The Earth Radiation Budget at the Top of the Atmosphere (ToA) governs the status of climate change on our planet. The ERB is the balance between the incoming Total Solar Irradiance (TSI) and total outgoing radiation at the ToA. If more energy is stored in the system the Earth Energy Imbalance is positive and the temperature in the system rises. The Compact Lightweight Absolute RAdiometer (CLARA) experiment onboard the Norwegian micro satellite NorSat-1 is an SI traceable radiometer with the primary science goal to measure TSI from space. Besides TSI, CLARA also measures the terrestrial Outgoing Longwave Radiation (OLR) at the ToA on the night side of Earth. We present the latest status of the data and degradation correction obtained with this SI-traceable radiometer and compare the CLARA TSI and OLR time series with other available observations and reanalysis data. The validation of these measurements is key to advance our capability to determine the Earth Energy Imbalance from space.

Total Solar Irradiance (TSI) is one of the Essential Climate Variables (ECV) identified by the World Meteorological Organization's Global Climate System (GCOS). The Compact Lightweight Absolute RAdiometer (CLARA) experiment onboard the Norwegian micro satellite NorSat-1 is a SI traceable radiometer and was launched July 14, 2017 with the primary science goal to measure TSI from space. We present the latest status of the data and degradation correction obtained with this SI-traceable radiometer. Besides TSI, CLARA also measures the total outgoing radiation (TOR) at the top of the Earth atmosphere on the night side of Earth, which is extremely important to understand the Earth Radiation Budget. It is to our knowledge the first time that TSI and the emitted radiation from Earth are measured simultaneously with one SI-traceable absolute radiometer. We will compare the CLARA TSI and TOR time series with other available datasets. Ultimately, we aim towards determining the Earth Energy Imbalance from space. We will discuss the achievements and limitations in direction of this goal.

AbstractThe Compact Lightweight Absolute Radiometer (CLARA) is orbiting Earth on-board the Norwegian NorSat-1 micro-satellite since 14th of July 2017. The first light total solar irradiance (TSI) measurement result of CLARA is 1360.18 W m−2 for the so far single reliable Channel B. Channel A and C measured significantly lower (higher) TSI values and were found being sensitive to satellite pointing instabilities. These channels most likely suffer from electrical interference between satellite components and CLARA, an effect that is currently under investigation. Problems with the satellite attitude control currently inhibit stable pointing of CLARA to the Sun.

The compact lightweight absolute radiometer (CLARA) experiment aims at measuring the total solar irradiance (TSI) in space and is scheduled to fly on the Norwegian NORSAT-1 micro satellite. The CLARA experiment will contribute to the long term monitoring of the TSI variability to support the analysis of potential long term trends in the Sun's variability. CLARA is traceable to the National Institute of Standards and Technology radiometric scale and will provide further evidence for the TSI value on an absolute scale. In this paper we present the design, characterization, and calibration details of the CLARA instrument. The combined measurement uncertainty for the calibrated SI-traceable CLARA flight instrument is 567-912 ppm (k = 1) depending on the measuring channel.

Solar gravity modes (or g modes)—oscillations of the solar interior on which buoyancy acts as the restoring force—have the potential to provide unprecedented inference on the structure and dynamics of the solar core, inference that is not possible with the well-observed acoustic modes (or p modes). The relative high amplitude of the g-mode eigenfunctions in the core and the evanesence of the modes in the convection zone make the modes particularly sensitive to the physical and dynamical conditions in the core. Owing to the existence of the convection zone, the g modes have very low amplitudes at photospheric levels, which makes the modes extremely hard to detect. In this article, we review the current state of play regarding attempts to detect g modes. We review the theory of g modes, including theoretical estimation of the g-mode frequencies, amplitudes and damping rates. Then we go on to discuss the techniques that have been used to try to detect g modes. We review results in the literature, and finish by looking to the future, and the potential advances that can be made—from both data and data-analysis perspectives—to give unambiguous detections of individual g modes. The review ends by concluding that, at the time of writing, there is indeed a consensus amongst the authors that there is currently no undisputed detection of solar g modes.

The Phoebus group is an international collaboration of helioseismologists, its aim being to detect low-frequency solar g modes. Here, we report on recent work, including the development and application of new techniques based on the detection of coincidences in contemporaneous datasets and the asymptotic properties of the g-mode frequencies. The length of the time series available to the community is now more than ten years, and this has reduced significantly the upper detection limits on the gmode amplitudes. Furthermore, low-degree p modes can now be detected clearly at frequencies below 1000 μHz.

Europe invests only about one-sixth of the United States' spending in various space activities. Given the complicated organizational structure of government space spending in Europe and the lack of will or ability to increase the overall budgets, it will be difficult for Europe to maintain its place as a major player in the world's space activity. The author of this [Policy Forum][1] thinks that either the ambitions of Europe should be lowered in accordance with the available budgets, or the budgets should be adjusted upward. Without substantial increases in the budgets, Europe should not enter into new fields of space activity. [1]: http://www.sciencemag.org/cgi/content/full/307/5713/1206

Using both VIRGO and MDI data we have previously studied the amplitude variation of the l=0 p-modes for radial orders 12 to 32. In this study we extend the investigation backward in time to 1992 by including data from the BISON network. For the large amplitude modes there is a strong correlation between the space based radiance measurements from VIRGO and the ground based Doppler shift measurements from BISON. The extreme rotational modulation of l=0, n=22 is confirmed to be a phenomenon confined to the period of minimum solar activity. Also with neighbouring l=1, n=21 a clear modulation is seen at slightly lower frequency. Some persistent frequencies occur in other l=0, 1 modes, but not to the same level in time and amplitude.

The amplitude modulation of solar radial p-modes has been studied in irradiance and radiance data from VIRGO and velocity data from MDI onboard SOHO. The amplitudes vary substantially with time. For two modes, l=0, n=21 and 22 we find a strong rotational modulation at the end of the old solar cycle (number 22). The modulation vanishes during solar minimum and only weakly reappears during the rise of the new cycle. There is a decrease in the integrated mode amplitudes with increased activity for the modes that show rotational modulation. At low solar activity there is little correlation between modes of varying order, but the correlation seems to increase with increasing solar activity.

We review the recent developments in determining the upper limits to g-mode amplitudes obtained by SOHO instruments, GONG and BiSON. We address how this limit can be improved by way: of new helioseismic instruments and/or new collaborations, hopefully providing in the not too distant future unambiguous g-mode detection.

A concerted effort to detect global solar g modes using observational data from SOHO and groundbased networks has been carried out. The data from the SOHO SOI/MDI and VIRGO investigations as well as data from the BiSON network have been used. The emphasis has been to look for the dipole modes of low order. Several different approaches have been attempted to enhance the possible g-mode signatures. These methods include: correlation with different time intervals with the same instruments to look for coherent structures; correlation of signals between different instruments to reduce non-coherent solar signals; linear filtering of data from different colours to enhance differences. The detection limit is set by the presence of semi-coherent signal caused by the time development and rotation of solar surface structures. Several peaks have been identified as possible g modes, but unfortunately these results are not consistent either in time or between different reduction methods. We estimate the upper limit of the g-mode amplitudes as 1 mms(-1) and 0.1 ppm.

The time variation of the solar irradiance signal has been investigated for frequencies above about 15 mu Hz. The data used are from the VIRGO spectral irradiance measurements covering a period of slightly more than two years. The onset of activity is clearly seen in the low frequency below 25 mu Hz. For higher frequencies very little temporal variation is seen, this applies both to possible rotational modulation and the effects of the onset of the activity cycle. There are some marginal indications that the increase of activity at the end of 1997 increases the power around 1.2 mHz. No general correlation is seen between different frequency bands of the noise spectrum or with the rotation of active regions. Some rotational modulation may be present in the range 20-200 mu Hz.

We have studied the amplitude variation of the l = 0 p-modes for radial orders 12 to 32 assuming that they are stochastic processes. The results indicate that the time series can be described as similar ARIMA processes with a significant variation in the dominant parameter describing the <> of the process. The highest radial order modes show the same characteristics as the solar granulation signal. There is a significant change in the dominant parameter between radial orders 22 and 23. This change indicates that there may be a change in the way the modes interact with the solar atmosphere.

The amplitude modulation of the low degree solar p-modes is assumed to be connected to the line profile structure of the individual modes. Using this assumption we have attempted to deconvolve the effects of the amplitude modulation on the mode profiles for the radial modes of order 15-25. Here we present results of the effect on the mode asymmetry of the amplitude modulation of low degree modes observed with VIRGO and SOI/MDI. The range in timescales is from a few days to a few solar rotations. The deconvolution produces slightly narrower mode profiles. The results indicate that the effects on the frequency fitting with symmetric profiles are measurable and may have to be considered. If the modes are fitted with asymmetric profiles the effect of deconvolution is smaller.

The radial order solar p-modes show an amplitude modulation at the equatorial siderial rotation frequency of the Sun. The peak is clearly separated from the peak at the synodic rotation visible in the irradiance data.

We study the amplitude modulation of low degree solar p-modes using time-frequency methods. Previous results, showing a clear rotational modulation for selected modes, are confirmed. The modulation is dearly connected to the level of solar activity and the frequency of the modulation is confirmed to be dose to the siderial rotation frequency of the latitude of the dominant activity. The dominant rotational modulation is seen in the l=0 modes with radial orders 13, 16, 21 and 22. The modulation is nearly identical for the same modes as observed in irradiance and radiance with VIRGO and observed in radial velocity with MDI. No other clear and persistent peaks of similar amplitude are seen in the l=1-2 modes.

The amplitudes of solar p modes decrease steeply with decreasing radial order below about 17. The background solar signal (solar noise) in general increases steadily with decreasing frequency. For the irradiance and radianace measurements with VIRGO or SOI/MDI on SOHO, this combination makes it difficult to detect low degree modes below about 1.8 mJz. The solar noise as oberverved in velocity with SOI/MDI or the ground based BiSON network is significantly lower in this region than in intensity measurements. This permits low-degree modes to be observed close to 1 mHz.We present results of detection and characterization of the lowest-order observable p modes both in velocity and intensity measurements. Where applicable the properties of the modes observed with the two methods are compared.

sSOHO 6/GONG 98 WorkshopStructure and Dynamicsof the Interior of the Sunand Sun-like Stars1-4 June 1998Boston Park Plaza Hotel, Boston, USAScientific Organizing CommitteeBo Andersen (NSC, Norway)Sarbani Basu (Princeton, USA)Timothy Brown (HAO/NCAR, USA)Frank Hill (GONG/NSO, USA)Sylvain Korzennik (SAO, USA; Chairman)Alexander Kosovichev (Stanford, USA)Robert Noyes (SAO, USA)Sylvaine Turck-Chieze (CEA/Saclay, France)Local Organizing CommitteeFr'ed'eric BaudinStephanie...