Page 1 |
Save page Remove page | Previous | 1 of 156 | Next |
|
small (250x250 max)
medium (500x500 max)
Large (1000x1000 max)
Extra Large
large ( > 500x500)
Full Resolution
All (PDF)
|
This page
All
|
REVISED CALIBRATION OF A LONG-TERM SOLAR EXTREME ULTRAVIOLET IRRADIANCE DATA SET
by
Seth Wieman
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(ASTRONAUTICAL ENGINEERING)
May 2015
Object Description
| Title | Revised calibration of a long-term solar extreme ultraviolet irradiance data set |
| Author | Wieman, Seth R. |
| Author email | wieman@usc.edu;seth.wieman@usc.edu |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Astronautical Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2015-02-24 |
| Date submitted | 2015-04-10 |
| Date approved | 2015-04-10 |
| Restricted until | 2015-04-10 |
| Date published | 2015-04-10 |
| Advisor (committee chair) | Gruntman, Michael |
| Advisor (committee member) |
Didkovsky, Leonid Rhodes, Edward J., Jr. Wang, Joseph |
| Abstract | Solar irradiance measurements in the extreme ultraviolet (EUV) and soft X‐ray (SXR) spectral ranges are important to studies of solar variability and its impact on the geospace environment and to operations affected by space weather. While the availability of solar EUV measurements has increased over the last two decades, data from the Solar EUV Monitor (SEM), part of the Charge, Element, and Isotope Analysis System (CELIAS) on board the Solar and Heliospheric Observatory (SOHO) remain unique in that they are continuous with high time cadence over a long time period which includes two solar minima, and their accuracy has been maintained based on a long series of sounding rocket calibration underflights, resulting in their use as the basis for a solar activity index for space weather operations. The purpose of this work is to further improve the absolute calibration of the SEM EUV irradiance measurements using data unavailable during earlier SEM calibrations. Solar EUV variability occurs over a range of timescales, including periodic changes associated with the 11‐year solar sunspot cycle (i.e. the 22‐year solar magnetic cycle). Thus, long‐term stable irradiance measurements are important in order to understand this variability and its relation to long‐term changes in the geospace environment. Maintaining the absolute accuracy of irradiance measurements is required to avoid data inconsistencies and the misinterpretation of instrument-related bias when compiling long‐term data sets comprised of measurements from more than one instrument. ❧ Although analyses of the SEM absolute calibration have been ongoing since the launch of SOHO and have incorporated measurements from a series of sounding rocket underflights, in recent years additional data have become available which have created opportunities and motivation for further refinement of the SEM measurements. Firstly, converting the SEM raw data into irradiance values depends on the instrument response function and on the spectral distribution of solar irradiance (i.e. reference spectrum) within the SEM sensitivity range, and both of these parameters have been determined with greater accuracy than those used in SEM data processing to date. Secondly, reliable EUV irradiance measurements in a spectral range overlapping that of SEM are available from the Solar Dynamics Observatory’s EUV Variability Experiment (SDO/EVE) which includes provisions for in‐flight calibration and degradation monitoring, and these measurements differ from concurrent SEM values (obtained using the original response function and reference spectrum) by an amount that is consistent throughout the SDO and SOHO mission overlap suggesting there may be a systematic offset in the SEM irradiance values. Thirdly, the SEM measurements show lower (by ~15%) irradiance values for the minimum of Solar Cycles 22 and 23 compared to Solar Cycles 23 and 24—this inter‐minima change is consistent with the response of the earth’s upper atmosphere over the same period with regard to some solar EUV‐driven processes (i.e. thermospheric neutral density) but inconsistent with others (i.e. global mode ionospheric total electron content). Further investigation is thus required to determine whether the lower EUV irradiance measured by SEM is real or an artifact of long‐term instrument degradation. ❧ Resolving these three issues concerning the SEM data set is the objective of this dissertation, and the included work has several key results. It demonstrates that the differences between SOHO/SEM and SDO/EVE EUV irradiance measurements are resolved by reprocessing the SEM raw data using an updated SEM instrument response function (introduced as part of this work) and time‐dependent solar reference spectra. Additionally, it provides an updated time and wavelength dependent SEM instrument degradation function which is necessary to refine the estimate of inter‐minima change in EUV irradiance based on the SEM data. Finally, this work provides a procedure for producing a SEM‐equivalent EUV irradiance index based on SDO/EVE measurements. The motivation for this final effort is that SOHO/SEM irradiance values based on the previous response function and reference spectrum have already been adopted as a solar irradiance index used for modeling thermospheric density, and because such space weather operations are concerned with long‐term consistency, it is desirable to continue providing an irradiance index equivalent to that provided thus far by SEM using newer EUV instrumentation after the SOHO mission has ended. |
| Keyword | solar EUV irradiance; solar soft X-ray irradiance; EUV instrumentation; solar EUV monitor |
| Language | English |
| Format (imt) | application/pdf |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m |
| Contributing entity | University of Southern California |
| Rights | Wieman, Seth R. |
| Physical access | The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright. The original signature page accompanying the original submission of the work to the USC Libraries is retained by the USC Libraries and a copy of it may be obtained by authorized requesters contacting the repository e-mail address given. |
| Repository name | University of Southern California Digital Library |
| Repository address | USC Digital Library, University of Southern California, University Park Campus MC 7002, 106 University Village, Los Angeles, California 90089-7002, USA |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-WiemanSeth-3273.pdf |
| Archival file | Volume1/etd-WiemanSeth-3273.pdf |
Description
| Title | Page 1 |
| Repository email | cisadmin@lib.usc.edu |
| Full text | REVISED CALIBRATION OF A LONG-TERM SOLAR EXTREME ULTRAVIOLET IRRADIANCE DATA SET by Seth Wieman A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (ASTRONAUTICAL ENGINEERING) May 2015 |
