its embedded magnetic field.

McKenzie, David E.↗
NASA NTRS2012

Thermal Structure of Supra-Arcade Plasma in Two Solar Flares

In this work, we use Hinode/XRT and SDO/AIA data to determine the thermal structure of supra-arcade plasma in two solar flares. The first flare is a Ml.2 flare that occurred on November 5, 2010 on the east limb. This flare was one of a series of flares from AR 11121, published in Reeves & Golub (2011). The second flare is an XI.7 flare that occurred on January 27, 2012 on the west limb. This flare exhibits visible supra-arcade downflows (SADs), where the November 2010 flare does not. For these two flares we combine XRT and AlA data to calculate DEMs of each pixel in the supra-arcade plasma, giving insight into the temperature and density structures in the fan of plasma above the post-flare arcade. We find in each case that the supra-arcade plasma is around 10 MK, and there is a marked decrease in the emission measure in the SADs. We also compare the DEMs calculated with the combined AIA/XRT dataset to those calculated using AIA alone.

Reeves, Katharine K.↗
NASA NTRS2012

Low-Altitude Reconnection Inflow-Outflow Observations During a 2010 November 3 Solar Eruption

For a solar flare occurring on 2010 November 3, we present observations us- ing several SDO/AIA extreme-ultraviolet (EUV) passbands of an erupting flux rope followed by inflows sweeping into a current sheet region. The inflows are soon followed by outflows appearing to originate from near the termination point of the inflowing motion an observation in line with standard magnetic reconnection models. We measure average inflow plane-of-sky speeds to range from approximately 150 - 690 km s-1 with the initial, high-temperature inflows being the fastest. Using the inflow speeds and a range of Alfven speeds, we estimate the Alfvenic Mach number which appears to decrease with time. We also provide inflow and outflow times with respect to RHESSI count rates and find that the fast, high- temperature inflows occur simultaneously with a peak in the RHESSI thermal light curve. Five candidate inflow-outflow pairs are identified with no more than a minute delay between detections. The inflow speeds of these pairs are measured to be approximately 10(exp 2) km s-1 with outflow speeds ranging from approximately 10(exp 2) - 10(exp 33 km s-1 indicating acceleration during the reconnection process. The fastest of these outflows are in the form of apparently traveling density enhancements along the legs of the loops rather than the loop apexes themselves. These flows could possibly either be accelerated plasma, shocks, or waves prompted by reconnection. The measurements presented here show an order of magnitude difference between the retraction speeds of the loops and the speed of the density enhancements within the loops presumably exiting the reconnection site.

Savage, Sabrina L.a↗
NASA NTRS2011

Current Sheet and Reconnection Inflow-Outflow Observations During Solar Eruptions

Magnetic reconnection is widely accepted as a dominant source of energy during solar flares; however, observations of it have been indirect and/or incomplete. Using the suite of instruments available spanning wavelength space, we will provide observations and measurements of both the inputs and outputs predicted from reconnection in the form of inflows preceding outflows (i.e. supra-arcade downflows, supra-arcade downflowing loops, upflows, and disconnection events). We will also present evidence for current sheets through which reconnection is expected to occur and discuss current sheet motion during flare progression.

Savage, Sabrina↗
NASA NTRS2011

Quantitative Examination of a Large Sample of Supra-Arcade Downflows in Eruptive Solar Flares

Sunward-flowing voids above post-coronal mass ejection flare arcades were first discovered using the soft X-ray telescope aboard Yohkoh and have since been observed with TRACE (extreme ultraviolet (EUV)), SOHO/LASCO (white light), SOHO/SUMER (EUV spectra), and Hinode/XRT (soft X-rays). Supra-arcade downflow (SAD) observations suggest that they are the cross-sections of thin flux tubes retracting from a reconnection site high in the corona. Supra-arcade downflowing loops (SADLs) have also been observed under similar circumstances and are theorized to be SADs viewed from a perpendicular angle. Although previous studies have focused on dark flows because they are easier to detect and complementary spectral data analysis reveals their magnetic nature, the signal intensity of the flows actually ranges from dark to bright. This implies that newly reconnected coronal loops can contain a range of hot plasma density. Previous studies have presented detailed SAD observations for a small number of flares. In this paper, we present a substantial SADs and SADLs flare catalog. We have applied semiautomatic detection software to several of these events to detect and track individual downflows thereby providing statistically significant samples of parameters such as velocity, acceleration, area, magnetic flux, shrinkage energy, and reconnection rate. We discuss these measurements (particularly the unexpected result of the speeds being an order of magnitude slower than the assumed Alfven speed), how they were obtained, and potential impact on reconnection models.

Savage, Sabrina L.↗