Resolving Differences in Absolute Irradiance Measurements Between the SOHO/CELIAS/SEM and the SDO/EVE

Wieman, Seth; Didkovsky, L. V.; Judge, D. L.

doi:10.1007/978-1-4939-2038-9_18

Cited by 8 publications

(13 citation statements)

References 38 publications

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“…If the 26–34 nm SEE EUV is used as the calibration reference as mentioned previously, the SEM 26–34 nm data during 2008 will be uplifted more, then even smaller X and R are expected. It is worth noting an updated version of the SEM 26–34 nm measurements based on a more accurate response function [ Wieman et al , ], and a new estimation of X = 12 ± 4% given by Didkovsky and Wieman []. This X value is lower than that based on the published version 3.1 SEM data as cited in this paper, and much close to X based on our adjusted SEM data.…”

Section: Resultssupporting

confidence: 63%

“…This agrees well with our results in Figures and . Wieman et al [] did not show whether the SEM deviation is constant or evolving with time; thus, it is worth noting the increase of SEM deviation with time as shown in Figure . This deviation could be the result of either underestimated EUV flux by SEM or overestimated data by SEE, and the trend implies possible long‐term sensitivity drift of the instrument or inappropriate correction of the drift.…”

Section: Resultsmentioning

confidence: 94%

“…It is obvious that the SEM flux is lower compared to both both SEE and EVE, and the discrepancy gets enlarged with time to 10–20% in average after 2008. Wieman et al [] analyzed the deviation of SEM from EVE during 2010–2013 and found that the SEM data are 10–20% lower than EVE in 7–50 nm band. This agrees well with our results in Figures and .…”

Section: Resultsmentioning

confidence: 99%

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Revisiting interminima solar EUV change using adjusted SOHO SEM data

et al. 2017

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The change of solar EUV irradiance between the 1996 and 2008 minima is still in active debate due to a possible trend in the data from the Solar EUV Monitor (SEM) on board the Solar and Heliospheric Observatory (SOHO). For the period of years 2002–2012, i.e., the descending phase of solar cycle 23 (SC23) and the ascending phase of SC24, concurrent observations from the Solar EUV Experiment (SEE) on board the Thermospheric Ionospheric Mesospheric Energy and Dynamics spacecraft are available. We compare the data from the two instruments in terms of an expected linear relation between the EUV irradiance and the ionospheric peak electron density (NmF2). For the SEE data the NmF2‐EUV function is solar cycle invariant, but for the SEM data the function is found to be different between SC23 and SC24, which is hard to explain at present. An attempt is therefore made to obtain a unbiased SEM data set by using the SEE data as a calibration source. As a result, a temporal sensor drift coefficient of ∼−2%/yr is fitted, and the trend causing the unnatural solar cycle different NmF2‐EUV function is removed from the data. A new estimation of the interminima change of EUV irradiance based on the adjusted SEM data is ∼10% reduction in 2008 compared to 1996, much smaller than previous results. After adjustment the SOHO SEM could continue to be a reliable data source for solar EUV and aeronomic studies over both SC23 and SC24.

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Section: Resultssupporting

confidence: 63%

Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

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Revisiting interminima solar EUV change using adjusted SOHO SEM data

et al. 2017

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“…It should be noted that EUV observations aboard satellites usually have instrument degradations. This degradation also exists in the SOHO/SEM recent measurements (Didkovsky and Wieman, 2014;Solomon et al, 2013;Wieman et al, 2014), which possibly affects the results of EUV long-term variations to some extent. This effect is not prominent for the SOHO/SEM EUV flux measurements in solar cycle 23 according to the calibrations with other EUV measurements shown in Didkovsky et al (2010) and Solomon et al (2010).…”

Section: Datamentioning

confidence: 95%

Discrepant responses of the global electron content to the solar cycle and solar rotation variations of EUV irradiance

Chen

Liu

et al. 2015

Earth Planet Sp

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In this paper, the responses of the ionosphere to the solar cycle and solar rotation variations of extreme ultraviolet (EUV) irradiance are comparatively investigated using daily mean global electron content (GEC) and 0.1-50 nm EUV daily flux. GEC is well correlated with EUV on both the solar cycle and solar rotation timescales; however, the responses of GEC to the solar cycle and solar rotation variations of EUV are significantly different in terms of the following two aspects: (1) There is a significant time lag between the solar rotation variations of GEC and EUV; the lag is dominated by a 1-day lag and generally presents a decrease trend with solar activity decreasing. For the solar cycle variations of GEC and EUV, however, there are no evident time lags. (2) The GEC versus EUV slopes are different for the solar cycle and solar rotation variations of GEC and EUV; the solar cycle GEC versus EUV slope is higher than the solar rotation GEC versus EUV slope, and this difference occurs in different seasons and latitudinal bands. The results present an aspect of the difference between ionospheric climatology and weather.

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“…The H Lyman‐a compilation (Woods et al, ) is in good agreement with the Viereck et al MgII analysis. In the case of the SOHO/SEM data, it is clear that the earlier releases suffered from some instrumental degradation, but these data have been revised (Wieman et al, ) and are now in better alignment with index‐based variability.…”

Section: Discussionmentioning

confidence: 99%

Ionospheric Electron Content During Solar Cycle 23

2018

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The solar minimum period between solar cycles 23 and 24 has generated extensive study, in part because the changes in the upper atmosphere and ionosphere were so dramatic. Thermospheric density during 2008-2009, at the benchmark 400-km altitude, was shown to be approximately 30% lower than the previous solar minimum during 1996, in observations and in model simulations. Ionospheric densities were also estimated to be lower, by 10% to 20%. However, earlier analyses using data from the global network of Global Navigation Satellite System receivers did not find any significant reduction in global mean total electron content. Recent work reexamining those data using a limited set of receivers, but with consistent processing, identified a 19% reduction (Emmert et al., 2017, https://doi.org/10.1002/2016JA023680). In this study, we compare model simulations of the thermosphere-ionosphere system during the 2008-2009 solar minimum to its predecessor and estimate a 16% reduction in global mean total electron content. This is consistent with the neutral thermosphere density change seen in model simulations and in satellite drag observations. In the model simulations, the primary driver is a 10% reduction in solar extreme ultraviolet irradiance, with a smaller contribution from lower geomagnetic activity, and a very small decrement due to increase in atmospheric carbon dioxide.Plain Language Summary The Sun goes through 11-year activity cycles, best known with regard to the number of sunspots. At solar minimum, when sunspots mostly vanish, the extreme ultraviolet region of the solar spectrum also diminishes. This causes lower temperature and density in the ionosphere and upper atmosphere above 100 km, where the extreme ultraviolet radiation is absorbed. Past solar minimum periods have seemed basically similar with regard to extreme ultraviolet radiation, and other manifestations of solar activity. However, the solar minimum during 2008-2009 was longer and had fewer sunspots than its predecessor during 1996, or than any minimum period in the past century. The thermosphere was also lower in density, and the ionosphere also appeared to be lower in density, but there were some contradictory measurements. Recent reanalysis of ionospheric measurements found better agreement with the thermospheric measurements. Modeling studies attempting to explain the changes in the ionosphere and thermosphere have suggested that they were caused by a decrease of about 10% in solar extreme ultraviolet radiation. Here we show that the model results and the ionospheric measurements are now in good agreement. This demonstrates that solar minima are not all the same and may have implications for understanding the Sun during extended periods of very low activity.

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Resolving Differences in Absolute Irradiance Measurements Between the SOHO/CELIAS/SEM and the SDO/EVE

Cited by 8 publications

References 38 publications

Revisiting interminima solar EUV change using adjusted SOHO SEM data

Revisiting interminima solar EUV change using adjusted SOHO SEM data

Discrepant responses of the global electron content to the solar cycle and solar rotation variations of EUV irradiance

Ionospheric Electron Content During Solar Cycle 23

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