scholarly journals Modelling solar irradiance from ground-based photometric observations

2020 ◽  
Vol 10 ◽  
pp. 45 ◽  
Author(s):  
Theodosios Chatzistergos ◽  
Ilaria Ermolli ◽  
Fabrizio Giorgi ◽  
Natalie A. Krivova ◽  
Cosmin Constantin Puiu
Keyword(s):  
Solar Cycle ◽  
Solar Irradiance ◽  
Total Solar Irradiance ◽  
Visible Range ◽  
Solar Cycles ◽  
Term Trend ◽  
Photometric Observations ◽  
San Fernando ◽  
Long Term Trend

Total solar irradiance (TSI) has been monitored from space since 1978, i.e. for about four solar cycles. The measurements show a prominent variability in phase with the solar cycle, as well as fluctuations on timescales shorter than a few days. However, the measurements were done by multiple and usually relatively short-lived missions. The different absolute calibrations of the individual instruments and the unaccounted for instrumental trends make estimates of the possible long-term trend in the TSI highly uncertain. Furthermore, both the variability and the uncertainty are strongly wavelength-dependent. While the variability in the UV irradiance is clearly in-phase with the solar cycle, the phase of the variability in the visible range has been debated. In this paper, we aim at getting an insight into the long-term trend of TSI since 1996 and the phase of the solar irradiance variations in the visible part of the spectrum. We use independent ground-based full-disc photometric observations in Ca II K and continuum from the Rome and San Fernando observatories to compute the TSI since 1996. We follow the empirical San Fernando approach based on the photometric sum index. We find a weak declining trend in the TSI of $ {-7.8}_{-0.8}^{+4.9}\times 1{0}^{-3}$ Wm−2 y−1 between the 1996 and 2008 activity minima, while between 2008 and 2019 the reconstructed TSI shows no trend to a marginally decreasing (but statistically insignificant) trend of $ {-0.1}_{-0.02}^{+0.25}\times 1{0}^{-3}$ Wm−2 y−1. The reference TSI series used for the reconstruction does not significantly affect the determined trend. The variation in the blue continuum (409.2 nm) is rather flat, while the variation in the red continuum (607.1 nm) is marginally in anti-phase, although this result is extremely sensitive to the accurate assessment of the quiet Sun level in the images. These results provide further insights into the long-term variation of the TSI. The amplitude of the variations in the visible is below the uncertainties of the processing, which prevents an assessment of the phase of the variations.

Solar Irradiance: Instrument-Based Advances

2018 ◽  
Vol 14 (A30) ◽  
pp. 354-357
Author(s):  
Greg Kopp
Keyword(s):  
Solar Cycle ◽  
Solar Flares ◽  
Solar Irradiance ◽  
Large Scale ◽  
Total Solar Irradiance ◽  
Climate Forcing ◽  
Solar Cycles ◽  
Climate Stability ◽  
Measurement Results ◽  
Measuring Space

AbstractVariations of the total solar irradiance (TSI) over long periods of time provide natural Earth-climate forcing and are thus important to monitor. Variations over a solar cycle are at the 0.1 % level. Variations on multi-decadal to century timescales are (fortunately for our climate stability) very small, which drives the need for highly-accurate and stable measurements over correspondingly long periods of time to discern any such irradiance changes. Advances to TSI-measuring space-borne instruments are approaching the desired climate-driven measurement accuracies and on-orbit stabilities. I present a summary of the modern-instrument improvements enabling these measurements and present some of the solar-variability measurement results from recent space-borne instruments, including TSI variations on timescales from solar flares and large-scale convection to solar cycles.

scholarly journals Analysis of 24 years of mesopause region OH rotational temperature observations at Davis, Antarctica – Part 1: long-term trends

2020 ◽  
Vol 20 (11) ◽  
pp. 6379-6394 ◽  
Author(s):  
W. John R. French ◽  
Frank J. Mulligan ◽  
Andrew R. Klekociuk
Keyword(s):  
Solar Cycle ◽  
Rotational Temperature ◽  
Winter Season ◽  
Pressure Level ◽  
Recent Analysis ◽  
Research Station ◽  
Mesopause Region ◽  
Term Trend ◽  
Long Term Trend

Abstract. The long-term trend, solar cycle response, and residual variability in 24 years of hydroxyl nightglow rotational temperatures above Davis research station, Antarctica (68∘ S, 78∘ E) are reported. Hydroxyl rotational temperatures are a layer-weighted proxy for kinetic temperatures near 87 km altitude and have been used for many decades to monitor trends in the mesopause region in response to increasing greenhouse gas emissions. Routine observations of the OH(6-2) band P-branch emission lines using a scanning spectrometer at Davis station have been made continuously over each winter season since 1995. Significant outcomes of this most recent analysis update are the following: (a) a record-low winter-average temperature of 198.3 K is obtained for 2018 (1.7 K below previous low in 2009); (b) a long-term cooling trend of -1.2±0.51 K per decade persists, coupled with a solar cycle response of 4.3±1.02 K per 100 solar flux units; and (c) we find evidence in the residual winter mean temperatures of an oscillation on a quasi-quadrennial (QQO) timescale which is investigated in detail in Part 2 of this work. Our observations and trend analyses are compared with satellite measurements from Aura/MLS version v4.2 level-2 data over the last 14 years, and we find close agreement (a best fit to temperature anomalies) with the 0.00464 hPa pressure level values. The solar cycle response (3.4±2.3 K per 100 sfu), long-term trend (-1.3±1.2 K per decade), and underlying QQO residuals in Aura/MLS are consistent with the Davis observations. Consequently, we extend the Aura/MLS trend analysis to provide a global view of solar response and long-term trend for Southern and Northern Hemisphere winter seasons at the 0.00464 hPa pressure level to compare with other observers and models.

scholarly journals Solar Monitoring has a Past and Present: Does it have a Future?

1994 ◽  
Vol 143 ◽  
pp. 4-10 ◽  
Author(s):  
Richard C. Willson
Keyword(s):  
United States ◽  
Solar Irradiance ◽  
The United States ◽  
Total Solar Irradiance ◽  
Collaborative Effort ◽  
Solar Cycles ◽  
Earth Observing System ◽  
Total Irradiance ◽  
Sustained Effort

Intrinsic variations of total solar irradiance have, after nearly a century of sustained effort, been demonstrated by flight experiments during solar cycles 21 and 22. This accomplishment has been the result of a collaborative effort on behalf of several groups of researchers in both the United States and Europe. The overriding concern at this point of time is whether the integrity of the precision long-term solar total irradiance database, which began at the maximum of solar cycle 21 and continues in the present, will be lost in the late 1990’s, prior to the inception of experiments planned for the NASA Earth Observing System beginning in 2002. Experiments are not currently in place to prevent an unbridgeable discontinuity in the precision total solar irradiance database.

scholarly journals Latitudinal variation of <I>fo</I>F2 hysteresis of solar cycles 20, 21 and 22 and its application to the analysis of long-term trends

2008 ◽  
Vol 26 (5) ◽  
pp. 1269-1273 ◽  
Author(s):  
N. Ortiz de Adler ◽  
A. G. Elias
Keyword(s):  
Time Series ◽  
Solar Cycle ◽  
Geomagnetic Latitude ◽  
Activity Levels ◽  
Solar Cycles ◽  
Long Term Trends ◽  
The Difference ◽  
Long Term Trend ◽  
Term Data

Abstract. Noon foF2 monthly median values for equinoctial months of solar cycles 20, 21 and 22, were analyzed for 37 worldwide stations. For each solar cycle and for a given Rz, the difference between foF2 in the falling branch of the cycle and the corresponding value of the rising branch is evaluated. The maximum difference, considered as the hysteresis magnitude, varies systematically with geomagnetic latitude. The pattern is similar for every cycle, with greater hysteresis magnitudes for stronger solar cycles. It is positive between 45° S and 45° N, with minimum values at equatorial latitudes and maximum at around 25°–30° on either side of the equator. For latitudes greater than 50° negative values are observed. At around 25°–30° and at high latitudes the hysteresis magnitude reaches 2 MHz for solar cycle with high activity levels, which represents around 20% of foF2. The effects of foF2 hysteresis on the analysis of long-term data sequences is analyzed. In the case of long-term trend analysis, the hysteresis behavior may induce spurious trends as a consequence of the filtering processes applied to foF2 time series previous to trend values estimation. This problem may be solved by considering time series covering several solar cycles.

scholarly journals Revisiting the Question: The Cause of the Solar Cycle Variation of Total Solar Irradiance

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
N. B. Xiang
Keyword(s):  
Time Series ◽  
Solar Cycle ◽  
Solar Irradiance ◽  
Total Solar Irradiance ◽  
Sunspot Area ◽  
Wavelet Coherence ◽  
Solar Cycle Variation ◽  
Cycle Variation ◽  
Magnetic Features

The Mg II index and sunspot area are usually used to represent the intensification contribution by solar bright structures to total solar irradiance (TSI) and sunspot darkening, respectively. In order to understand the cause of the solar cycle variation of TSI, we use extension of wavelet transform, wavelet coherence (WTC), and partial wavelet coherence (PWC), to revisit this issue. The WTC of TSI with sunspot area shows that the two time series are very coherent on timescales of one solar cycle, but the PWC of TSI with sunspot area, which can find the results of WTC after eliminating the effect of the Mg II index, indicates that the solar cycle variation of TSI is not related to sunspots on the solar surface. The coherence of two time series at these timescales should be due to a particular phase relation between sunspots and TSI. The WTC and PWC of TSI with Mg II index show that the solar cycle variation of TSI is highly related to Mg II index, which reflects the relation of TSI with the long-term part of Mg II index that shows the intensification contribution by the small magnetic features to TSI. Consequently, the solar cycle variation of TSI is dominated by the small magnetic features on the solar full disk. Additionally, we also show the combined effects of the sunspot darkening and the intensification contribution represented by Mg II index to TSI on timescales of a few days to several months and indicate that the faculae increase TSI and contribute to its variation at these timescales.

scholarly journals Analysis of 24 years of mesopause region OH rotational temperature observations at Davis, Antarctica – Part 1: Long-term trends

2020 ◽  
Author(s):  
W. John R. French ◽  
Frank J. Mulligan ◽  
Andrew R. Klekociuk
Keyword(s):  
Solar Cycle ◽  
Rotational Temperature ◽  
Winter Season ◽  
Recent Analysis ◽  
Research Station ◽  
Mesopause Region ◽  
Term Trend ◽  
Hemisphere Winter ◽  
Long Term Trend

Abstract. The long term trend, solar cycle response and residual variability in 24 years of hydroxyl nightglow rotational temperatures above Davis Research Station, Antarctica (68° S, 78° E) is reported. Hydroxyl rotational temperatures are a layer-weighted proxy for kinetic temperatures near 87 km altitude and have been used for many decades to monitor trends in the mesopause region in response to increasing greenhouse gas emissions. Routine observations of the OH(6–2) band P-branch emission lines using a scanning spectrometer at Davis station have been made continuously over each winter season since 1995. Significant outcomes of this most recent analysis update are (a) a record low winter-average temperature of 198.3 K is obtained for 2018 (1.7 K below previous low in 2009) (b) a long term cooling trend of 1.2 K/decade persists, coupled with a solar cycle response of 4.3 K/100 solar flux units and (c) we find evidence in the residual winter mean temperatures of an oscillation on a quasi-quadrennial (QQO) timescale which is investigated in detail in part 2 of this work. Our observations and trend analyses are compared with satellite measurements from Aura/MLS version v4.2 level 2 data over the last 14 years and we find close agreement (a best fit) with the 0.00464 hPa pressure level values. The solar cycle response, long-term trend and underlying QQO residuals are consistent with the Davis observations. Consequently, we extend the Aura/MLS trend analysis to provide a global view of solar response and long term trend for southern and northern hemisphere winter season to compare with other observers and models.

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