Over the past couple of days we have had a smoke "cloud" sitting over much  of Victoria.  The sky in Melbourne is clear near the ground, but has a thick haze above.  The sun can be seen through it as a bright red ball in the sky. The Melbourne sounding for this morning is not up on the web yet; but at the VRO chart discussion this morning, we were told the smoke is above the inversion (so has a base at around 3,00 feet?) and extends up to about 8,000- feet, from pilot (aircraft) observations.

    On my web-page I have put this morning's visible satellite image showing the smoke cloud covering the eastern and southern sections of the state.  The smoke is caused mainly by the fires that have been going for the past several weeks over the northeast of the state.  On my web-page I have also put up the current fire-situation map from the state Department of Sustainability and Environment.

Visible satellite image

Current fire situation: 24-01-03

There is also a good picture of the event on the NASA earth observatory "natural hazards" page (http://earthobservatory.nasa.gov/NaturalHazards/).  I have placed one of their images, from on my web-page as well:  (I think the NASA image is from the 23rd... it is difficult to tell from the labelling on the natural hazards -page, and the MODIS page is down at the moment).

 Now for some meteorology.

* Clearly the smoke is a hazard for aircraft and is a factor in issuing TAFS, and apparently a couple of inward Qantas flights were diverted from Melbourne yesterday (at least I think thats what "hapers" said at chart discussion this morning)._

*  I believe the smoke is keeping the surface temperatures down, maximum temperatures in the northeast of the state generally being in the high twenties yesterday, compared with in the 30's in the west of the state.

*  Smoke only stays in a large contiguous cloud like this when there are light winds: i.e associated with a large "still" airmass.  From scanning the internal web for analysed charts, I found this a little hard to document; but I do have the single sounding for Melbourne last night, where you will see winds are below 20 kts through almost the entire depth of the troposphere.

* Whats going to happen now?  Presumably one we get a bit of wind the smoke will form a plume and will advect away (e.g in the northerlies sometime tomorrow ahead of the forecast change).

*  Smoke, having close to zero terminal velocity) must have similar properties to dust.... so there is a chance that if the change comes in quickly enough the smoke can be entrained over the top and into the cold-air dome.... so we could have a wall of smoke moving in from the west, similar to the walls of dust we have seen in the cool-changes earlier in the summer.... probably unlikely.... but worth speculating on.

cheers

 John mcB

Gary Weymouth
After any excuse not to work this Friday arvo
- thanks for the email!

If we are to get to 37C today we must have mixing and at least partial breaking down of the inversion
- hence ground level haze I can see outside with 20/20 hindsight.
Looks like a very week bay breeze trying to get in, but that by definition involves a vertical circulation too.

Looking at the sounding, the lower atmosphere (say below 700 hPa) is not as warm as one might expect from the thickness,
and synoptic gradient is light giving sea breezes in places,so it's not just lack of turbulent mixing due to lack of solar heating
due to smoke haze that's keeping temps down in places today; didn't look at NE yesterday.

Andrew Watkins

For those interested and/or out of smokey town, (a.k.a Melbourne) I have attached 2 images.

The first image is the "red sun" on Monday, our previous smoke day.

The second is a combined image - the left side from Monday morning looking south out the HO 27th floor (library)
window, approx 9am, the right side the same view almost exactly 24 hours later (tues). Note the difference in vis for the
Arts centre spire -that is only approx 1500metres from BoM HO.

 

Remember, as well as Johns earthobservatory images, also to check out the MODIS images at:
http://rapidfire.sci.gsfc.nasa.gov/gallery/

Or for a taste of whats really going on, the snow(/smoke) cams at
http://www.ski.com.au/info/snowcams/nsw.html and
http://www.ski.com.au/info/snowcams/vic.html
(all from www.ski.com.au)

Cheers,
Andrew.

---
Dr Andrew B Watkins
Climate Analysis and Prediction
Australian Bureau of Meteorology