In my apartment, we have a thermometer which reports the temperature. We feel it’s accurate because it jives with another thermometer, and it’s a brand-name high tech thermometer.
When I wake up before the sun rises, I often note the temp on the thermometer. As I feel chilly or warm, I’ll check the temp again and see if it’s just me, or if I need to adjust the temp in the room.
I’ve noticed something odd recently - the temperature seems to go DOWN right after the sun rises, not up. I can think of some “explanations” but none of them sound very scientific.
So if I notice it says 71.2, about 20 minutes before the sun rises… about 10 minutes after the sun rises, it will read 68.9.
If this just happened once or twice, I would figure it’s a fluke of air temperature movement in the room, but I’ve noticed it almost every day for the last two weeks. Today it was 69 before the sun came up, and 66 after. Yesterday it was 69 before, 67 after. The day before, 70 before, 68 after.
So what makes the temperature inside the apartment drop 2-3 degrees after the sun rises?
We have no windows open, no air conditioner or heater running, no one is taking a hot or cold shower. It’s just one or two people moving around the apartment, maybe turning on a computer.
I suspect it’s the same reason that the hottest part of the day is 4pm, not Noon. The temperature is lagging behind the main heat source (the sun), because of thermal mass, and because the outside temperature is still colder than the inside, even after the sun has been up for a while.
Also, it sounds like you’re in an urban setting. There could be other, more immediately localized heat sources besides the sun (heating from other apartments, outlet ducts, lighting, car/truck exhaust, etc.) that can affect your sensor by a few degrees. These can add some +/- to the ambient temperature where your sensor is located.
In a manner similar to the one described by the above poster, they might also have ‘shut down’ for awhile and you’re seeing the lag in your readings.
How do you adjust the temperature if you don’t have a heater running? Do you really not have any heat? If you actually do have central heating with a thermostat, does the sun shine on it in the morning by any chance?
It it true that the lowest temperature of the day tends to be just after sunrise. When the sun is at a low angle the incoming “heat” is still less than that being radiated off into space, so it continues getting colder. Your indoor temperature dropping 2-3 degrees in 30 minutes makes me think something else is going on as well though.
Any heat that the earth and the surrounding environment would have absorbed during the day is usually dissipated about an hour before sunrise. Your home would be affected by this unless your had good insulation, weatherstripping and double-paned windows.
Thermal conductivity (how well something conducts heat). Thermal mass (how much heat something can store). And finally temperatures that vary with time.
The very short answer is that the cold that is outside takes some time to make its way from outside of the house to the inside of the house.
Lets say it takes an hour for a “packet” of cold to “work” its way from the outside to the inside. If the nightly temp drops about 2 degrees an hour and it is coldest at sunrise or a bit after, then about an hour later the temp of the inside of the house is going to bottom out at about 2 degrees lower than it was when the sun rose.
At the very least, this assumes that there is no heater in the house, or if there is one it is running at a constant output the whole time.
I’ve been in houses and apartments where this effect is quite noticeable.
We have a/c and heater, they just aren’t on at the time, so they aren’t a factor. If we need to change the temp, we can do the normal stuff - open or close windows, turn on a ceiling or portable fan, run heater or a/c.
But in the morning when it’s 71 degrees, I don’t feel it’s necessary to adjust the temp. Then the sun rises and it drops to 68 degrees and I’m going, “OK, now that the sun is up, turn on the heater??”
If it really changes that quickly once the sun comes up, then I’d go with the poster who theorized that the sunlight coming through the window is driving a convective current, somehow. Does it really drop 3 degrees in 10 minutes?
3 in 10-30 minutes - I don’t really watch the thermometer as it happens. I just notice that after some time goes by, the temperature consistently goes down instead of up.
I have heard several TV weatherfolk mention this giving various explanations. And since there isn’t one answer given and the usual lack of science knowledge among such people is low, I don’t know what to believe (or than it is a real effect).
Right before sunrise (where you are) it IS sunrise just over the horizon. There, the sun is coming up and begining to warm. This causes an outward expansion of air which in turn disturbs the air in areas around it (where you are) This disturbance stirs the air up, causing air close to the surface, which has been able to stay slightly warmer (due to earth temperature, industry, nearby bodies of water, condensation of dew etc, all of which release small amounts of energy to their environment) to mix with air further from the surface, which didn’t have these warming influences. Now some of that colder “high” air is on the surface, so the saurface air temperature drops slightly.
Me: So you dig, air on the surface is warmer due to earth temperature, industry, houses/buildings, nearby bodies of water, condensation of dew etc, all of which release small amounts of energy to their environment. This air gets mixed up with air higher up, which is colder, when the suns rays start to approach your region.
The question was why does the temperature drop shortly aftersunrise, not before, and also the op was referring to his indoor temperature. BTW, the outside temps do drop shortly after sunrise for the reason explained by beowulff.
I’ll just note that the OP’s data don’t necessarily imply a cooling after sunrise, per se. It could be, for instance, that it’s 71.2 20 minutes before, and then continues to cool off to, say, 68.5 in the time before sunrise, and that then once the sun rises, it starts warming up again, reaching 68.9 by 10 minutes after sunrise.
Also, I have no doubt that the thermometer is accurate, but that does not necessarily imply that it’s precise, and unless it’s something intended for precision laboratory use, I wouldn’t pay too much attention to the digits past the decimal point.
I’m not talking about a tenth of a degree or so. Sometimes it may drop several degrees right after sunrise. In Chicago, it’s so cold you may not pay any attention to that. But here in the “balmy” south, I can tell the drop in temp even after sunrise. You can check that in the newspaper comparing the sunrise time and when the temp finally starts to climb; however, it may be warmer at eight in the morning, about 45 minutes after sunrise. Sometimes there is a notable drop right before sunrise and it continues to drop after sunrise.
Evaporation is a cooling process.
As the sun is preparing to rise over the horizon there is an interaction of two diverse temperatures cool and warm.These two temp differences coming into contact causes any moisture to evaporate which always lowers the temperature until equalibrium is reached.
Evaporative coolers are a good example. Warm air flowing over cool water evaporates the water and drives temperature down. to cool even more the cool air blown over a warmer body(you) evaporates the slight moisture on your skin and you cool down further through this evaporative process.
Of course your body “wicks” moisture out of the skin into the atmosphere contineously,so the more wind/cooling, keeps you cool
+1 on this being part of the answer. The first heat from the sun evaporates moisture on outdoor surfaces. The change in state from liquid to gas requires energy and it causes an initial drop in temperature. The earth is also still radiating more heat than the sun is pumping in. The outdoor temperature lags behind the sun and the indoor temp follows on from that.