At this point, you might be wondering, "What does taking atmospheric measurements using UAV's mean?" Let me elaborate.
The UAVs measure temperature, wind speed, wind direction, pressure, and relative humidity. For this project, we are interested in how these variables change with height above the surface. In order to obtain this information, the plane launches and flies to 85 m above the surface (this is roughly the top of Tall Tower). Once the plane is at this height, it flies a complete circle (with a diameter of 300 m), sampling the atmosphere at this height. Upon completion of the circle, the plane climbs to 105 m and completes another circle. The plane continues with this pattern, completing full circles every 20 m between 85 m to 165 m and every 100 m between 165 m to 865 m. The interval is smaller near the surface because the atmospheric variables (i.e. temperature, wind speed, etc.) change quicker in this region.
With this information, we will know how the temperature and wind speeds change with height (i.e. when do they increase or decrease with height and by how much).
Your next question might be, "Why do you need to take these measurements in Antarctica instead of somewhere closer to home?" Great question! We take these measurements over the Ross Ice Shelf, Antarctica, because the atmosphere over an ice shelf behaves very differently than the atmosphere over the ground in the mid-latitudes.
SUMO UAV infront of Tall Tower
(Photo courtesy of John Cassano)
The UAVs measure temperature, wind speed, wind direction, pressure, and relative humidity. For this project, we are interested in how these variables change with height above the surface. In order to obtain this information, the plane launches and flies to 85 m above the surface (this is roughly the top of Tall Tower). Once the plane is at this height, it flies a complete circle (with a diameter of 300 m), sampling the atmosphere at this height. Upon completion of the circle, the plane climbs to 105 m and completes another circle. The plane continues with this pattern, completing full circles every 20 m between 85 m to 165 m and every 100 m between 165 m to 865 m. The interval is smaller near the surface because the atmospheric variables (i.e. temperature, wind speed, etc.) change quicker in this region.
With this information, we will know how the temperature and wind speeds change with height (i.e. when do they increase or decrease with height and by how much).
Me monitoring the auto pilot during a UAV flight
(Photo courtesy of John Cassano)
Your next question might be, "Why do you need to take these measurements in Antarctica instead of somewhere closer to home?" Great question! We take these measurements over the Ross Ice Shelf, Antarctica, because the atmosphere over an ice shelf behaves very differently than the atmosphere over the ground in the mid-latitudes.
In
the mid-latitudes, the shortwave radiation from the sun is absorbed by the ground. This absorption warms the ground, which subsequently warms the air just above the ground. This causes the atmosphere near the surface to be warmer than the atmosphere farther away from the surface. In other words, the temperature decreases with height in the atmosphere. Conversely, over an ice sheet, a large majority of the incoming solar radiation is reflected, or not absorbed, by the surface. In this instance, the ground is colder than the atmosphere and air just above the ground is cooled. This causes the atmosphere near the surface to be colder than the atmosphere farther away from the surface. In other words, the temperature increases with height in the atmosphere. This is called a surface inversion.
The
example given above of the Antarctic surface inversion is generally true for
calm, clear conditions. Things such as strong surface winds, low-level clouds,
and warm air advection (warm air moving into a region from another location)
are all mechanisms in which the cold air near the surface is mixed with the warmer air aloft. This results in a well mixed boundary layer instead of a near surface inversion layer. The processes that mix out the near surface inversion layer are what we are trying to better understand with our measurements.
In order to better understand these processes, we will use the UAV data, the Tall Tower AWS data (which will give us the temperature and wind measurements for the levels below 85 m), data from two Snow Web stations (http://www.phys.canterbury.ac.nz/atmos/research/student_projects/jack_coggins_project.shtml), and model output from the Atmospheric Mesoscale Prediction System. By combining these data sets, we are hoping to be able to fully understand the processes that are involved in the evolution of the summertime boundary layer in the region of Tall Tower.
Ben Jolly and one of the Snow Web stations
Also, if you're interested in our adventures from another perspective, you should check out John's blog at:
And if you're interested in what the other half of our group is up to, you should check out Dave's blog at:
Hey there - last comment didn't post right so sorry if this ends up as a duplicate:
ReplyDeleteI was reading the first part of your entry and thinking to myself, why do they have to do this in Antarctica (honestly!). Question answered! Next question: Is there anything cool you can extrapolate from the information you are collecting about atmospheric behavior over the ice shelf to patterns elsewhere? Amazing that you are measuring the atmosphere in the one place on earth that it behaves differently than anywhere else!
Haha - I'm glad I was able to anticipate your question! :)
ReplyDeleteWe have only quickly looked at the data, so I'm not sure that we have any big conclusions just yet. Although, our findings are more than likely going to be relevant to other ice covered areas on the Earth. I hope that answers your question. If not, let me know.