Hi Nick,

Design day is the day at which design or peak load calculations are done.
It is not a very big deal to have climate as Tropical as it would be
between the Tropic of Cancer to Tropic of Capricorn.
In the midst of which there is equator.
It is mere a margin to show that the Tropical shows that the location is in
the margin of 23.5 degree south of equator to 23.5 degree North of the
equator.

The Mid-latitude can be the location near to the equator as it is the
middle or zero degree latitude of the earth.

The Subarctic region is the space near and hence off the polar to sub polar
region.

The thing that you are missing is the temperate zone which is in between
the 23.5 to 66.5 degree region.

The climate is very hot and warm in tropical region.
The climate is of mild nature in the temperate zone and very cold in the
sub arctic region.
As the solar angle declines away from the equator to the pole.
The solar angle is very less at polar and sub polar region and hence very
cold climate. The solar angle is directly over the head in the equator
region for major part of the year. Hence a sign of mid latitude as it is in
the midst of the globe.

*Thanks,*
Sharad.

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