flat light

2014/12/17

Low Angles in High Latitudes

As we rapidly approach the calendar start of winter – the Winter Solstice occurring on December 21st this year at 14:03 AKST while the meteorological start to the season was December 1st – I once again find myself contemplating the boreal forest and the sky above its mix of birch and spruce trees.  I spend far too much time parked in front of a monitor but I do have a large window just three feet to my left which looks out from the second floor office into the immediate surroundings.  We still remain far short of snow with just 7.5 inches of snow pack and the temperatures have been see-sawing back and forth around the freezing point which is exceptionally warm.  All told this looks to be my second consecutive ‘winter that wasn’t’; while not happy with the prospect I am working to become more sanguine with this concept…maybe next year?

Yet there’s still a lot to marvel at in my new Alaskan home and one of those observations is the extremely low angle to the sunlight this time of year.  While out walking ‘the kidz’ yesterday early afternoon I was reflecting upon just how much the partly cloudy sky resembled an early sunrise or sunset; the underside of many of the Altocumulus stratiformis clouds of the mid-altitude cloud deck were orange and red while the few Cirrus intortus at a higher elevation were brilliant white tinged with fiery yellow against the azure sky.  I had to remind myself this was just 13:25 AKST and thus only a bit more than half way through our current 5 hour, 3 minute and 47 second direct sunlight period; according to my tables the solar ‘noon’ occurred at 12:56 AKST.  Although there were still many clouds on the western horizon when I could see it – the boreal forest really surrounds this area – the sun was indeed very low. Just how low is ‘low’?  Using NOAA’s Solar Position Calculator (http://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html) I calculated just 5.4 degrees above the horizon at 12:59 AKST.

This is extremely low; for comparison using Detroit (MI) on this same date and the same time (12:59 EST) I came up with an angle of 23.94 degrees.  No wonder this former Midwest boy thinks the sun is darn low up here!  Of course I was aware of this phenomenon as its fairly straightforward physics represented using geometry but to actually be standing on a shadowed, snow-covered back road surrounded by the immense and silent boreal forest while marveling the sun can hardly be seen even between the breaks in the trees really brings the concept home.  I know from previous experience that on the summer solstice a few hours later the sun will reach almost 52 degrees above the horizon; what a difference!

I’d heard many folks – mainly photographers – talk about ‘flat light’ and they often bemoaned its influence at the higher latitudes.  Only after I relocated up here did I come to understand just what flat light is and how it can negatively affect photographs.  The sunlight striking the higher latitudes in their winter season is forced to travel through a lot more atmosphere to reach the surface of the earth because of the curvature of the earth’s surface.  This helps create the lack of shadowing and an overall ‘softness’ to the resultant light which produces a dearth of real detail.  Thus many images taken under such circumstances lack a myriad of subtle visual clues the human eye uses to establish depth of field and hence a degree of three dimensionality to the picture.  I saw this many times when I first started shooting images up here although not until I actually relocated to ‘The Great Land’ did I really see this effect in winter shots.  My eyes and brain compensate for the loss of such cues when I’m just using my normal visual reception but these clues are not reproduced in an image and hence they often look two-dimensional and tending towards a lack of contrast and monochromatic.  As good as my eyes and brain are at dealing with this situation it becomes apparent to me when just walking around this area in the depth of winter; it seems as though everything is composed of either white (snow and birch trees), green (spruce trees) or black (shadows).  The sky will appear blue when clear but it is often overcast in winter and hence it is a shade of gray.   This can be somewhat disconcerting and I can easily see how trying to land aircraft on snow under such conditions causes crashes due to the loss of reference points.

Living in the higher latitudes remains endlessly fascinating to me as there is so much about these circumstances that is quite different from those found in the lower 48.  It often seems as though so many aspects are distorted and done so in the direction of exacerbation; I now more fully appreciate way Alaska is often referred to as a ‘land of extremes’.  I find the more I’m willing to look around me with an inquisitive eye the more I find that fascinates me in my new home.

Taken from my main floor this view is looking SSE across my property; further in the distance but not viewable is Question Lake

Taken from my main floor this view is looking SSE across my property; further in the distance but not viewable is Question Lake.  Notice the lack of depth and absence of any feeling of three dimensions…

2014/01/15

Higher Latitudes Mean Enhanced Everything..!

In my five and half months of living above 62 degrees north latitude I’ve learned many things regarding the effects that this location imposes upon daily life.  Without question the meteorological effects are more extreme and definitely more pronounced but so are other aspects such as light.  I recently experienced my first Winter Solstice above 62 degrees north latitude and it was definitely different from all those I experienced in the lower 48; the day was very short with not much light and a lot of darkness.  Now in the lower 48 I remember seeing almost no perceptible shift in the daylight until we were well into February and I am a sky watcher and hence more aware of such nuances.  However, up here, within two weeks I could definitely tell the daylight was increasing and that has continued to this writing.  We are currently adding 3 minutes and 30 seconds of daylight per day and it is very noticeable.  Yet this figure is the same regardless of where one is on the earth – okay, if you’re in the southern hemisphere then the daylight is decreasing but it’s still doing so by this same amount – so why is it so noticeable at higher latitudes yet becomes harder and harder to discern as one approaches the equator..?

My suspicion is it’s based upon the geometry of a sphere and one that’s tilted at roughly 23 degrees to the vertical in conjunction with the atmosphere.  I’ve never been good with mathematics in general and geometry in particular but I can imagine the earth as a roughly spherical object (if ya want to get picky I guess it’s closer to an egg shape…) tilted 23 degrees off the vertical axis and not just spinning but also orbiting the sun.  It’s the tilt that gives the earth its seasons; as it orbits the sun one of the two hemispheres (northern or southern) will at one point be closer to the sun – and hence have ‘summer’ – and at the opposite position in its orbit be tilted away from the sun and hence experience ‘winter’.  So far, so good…  Now, its known that the thickness of the atmosphere varies with location; it is thickest at the equator and slowly decreases as one moves towards the poles  This means that sunlight reaching the earth has to travel through different thicknesses of atmosphere to reach the surface.  The more atmosphere the light travels through the more diffuse it becomes; its scattered by all the various molecules in the atmosphere.  Therefore at lower latitudes incoming light travels through more atmosphere and is more scattered and hence more diffuse and so would appear to be ‘weaker’ than light striking the higher latitudes.  This could well account for the perceived slower shift to increasing daylight in the lower 48 as to up here; the more diffuse and ‘weaker’ light requires more time to finally begin to show a change where as in the higher latitudes the light is not scattered and diffused as much so smaller changes are more easily perceived by our eyes.  This also explains that phenomena of ‘flat light’ that photographers often speak to; it’s this same sharper, stronger light that traveled through less atmosphere.

Or at least this all sounds well and good; an interesting test would be to find a planet with the same tilt but no atmosphere to use as a baseline.  If this summation is correct the perceived increase/decrease of light on the planet without an atmosphere would appear to be the same regardless of one’s latitude.  It’s these kinds of situations I enjoy investigating; to me they are not immediately obvious yet they are undeniable.  Without question the less thick atmosphere produces some other effects at the higher latitudes; I suspect this is the reason I see such amazing barometric pressure swings up here.  Just this past Monday I saw a pressure reading of 28.88″ Hg (978.26 Mb) which is extremely low and would be something one might see in the eye of a medium strength hurricane in the lower 48 yet up here it was just low pressure; we did see a bit of snow along with it but no winds or other extreme weather.

It’s an interesting experience living in the higher latitudes; it makes me wonder what it would be like living at 80 degrees north latitude if not higher..?  I suspect I’ll never know as the farthest north piece of Alaska is around 71.5 degrees north latitude.  Still and all its fun to wonder…