Paris and Plume Measurements

We’ve had a busy couple of weeks in Halifax, and now the BORTAS campaign for this year is in full swing. As well as the lidar we have a large array of other scientific measurement equipment set up here on the roof of the physics building at Dalhousie University, including a wind monitoring radar and instruments that measure particle sizes and ozone levels directly. I don’t have much to do with those instruments but we were all kept busy last week preparing and learning to operate the ‘Portable Atmospheric Research Interferometric Spectrometer for the Infrared’. PARIS, as she is known, is an instrument which measures atmospheric trace gases and should give us a better idea of what the chemical constituents of smoke plumes actually are. We also had to build a shelter for PARIS, a small shed that’s been named FRANCE. I’m not sure what that stands for, suggestions on a postcard, or by comment, please...

Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR), operating on the roof of the physics building.

On the boreal biomass burning side of things: over the past week we’ve been getting a reasonably regular procession of biomass burning plumes passing overhead, as predicted by the GEOS-5 CO profile forecasts that Mark Parrington has been producing, and we’ve managed to measure the aerosols that we’d expected to be associated with that type of plume using the lidar. For example here’s the forecast and the lidar plot from measurements which took place on Wednesday and Thursday.

The CO from boreal biomass burning forecast profile over Halifax, showing high concentrations of CO at around 2km from 20 to 40 hours after the plot began (which was 1200 UTC on the 20th). This time corresponded to 0800 to 0400 UTC, and the lidar measurements from that time clearly show a similar shaped aerosol feature at roughly the same height and time. CO plot courtesy of Mark Parrington, University of Edinburgh.

You’ll notice that compared to the plot from the 9th July post, the aerosol layer here is much thicker, higher and more concentrated than the meagre one from that day. You’ll also notice how nicely it ties up with the CO forecast above. The smoke plume from a forest fire would be expected to carry high concentrations of carbon monoxide and high loads of aerosols, so it’s nice to see experimental data that seems to confirm this, and which also suggests that the CO forecasts are accurate.

We find out the locations of forest fires throughout North America from a number of sources. In particular Natural Resources Canada produce a daily plot showing where high concentrations of forest fires are occurring within Canada (http://cwfis.cfs.nrcan.gc.ca/en_CA/fm3maps/fwih), whilst FIRMS (Fire Information for Resource Management System, http://maps.geog.umd.edu/firms/kml.htm), of the University of Maryland, provide similar forest fire position plots for all of Northern North America as Google Earth files. Both services use satellite infrared measurements to find the fires.  As you will see from the plots below, we shouldn’t be running out of smoke plumes soon, we just hope that the wind brings them our way!

The Natural Resources Canada fire hotspots map for 22nd July , and the FIRMS google earth plot of fire locations during the 48 hours previous to the 22nd of July.

The google earth image above has been overlaid with a 72 hour Hysplit back trajectory matrix. The trajectories all end in a grid cantered on Halifax, with height and time relating to the aerosol layer discussed above. The trajectories seem to suggest that Halifax was at the focus of a region of converging air at that time, so the smoke plume could have come from anywhere in Northern and Western Canada, though it is tempting to assume that the fires visible to the west of Hudson Bay (which had also been burning for several days beforehand) were probably the source.

 Finally, if you take another look at the CO forecast plot above, you’ll notice an enormous concentration of CO due above Halifax around 60 hours after the plot began. Assuming the forecast is correct that plume should be overhead right about now, and that’s the reason why I’m sitting in the lab writing this blog at 02:30 on a Friday morning, hoping and waiting for the clouds to clear so that I can get the lidar fired up and start making some measurements!

Update from Dalhousie....

Post written by Eddy Barratt and Rob Trigwell

Well we’ve had a little practise and I (Eddy) had my first shift running the lidar solo on Monday night, though a combination of instant messaging, e-mails and phone calls meant that I had all the support that I needed. You might expect that the lidar can pretty much run itself, but there are still quite a lot of tasks that kept me busy. The most important of these is to do with aircraft safety.  We have a radar that shuts down the laser whenever an aircraft is in our vicinity. When this happens I have to go outside, look for the aircraft in question, then log it’s height and it’s direction before turning the laser back on. There are also helicopters that occasionally buzz over the city.  We have a microphone on the roof and we can hear them approaching from a fair distance, and we can shut off the lidar manually before the radar even detects them.

 The LIDAR running at night.

The data retrieval software also needs to be started every 60 minutes, and to produce the plots requires a little skill and patience. If you look carefully at the plot below (taken monday night, current plots can be found at http://aolab.phys.dal.ca/data/current/) you’ll see black bands at 5 and 5.5 km. These are where I’d set the normalisation limits. The software has to be told how much light to expect from clear, aerosol free air, and we do that by selecting a region and telling it that in that region the air is free of aerosols. Clearly if their are aerosols in that region the plots will look wrong, so selecting the right normalisation region is important. Usually you’d choose a region high up in the atmosphere but for that shift I was having to continually lower the region, to bring it under the cloud which had been steadily sinking all evening.

This plot demonstrates some interesting features. First, and most obviously, you can see the bottom edge of the cloud. It had fallen from about 9km at 2100 (GMT, 6pm local time) to 6km when I took the screenshot at 0230.. Occasionally, like between 2200 and 2300, the cloud was thin enough so that we were still getting some readings from above it, but for most of the evening the bottom of the cloud had been as far as our laser has reached. The second thing is the band of bright colours down low, in the first 700m or so. This is thin cloud or fog, it wasn’t thick enough to stop the beam, but it did provide enough reflections to show up quite significantly.

The third thing you might notice, with a keener eye, is the swirling blue tinted patterns between the two cloud layers. These are aerosols, which is exactly what we’re out here to look for. I’ll hand over to Rob who ran some further analysis, to try and find out where that aerosol came from...

Lidar profile above Halifax, and 5 days backward trajectory for air that was at 2000 m elevation at 2200 h on monday night, produced by the NOAA HYSPLIT model. Click on the figure to enlarge it.

Running the NOAA HYSPLIT model at the altitude at which the aerosols were being detected by lidar can give us an insight into source regions of these aerosols. The model uses what it knows about wind strengths and directions in the past few days to calculate what paths a given parcel of air has taken to be where it is now. As you can see from the plot, the back trajectories suggest that the aerosols could have originated somewhere in the US midwest, before making their way across Ontario and Quebec. These are not heavily industrialised regions so the aerosols are probably not anthropogenic. The actual source and type of these aerosols is a matter for further analysis. 

Back in Edinburgh, Mark Parrington is using forecast output from the NASA GEOS-5 system to predict the trajectories of biomass burning plumes, and when they pass over Halifax. The forecast CO profiles over Halifax (http://xweb.geos.ed.ac.uk/~mparring/BORTAS/Halifax/), plotted in a similar form to our lidar plots, highlight where Carbon Monoxide is strongly concentrated with the measured aerosol. CO is produced in a number of different processes, both industrial and natural, but in particular CO would be expected to coexist with aerosols from Biomass burning, so correlations between his plots and our own are very exciting.

CO forecast profiles over Halifax, plots courtesy of Mark Parrington, University of Edinburgh. Click to enlarge.

A last word from Eddy:

I should have mentioned in my last post that I’m here thanks to a grant awarded by the Nuffield Foundation, which I’m very grateful for, and very sorry not to acknowledge it last post.

First Taste of Atmospheric Research

Post written by Eddy Barratt. 

As Sarah mentioned in a previous post, the BORTAS project includes scientists from a number of different disciplines within the atmospheric science community. I can’t quite claim to be one of them, but happily the project is also offering me, an undergraduate student at Edinburgh University, the chance to take my first step into the world of atmospheric research.

Together with Rob Trigwell, who is due to start his Masters at Edinburgh in the Autumn, I arrived in Halifax yesterday to assist Tom Duck with the operation of his Lidar (see the 4th May entry) for five weeks this summer. Initially the idea was that we’d be flying out a couple of weeks ahead of the rest of the team, to familiarise ourselves with the instrument, and then during the flight campaign the information we gathered from lidar observations would continually be available for everybody else to assist analysis, flight planning, and the like. The fact that the flying campaign has been postponed hasn’t dramatically changed our particular role at all; measurements of aerosol levels in the sky above Nova Scotia can still tell us a lot about the transport of boreal fire smoke plumes. Together with the myriad of other scientific measurements being made this summer (by radiosonde, satellite, mountain top observatory; just not aircraft), Rob and I will hopefully be able to contribute some important observations that will help the rest of the team to refine their models, fine tune their science, and for us all to reach a better understanding of what goes on within a plume of smoke.

 The roof of the physics building at Dalhousie University. The white instrument is the RADAR (RAdio Detection And Ranging) instrument, and when it's running the LIDAR beam comes up through the hatch on the right.

So today we met Tom and his team, and we had our first introduction to the lidar, and our first safety briefing. At the heart of the lidar is a very powerful laser, so the introduction was as much about how to operate the machine safely as it was about gathering data from it. For example, the beam shoots directly upwards from the physics building in downtown Halifax, and could potentially cause a danger to passing aircraft; so the lidar is also equipped with a radar, and if a plane’s path brings it close enough overhead then the whole instrument is automatically shut off.

Over the course of the next week or so we will be learning the ins and outs of the machine, which Tom designed and built (and which, I should admit, seems a little Heath-Robinson to my un-accustomed eyes. The photons of light, which have reflected from aerosols in the atmosphere and have found their way down to the receiver telescopes of the lidar, are transported to photomultipliers, which count them, in optical fibres inside garden hoses). The lidar hasn’t been used much since last summer, so we’ll all be interested in what we discover over the next few weeks. We’ll keep you posted.

CO Forecasting for Flight Planning

Post written by Keith Tereszchuk

Since there will be a limited amount of scheduled flight time available during the month long campaign in Halifax next summer it is important that we take advantage of the time as best we can.  So flight planning will be an essential part of our flight preparation.  The FAAM aircraft has an operational range of 500 nautical miles and maximum flying time of approximately 5 hours, so it will be crucial to be able to locate biomass burning plumes over Maritime Canada and the North Atlantic before leaving the ground to ensure that we will successfully make useful measurements during each and every flight.  Therefore, we must be able to accurately forecast the location of biomass burning plumes in the troposphere.

Example plot of CO data from IASI. The circle represents the area within which the aircraft can operate.

 

To do this, we will be using data provided by IASI, the Infrared Atmospheric Sounding Interferometer. It is a key instrument on the METOP series of European meteorological polar-orbit satellites.  It is developed by CNES (Centre national d’études spatiales, French space agency) in co-operation with EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites). This instrument scans the entire globe up to 3 times a day and retrieves the concentrations of numerous molecular species in the free atmosphere including carbon monoxide (CO), a well-known biomass burning marker species.  Cathy Clerbaux from LATMOS-ULB (French national atmospheric science research centre at the Université Libre de Bruxelles) has kindly offered to provide us near-real time CO data from IASI (updated every 3 hours) for our forecasting purposes during the BORTAS campaign. We will be producing forecasts this summer and looking at ground based and satellite data to assess how well we are doing and any changes that need making before the forecasts are used for flight planning next summer.

New Instrument Cleared to Fly

There is a group in Italy led by Piero Di Carlo and based in the physics department at the University of L’Aquila that make measurements of reactive nitrogen species in the atmosphere using laser induced fluorescence (LIF). They have agreed to be part of the BORTAS project and have their instrument installed on the UK BAe 146 Atmospheric Research Aircraft. The operation of this instrument and analysis of the data it produces are the parts of the project I was employed to carry out so developments on this new instrument (well new to me anyway) are quite exciting! It was intended that we would use this nitrogen dioxide (NO2) LIF instrument to measure NO2 and through thermal decomposition also the sum of alkyl nitrates and the sum of peroxyacyl nitrates (PANs) during the BORTAS aircraft campaign this summer. Because this instrument has not been used on the research aircraft before it needs to go through testing and certification to allow it to fly. The schedule for this from our point of view is not so urgent any more but since the instrument is intended to fly on another campaign that is now taking place in the UK this summer this process is still taking place. So earlier this week we had brilliant news that on 9th June the instrument passed the BAe inspection and so will be installed on the aircraft, hopefully, next week.

Later this month I should be able to travel down to the airport at Cranfield to see the instrument on the aircraft and help with some operational testing. Then test flights start early July…..so fingers crossed the instrument is a good flier and there are no major hiccups. I’ll let you know how it all goes.