If you've been following our Smog Blog this last week, you probably noticed that we had quite some action going on in terms of long range transport of aerosols over the US.
On May 14th Alex posted a lidar image from Oklahoma which showed an aerosol layer around 9-11 km which was believed to be from the wildfires that had been occurring in Russia/China border, in the Manchuria region. Just for clarification, we should point out that when we observe layers this high in the atmosphere, i.e., stratosphere, it is usually indication of long range transport. As Alex mentioned in her post, the Manchurian fires generated a series of Pyrocumulonimbus (pyroCb) which are clouds that are only formed during very intense fires and that can overshoot smoke from the troposphere to the stratosphere. The stratosphere is a very stable layer, so once the smoke gets there, it can remain in the atmosphere for long periods of time and be transported very far.
Here at UMBC, in Maryland, we started observing that same layer on May 16th with our MPL (bottom), and it's still being observed (between 12 and 13 km above the cirrus clouds).
We also ran backtrajectories with HYSPLIT to confirm that this layer was indeed due to the Manchurian fires. As you can see in the image bellow (left), by tracking the airmass that we observed with our MPL to 100 hours back in time (~ 4 days), the end points of the trajectory are over Canada, where the HMS team had been reporting smoke from those very same fires. In fact, on Friday May 18th, the lidar group from City College of New York (CCNY) also observed those layers (bottom, right).
Now if you look carefully at the CCNY image, you'll see that they also observed a layer around 2 - 2.5 km. And on May 17th, Daniel posted an image of our measurements here in Maryland, from ELF, showing a big blob of aerosols right at the begging of the image at 15:00 which then lost intensity throughout the day, but remained in the atmosphere until yesterday, as can be seen in the images below. The image on the left is from May 18th and the one on the right is from May 19th.
As you can see, the layer appear to be finally mixing into the PBL on the 18th and on the 19th the layer is weaker and more stratified. Note that the colorscale is the same in both images but they are plotted in different altitude ranges.
Again, we ran backtrajectories to confirm the source of the layers we observed. As Daniel mentioned in his post from May 17th, smoke from fires in the US as well as the fire in the Russia are the ones to blame.
By running a 100h backtrajectory for that big blob we observed on May 17th at 15:00, we see that the airmass had originated from inside the US, more specifically, in the Midwest and Central regions of the US (bottom, left). However, when we track the layer of May 18th, we see that there were, most likely, contributions from the Russian fires as well (bottom, right).
Below are two HMS images. The one on the left side is an updated version of May 17th and the one in the right side is the one from May 19th. By looking at those two images it is easier to understand how we could have been measuring aerosol contributions from both multiple sources. In fact, if we look back at the ELF image that Daniel posted on May 17th, it is possible that we could be already observing both contributions starting to entrain, given the structure of the layer below 3km which starts to narrow down in a triangular shape, and the one aloft, which started descending from 4 km.