More Mesospheric Contrails

I wonder about these mesospheric contrails left after Space Shuttle launches. (The one on the left; the one on the right is a "regular" tropospheric contrail.) Turco et al. modeled them in 1982 (http://tinyurl.com/2b8d4n3) which was a long time ago and our understanding of the mesosphere and relevent processes was pretty meager then. Indeed, mesospheric temperatures and composition are significantly different since 1982 as earth's climate has changed. Maybe it is time for a second look?

Atlas V Soot Plume

Atlas V from last week's launch of X-37B showing soot plume from kerosene fueled booster engine. The plume is asymmetric because the Atlas V booster has two side by side nozzles. The soot emission index (EI) of kerosene rocket engines is 20 -40 grams of soot per kilogram of propellant. The soot EI of jet aircraft is 1000 times smaller. Does this soot add up and have a global effect?

Rocket Smoke is Like Cigarette Smoke

This image of a Soyuz rocket plume was taken far downrange from the launch site and shows the second stage of the Soyuz, which burns liquid oxygen and kerosene, in the upper stratosphere or lower mesosphere. The visible plume here is sunlight reflected from soot generated in the engine. The size of these soot particles has never been measured and is not well known but the particles likely have a diameter of about 0.1 micron. This is the same size as smoke from a cigarette which also has a bluish cast, for the same reason. The tiny soot particles preferentially scatter blue light.

What does soot from rocket engines do in the stratosphere? It absorbs sunlight and heats the surrounding air a little bit. Is it significant? Climate models must be run to answer this question.

What Might Have Been Thursdays

The Space Transportation System. The end of the Space Shuttle program is 4 or 5 flights away. I was just graduating from the University of Michigan when the first Space Shuttle was launched in 1981. Much has been written about Nixon's decision to press ahead with the Shuttle and the economic arguments that were based on projections of about 50 launches per year. That's a launch rate about an order of magnitude higher than what the Shuttle actually managed over the life of the program. Which means, of course, an order of magnitude larger emissions into the stratospheric each year.

By the time we appreciated how chlorine compounds and particles control stratospheric ozone, it was already clear that the Shuttle would never fly once a week. So global models for 50 launches per year were never run. How would 50 Shuttle launches per year affect ozone and climate? We will never know.

Commercial Space: Falcon 9

First flight of the Falcon 9 will take place in the next few months. This hydrocarbon fueled rocket introduced by the Space Exploration Technologies Corporation (informally, Space-X) is expected to be able to place about 5 metric tons into LEO. The propellants for Falcon 9's nine engines are conventional kerosene (RP-1) and liquid oxygen; important emissions include water vapor, carbon dioxide, and soot. A heavy lift version of Falcon 9 is planned. Kerosene fueled rocket engines emit about 3 times more carbon dioxide (per unit mass delivered to orbit) than standard solid rocket motors.

Three Interesting Plume Phenomena

This video of a recent Atlas V launch well illustrates a few of the many interesting ways that the exhaust plume of a kerosene fueled rocket engine interacts with the atmosphere.

First, notice the contrail that begins to form at 1:41 (video time) and continues for about the next 10 seconds. This is a typical aircraft type "linear contrail" consisting of ice particles.

Second, notice that the classic rocket plume "flame" (the radiant plume) shrinks with altitude. By 2:30, with the rocket well into the upper stratosphere, the radiant plume has become small and a wide and faint white-bluish plume, likely soot particles from the RD-180 rocket engines, becomes prominent.

Third, this video shows the acoustic waves that propagate from the vehicle and modify the surrounding cirrus cloud particles. In this video you can also see the faint soot trail behind the Atlas V rocket.

These localized plume phenomenon hint at the cumulative and global impacts of rocket emissions.

Commercial Space Transport and Science

The Next-Generation Suborbital Researchers Conference will be held next week. The idea here is that the science community can buy into the emerging suborbital space tourism sector. Instead of launching expendable sounding rockets, researchers would buy rides into the upper stratosphere, mesosphere, and lower thermosphere on reusable tourism vehicles. There is good potential for new data from little known regions of the atmosphere and more science at lower cost. Should the scientific community also investigate how the cumulative emissions from these vehicles will affect climate and ozone?

Sulfuric Acid Seduction

So-called "geoengineering" is a popular thing to discuss, even in polite company. The idea is simple: inject sulfur dioxide gas into the lower stratosphere and add a little bit - a few percent - to the natural sulfuric acid cloud layer there. The man made sulfuric acid particles would reflect a little bit more sunlight back into space than normal, thus cooling the planet. Massive volcanoes do this every decade or so and we think we understand how gases turn into particles and reflect sunlight and so on......

This plot is from a paper by Keith, Parker, and Morgan (Nature, 436, 2010) called "Research On Global Sunblock Needed Now". This idea is seductive. Relatively cheap and quick. But there are problems. First in line: this "purposeful pollution" of the stratosphere would cause a lot of ozone depletion, maybe 20%. Maybe more.

Second: It is sort of like a drug; each sulfur dioxide injection is temporary so once you start you can't stop. Look at the plot.

So where is the trade a good one? How much global ozone loss can we accept for a given amount of global cooling? Who decides?

Wild Card

Water vapor in the lower stratosphere plays an important role in the radiative balance of the atmosphere. This excellent paper by Solomon et al. (2010) reports on recent trends and changes in stratospheric water vapor levels and the relationship between water in the stratosphere and surface temperature. The processes that determine stratospheric water vapor levels, including rockets and aircraft combustion emissions, are poorly understood and so water vapor could be a climate change wild card.