It turns out that I am not referring to a large, mildly cute herbivorous African mammal. HIPPO stands for HIAPER Pole-to-Pole Observations of Carbon Cycle and Greenhouse Gases. That’s quite a mouthful. So what exactly is this? In short, it is a mission involving flying a specialized aircraft from the North Pole to the Antarctic waters, collecting information about the distribution of carbon dioxide and many other greenhouse gases along the way.

Before launching into details, let’s talk about why we’d want to do this in the first place. Humans are only just beginning to realize the extraordinary impact we are having on our dynamic atmosphere. We take for granted the delicate balance of gases that envelope and sustain the living Earth. Many of the problems we face today in terms of climate change and air pollution are a result of a dangerous combination of limited and poorly-channeled knowledge about the earth’s atmospheric system.

The HIPPO Project

This is where the HIPPO project comes in to the picture. In an effort to increase our understanding of the atmosphere, Harvard Professor Steven Wofsy and his colleagues are flying the HIAPER aircraft (a Gulfstream-V airplane, operated by the National Science Foundation) north to south along the mid-Pacific ocean.

There have been other aircraft missions in the past, and there are satellites constantly collecting atmospheric data, so what makes HIPPO so unique? It is the first attempt to collect physical and chemical atmospheric data on a global scale at very fine spatial resolution. Other aircraft missions have had a regional rather than global range (fine detail but limited spatial coverage); satellites have global coverage but not much detail. HIPPO reconciles these issues. Furthermore, HIPPO flights are being conducted over the course of a three-year period in a total of four to six phases. This means that in addition to fine detail and global coverage, these studies will also give detailed seasonal information, vital because time-of-year plays a critical role in regulating how much of each gas is present.  Depending on the season, there can be lower or higher amounts of high-energy sunlight penetrating the atmosphere, translating to colder or warmer temperatures. The speed and even occurrence of atmospheric chemical reactions are highly dependent on these variables. As Vidal Salazar, a HIPPO project manager at the National Center for Atmospheric Research (NCAR), points out, “this is the first time that anyone has systematically tried to map the distribution of carbon dioxide and related gases from the Arctic to the Antarctic and from near sea level to the upper atmosphere.”

But how is such a mighty goal to be achieved? Each HIPPO phase happens over a 27-day period, logging a hefty 30,000 miles of travel. The HIAPER aircraft is able to ascend to up to 45,000 feet. For comparison, a Boeing 747 cruises at around 35,000 feet. And that’s not all: atmospheric researchers are also interested in how the concentration of a gas varies with height in a specific location. This would mean that HIAPER should be able to make relatively fast descents (to as low as 1000 feet) as well. And it does.

On board the HIPPO aircraft (and under the wings) is an impressive collection of 24 state-of-the art instruments that sample atmospheric air every second! Some of the many gases studied are carbon dioxide, methane, ozone-depleting chlorofluorocarbons (or CFCs)—over a hundred different gases in total.  So, as the HIPPO flies through the skies, these instruments are collecting a massive amount of data about the concentration of many gases throughout the Earth’s atmosphere.

Team HIPPO has just completed the third phase, which extended from March 24, 2010 to April 16, 2010. The HIPPO scientists now have three phases of excellent data to process and explore, so they will be very busy between now and the beginning of the next phase.

How the information is used

Continuously sampling more than 100 different gases over 30,000 miles produces a lot of data to process and quality-check. The rewards, however, are huge and far-reaching.  Thanks to the HIPPO flights, we are receiving high-quality information about the distribution of many important greenhouse gases, from the surface to the upper atmosphere. Atmospheric researchers use this concentration data to understand and quantify the life-cycles of all these chemical species. Who or what is producing them? What breaks them down and removes them? How long do different gases stay in the atmosphere? How do gases interact with each other?

To do this, atmospheric scientists use a process called Inverse Modeling. To illustrate this, let’s first work forwards.  Take a coal power plant releasing gases into the atmosphere.  Scientists can know exactly what the carbon emissions of a given power plant are, because power plants are highly regulated and documented.  So we know how much comes out of the source, and where the source is located.  Once these gases leave the plant, they generally behave in a predictable way.  That can change when you factor in wind speed and direction, however this information is also recorded and available.  Once in the atmosphere, the gases from the coal plant might stick around, or they might interact with other gases and be rapidly consumed.  The HIPPO mission will collect data on what gases are currently in the atmosphere.  Using this information, plus what we know about the chemistry of the gases that are there, wind patterns, and the predicted behavior of gases as they are released, scientists can work backwards to identify major sources of the gases found in the atmosphere.

This is crucial information for policy-makers: for instance, to put an effective cap on carbon emissions in the most economically feasible way, legislators would need to know who or what the biggest sources are. Also, effective international efforts to mitigate climate change and air pollution would require global knowledge of which nations are the major contributors of pollutants.  Using data collected from the HIPPO mission, we can begin to steer legislative efforts towards the most effective ways to limit our global impact on the Earth’s atmosphere.

-Archana Dayalu, Graduate student in Department of Earth and Planetary Sciences at Harvard

Interested in Learning More and Keeping up-to-date?

Please visit for preliminary results, fun facts, videos, stunning pictures of “views from the top”, detailed flight plans….and much more. You can even follow HIPPO on Facebook and Twitter.


1. University Corporation for Atmospheric Research (UCAR) HIPPO Website.

2. Scoop Independent News. 10 November 2009. “Is it a bird? a plane? No, it’s a low-flying hippo.”

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