Why does mist rise from the lakes in the morning?

During the fall, there many morning when Third Sister Lake produces gouts of mist and steam:



What's going on here? Obviously, the lake is not boiling, and - obviously - there isn't a general fog blanketing the entire forest, so why does the lake look like a pot on the stove? Well, it's due to many of the same principles of what happens when water boils in a pot on the stove, namely evaporation and condensation, but you have to think of these things in terms of heat energy and NOT in terms of water temperature alone.

In the case of boiling water on a stove, water is heated, causing evaporation; the gaseous water requires a certain amount of heat energy to maintain its gaseous state, and if the heat energy of the gaseous water falls below the condensation point, it turns back into liquid water, forming a fine mist. The mist increases in density as the amount of condensing water increases. This is why you see more and more steam rising from a pot of water as it reaches boiling point.

However, it's not only the temperature of the water that you have to consider when thinking about steam formation. In addition to the process of condensation described above, there is also the humidity to consider. In other words, the air itself can only "hold" a certain amount of gaseous water, and this capacity is determined by the temperature of the air; the higher the air temperature, the more water can be held as a gas. This is why there's a lot more steam seen above a pot boiling in very humid conditions than in very dry conditions (even when the air temperatures are identical).

In the case of misty lakes in the morning, all these processes are happening, just like in the example of the boiling pot, except the temperatures are far lower. Throughout the summer, the lake has absorbed and retained a large amount of heat energy in the top layer of the lake. At night -- especially on cloudless nights -- the heat energy in the air rises away from the surface and escapes this local system, thus bringing down the temperature. There is evaporation taking place in the lake, both day and night, thanks to the higher temperatures of the surface of the lake. However, unlike during the heat of the day, at night, since there is a lower temperature, there is less capacity for the air to hold on to gaseous water, and we can measure this as an increase in humidity. As the humidity rises to 100%, the air has a diminishing capacity to hold on to all the water that is evaporating -- due to the heat of the water in the lake -- and so the water almost immediately condenses into mist as it rises from the lake. In fact, if you heat a pot to the same temperature of the lake water, you would see steam flowing up from your pot, even though the water temperature is nowhere near boiling.

Once the sun's rays strike the surface of the water, the humidity is "burned away", in that the local temperature increases enough so that the humidity drops below 100%, thus allowing the air to once again absorb the evaporating water.

Of course, the reason why the lake effectively billows with steam during early fall mornings is due to the relatively large amount of heat stored in the lake combined with one or two significantly cold mornings. The photo above was taken on September 24, 2012, and if we look at the weather conditions measured at the Ann Arbor airport (about five miles away), we see that the overnight temperature dropped to freezing, and the humidity was near saturation. (Of course, this was in an open field, not above a lake, where the saturation would have been 100%.)



Yeah, okay, so this was a bit of a rambling post, but I hope that it helped you understand (if you didn't already) why so much mist rises off the lake on cool autumnal mornings. Of course, there is little reason to necessarily understand the why in order to appreciate the effect. In the end, fall is a veritable feast of sights, just like spring was one of smells, and summer one of sounds.

Peak fall colors

I think that this is the day when the fall colors are likely the best:


It's all "downhill" toward winter now.

Fall colors in the forest

Slowly changing colors in the forest near the Lib-Wag parking lot.



Fall colors emerging beyond the green foliage.



Red maple leaves.



The buckthorn and honeysuckle are the only things that remain in full leaf.

SNRE Campfire is coming...

This coming Friday, October 12, is the SNRE Campfire. This will be the 106th* celebration of the school out in Saginaw Forest, ever since the celebration of "field days" began in 1906.

In preparation for the event, I cleaned up the base of the fire-pit (removing the dirt and grass that had built up over the years),



had a lot of the ash wood and pine wood that was lying around brought in,



carried over a log for the cross-cut saw competition,



and chopped wood for the campfire.



The deliveries of straw bales, pumpkins, event tent & tables, port-a-johns, and trash cans are due to come later in the week.


* I am making the assumption that the School of Forestry continued the tradition during the US involvement in the two World Wars (i.e., 1917-1918 and 1941-1945).

Thanks to PitE student help in the forest

Today, I had a lot of help from PitE students who came out to the forest and - among other things - helped do some work out in the forest. Over the course of about an hour, these 20 students helped clip brush, haul wood, and clean some trails:







Thanks! ...and feel free to come out again to do some more work. ;)

Regional impacts due to Arctic melting: The future doesn't look anything like the past

Out of the University of Wisconsin - Madison, there is a brief on the potential future impacts of climate change on the region. (Well, the statements are about Wisconsin, but the impacted areas are definitely not going to stop at the Wisconsin state line.)

Vavrus, an expert on the arctic climate, says the dramatic melting trend is due to rising concentrations of greenhouse gases in the atmosphere warming the planet. He says natural variability may have accelerated the loss of ice in recent years, and he adds that the far north has physical characteristics that make it more sensitive to warming than other parts of the globe.

For one, he explains, snow and ice that normally cover the region reflect most incoming solar radiation back to space, but increased melting exposes land or ocean water that absorb more solar energy and accelerate any warming trend.

In addition, the lowest layer of the atmosphere in the Arctic is thin and prone to temperature inversions that hold warmer air near the ground, promoting even more melting as the region warms.

Vavrus says the Arctic is likely to continue to see pronounced downward trends in sea ice, snow cover, glacier extent, and permafrost. He says that will have major impacts on both natural ecosystems and human communities in the northernmost latitudes.

But the impacts of a warming Arctic could also be felt far beyond the region, including in the Midwest, according to research conducted by Vavrus and his colleague Jennifer Francis at Rutgers University published in the journal Geophysical Research Letters last spring.

"We believe that the winds aloft at the level of the jet stream will weaken and lead to slower-moving and 'wavier' atmospheric circulation patterns," he explains. "Such a change would favor more extreme weather events in middle latitudes, such as heat waves, droughts, floods, and�ironically�cold snaps."

What this means is that we can expect more weather patterns like what we saw this year: warmer winters, warmer springs, warmer summers, less rain on average, more rain in concentrated events, sudden cold snaps; you know: nothing like it used to be.

For Saginaw Forest, this will mean continued take-over by vines, continued lowering of the lake level, accelerated death of pine species, and rapid changes in the plant communities (as well as the insect, amphibians, reptiles, mammals, and birds that live in the forest). Furthermore, if lake levels get any lower than they are now, the near-shore habitat will be completely out of the water, severely limiting the available area for the fish currently in the lake to spawn, thus potentially causing a decline in the total number of fish in the lake.

... good times.

Chipmunk sighting - stranger than you might think

This morning I saw a chipmunk. While a chipmunk in the forest might not seem like such a strange thing, there haven't been any ever since I noticed their disappearance back in 2009... thanks to the feral cat that was shacked up in the barn.

My thought is that the many chipmunks that I saw prior to the feral cat's presence were pretty much all killed by the momma cat to feed her litter. With the disappearance of the cat, the population of chipmunks were able to recover.

If we do some very basic back-of-envelope calculations, this makes a kind of sense:

• Chipmunks take a year to reach maturity, producing one or two litters each year (Feb-Apr and Jun-Aug).
• June 2009: Widespread death of chipmunks near the barn; assume no surviving females nor young, therefore no young litter from the June-August litters and no juveniles.
• Feb-Apr 2010: Cold average temperatures: assume unlikely that chipmunks in surrounding areas have new litters; death of juveniles likely high.
• Jun-Aug 2010: Production of first viable litters in 2010 in surrounding areas.
• Jun-Aug 2011: Production of second viable litters moving into the area around the barn.
• Feb-Apr 2012: Anomalously warm winter and spring create further litters in the surrounding areas.
• Jun-Aug 2012: Relatively high number of chipmunks in the area surrounding the barn.
• Sep 2012: Mast year for nuts mean that chipmunks are running around, looking for nuts

Yeah, it's just guessing. And, yeah, I've been hearing the chipmunks through this summer, too. However, I didn't recognize how much I missed those little beasties until I saw that one this morning.

Still, it's a further reminder of the predatory potential of house cats. One more reason why people should spay and neuter their cats: so feral cats won't have litters and end up killing small mammals and birds.