Welcome to the SAGE III/ISS portal for a “quick-look” at mission Level 2 solar data products. Primarily, the vertically resolved data are segregated by time progressing from the entire length of the mission to-date, to monthly zonal means, to weekly curtains and culminating in daily groupings of individual profiles. The monthly zonal means combine both sunrise and sunset events, while all other images are grouped by the rising or setting of the sun as seen from the ISS. For all but a few days a year the solar event is the same at the ground/atmosphere as it is from the ISS.
There are two streams of data to view: publicly released, which is available at the Atmospheric Sciences Data Center (ASDC), and expedited pre-release results. The main difference between the two streams is the latency, which in turn is driven by the ancillary meteorological inputs.
SAGE III takes measurements across the globe using a technique called occultation, which involves looking at the light from the Sun or Moon as it passes through Earth’s atmosphere at the edge, or limb, of the planet. The ISS provides a unique vantage point from which to take those measurements.
Every time the sun, or moon, rises and sets, SAGE uses the light that passes through the atmosphere to measure gases and particles in that region of the atmosphere.
The coverage from the ISS occurs over 30 times per day, taking about a month to cover the Southern Hemisphere, tropics, and Northern Hemisphere, as shown in this figure on the right.
Click here to view an animation of the SAGE measurement occultation technique.
All SAGE measurements for a month, then grouped by latitude and averaged.
SAGE III’s main job is to measure the good ozone in the upper atmosphere that provides the “Earth’s sun-screen.”
SAGE reports ozone concentration as number of molecules per volume. At the peak (about 25 km) there can be about 10 trillion ozone molecules in a cubic centimeter. That may sound like a lot, but relative to all the other molecules also in that cubic centimeter ozone is about 10 in-a-million!
The size of the concentration is the balance between processes that create and destroy ozone. The main creation path is sunlight splitting diatomic oxygen, the familiar O2 we breath, to make atomic oxygen, O, that can combine with O2 to make triatomic oxygen, aka ozone. Chemical reactions with natural and man-made molecules can destroy ozone. Increases in ozone destroying man-made molecules forces the balance to less ozone and was the basic cause of the ozone layer declining globally. In general, ozone is created in the tropical mid-stratosphere and moves toward the poles, both North and South by winds in the upper atmosphere.
Think of it this way: when you breathe in air, you’re actually breathing in a mixture of gases, including oxygen, nitrogen, and carbon dioxide. Water vapor is also present in the air, and it’s what makes the air feel humid or dry.
The mixing ratio is a way to express how much water vapor there is in comparison to the other gases in the air. For example, a mixing ratio of 0.01 means that for every 100 units of dry air, there is 1 unit of water vapor.
Water vapor is greenhouse gas and concentrations in the stratosphere can heat the upper troposphere. It also plays a role in many chemical reactions in the stratosphere. The main source of stratospheric water vapor (SWV) is from the relatively moist troposphere, after air has traversed the frigid temperatures of the tropopause (invisible transition zone between the troposphere below and the stratosphere above) where air becomes freeze dried. In the various types of plots notice the relatively large values of water vapor mixing ratio in the troposphere and the small values in the stratosphere.
Water vapor mixing ratio also illustrates the general movement of air in the stratosphere. Looking at the tropics lining-up SAGE measurements one after the other you can see the injection of dry air (low water vapor mixing ratio) every Jan/Feb when the tropopause (~17 km) is the coldest. This dry air rises higher and higher with time so that the following February the air has reached 25 km. Likewise, in Aug/Sep when the tropopause is the warmest, more humid air enters the stratosphere and can be seen to rise at a rate so that by same time next year the moist air has reached ~25 km. The feature of being able to trace the humidity of stratospheric air back in time to entry into the stratosphere and into the future at greater heights is commonly referred to as the “tropical tape recorder.”
Extinction coefficient is typically measured in units of inverse distance, such as 1/kilometer (km). The higher the value of the aerosol extinction coefficient, the more particles are present in the air and the more they will scatter and absorb light. This can result in hazy or smoggy conditions, especially in urban areas with high levels of pollution.
Aerosol extinction coefficient is an important factor in climate modeling because it can affect the amount of sunlight that reaches the Earth’s surface, as well as the way that light interacts with clouds and other atmospheric components. Scientists use instruments such as lidar or sun photometers to measure the aerosol extinction coefficient, which helps them better understand the impact of aerosol particles on the environment and human health.
The majority of aerosols are in the troposphere, but a thin, persistently variable layer exists in the stratosphere. This layer is predominantly sulfuric-acid droplets that reflect sunlight, ever so slightly shading the Earth’s surface.
In simpler terms, imagine looking at a clear blue sky. The molecules in the air (like nitrogen and oxygen) scatter sunlight, making the sky appear blue. However, if there are additional particles in the air (such as dust, smoke, or pollution), they can also scatter sunlight and cause the sky to appear hazy or even grayish.
The ratio of how much the particles scatter light compared to the molecules in the air is what we call the aerosol-to-molecular extinction ratio. This ratio can vary depending on the type and amount of particles present in the air, and it can be used to estimate the concentration of particles in the atmosphere, which is important for understanding air quality and climate change.
When we talk about NO2 concentration, we are essentially measuring the amount of NO2 molecules present in a specific volume of air. This is typically measured in parts per billion (ppb) or parts per million (ppm).
NO2 is harmful to both humans and the environment. It can irritate the respiratory system and worsen asthma and other respiratory conditions. It can also contribute to the formation of smog and acid rain, which can damage crops and buildings.
But that’s all in the troposphere. In the stratosphere, NO2 is intertwined with chemical reactions creating/destroying stratospheric ozone. Sunlight greatly affects NO2 concentrations with amounts at sunrise less than sunset, by as much as 3 times is not uncommon. The zonal mean plot combine both sunrise and sunset measurements to generally, but not always, provide an average amount.
Note: Bands at higher latitudes are likely to contain larger sampling gaps and plots may exhibit discontinuities.