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HP Warren

Publications and source records attributed to HP Warren.

4 recordsLinked to original sources
PubMed2000

Fine Structure in Solar Flares.

We present observations of several large two-ribbon flares observed with both the Transition Region and Coronal Explorer (TRACE) and the soft X-ray telescope on Yohkoh. The high spatial resolution TRACE observations show that solar flare plasma is generally not confined to a single loop or even a few isolated loops but to a multitude of fine coronal structures. These observations also suggest that the high-temperature flare plasma generally appears diffuse while the cooler ( less, similar2 MK) postflare plasma is looplike. We conjecture that the diffuse appearance of the high-temperature flare emission seen with TRACE is due to a combination of the emission measure structure of these flares and the instrumental temperature response and does not reflect fundamental differences in plasma morphology at the different temperatures.

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PubMed2000

Small Scale Structure in the Solar Transition Region.

We present analysis of a high spatial resolution ( approximately 1&farcs;5) O vi lambda1032 spectroheliogram taken with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory. This image shows numerous narrow, looplike structures. The widths of the narrowest resolved features are at the spatial resolution of the SUMER spectrometer. In contrast to earlier Skylab observations, however, comparisons with a Michelson Doppler Imager magnetogram reveals that the majority of these looplike structures do not connect network magnetic fields. Instead, they extend from the supergranulation network into the cell-center regions where no magnetic fields are detected in these data. We conjecture that these fine structures are related to spicules and are highly dynamic.

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PubMed1999

TRACE and Yohkoh Observations of High-Temperature Plasma in a Two-Ribbon Limb Flare.

The ability of the Transition Region and Coronal Explorer (TRACE) to image solar plasma over a wide range of temperatures (Te approximately 104-107 K) at high spatial resolution (0&farcs;5 pixels) makes it a unique instrument for observing solar flares. We present TRACE and Yohkoh observations of an M2.4 two-ribbon flare that began on 1999 July 25 at about 13:08 UT. We observe impulsive footpoint brightenings that are followed by the formation of high-temperature plasma (Te greater, similar10 MK) in the corona. After an interval of about 1300 s, cooler loops (Te<2 MK) form below the hot plasma. Thus, the evolution of the event supports the qualitative aspects of the standard reconnection model of solar flares. The TRACE and Yohkoh data show that the bulk of the flare emission is at or below 10 MK. The TRACE data are also consistent with the Yohkoh observations of hotter plasma (Te approximately 15-20 MK) existing at the top of the arcade. The cooling time inferred from these observations is consistent with a hybrid cooling time based on thermal conduction and radiative cooling.

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