Post by tmcewan on May 15, 2009 10:23:34 GMT
Hi all,
Posting the following with Mark Zalcik's permssion:
Tom
===============================================
QUICKSILVER
YEARLY NEWSLETTER OF NLC CAN AM
Vol. 17 2009
Hello NLC observers in 2009!
The prevalent theory of NLC formation is that the greenhouse gas methane is given off by various sources on the Earth and diffuses up into the atmosphere, as high as the stratosphere, where it is broken down by sunlight into various compounds, including water vapour, which then continues traveling upward until it reaches the mesosphere at the 80km level, where it accretes upon meteoric dust and large ions.
Current concentrations of methane are nearly 1800ppb, with 18% of total greenhouse gas radiative forcing due to methane, which is 22 times more effective than carbon dioxide in absorbing long-wave radiation. The concentration of methane in the atmosphere is determined by the balance between emissions from Earth's surface and, in turn, destruction of methane by hydroxyl free radicals in the troposphere, hydroxyl free radicals being the highly reactive form of the hydroxide ion; it is reactive because it contains an unpaired electron.
Measurements of atmospheric methane in the latter half of the 20th century indicated persistent increases in concentrations, followed by a period from about 1999-2006 when levels remained constant. But near the beginning of 2007, concentrations were once again on the rise. Scientists, led by Matt Rigby, pointed out that observed concentrations of hydroxyl free radicals had dropped, resulting in the methane increase, with a bias toward the northern hemisphere.
In arctic areas, the natural release of methane is easily detectable. In early winter, holes can be seen in lake ice; these holes are made from methane bubbling from the permafrost beneath the lake. Permafrost of course is an even more noticeable source of carbon, with some estimates indicating some 700-950 pentagrams of carbon are harboured in the top 1-25m of permafrost.
During some NLC seasons, incidences of consecutive-night, equatorward-moving “storms” are witnessed, and a notable one occurred in 2008. On the night of Jun 12/13, over half a dozen observers in Alberta glimpsed a widespread NLC display, and the automated camera at the Athabasca University Geophysical Observatory detected it, too, with the first sighting in bright twilight at 0525 UT and the last close to dawn at 0950 UT. From Edmonton, the NLC rose to 10-15 degrees elevation, with the most prominent type being bands. The following night, the 13/14, the only report of NLC anywhere in the network was from way down south in North Dakota, where Jay Brausch saw and photographed NLC to nearly 25 degrees elevation in morning twilight (see picture). Was the activity of Jun 12/13 / 13/14 one of those instances of NLC hovering over the subarctic on the first night, and then on the next night drifting southward so that they can be seen from way down in the northern US? Interestingly, there were no reports of NLC on the 14/15, but on the following night, the 15/16, as if on cue, the phenomenon started its commonly-observed one month peak run in the boreal skies.
During some NLC seasons, we are blessed with an early display in the month of May. Are seasons with multiple active nights in May generally better years with regard to the total number of active nights? For that matter, are years with many displays in August and September good years as well? To answer these questions, we refer to our NLC CAN AM data dating back to 1988, and also to the data from observations in Great Britain to 2006, as reported in a recent paper by Sheila Kirkwood, Peter Dalin, and A. Rechou.
Year # Active Nights Before Jun 1-2 # Active Nights After Jul 31-Aug 1 Total Active Nights
NLC CAN AM Britain NLC CAN AM Britain NLC CAN AM Britain
1988 0 4 4 2 38 35
1989 4 4 11 2 45 38
1990 1 3 4 0 35 24
1991 0 0 3 0 32 14
1992 0 0 0 0 12 14
1993 1 0 3 1 38 20
1994 1 2 7 1 35 32
1995 2 3 7 2 49 46
1996 2 2 1 2 24 45
1997 2 4 3 0 34 40
1998 2 0 1 2 18 27
1999 0 0 2 0 38 27
2000 1 2 9 3 35 32
2001 1 1 8 2 39 29
2002 2 2 5 0 30 25
2003 4 2 13 2 54 37
2004 0 0 8 0 50 28
2005 3 0 11 5 45 39
2006 0 1 10 3 47 47
2007 1 11 51
2008 0 8 47
Three notable things one can see in these data are: a) the NLC-quiet years of 1991-1992 in both North America and Britain revealed a complete lack of NLC in May, and in Britain, one can add 1990 and make a string of 3 straight years with no activity in August as well. b) on the other hand, the apparent upswing in activity in overall NLC activity starting in about 2003 is not necessarily heralded by many, or any, activity in the month of May, a case in point being 2004, with no sightings in May anywhere, yet with a robust total of 50 active nights in North America. c) the overall higher incidence of August-September in North America compared with Britain. This difference can be explained by the presence of high latitude sites in North America, like Baker Lake and Rankin Inlet, whose staff have caught displays far later in the season than is usually possible in Great Britain. One may argue that the high grand total of displays in North America in some years, notably 2003 and 2007, was due in part to the contribution of the large number of high latitude sightings in August (13 and 11, respectively). See the second photo for a beautiful example of one of these NLC displays recorded from a high latitude site.
The 2009 season marks the 10th anniversary of the huge NLC display of Jun 22/23, 1999, when several observers as far south as southern Colorado reported the phenomenon. Since that momentous night, the ensuing decade has had other instances of, for the most part, widely-observed midlatitude-encroaching displays:
Jun 30/Jul 1, 2000 - seen in UT, ND
Jul 2/3, 2001 – seen in UT, ND
Jun 27/28, 2003 – to OR
Jun 30/Jul 1, 2004 – a lone sighting over the Atlantic Ocean at 45N
Jul 9/10, 2005 – a lone sighting from DE, just below the 40th parallel
Jun 19/20 and Jul 3-4, 2007 – to WA and OR
Jul 3-4, 2008 to UT and Jul 6/7, 2008 to MI and southern ON
Notice that all these occurred in that critical ~20-night span consisting of the last ten nights in June and the first ten nights in July.
The latest graph on the AIM (Aeronomy of Ice in the Mesosphere) satellite shows 2008 data from the SOFIE (Solar Occultation for Ice Experiment) instrument. The graph suggests that the onset and the dropoff of NLC activity is pretty abrupt, occurring during the last 10 days in May and the last 10 days of August, respectively. There is also a nice video clip of NLC produced by the recent space shuttle launch; see the video at www.aim.hamptonu.edu/outreach/sts119.html.
All the best to our enthusiastic observers for the 2009 season!
Mark Zalcik, Coordinator, NLC CAN AM
First Photo: NLC display as seen from Glen Ullin, ND (46.8N) on Jun 13/14, 2008. Photo by Jay Brausch.
Second Photo: NLC from Iqaluit, NU (63.8N) on Aug 1-2, 2008. Photo by Kelly Otto.
===============================================
Posting the following with Mark Zalcik's permssion:
Tom
===============================================
QUICKSILVER
YEARLY NEWSLETTER OF NLC CAN AM
Vol. 17 2009
Hello NLC observers in 2009!
The prevalent theory of NLC formation is that the greenhouse gas methane is given off by various sources on the Earth and diffuses up into the atmosphere, as high as the stratosphere, where it is broken down by sunlight into various compounds, including water vapour, which then continues traveling upward until it reaches the mesosphere at the 80km level, where it accretes upon meteoric dust and large ions.
Current concentrations of methane are nearly 1800ppb, with 18% of total greenhouse gas radiative forcing due to methane, which is 22 times more effective than carbon dioxide in absorbing long-wave radiation. The concentration of methane in the atmosphere is determined by the balance between emissions from Earth's surface and, in turn, destruction of methane by hydroxyl free radicals in the troposphere, hydroxyl free radicals being the highly reactive form of the hydroxide ion; it is reactive because it contains an unpaired electron.
Measurements of atmospheric methane in the latter half of the 20th century indicated persistent increases in concentrations, followed by a period from about 1999-2006 when levels remained constant. But near the beginning of 2007, concentrations were once again on the rise. Scientists, led by Matt Rigby, pointed out that observed concentrations of hydroxyl free radicals had dropped, resulting in the methane increase, with a bias toward the northern hemisphere.
In arctic areas, the natural release of methane is easily detectable. In early winter, holes can be seen in lake ice; these holes are made from methane bubbling from the permafrost beneath the lake. Permafrost of course is an even more noticeable source of carbon, with some estimates indicating some 700-950 pentagrams of carbon are harboured in the top 1-25m of permafrost.
During some NLC seasons, incidences of consecutive-night, equatorward-moving “storms” are witnessed, and a notable one occurred in 2008. On the night of Jun 12/13, over half a dozen observers in Alberta glimpsed a widespread NLC display, and the automated camera at the Athabasca University Geophysical Observatory detected it, too, with the first sighting in bright twilight at 0525 UT and the last close to dawn at 0950 UT. From Edmonton, the NLC rose to 10-15 degrees elevation, with the most prominent type being bands. The following night, the 13/14, the only report of NLC anywhere in the network was from way down south in North Dakota, where Jay Brausch saw and photographed NLC to nearly 25 degrees elevation in morning twilight (see picture). Was the activity of Jun 12/13 / 13/14 one of those instances of NLC hovering over the subarctic on the first night, and then on the next night drifting southward so that they can be seen from way down in the northern US? Interestingly, there were no reports of NLC on the 14/15, but on the following night, the 15/16, as if on cue, the phenomenon started its commonly-observed one month peak run in the boreal skies.
During some NLC seasons, we are blessed with an early display in the month of May. Are seasons with multiple active nights in May generally better years with regard to the total number of active nights? For that matter, are years with many displays in August and September good years as well? To answer these questions, we refer to our NLC CAN AM data dating back to 1988, and also to the data from observations in Great Britain to 2006, as reported in a recent paper by Sheila Kirkwood, Peter Dalin, and A. Rechou.
Year # Active Nights Before Jun 1-2 # Active Nights After Jul 31-Aug 1 Total Active Nights
NLC CAN AM Britain NLC CAN AM Britain NLC CAN AM Britain
1988 0 4 4 2 38 35
1989 4 4 11 2 45 38
1990 1 3 4 0 35 24
1991 0 0 3 0 32 14
1992 0 0 0 0 12 14
1993 1 0 3 1 38 20
1994 1 2 7 1 35 32
1995 2 3 7 2 49 46
1996 2 2 1 2 24 45
1997 2 4 3 0 34 40
1998 2 0 1 2 18 27
1999 0 0 2 0 38 27
2000 1 2 9 3 35 32
2001 1 1 8 2 39 29
2002 2 2 5 0 30 25
2003 4 2 13 2 54 37
2004 0 0 8 0 50 28
2005 3 0 11 5 45 39
2006 0 1 10 3 47 47
2007 1 11 51
2008 0 8 47
Three notable things one can see in these data are: a) the NLC-quiet years of 1991-1992 in both North America and Britain revealed a complete lack of NLC in May, and in Britain, one can add 1990 and make a string of 3 straight years with no activity in August as well. b) on the other hand, the apparent upswing in activity in overall NLC activity starting in about 2003 is not necessarily heralded by many, or any, activity in the month of May, a case in point being 2004, with no sightings in May anywhere, yet with a robust total of 50 active nights in North America. c) the overall higher incidence of August-September in North America compared with Britain. This difference can be explained by the presence of high latitude sites in North America, like Baker Lake and Rankin Inlet, whose staff have caught displays far later in the season than is usually possible in Great Britain. One may argue that the high grand total of displays in North America in some years, notably 2003 and 2007, was due in part to the contribution of the large number of high latitude sightings in August (13 and 11, respectively). See the second photo for a beautiful example of one of these NLC displays recorded from a high latitude site.
The 2009 season marks the 10th anniversary of the huge NLC display of Jun 22/23, 1999, when several observers as far south as southern Colorado reported the phenomenon. Since that momentous night, the ensuing decade has had other instances of, for the most part, widely-observed midlatitude-encroaching displays:
Jun 30/Jul 1, 2000 - seen in UT, ND
Jul 2/3, 2001 – seen in UT, ND
Jun 27/28, 2003 – to OR
Jun 30/Jul 1, 2004 – a lone sighting over the Atlantic Ocean at 45N
Jul 9/10, 2005 – a lone sighting from DE, just below the 40th parallel
Jun 19/20 and Jul 3-4, 2007 – to WA and OR
Jul 3-4, 2008 to UT and Jul 6/7, 2008 to MI and southern ON
Notice that all these occurred in that critical ~20-night span consisting of the last ten nights in June and the first ten nights in July.
The latest graph on the AIM (Aeronomy of Ice in the Mesosphere) satellite shows 2008 data from the SOFIE (Solar Occultation for Ice Experiment) instrument. The graph suggests that the onset and the dropoff of NLC activity is pretty abrupt, occurring during the last 10 days in May and the last 10 days of August, respectively. There is also a nice video clip of NLC produced by the recent space shuttle launch; see the video at www.aim.hamptonu.edu/outreach/sts119.html.
All the best to our enthusiastic observers for the 2009 season!
Mark Zalcik, Coordinator, NLC CAN AM
First Photo: NLC display as seen from Glen Ullin, ND (46.8N) on Jun 13/14, 2008. Photo by Jay Brausch.
Second Photo: NLC from Iqaluit, NU (63.8N) on Aug 1-2, 2008. Photo by Kelly Otto.
===============================================
