LASP: Laboratory for Atmospheric and Space Physics

Over the last three decades the LASP Solar Influence Group has established an extremely strong program devoted to measuring the Sun's irradiance over an ever-widening wavelength range, from soft X-rays through the near infrared. The scientific objectives for the Solar Influence Group are to measure irradiance with state-of-the-art accuracy and precision and to understand solar variability and its influence on the terrestrial environment (with emphasis on atmospheric processes and climate). (Read more...)

The Science

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Solar radiation is the dominant energy source for our solar system: the Earth, planets, and minor bodies such as planetary moons, comets, and asteroids. In the case of the Earth and planets, this radiation fuels the chemical and dynamical processes of the atmospheres, and any variations in solar radiation will change the atmosphere's structure, temperature, and composition. It is little wonder that studies of the planets and of the Earth require precise and accurate knowledge of both the intensity of solar radiation and the amount by which it varies. The Sun's radiation spans the color spectrum from very energetic x-rays, through the visible, and out to the infrared.

Fraction of solar radiation that is transmitted to the Earth’s surface over a spectral region accounting for approximately 95% of the total energy from the Sun. The spectrum of total atmospheric column transmittance is shown in black, while the colored curves show the contribution from individual species in Earth’s atmosphere.

The careful measurement of the Sun is indeed challenging because our atmosphere absorbs and scatters the light. For this reason precise measurements were not made until special instruments could be sent above the atmosphere in order to make the observations from space.

The solar UV radiation is a primary energy input to Earth’s atmosphere. This radiation includes the middle UV (MUV: 200-300 nm), the far UV (FUV: 120-200 nm), the extreme UV (EUV: 30-120 nm), and the x-ray UV (XUV: 1-30 nm). The photochemistry and heating of the atmosphere vary with altitude and are strongly dependent on the wavelength of the solar radiation and the absorption cross sections of the atmospheric species.

Solar terrestrial physics in general deals with data from the Earth's upper atmosphere (the stratosphere (where the ozone layer resides), the mesosphere, the ionosphere (part of the thermosphere), and the thermosphere) and the space environment from the Earth to the surface of the Sun. Most observations are taken from satellites in space with an emphasis on determining the chemical and physical impact of the Sun's emissions on the Earth system.

The Sun’s energy sustains and nurtures all life including plant, animal, and human. There are also many indirect effects that are at least as important. Other factors entering the climate puzzle, including greenhouse gases, aerosols, and atmospheric circulation, are driven by solar radiation, and they influence each other by complex feedbacks. To establish the impact humans have on climate, we must have solid knowledge of any natural factors impacting climate, the most important being the Sun. LASP researchers strive to better understand the Sun’s influence on Earth by monitoring total solar irradiance (TSI) and spectral solar irradiance (SSI) variations daily.

The University of Colorado at Boulder's Upper Air Laboratory (the predecessor of LASP) made some of the very first observations of the Sun from space in the 1950s. In 1972 a LASP rocket instrument was launched to provide a solar measurement to accompany lunar observations being made by Apollo 17. The data obtained on this first rocket achieved a new level of accuracy, and they were soon widely used by scientists trying to understand the chemistry of our stratosphere the atmospheric layer where the ozone lies.

Interest in these solar measurements was intensified when concern for ozone in the stratosphere was first postulated in 1974. NASA encouraged LASP to expand the solar program and the frequency of rocket observations increased. LASP was awarded a contract to develop its own small satellite, the Solar Mesosphere Explorer (SME), specifically designed to study atmospheric ozone and changes it was undergoing. One of the SME instruments was a small spectrometer to study and record solar radiation. SME was extremely successful, providing both atmospheric and solar observations for almost eight and a half years, and has led to a legacy of solar terrestrial physics observations at LASP.

The LASP Solar Influences Group would like to continue this legacy by making the data from these solar terrestrial physics observations available to everyone. In this effort, LASP has begun development of the LASP Interactive Solar Irradiance Datacenter or LISIRD. LASP plans to have LISIRD provide convenient interactive access to a comprehensive set of solar irradiance measurements, models, and composite solar irradiance spectra and time series.

Below is a graphic of available solar irradiance measurements from missions that LASP has taken part (by clicking on different areas of the image, you will be taken to that mission's website).