28% difference in irradiance, shouldn't poles be symmetric?

[jh-deepmap]

When I look at 80N 0E at the summer solstice vs 80S 0E at the winter solstice, I get 746 vs 955 W/m^2, which seems weird.

Fri Dec 21 12:00:00 2018 +0000 Winter solstice at 80S: 33.4563051296 deg 955.544296665 W/m^2 distance= 0.983705043957
Thu Jun 21 12:00:00 2018 +0000 Summer solstice at 80N: 33.4587699932 deg 746.293140683 W/m^2 distance= 1.01623557581

I iterated around those times and verified that the sun is at the same elevation and that it's the local maximum, and even checked the earth-sun distance. Neither of those seem like they should account for such a large difference in irradiance. Are you modeling the ozone hole or something?

Test code:

from pysolar import solar
from pysolar import solartime
import datetime

def get_jme(when):
  jde = solartime.get_julian_ephemeris_day(when)
  jce = solartime.get_julian_ephemeris_century(jde)
  jme = solartime.get_julian_ephemeris_millennium(jce)
  return jme

winter_solstice = datetime.datetime(2018, 12, 21, 12, 0, tzinfo=datetime.timezone.utc)
solar_angle = solar.get_altitude(-80, 0.0, winter_solstice)
irradiance = solar.radiation.get_radiation_direct(winter_solstice, solar_angle)
distance = solar.get_sun_earth_distance(get_jme(winter_solstice))

print(winter_solstice.strftime("%c %z"), "Winter solstice at 80S:", solar_angle, "deg", irradiance, "W/m^2", "distance=", distance)

summer_solstice = datetime.datetime(2018, 6, 21, 12, 0, tzinfo=datetime.timezone.utc)
solar_angle = solar.get_altitude(80, 0.0, summer_solstice)
irradiance = solar.radiation.get_radiation_direct(summer_solstice, solar_angle)
distance = solar.get_sun_earth_distance(get_jme(summer_solstice))

print(summer_solstice.strftime("%c %z"), "Summer solstice at 80N:", solar_angle, "deg", irradiance, "W/m^2", "distance=", distance)

[pingswept]

That does seem weird. To investigate more, I'd recommend looking at the elements of get_radiation_direct, which can be found here: https://github.com/pingswept/pysolar/blob/master/pysolar/radiation.py#L43

[jh-deepmap]

winter_solstice = datetime.datetime(2018, 12, 21, 12, 0, tzinfo=datetime.timezone.utc)
summer_solstice = datetime.datetime(2018, 6, 21, 12, 0, tzinfo=datetime.timezone.utc)
radiation_direct = radiation.get_radiation_direct(winter_solstice, -80)
print(radiation_direct)
radiation_direct = radiation.get_radiation_direct(summer_solstice, -80)
print(radiation_direct)
radiation_direct = radiation.get_radiation_direct(winter_solstice, 80)
print(radiation_direct)
radiation_direct = radiation.get_radiation_direct(summer_solstice, 80)
print(radiation_direct)

Yields:

0.0
0.0
1069.24796579
880.467313503

[jh-deepmap]

Adding debug prints to that function:

def get_radiation_direct(when, altitude_deg):
# from Masters, p. 412
if int(altitude_deg) <= 0:
return 0.0
day = when.utctimetuple().tm_yday
print("Day:", day)
flux = get_apparent_extraterrestrial_flux(day)
print("Flux:", flux)
optical_depth = get_optical_depth(day)
print("Depth:", optical_depth)
air_mass_ratio = get_air_mass_ratio(altitude_deg)
print("Air mass ratio:", air_mass_ratio)
return flux * math.exp(-1 * optical_depth * air_mass_ratio)

Day: 355
Flux: 1233.59798527
Depth: 0.1408073447
Air mass ratio: 1.01542661189
1069.24796579
Day: 172
Flux: 1086.52897313
Depth: 0.20709587356
Air mass ratio: 1.01542661189
880.467313503