TM 5-852-1/AFR 88-19, Volume 1
CHAPTER 2
ARCTIC AND SUBARCTIC REGIONS
structures, the ratios of design to mean indexes
2-1.
Introduction
determined at the closest stations that do have 30 years
a. The Arctic and Subarctic may be defined in
of record may usually be employed for estimating such
several different ways, depending on whether they are
design indexes at stations that have means based on at
looked at from the point of view of astronomy, botany,
least 10 years of record.
physics, climatology, ocean navigation or other
specialized field.
For engineering, the Arctic and
2-3.
Precipitation snow cover and snow loads
Subarctic are best defined on basis of the prevailing air
temperature conditions.
Definitions based on air
the Arctic, much of it falling as snow. Considerably
temperature are given in paragraphs 1-4a(l) and 1-4a(2).
Figure 2-1 shows the limits of the Arctic and Subarctic in
that are under the influence of maritime storm paths. TM
accordance with these definitions, together with the
852-7/AFM 88-19, Chap. 7 presents hydrologic criteria,
northern limit of trees.
b. Climatic data for all stations that report to
together with general information on icing and special
design considerations, for arctic and subarctic
the U.S. National Weather Service are available from
conditions. Figure 2-5 shows mean monthly and annual
the U.S. Department of Commerce, National Weather
precipitation at selected stations.
Records Center, Asheville, North Carolina. In addition,
b. Icing on structures, vehicles and aircraft can
climatic data for a large number of sites are given in TM
be a serious problem in some parts of the Arctic and
5-785/NAVFAC P-89/AFM 8829. For foreign countries,
Subarctic, particularly in coastal areas near open water.
attempts should be made to obtain climatic data from
c. Snow cover may be a factor in planning
their respective national climatic centers. Department of
Defense agencies should request additional climatic
field activities. Figures 2-6 and 2-7 provide measures of
information through the U.S. Air Force Environmental
the snow cover season. Over large areas of the Arctic
Technical Applications Center (ETAC), Scott Air Force
and Subarctic the mean depth of snow at the end of the
Base, Illinois. Included in data obtainable through ETAC
month with maximum seasonal snow depth may not
are weather records for all military airfields.
exceed about 2 to 2'1/ feet. For some areas the value
c. Climatological, ground temperature and soil
may be as little as about 10 inches, and for others it may
data have been obtained from the 21 locations in Alaska
be several feet. Absolute maximum values may exceed
and Canada that are shown in figure 2-2.
the mean by about half.
d. Detailed records for Canadian observation
d. Extreme local variations precluded state-
stations are available from Atmospheric Environment
wide mapping of ground snow loads for Alaska. Design
Service, Department of the Environment Canada,
snow loads for specific sites should only be adopted after
Toronto.
consideration of local conditions. Maximum snow loads
e. Some specific features of these regions of
may vary not only with snow cover depths but also with
regional and seasonal variations in snow cover density.
significance to engineering are outlined in the remainder
The general variation of maximum snow load on the
of this chapter.
ground in Canada is illustrated in figure 2-8. Differences
in elevation and in topographic position, as well as details
2-2.
Temperature conditions
of the engineering feature itself, can produce substantial
a. As may be seen in figures 2-3 and 2-4,
differences in effective maximum snow loads.
temperatures decrease generally from south to north,
although not strictly according to latitude. On both
2-4.
Ice cover
continents, the lowest mean annual temperature is about
The freezing of lakes, rivers and coastal waters in winter
5F. Appendix A presents some general information
can be a major controlling factor in the scheduling and
about freezing and thawing index data from the two
effectiveness of field activities in the Arctic and
continents.
Subarctic. Waterways that can be used for boats or
b. Air temperature records for some arctic and
float-equipped aircraft in the summer become unusable
subarctic stations may not be of sufficient duration to
for these vehicles when freezeup starts in the period of
permit determination of design freezing or thawing
September to November. Several weeks are then
indexes on the basis of 30 years of record. For
required before the ice becomes thick enough to support
pavement design, as explained in paragraphs 1-4c(6)
other types of vehicles. During the winter, ice surfaces
and 14c(7), the extreme values in 10 years of record
can often be extremely valuable as aircraft
may be used. For foundations of average permanent
2-1