The paper goes into great detail about their cloud tracking methods and the errors involved; I won't go into that. I'll focus instead on their results. First, the stuff that can be compared with previous work, a summary of Venus' atmospheric motion:

Averaging all the wind measurements together provides a picture of wind speeds in Venus' southern hemisphere. Roughly speaking, from the equator down to about 40 or 50 degrees south, the winds move at a pretty constant speed, about 90 to 100 meters per second; sometimes there's a "jet" of faster-moving air at that mid-latitude region, sometimes there isn't. Wind speed then falls off rapidly from the midlatitudes to the pole. This is consistent with previous results. Always nice to see a new data set agree with an old data set!

But think for a minute what it means that wind speeds are constant from the equator to the midlatitudes. Venus is a sphere. There is less planet to go around at the midlatitudes than there is at the equator. So it takes five days for the atmosphere to circle the planet at the equator, but only three days at the midlatitudes. From midlatitudes to the pole, the rotation period stays constant -- three days -- so the polar "cap" of the atmosphere is almost acting like a solid body, rotating around the planet as a unit. This part doesn't contradict previous results, but previous missions had little to say about the poles.

They did some cloud tracking in infrared images, which see deeper into Venus' atmosphere than the ultraviolet images do. But they're also more difficult to interpret. They found that wind speeds seem to be slower at a deeper level, which is consistent with what was measured by descent probes like the Pioneer Venus and Venera probes.

But where the paper really gets interesting is when it talks about how things varied with time. They saw variations on just about any time scale: over the course of a single orbit, and also over the course of the 10 Venusian years of the Venus Express mission. There's never been a data set that can really get at Venus' temporal variability before, not in such detail.

From one Venus Express observation season to the next, there were distinctly different east-west speeds of atmospheric rotation. Things poleward of those midlatitudes were pretty constant -- the polar atmosphere just sat there and rotated like a solid body once every three days, all the while that Venus Express was watching -- but the east-west motion of the low-latitude atmosphere ranged from about 80 to about 120 meters per second over the course of Venus Express' observations.

Not only that, but there was secular change over time. The atmosphere appears to be speeding up very gradually. There's a lot of noise, but the trend is clear. " One of the main results of more than half a decade long VMC observations is that the mean zonal wind velocity in the low latitudes gradually increased from 85 ± 3 m/s in 2006 to 110 ± 3 m/s in 2012."

There's a lot of noise because wind speeds vary a lot from orbit to orbit. They tried to look for periodicities in wind speeds, and found one at about 4.1 to 5 days, meaning that the variation in wind speeds could have to do with some kind of wave propagating around the atmosphere. Here were are getting to the limit of my ability to comprehend atmospheric science. I'm a geologist, not a weather-lady. They did say this was consistent with earlier results and that it might be a Kelvin wave. Like you, I can do a Google search on Kelvin waves in the atmosphere but I don't feel confident translating the results for you.

There is a clear correlation between wind speed and local time of day: winds are slowest near noon and fastest in morning and evening.

What does all this mean? In particular, what does the very-short-time-scale variability of the wind speeds mean? One possibility, which makes my head hurt a bit, is hinted at in the very title of the paper. I'll remind you of it: "Cloud level winds from the Venus Express Monitoring Camera imaging." Think about clouds on Earth. They don't always form at the same altitude. Air gets pushed around and stuff in the air condenses when conditions change. They're not like floating tracer particles, but that's more or less how they've been treated in the paper. If the altitudes of the cloud tops could be changing, that would result in changes of the altitude at which the mysterious ultraviolet absorber forms, which means they're not really measuring the same place in the atmosphere from orbit to orbit, which might imply that the speed of the winds really isn't changing like it seems to be. So are we really seeing secular variation in wind speed, or are we seeing variation in the altitude at which clouds form? I can't say that the authors really provide a way to discern between the two cases, which is a little bit of a problem.

And that's pretty much it. This paper describes ten Venus years of observations. It represents experimentalists collecting data and lobbing it back to the theorists, who now have to take these results and see if the models for Venus' atmosphere that they built from Mariner 10, Pioneer, Galileo, and early Venus Express results can be made to produce data that look like this. The ball is now in the Venus climate modelers' court. Can they produce these trends over time? Can they produce the atmospheric waves? It's the next big Venus atmospheric puzzle to solve.

Venus Express is still working at Venus, so there will be more data to add in to this puzzle. But probably not a lot more. The spacecraft is running very low on fuel. ESA will certainly operate it as long as it can, but once the fuel goes, the spacecraft's orbit will decay pretty rapidly. I'll write a bit more about that in a future post.

I have one last comment that has nothing to do with the science content of the paper. It has to do with the journal editing. The paper contains many grammar and syntax errors of the kind that are common in text written by someone for whom English is not the native language. The authors of this paper are predominantly Russian, so it's no surprise that their manuscript contained such errors. In my opinion, while it is the authors' responsibility to do the best they can in their non-native tongue, it's not on them to get it perfect. It reflects badly on the journal editors (in this case, Elsevier and Icarus) to publish a paper without editing to correct grammar and syntax errors. I made a comment to this effect on Twitter, and researchers have written to me to say that academic publishing is just different from other kinds of publishing; that it's not journal editors' jobs to edit for readability. That they're just providing a publishing service for researchers -- that if an article is poorly written, it will be rejected, and if it achieves good enough quality writing so as not to obscure the science, it's accepted. It still seems kind of crazy that professional writers (like me) see our work carefully edited before print publication, while scientists don't seem to enjoy such services. Poor editing made this paper harder to read than it needed to be. Whose responsibility should it be to edit scientific papers? I welcome discussion in the comments.