Atmospheric Boundary Layer Science

What is the Atmospheric Boundary Layer?

We live above the land’s surface. Although this is not something we often ponder, when looked at in another way, we can think of ourselves as living in the lowest part of the atmosphere. Atmospheric pressure at sea level is as much as 1000 hPa, but this means for every 1m2 there is 10t(104kg) of air above. The atmospheric boundary layer refers to the atmospheric layer extending from the atmosphere’s lowest point - where it meets the earth’s surface – to an altitude of approximately 1-2km.

Figure 1. Conceptual Diagram of the Atmospheric Boundary Layer

Role of the Atmospheric Boundary Layer

Cloud formation, convective activity, and large and small-scale flows including everything from turbulence at a spatial scale of a few meters, to large atmospheric fluctuations on the order of a thousand kilometers occur in the atmosphere included in the atmospheric boundary layer. Sunlight provides the energy source causing these, but much of this passes through the transparent atmospheric layer and gets absorbed once by the earth’s surface (land and sea). The earth’s surface then emits energy into the atmosphere in the form of sensible heat (direct heating), latent heat (heat associated with the evaporation and condensation of water vapor), and long-wave radiation (infrared rays). The sun’s energy is passed into the atmosphere this way, but the first area to receive this energy is the layer closest to the earth’s surface: the atmospheric boundary layer. Also, anthropogenic emission of Co2 occurs first in this atmospheric boundary layer. In this way, the atmospheric boundary layer plays an important role in acting as a pipeline between earth’s surface and the atmosphere as a whole.

The atmospheric boundary layer is also an area where we carry out our lives. The heat, cold, humidity, asthma, and allergies we experience due to air pollution, the dispersal of pollen, and so forth, are all due to atmospheric boundary layer conditions.

Figure 2. Visualization of a daytime atmospheric boundary layer.

The turbid area below cumulus clouds is the atmospheric boundary layer. Because the water vapor and pollutants emitted from earth’s surface are trapped in this layer, there are clear differences here from the cleaner air higher above (the group of buildings seen at the bottom is central Sapporo).

Atmospheric Boundary Layer Research

Given the situation, it is important to understand the state of the atmospheric boundary layer and its spatio-temporal changes, but in reality this is not a simple task. This is because the atmospheric boundary layer, as the name states, forms the “boundary” between the atmosphere and earth’s surface and is hence influenced from both sides. Influence from the earth’s surface is particularly important for the following: the large diurnal temperature differences between day and night; differences between land and ocean; and difference in energy emission due to different land cover such as desert, vegetation, snow and ice, urban areas, and farmland, strongly influencing the condition of atmospheric boundary layer. Therefore, it is necessary to continue researches not limited to physics of atmosphere, but in wide range of academic fields including physiology and ecology of plant, snow and ice properties, and soil hydrology.

Figure 3. Balloon-based Observations of a Nighttime Atmospheric Boundary Layer.

At night, it earth’s surface cools due to the net emission of long-wave radiation, cooling the atmosphere. By being colder than the atmosphere, the earth’s surface takes the heat from the atmosphere. This results in the formation of a stable boundary layer where air temperature is lower the closer it is to the earth’s surface. By dangling several types of sensors from balloons, like the ones in the photo, and letting the balloons rise into the atmosphere above, we can observe the nighttime atmospheric boundary layer.

Figure 4. Observations of Snow Cover Radiation Balance

Snow cover has strong adiabatic characteristics because it traps large amounts of air in the gaps between its ice particles. For that reason, only the surface of accumulated snow experiences strong cooling and lower temperatures at nighttime, thus easily stealing heat from the atmosphere. In addition, because snow reflects a large proportion of sunlight during the daytime, it does not deliver this energy into the atmosphere. As a result, it is easy for the temperature of snow-covered land to drop. By observing the radiation budget, it is possible to clarify these kinds of characteristics of snow cover.


We conduct atmospheric boundary layer research in several groups. Other instructors and groups doing atmosphere research are also, more or less, conducting atmospheric boundary layer research (observations, modeling, development of observation equipment).