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Post by Morningrise on May 16, 2020 23:45:43 GMT -5
Does a particular sun angle have the exact same intensity of UV radiation at different latitudes, and if not are there other latitude-dependent factors that can affect solar intensity?
I ask because I’ve been to the tropics in winter a couple of times, in places/times where the peak sun angle was in the mid-40s (roughly equal to late August/early September or early/mid April in Saskatoon), and I always felt like that same sun angle was much stronger in the tropics. For instance there was a time where I stayed out a little too long one morning (still a couple hours before peak sun angle) and got a pretty decent tan from that, whereas I would never normally get any kind of tan from being out at that time of day in that sun angle in Saskatoon.
So is a 45 degree sun angle in tropics stronger than one at high latitudes? Or are there other factors at play here?
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Post by AJ1013 on May 16, 2020 23:49:51 GMT -5
Does a particular sun angle have the exact same intensity of UV radiation at different latitudes, and if not are there other latitude-dependent factors that can affect solar intensity? I ask because I’ve been to the tropics in winter a couple of times, in places/times where the peak sun angle was in the mid-40s (roughly equal to late August/early September or early/mid April in Saskatoon), and I always felt like that same sun angle was much stronger in the tropics. For instance there was a time where I stayed out a little too long one morning (still a couple hours before peak sun angle) and got a pretty decent tan from that, whereas I would never normally get any kind of tan from being out at that time of day in that sun angle in Saskatoon. So is a 45 degree sun angle in tropics stronger than one at high latitudes? Or are there other factors at play here? Generally higher latitudes have equal or stronger UV rays at the same sun angle as tropical latitudes. This is because, generally, the ozone layer is thinner closer to the poles. You may have felt that you tanned more at tropical latitudes than in Saskatoon despite identical sun angles but, imo, this is likely a product of tropical locations being much warmer at a time that would get 45* sun angles than saskatoon encouaging you to expose more skin that generally gets less sun and, additionally, amplifying how burned you feel by increasing skin flushing due to bodily responses to heat. |
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Post by Morningrise on May 17, 2020 11:29:16 GMT -5
Huh, very interesting, I had no idea about the ozone thing.
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Post by nei on May 17, 2020 12:12:24 GMT -5
Does a particular sun angle have the exact same intensity of UV radiation at different latitudes, and if not are there other latitude-dependent factors that can affect solar intensity? I ask because I’ve been to the tropics in winter a couple of times, in places/times where the peak sun angle was in the mid-40s (roughly equal to late August/early September or early/mid April in Saskatoon), and I always felt like that same sun angle was much stronger in the tropics. For instance there was a time where I stayed out a little too long one morning (still a couple hours before peak sun angle) and got a pretty decent tan from that, whereas I would never normally get any kind of tan from being out at that time of day in that sun angle in Saskatoon. So is a 45 degree sun angle in tropics stronger than one at high latitudes? Or are there other factors at play here? Generally higher latitudes have equal or stronger UV rays at the same sun angle as tropical latitudes. This is because, generally, the ozone layer is thinner closer to the poles. You may have felt that you tanned more at tropical latitudes than in Saskatoon despite identical sun angles but, imo, this is likely a product of tropical locations being much warmer at a time that would get 45* sun angles than saskatoon encouaging you to expose more skin that generally gets less sun and, additionally, amplifying how burned you feel by increasing skin flushing due to bodily responses to heat. I thought the ozone layer didn't become thin until the poles, temperate latitudes are about he same as tropics. Most of the heat feel from the sun is from visible and infrared; UV is only 10% or so the sun's energy, so the heating feel won't have much to do with ozone blocking UV. |
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Post by AJ1013 on May 17, 2020 12:30:48 GMT -5
Generally higher latitudes have equal or stronger UV rays at the same sun angle as tropical latitudes. This is because, generally, the ozone layer is thinner closer to the poles. You may have felt that you tanned more at tropical latitudes than in Saskatoon despite identical sun angles but, imo, this is likely a product of tropical locations being much warmer at a time that would get 45* sun angles than saskatoon encouaging you to expose more skin that generally gets less sun and, additionally, amplifying how burned you feel by increasing skin flushing due to bodily responses to heat. I thought the ozone layer didn't become thin until the poles, temperate latitudes are about he same as tropics. Most of the heat feel from the sun is from visible and infrared; UV is only 10% or so the sun's energy, so the heating feel won't have much to do with ozone blocking UV. Morningrise was talking about tanning though, which is directly correlated with UV. Regarding ozone it’s, as I said in my post, usually about the same in temperate areas as in the tropics, meaning UV is roughly equal at equivalent sun angles. However, depending on the season, particularly in the southern hemisphere, ozone can be thinner in populated temperate latitudes. @logan5 has talked about this being present at times in NZ. |
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Post by Babu on May 18, 2020 11:08:01 GMT -5
Does a particular sun angle have the exact same intensity of UV radiation at different latitudes, and if not are there other latitude-dependent factors that can affect solar intensity? I ask because I’ve been to the tropics in winter a couple of times, in places/times where the peak sun angle was in the mid-40s (roughly equal to late August/early September or early/mid April in Saskatoon), and I always felt like that same sun angle was much stronger in the tropics. For instance there was a time where I stayed out a little too long one morning (still a couple hours before peak sun angle) and got a pretty decent tan from that, whereas I would never normally get any kind of tan from being out at that time of day in that sun angle in Saskatoon. So is a 45 degree sun angle in tropics stronger than one at high latitudes? Or are there other factors at play here? Generally higher latitudes have equal or stronger UV rays at the same sun angle as tropical latitudes. This is because, generally, the ozone layer is thinner closer to the poles. You may have felt that you tanned more at tropical latitudes than in Saskatoon despite identical sun angles but, imo, this is likely a product of tropical locations being much warmer at a time that would get 45* sun angles than saskatoon encouaging you to expose more skin that generally gets less sun and, additionally, amplifying how burned you feel by increasing skin flushing due to bodily responses to heat. This is actually false. The equator tends to have much much thinner ozone than higher latitudes. Umeå has almost twice the ozone thickness on average as the equator. |
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Post by Babu on May 18, 2020 11:12:15 GMT -5
Ozone thickness for today:  UV radiation depletes ozone, which is why spring has thicker ozone on average and autumn stronger, which is why the equatorial ozone band is skewed towards the southern hemisphere. |
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Post by Ethereal on May 1, 2022 5:53:49 GMT -5
Not sure about the tropics, but Sydney has sustained, higher UV rays in the summer than Phoenix, Cairo and Baghdad.
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Post by alex992 on May 1, 2022 9:54:05 GMT -5
Could also be a case that you're coming from much higher latitudes in winter, so you're more used to a low sun angle, so a 45 degree sun angle feels comparatively strong. While in late August / early September in Saskatoon you're just coming out of the time of year with 50-55+ degree sun angles, so a 45 degree sun angle feels comparatively weak.
If anything, the same sun angle at higher latitudes will give off more solar radiation, due to much longer days at the same angle and more time spent near the peak sun angle because of slower sun path.
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Post by Donar on May 1, 2022 15:26:20 GMT -5
Received energy at the surface at the same sun angle and cloud conditions would still depend on atmosphere's optical depth, i.e. the amount and composition of aerosols and gaseous molecules. Aerosol OD especially is very variable in space and time, so a definite answer is difficult, though I would expect in general the optical depth (on a cloudless day) is higher in the tropics than in the mid-latitudes.
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