Martin Snow

The South African National Space Agency | SANSA · Space Science -- Hermanus

Space weather refers to conditions around a star, like our Sun, and its interplanetary space that may affect space- and ground-based assets as well as human life. Space weather can manifest as many different phenomena, often simultaneously, and can create complex and sometimes dangerous conditions. The study of space weather is inherently trans-dis...

The SOLar-STellar Irradiance Comparison Experiment (SOLSTICE: McClintock, Rottman, and Woods, Solar Phys. 230 , 225, 2005) onboard the SOlar Radiation and Climate Experiment (SORCE: Rottman, Solar Phys. 230 , 7, 2005) observed ultraviolet solar spectral irradiance (SSI) from 2003 – 2020. This article gives an overview of the end-of-mission algorith...

The Solar Radiation and Climate Experiment (SORCE) was a NASA mission that operated from 2003 to 2020 to provide key climate-monitoring measurements of total solar irradiance (TSI) and solar spectral irradiance (SSI). This 17-year mission made TSI and SSI observations during the declining phase of Solar Cycle 23, during all of Solar Cycle 24, and a...

An accurate solar-irradiance spectrum is needed as an input to any planetary atmosphere or climate model. Depending on the spectral characteristics of the chosen model, uncertainties in the irradiance may introduce significant differences in atmospheric and climate predictions. This is why several solar spectral-irradiance data sets have been publi...

The Solar Radiation and Climate Experiment (SORCE) was a NASA mission that operated from 2003 to 2020 to provide key climate-monitoring measurements of total solar irradiance (TSI) and solar spectral irradiance (SSI). Three important accomplishments of the SORCE mission are i) the continuation of the 42-year-long TSI climate data record, ii) the co...

Context. Solar spectral irradiance (SSI) is the wavelength-dependent energy input to the top of the Earth’s atmosphere. Solar ultraviolet (UV) irradiance represents the primary forcing mechanism for the photochemistry, heating, and dynamics of the Earth’s atmosphere. Hence, both temporal and spectral variations in solar UV irradiance represent cruc...

The Flare Irradiance Spectral Model (FISM) is an important tool for estimating solar variability for a myriad of space weather research studies and applications, and FISM Version 2 (FISM2) recently was released. FISM2 is an empirical model of the solar ultraviolet irradiance created to fill spectral and temporal gaps in the satellite observations....

The accurate measurement of the solar spectrum at the top of the atmosphere and its variability are fundamental inputs for solar physics (Sun modeling), terrestrial atmospheric photochemistry, and Earth’s climate (climate’s modeling). These inputs were the prime objective set in 1996 for the SOLAR International Space Station (ISS). The SOLAR packag...

Abstract The Earth system responds to solar variability on a wide range of timescales. Knowledge of total solar irradiance (TSI) and solar spectral irradiance (SSI) spanning minutes to centuries is needed by scientists studying a broad array of research applications. For these purposes, the NOAA National Centers for Environmental Information (NCEI)...

Plain Language Summary When ultraviolet light from the Sun is absorbed in the Earth's upper atmosphere above 70 km, it can impact radio communications and satellite orbits. The brightest solar wavelength in the ultraviolet is called the Lyman‐alpha line and is emitted by hydrogen in the Sun's atmosphere. Because ultraviolet light is absorbed by the...

Abstract Whole atmosphere chemistry‐climate model (CCM) transient studies require a solar spectral irradiance (SSI) time series with very broad wavelength coverage with an uninterrupted daily cadence over a full solar cycle time period. Herein is described the construction of a SSI record valid over Solar Cycles 23 and 24 (SC23 and SC24) specifical...

The Geostationary Operational Environmental Satellite R (GOES-R) series of four satellites are the next generation NOAA GOES satellites. Once on orbit and commissioned, they are renamed GOES 16-19, making critical terrestrial and space weather measurements through 2035. GOES 16 and 17 are currently on orbit, having been launched in 2016 and 2018, r...

The Magnesium II core‐to‐wing ratio (also known as the Mg II index) is a widely used proxy for ultraviolet solar spectral irradiance variability. We have developed a new algorithm for calculating this index from the SOLar‐STellar Irradiance Comparison Experiment (SOLSTICE) on the SOlar Radiation and Climate Experiment (SORCE). The new method uses w...

Interplanetary background measurements can be used to derive the solar flux that is illuminating the atoms in the interplanetary medium. We present a new algorithm combining measurements from the Solar Wind ANisotropies (SWAN)‐Solar Heliospheric Observatory (SOHO) Lyman α photometer with Earth‐based solar flux measurements to derive the solar illum...

The Geostationary Operational Environmental Satellite R (GOES-R) series of four satellites are the next generation NOAA GOES satellites. Once on orbit and commissioned, they are renamed GOES 16–19, making critical terrestrial and space weather measurements through 2035. GOES 16 and 17 are currently on orbit, having been launched in 2016 and 2018, r...

A large outburst of flares occurred between 4–10 September 2017 when new magnetic flux emerged into and strengthened an existing active region, National Oceanic and Atmospheric Administration Region 12673. This intense solar storm period included X9.3 (6 September) and X8.2 (10 September) flares, the largest flares that have occurred during Solar C...

The solar spectral irradiance (SSI) dataset is a key record for studying and understanding the energetics and radiation balance in Earth’s environment. Understanding the long-term variations of the SSI over timescales of the 11-year solar activity cycle and longer is critical for many Sun–Earth research topics. Satellite measurements of the SSI hav...

We propose a simple model that computes the spectral profile of the solar irradiance in the hydrogen Lyman alpha line, H Ly-α (121.567 nm), from 1947 to present. Such a model is relevant for the study of many astronomical environments, from planetary atmospheres to interplanetary medium. This empirical model is based on the SOlar Heliospheric Obser...

Ultraviolet (UV) Solar spectral Irradiance (SSI) has been measured from orbit on a regular basis since the beginning of the space age. These observations span four Solar Cycles, and they are crucial for our understanding of the Sun-Earth connection and space weather. SSI at these wavelengths are the main drivers for the upper atmosphere including t...

The solar magnesium II core-to-wing ratio has been a well-studied proxy for chromospheric activity since 1978. Daily measurements at high spectral (0.1 nm) resolution began with the launch of the Solar Radiation and Climate Experiment (SORCE) in 2003. The next generation of measurements from the Extreme Ultraviolet Sensor (EUVS) on the Geostationar...

We describe spectral and time-dependent variations in solar irradiance, discuss their implications for Earth science, and summarize ongoing work in developing the next generation of observationally-consistent models of solar irradiance variability.

Polar Mesospheric Cloud (PMC) observations from the Solar Occultation for Ice Experiment (SOFIE) and the Cloud Imaging and Particle Size (CIPS) experiment are used to investigate the response of PMCs to forcing associated with the 27-day solar rotation. We quantify the PMC response in terms of sensitivity values. Analysis of PMC data from 14 season...

Several currently operating instruments are able to measure the full EUV spectrum at sufficient wavelength resolution for use in upper-atmosphere modeling, the effects of space weather, and modeling satellite drag. However, no missions are planned at present to succeed the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) and Solar...

We present a new climate data record for total solar irradiance and solar spectral irradiance between 1610 and the present day with associated wavelength and timedependent uncertainties and quarterly updates. The data record, which is part of the National Oceanic and Atmospheric Administration's (NOAA) Climate Data Record (CDR) program, provides a...

A different approach to studying solar spectral irradiance (SSI) variations, without the need for long-term (multi-year) instrument degradation corrections, is examining the total energy of the irradiance variation during 6-month periods. This duration is selected because a solar active region typically appears suddenly and then takes 5 to 7 months...

This Climate Data Record (CDR) contains solar spectral irradiance (SSI) as a function of time and wavelength created with the Naval Research Laboratory model for spectral and total irradiance (version 2). Solar spectral irradiance is the wavelength-dependent energy input to the top of the Earth's atmosphere, at a standard distance of one Astronomic...

This Climate Data Record (CDR) contains total solar irradiance (TSI) as a function of time created with the Naval Research Laboratory model for spectral and total irradiance (version 2). Total solar irradiance is the total, spectrally integrated energy input to the top of the Earth's atmosphere, at a standard distance of one Astronomical Unit from...

A solar spectrum extending from the extreme ultraviolet to the near-infrared is an important input for solar physics, climate research, and atmospheric physics. Ultraviolet measurements have been conducted since the beginning of the space age, but measurements throughout the contiguous visible and infrared (IR) regions are much more sparse. Ageing...

Solar magnetism displays a host of variational timescales of which the enigmatic 11-year sunspot cycle is most prominent. Recent work has demonstrated that the sunspot cycle can be explained in terms of the intra-and extra-hemispheric interaction between the overlapping activity bands of the 22-year magnetic polarity cycle. Those activity bands app...

We present the results of Hapke photometric modeling of the lunar surface in the ultraviolet using SOLSTICE data.

This article describes an update of the physical models that we use to reconstruct the FUV and EUV irradiance spectra and the radiance spectra of the features that at any given point in time may cover the solar disk depending on the state of solar activity. The present update introduces important modifications to the chromosphere–corona transition...

The MgII index is an important proxy for solar activity; in particular it correlates well with the EUV which is important for understanding the upper atmosphere. We compare the measurements from all of the instruments making daily measurements during the most recent solar minimum. After adjustments to the data to account for instrumental effects, w...

The SOLar-STellar Irradiance Comparison Experiment (SOLSTICE) on the SOlar Radiation and Climate Experiment (SORCE) observes both the Sun and stars in the ultraviolet (115–300 nm). Prior to launch, it was calibrated at the SURF-III synchrotron. Spectra from the International Ultraviolet Explorer (IUE) corrected to the white dwarf flux scale are in...

The Moon has been shown to be an extremely stable radiometric reference for calibration and long-term stability measurements of on-orbit sensors. The majority of the previous work on characterizing the lunar reflectance has been in the visible part of the spectrum using ground-based lunar images. The SOLar-STellar Irradi-ance Comparison Experiment...

The Magnesium II index has been continuously measured by a variety of instruments since 1978. It is a widely used proxy for solar activity, particularly for ultraviolet variability which is critical for the chemistry and dynamics of the upper atmosphere. Combining the measurements from instruments with different spectral resolution, observing caden...

From models of the interplanetary Lyman-α glow derived from observations by the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) interplanetary Lyman-α data obtained in 2009-2011 on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft mission, daily all-sky Lyman-α maps were generated for use by t...

In November 2007, the Solar Wind Anisotropy (SWAN) instrument on the Solar and Heliospheric Observatory (SOHO) and the SOLar-STellar Irradiance Comparison Experiment (SOLSTICE) on the SOlar Radiation and Climate Experiment (SORCE) both made observations of comet 17P/Holmes at Lyman-α wavelengths. The intent of these observations was to compare the...

The hydroxyl radical (OH) plays an important role in middle atmospheric photochemistry, particularly in ozone (O(3)) chemistry. Because it is mainly produced through photolysis and has a short chemical lifetime, OH is expected to show rapid responses to solar forcing [e.g., the 11-y solar cycle (SC)], resulting in variabilities in related middle at...

In this book we discuss the problems encountered for calibrating space-borne instruments in the spectral range 50-300 nm. We also discuss the level of accuracy that can be achieved, and review the different sources of emissions that can be used in that range, i.e. the interplanetary background, stars, and solar system bodies such as planets, moons,...

This book is the result of a working group sponsored by ISSI in Bern, which was initially created to study possible ways to calibrate a Far Ultraviolet (FUV) instrument after launch. In most cases, ultraviolet instruments are well calibrated on the ground, but unfortunately, optics and detectors in the FUV are very sensitive to contaminants and it...

This book is the result of a working group sponsored by ISSI in Bern, which was initially created to study possible ways to calibrate a Far Ultraviolet (FUV) instrument after launch. In most cases, ultraviolet instruments are well calibrated on the ground, but unfortunately, optics and detectors in the FUV are very sensitive to contaminants and it...

Comet Lovejoy (C/2011 W3) was the first sungrazing comet, observed by space-based instruments, to survive perihelion passage. First observed by ground-based telescopes several weeks prior to perihelion, its journey towards the Sun was subsequently recorded by several solar observatories, before being observed in the weeks after perihelion by a furt...

We have obtained the first disk-integrated measurement of the lunar polarization in at ultraviolet wavelengths using the SOLar-STellar Irradiance Comparison Experiment (SOLSTICE). SOLSTICE is an instrument onboard the Solar Radiation and Climate Experiment (SORCE) and made measurements of the lunar irradiance from 2006 through 2010. In "lunar" mode...

As we become more and more dependent on our satellite-based technology, accurate and reliable space weather prediction becomes increasingly more critical. Flares and Coronal Mass Ejections (CMEs) from solar activity are of primary interest for affecting Earth's environment. Because flare X-ray and extreme ultraviolet (EUV) radiation is first observ...

Given the numerous ground-based and space-based experiments producing the database for the Cycle 23 – 24 Minimum epoch from September 2008 to May 2009, we have an extraordinary opportunity to understand its effects throughout the heliosphere. We use solar radiative output in this period to obtain minimum values for three measures of the Sun’s radia...

The Research Experience for Undergrads (REU) program in Solar and Space Physics at the University of Colorado begins with a week of lectures and labs on Solar and Space Physics. The students in our program come from a variety of majors (physics, engineering, meteorology, etc.) and from a wide range of schools (small liberal arts colleges up through...

The Solar Radiation and Climate Experiment (SORCE) Spectral Irradiance Monitor (SIM) measures solar spectral variability in the 200-2400 nm range accounting for about 97% of the total solar irradiance (TSI). SIM concurrently measures ultraviolet variability from 200-310 nm with the higher spectral resolution Solar-Stellar Irradiance Comparison Expe...

There are currently many observations and models of the Solar Spectral Irradiance (SSI) in the ultraviolet (UV). The models and the observations are often in agreement, but sometimes have significant differences. Using the decline of solar cycle 23 and the rise of solar cycle 24 as a test case, we will investigate the systematic differences between...

Since the Extreme ultraviolet (EUV) Variability Experiment (EVE) instrument on NASA's Solar Dynamic Observatory (SDO) went operational on 1 May 2010, solar spectral irradiance data in the EUV are now available within minutes. EVE data are potentially important for forecasting coronal mass ejections (CMEs) using associated coronal dimmings. Some fla...

Variations in the Earth's magnetic field affect the location and strength of the South Atlantic Anomaly (SAA), a region above the Earth's surface with high levels of radiation due to the offset of the magnetic field and subsequent magnetic field minimum. Several studies have reported a westward drift rate (0.05-1.0 deg/year) and a northward drift r...

This paper presents new extremely high-resolution solar spectral irradiance (SSI) calculations covering wavelengths from 0.12 nm to 100 micron obtained by the Solar Irradiance Physical Modeling (SRPM) system. Daily solar irradiance spectra were constructed for most of Solar Cycle 23 based on a set of physical models of the solar features and non-LT...

Context. The solar irradiance in the UV is a key ingredient in space weather applications; however, because of the lack of continuous and long-term observations, various indices are still used today as surrogates for the solar spectral irradiance. Aims: As an alternative to current spectrometers we use a few radiometers with properly chosen passban...

The Research Experience for Undergraduates (REU) program in Solar and Space Physics is a collaboration between the University of Colorado's Laboratory for Atmospheric and Space Physics (LASP), the National Center for Atmospheric Research's High Altitude Observatory (HAO), the National Oceanic and Atmospheric Administration's Space Weather Predictio...

Last year the Laboratory for Atmospheric and Space Physics at the University of Colorado launched a new version of a web application called LISIRD to serve solar irradiance and other related scientific data products. LISIRD's interactive plotting and download capabilities have been well received. LISIRD has been successful in large part to its reli...

Sunlight reflected from the lunar surface is known to be partially polarized. The degree of polarization is strongly dependent on phase angle and inversely proportional to albedo. Measurements in the visible and near-infrared have been accomplished from ground-based observatories, but ultraviolet wavelengths cannot be observed from the ground due t...

Interplanetary hydrogen resonantly scatters solar Lyman-alpha radiation, producing an intense ultraviolet (UV) emission. This hydrogen comes from interstellar space from the "upwind" direction and forms a cavity depleted in slow neutral hydrogen near the Sun due to charge-exchange with solar wind protons and solar extreme ultraviolet photoionizatio...

Observations from the SOLar-STellar Irradiance Comparision Experiment (SOLSTICE) on the SOlar Radiation and Climate Experiment (SORCE) began in 2003 and continue through the present. This time period includes the decline of solar cycle 23 through solar minimum. SOLSTICE measures solar irradiance from 115 nm to 300 nm with a spectral resolution of 0...

The Solar Stellar Irradiance Comparison Experiment (SOLSTICE) instrument on board the Solar Radiation Climate Experiment (SORCE) spacecraft in low Earth orbit observes stars every orbit for in-flight calibration. It also observes several star-free regions of the sky near the wavelength of Lyman alpha to correct for airglow emission in the stellar m...

Long records of solar spectral irradiance are quite rare and differentiating between solar variability and instrumental changes can be a challenge. Proxies for solar irradiance have provided independent measures of solar variability and can be used to extend the data record beyond the observation period and to help differentiate solar variability f...

The SOLar-STellar Irradiance Comparison Experiment (SOLSTICE) on the SOlar Radiation and Climate Experiment (SORCE) has been measuring the solar spectral irradiance on a daily basis since early 2003. This time period includes near-solar maximum conditions, the Halloween storms of 2003, and solar minimum conditions. These results can be compared to...

The Spectral Irradiance Monitor (SIM) on board the NASA SORCE satellite (Solar Radiation and Climate Experiment) was launched on 25 January 2003 and has been making twice-daily measurements of solar variability in the 220 to 1630nm range and daily measurements in the 1600 to 2400 nm range. This study presents preflight and postlaunch calibration ac...

Description of ultraviolet lunar irradiance dataset from SOLSTICE.