Refuge Notebook
Peninsula Clarion Article
Dated
8 September 2000
Lightening is Rare but Important in Kenai Peninsula Fires
by Ed Berg
As a born-and-raised Midwesterner, I
love a good thunderstorm with lots of lightning, especially at night. On the Kenai
Peninsula I miss these grand pyrotechnic shows and that mixture of awe, terror,
and relief, when you say, "Boy, that one was close!!"
On a recent Saturday
(Aug 19) we had just such a display as a thunderstorm rolled up the central Peninsula,
crossing Tustumena Lake and passing over Sterling. Mark Wegner was fishing at
Nikolai Creek, and saw lots of lightning on both sides of Tustumena Lake. Two
fires were reported the next day, which were probably caused by lightning strikes.
One fire was just south of Windy Point on Tustumena Lake, and the other was on
the East Fork of the Moose River. We are monitoring these spots, and no smoke
has been seen at the Tustumena Lake site for a week. Local pilots did report smoke
at the East Fork site last weekend, however. The burned areas are less than an
acre. Both fires are in the zone of limited suppression, so we would not extinguish
them unless they threatened to move toward populated areas.
I have always been
puzzled about the lack of lightning and lightning-caused fires on the Kenai. The
vast majority of our wildfires can be clearly traced to human beings (campfires,
cigarettes, etc.). Jim Peterson at the Alaska Division of Forestry in Soldotna
estimates that maybe one fire per year might be traceable to lightning, although
he did recall one thunderstorm in the late 1980's which started seven fires simultaneously
in the Caribou Hills.
The Kenai's general lack of lightning contrasts strongly
with Interior Alaska, which can have several thousand lightning strikes and dozens
of fires in a single thunderstorm. Alaska Fire Service (AFS) data for the Interior,
for example, show an average of 26,000 cloud-to-ground lightning strikes per year
during the period 1986-97, most occurring between 4 and 6pm during late June and
early July.
The electrical impulses from lightning strikes are recorded by
electrical sensors at nine stations in Alaska, mostly north of the Alaska Range,
and AFS prepares daily lightning maps during the summer. Unfortunately, it takes
quite a blast on the Kenai to reach the sensors. When I checked with AFS about
our Aug 19 lightning strikes, they hadn't recorded anything at all. If we had
more lightning, I was informed, they would put some sensors down here, but they
want the biggest bang for the buck, one might say.
So, why don't we have more
lightning on the Kenai? I discussed this with Dorte Dissing, who is doing a graduate
thesis at UAF on lightning and the boreal forest in Alaska. She pointed out that
to get a good thunderstorm going, you need a very unstable airmass that would
rise "forever" if given the chance. You also need some kind of triggering mechanism
to set off the instability and get the air churning. The problem in coastal areas
like the Kenai is that most marine air masses are very stable, and do not want
to rise. In coastal areas it is hard to heat up the ground enough to get the air
moving upward by convection, because of the cool ocean air and the extensive cloud
cover. Furthermore, the coastal air aloft is much warmer than in the Interior,
and it makes a ceiling that prevents any hot air from continuing to rise, because
air only rises until it is no longer warmer than the surrounding air.
In the
Interior there are triggering mechanisms like thermal troughs and high-pressure
ridges, which are uncommon along the coast. On the Kenai the main triggering mechanism
is probably the "orographic" effect of the mountains: when a moisture-laden airmass
approaches the Kenai Mountains from the west, the flow of air lifts it upwards
and cools it. The moisture condenses and we get rain, at least. If the lift is
high enough, the water will freeze and ice crystals (and hail) start forming.
Ice crystals are necessary to get the separation of electrical charge required
for lightning. Orographic lifting thus explains why the big cumulus clouds and
(rarely) thunderstorms and lightning usually form near the mountains and not over
the Inlet or Kenai-Soldotna.
At the Kenai Refuge, we are starting to rethink
the role of lightning in the Peninsula forests. In 1998 we pulled a 9-meter core
of sediments from a lake along Swanson River Road. Dr. Scott Anderson of Northern
Arizona University has been analyzing the charcoal in this core, in 1-centimeter
slices. When he is finished, we will have a 13,100-year record of fire in this
drainage, which essentially covers the time since the retreat of the last major
glaciation. We can see already that there were fires during the tundra period
before spruce arrived 8000 years ago, as well as numerous fires once spruce was
established. It is highly unlikely that the native people caused many (if any)
of these fires, so lightning as a fire source becomes important on a timescale
of decades and centuries.
If you would like learn more about lightning in Alaska,
check out Dorte Dissing's website at http://www.lter.uaf.edu/~dverbyla/dorte.htm.
----------------------------------------
Ed Berg has been the ecologist
at the Kenai National Wildlife Refuge since 1993. Previous Refuge Notebook columns
can be viewed on the Web at http://kenai.fws.gov.
Last updated: June 16, 2008
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