It is a photograph after 2 days when the watering was done all together in spite of winter.
The following two photographs
The plant pot of the completely weather-beaten place.
The plant pot under the eaves.
If it rains even if it is under the eaves, it is a place that becomes water-soak according to the wind.
There are not fluctuated the temperatures, because it puts two plant pots on the place of about one meter.
Why is it different?
Is it frost?
Frost is the solid deposition of water vapor from saturated air.
If a solid surface is chilled below the dew point of the surrounding air and the surface itself is colder than freezing, frost will form on the surface. Frost consists of spicules of ice which grow out from the solid surface. The size of the crystals depends on time, temperature, and the amount of water vapor available. Based on wind direction, "Frost arrows" might form.
In general, for frost to form the deposition surface must be colder than the surrounding air. For instance frost may be observed around cracks in cold wooden sidewalks when moist air escapes from the ground below. Other objects on which frost tends to form are those with low specific heat or high thermal emissivity, such as blackened metals; hence the accumulation of frost on the heads of rusty nails. The apparently erratic occurrence of frost in adjacent localities is due partly to differences of elevation, the lower areas becoming colder on calm nights. It is also affected by differences in absorptivity and specific heat of the ground which in the absence of wind greatly influences the temperature attained by the superincumbent air.
From Wikipedia "http://en.wikipedia.org/wiki/Frost".
When easily explaining
1. A potting compost becomes cold.
2. A certain atmospheric steam is frozen near potting compost.
3. 2 is repeated.
We say "Frost falls from the sky toward ground" in Japan.
However, it is actually what freezes sequentially from ground.
If frost is not falls from the sky toward ground, eaves are unrelated.
But the plant pot under the eaves is not frozen.
About the radiational cooling.
Radiative cooling is the process by which a body loses heat by radiation. In the case of the earth-atmosphere system it refers to the process by which long-wave (infra red) radiation is emitted to balance the absorption of short-wave (visible) energy from the sun.
The exact process by which the earth loses heat is rather more complex than often portrayed. In particular, convective transport of heat, and evaporative transport of latent heat are both important in removing heat from the surface and redistributing it in the atmosphere. Pure radiative transport is more important higher up. Diurnal and geographical variation further complicate the picture.
The large-scale circulation of the Earth's atmosphere is driven by the difference in absorbed solar radiation per square meter, as the sun heats the Earth more in the Tropics, mostly because of geometrical factors. The atmospheric and oceanic circulation redistributes some of this energy as sensible heat and latent heat partly via the mean flow and partly via eddies, known as cyclones in the atmosphere. Thus the tropics radiate less to space than they would if there were no circulation, and the poles radiate more; however in absolute terms the tropics radiate more energy to space.
Radiative cooling is commonly experienced on cloudless nights, when heat is radiated into space from the surface of the Earth, or from the skin of a human observer. The effect is well-known among amateur astronomers, and can personally be felt on the skin of an observer on a cloudless night. To feel the effect, one compares the difference between looking straight up into a cloudless night sky for several seconds, to that of placing a sheet of paper between one's face and the sky. Since outer space radiates at about a temperature of 3 kelvins (-270 degrees Celsius or -450 degrees Fahrenheit), and the sheet of paper radiates at about 300 kelvins (room temperature), the sheet of paper radiates more heat to one's face than does the darkened cosmos. The effect is blunted somewhat by Earth's surrounding atmosphere which also traps heat. Note that it is not correct to say that the sheet "blocks the cold" of the night sky; instead, the sheet is literally warming your face, just like a camp fire warms your face; the only difference is that a campfire is several hundred degrees warmer than a sheet of paper, just like a sheet of paper is several hundred degrees warmer than the deep night sky.
From Wikipedia "http://en.wikipedia.org/wiki/Radiative_cooling".
As for the plant pot of the weather-beaten place, an electromagnetic wave of the potting compost is effused in preparation for outer space, and temperature of the potting compost deteriorates.
As for the plant pot of under the eaves, a temperature fall of the potting compost shrinks by the electromagnetic wave which the wall and the eaves emit.
It is a little difference whether freeze or do not freeze, it is a turning point.
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