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Post Info TOPIC: Aurora Alert


L

Posts: 131433
Date:
NOAA 10759
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Title: The Eruption from a Sigmoidal Solar Active Region on 2005 May 13
Authors: Chang Liu, Jeongwoo Lee, Vasyl Yurchyshyn, Na Deng, Kyung-Suk Cho, Marian Karlicky, Haimin Wang

This paper presents a multiwavelength study of the M8.0 flare and its associated fast halo CME that originated from a bipolar active region NOAA 10759 on 2005 May 13. The source active region has a conspicuous sigmoid structure at TRACE 171 A channel as well as in the SXI soft X-ray images, and we mainly concern ourselves with the detailed process of the sigmoid eruption as evidenced by the multiwavelength data ranging from Halpha, WL, EUV/UV, radio, and hard X-rays (HXRs). The most important finding is that the flare brightening starts in the core of the active region earlier than that of the rising motion of the flux rope. This timing clearly addresses one of the main issues in the magnetic eruption onset of sigmoid, namely, whether the eruption is initiated by an internal tether-cutting to allow the flux rope to rise upward or a flux rope rises due to a loss of equilibrium to later induce tether cutting below it. Our high time cadence SXI and Halpha data shows that the first scenario is relevant to this eruption. As other major findings, we have the RHESSI HXR images showing a change of the HXR source from a confined footpoint structure to an elongated ribbon-like structure after the flare maximum, which we relate to the sigmoid-to-arcade evolution. Radio dynamic spectrum shows a type II precursor that occurred at the time of expansion of the sigmoid and a drifting pulsating structure in the flare rising phase in HXR. Finally type II and III bursts are seen at the time of maximum HXR emission, simultaneous with the maximum reconnection rate derived from the flare ribbon motion in UV. We interpret these various observed properties with the runaway tether-cutting model proposed by Moore et al. in 2001.

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L

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RE: Aurora Alert
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AuroraWatch Alert at 06:01 UT  16 May 2005:
High local activity, and possible start of a geomagnetic storm.


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L

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May 15, 2005


Forecasters at the NOAA Space Environment Center in Boulder, Colo., observed a geomagnetic storm on Sunday, May 15, which they classified as an extreme event, measuring G-5 the highest level on the NOAA Space Weather Scales.


"This event registered a 9 on the K-Index, which measures the maximum deviation of the Earth's magnetic field in a given three-hour period. The scale ranges from 0 to 9, with 9 being the highest. This was a significant event." - Gayle Nelson, lead operations specialist at NOAA Space Environment Center.



Possible impacts from such a geomagnetic storm include widespread power system voltage control problems; some grid systems may experience complete collapse or blackouts. Transformers may experience damage. Spacecraft operations may experience extensive surface charging; problems with orientation; uplink/downlink and tracking satellites. Satellite navigation may be degraded for days, and low-frequency radio navigation can be out for hours. Reports received by the NOAA Space Environment Center indicate that such impacts have been observed in the United States.



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Sunspot 758 ejected a coronal mass ejection (CME) into space on May 11th, 2030 UT.
Auroras are expected on Mat 13th.

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Aurora Alert for 17:01 UT 29 Apr 2005...

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