The ‘Sonde Map’ tab showcases daily updated plots comparing SAGE data products with external data. The goal of this tab is to provide a general assessment of SAGE data relative to our network of validation partners and sonde stations around the world.
Sonde data files are ingested nightly as they are uploaded to NDACC, SHADOZ, and WOUDC. The profiles are passed through a minimal quality filter to remove nonphysical values. Profiles are considered coincident if they are within 10 deg latitude, 5 deg latitude, and 24 hours of a SAGE observation. If coincident profiles are found, the comparison statistics are recalculated, and the website plot is updated. Sonde profiles may be matched to multiple sequential SAGE events, but only one sonde profile will be chosen as the ‘best match’ for each SAGE event.
Several updates to this page are planned for the coming months. These changes include: adding aerosol and lidar comparisons, including additional stations, transitioning to homogenized datasets (ex. HEGIFTOM), and providing overpass information. Feedback is encouraged! Please let us know how we can make this tool more valuable or user friendly.
Hunga Tonga-Hunga Haʻapai (HTHH) erupted over a series of days during January 2022, culminating in a set of highly explosive events on 15 January 2022. While activity from HTHH is not uncommon, with previous eruptive and terraforming events in 2014 and 2009 in recent history, the nature of the 2022 eruption and the impacts on the stratosphere are unique in records from the satellite era. The sulfur dioxide and ash contributions from HTHH were unremarkable, but the water vapor added to the stratosphere was unprecedented and was visible in satellite measurements for years afterward.
The HTHH caldera sat approximately 150 m below sea level before the explosive event. The eruptions in 2009 and especially in 2014 had significantly altered the land comprising the adjoining islands of Hunga Tonga and Hunga Ha'apai on the caldera rim to which HTHH owes its name. The 2014 eruption, in particular, had joined the two islands with a land bridge which persisted until 2022. The 2022 eruption destroyed the land bridge connecting the two islands, and that land and the water contained in the caldera became a source of a significant perturbation to stratospheric composition following the 2022 eruption. The location of HTHH and nearby SAGE measurements that observed significant changes in the stratosphere are shown in Figure 1.
Initial observations and reports following the 2022 HTHH eruption suggested an aerosol injection up to the mesosphere. SAGE III/ISS had a serendipitous sampling opportunity around the same latitude as HTHH in the days preceding and following the eruption on January 15. SAGE III/ISS was able to corroborate the high altitude injection, showing increased aerosol still above 42 km 2 days later, and more significant aerosol layers descending over the following days. Figure 2 shows vertically resolved profiles of aerosol extinction coefficient (km-1) which is natively retrieved by occultation measurements. The enhancement is visible as the colored lines extend to the right of the dashed line representing the background state of the atmosphere for the week prior to the event. The magnitude of the increase over background levels highlights the early impact of the eruption on stratospheric composition and foreshadowed the longevity the ejected material would have.
Notably, early estimates suggested relatively low amounts of sulfur dioxide (SO2) around 0.4 Tg, which is significantly lower than other eruptions of similar or even smaller explosive potential (Bourassa et al., 2023, Duchamp et al., 2023). In contrast, approximately 100 Tg of water vapor was added to the stratosphere (Randel et al., 2023), with nearly all of it constrained to equatorial and mid-latitudes as a result of a particularly strong polar vortex in the Southern Hemisphere (Manney et al., 2023).
Despite the low amounts of SO2 injected into the stratosphere, the impact to aerosol composition in the stratosphere from HTHH has been pronounced. The unprecedented increase in water vapor provided an additional pathway to convert SO2 into sulfuric acid particles (Zhu et al., 2022). Measurements of Stratospheric Aerosol Optical Depth (SAOD) illustrate the impacts of major events on total stratospheric aerosol burden in both spatial and temporal extents. Figure 3 shows SAGE III/ISS measurements of SAOD averaged monthly and zonally (in latitude). SAGE III/ISS had measured events including volcanic eruptions - such as the eruptions of Ambae in 2018, Raikoke in 2019, and Ulawun in 2019 - and pyrocumulonimbus (PyroCb) events from wildfires in the Pacific Northwest (PNW) in 2017 and Australia in 2020. However, the geographic extent and longevity of the produced aerosol are significantly pronounced in the SAGE III/ISS record of global SAOD. Figure 4 shows a more granular view, focusing in on latitudes with repeated aerosol perturbations in the Northern Hemisphere (upward pointing blue triangles) and Southern Hemisphere (downward pointing red triangles). In this view, the large perturbation of SAOD from HTHH is less dramatic and on par with the Raikoke eruption in the Northern Hemisphere from 2019. However, the longevity is clearly apparent, with SAOD values exceeding the peaks of the large pyrocb events for the entirety of the following year.
The HTHH water vapor injection impacts are far more pronounced, since stratospheric water vapor variability is typically dominated by the annual water vapor cycle or "tropical tape recorder" (Mote et al., 1996 and Park et al., 2021). Stratospheric water vapor varies with tropical tropopause temperatures from months prior. In the summer, the tropopause in the tropics is at its highest, temperatures at the tropopause are at the coldest, and a "freeze drying" effect can be observed. The wet phases of the tape recorder cycle are correlated to time-lagged convective transport of moist air from monsoon season in the Northern Hemisphere, and the wettest phases correspond to relatively warmer tropopause temperatures. The injection of HTHH water vapor is a relatively massive impulse in the time series, drowning out and disrupting the annual variability, but still ultimately ascending through the stratosphere. Figures 5-7 illustrate this geographically (5), temporally (6), and more granularly (7).
In Figure 5, the annual variability in water vapor is visible with dryer (lighter) and wetter (darker) periods in each year. The addition of the HTHH water vapor effectively erases the tape recorder signal from the water vapor column measurements, with a 40-50% increase in total stratospheric water vapor burden for the affected regions for at least the following year.
Figure 6 shows a snapshot mission overview plot of SAGE III/ISS measured water vapor mixing ratio from this site. The values of water vapor mixing ratio saturate the scale used on the plot in the month following the eruption, and elevated amounts of water vapor are visible up to 45 to 50 km for two years following the eruption through 2023. In aggregate analyses, such as the monthly zonal mean imagery on this site, the elevation over background at higher altitudes is still visible into 2024.
Figure 7 shows a more granular view comparing Northern (upward pointing blue triangles) and Southern Hemisphere (downward pointing red triangles) column water vapor amounts. The latitude ranges match with those shown in the aerosol section of this discussion, and the comparison is useful in that the Northern Hemisphere latitudes were less impacted by HTHH water vapor. The annual water vapor cycle is clearly dominant in both hemispheres prior to 2022 with no significant perturbations or trends. After the HTHH eruption in 2022, however, an impulse of approximately 40-50% over previous levels on a daily basis can be seen. For the impacted altitudes, the water vapor mixing ratio can frequently be seen in excess of a 20 times increase over typically measured values. A rapid decay is observed that asymptotes well above the previously measured maxima, and average Southern Hemisphere water vapor abundances now exceed the maxima observed in the Northern Hemisphere.
Satellite measurements of properties from impactful events such as the Hunga Tonga-Hunga Haʻapai eruption are useful for testing our understanding of atmospheric processes. SAGE III/ISS measurements of events such as this are used to inform modeling efforts and supporting climatologies such as the Global Space-based Stratospheric Aerosol Climatology (GloSSAC) (Kovilakam et al., 2022). As these events occur, the validation and outreach team try to release articles detailing what was seen and measured as close to the events as possible, such as SAGE III Sees Tonga Aerosols, Water Vapor Months After Eruption.
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.
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.