南京大学：《大气环流》课程教学资源（课件讲稿）第二章大气环流的外部强迫（1/3）.pdf_大学文库

From the solar radiation... 授课教师：张洋 9 TOA surface energy budget SW ~ LW S(1 ↵) Long term, global average: SW(net) + LW(net) + LH +SH ~0 Energy and moisture budgets of the surface and atmosphere The planetary radiation budget has already been briefly discussed. We now consider the energy and moisture budgets of the Earth’s surface and the atmosphere. It is a shocking fact that we do not know enough about the globally averaged surface energy budget to do more than sketch rough annual mean values, as shown in Table 2.2. None of the numbers in the table is known to better than 20% accuracy. Of the 240 W m-2 that is absorbed by the Earth-atmosphere system, 176 W m-2 is absorbed by the Earth’s surface. Thus only about 240 - 176 = 64 W m-2 of solar radiation is absorbed by the atmosphere. That is only about 1/4 of the total solar radiation absorbed by the Earth-atmosphere system. It should be noted, however, that the partitioning of the absorbed solar radiation between the atmosphere and the Earth’s surface is currently a matter of some controversy. The surface receives a total (LW! + SW; see notation defined in Table 2.2) of 488 W m-2, which is given back in the form of LW", LH and SH. By far the largest of these is LW". Keep in mind that the oceans can transport energy from one place to another, so that the energy absorbed by the oceans is not necessarily given back in the same place where it is absorbed. Also, the large heat capacity of the upper ocean allows energy storage on seasonal time scales. In contrast, the continents cannot transport energy internally at a significant rate, and their limited heat capacity forces near energy balance, everywhere, on time scales longer than a few days (at most). Note that the net radiative heating of the surface, which amounts to 103 W m-2, is balanced primarily by evaporative cooling of the surface at the rate of 79 W m-2. As discussed below, moisture is of comparable importance in the energy budget of the atmosphere. The globally averaged energy budget of the atmosphere is shown in Table 2.3. Again, most of the numbers in Table 2.2 and Table 2.3 are only rough estimates. One interpretation of Table 2.3 is that the atmosphere sheds energy through infrared radiation at the rate required to Absorbed solar (SW) Downward infrared (LW!) Upward infrared (LW") Net longwave (LW) Net radiation (SW + LW) Latent heat (LH) Sensible heat (SH) 176 W m-2 312 W m-2 -385 W m-2 -73 W m-2 103 W m-2 -79 W m-2 -24 W m-2 Table 2.2: Components of the globally and annually averaged surface energy budget. A positive sign means that the surface is warmed. Revised Tuesday, February 10, 2009 18 An Introduction to the General Circulation of the Atmosphere Table: globally and annually averaged surface energy budget

From the solar radiation... 授课教师：张洋 10 TOA surface energy budget SW ~ LW S(1 ↵) Long term, global average: SW(net) + LW(net) + LH +SH ~0 Incident solar radiation 340 W/m^2 Planetary albedo 0.3 Absorbed solar radiation 240 W/m^2 Outgoing longwave radiation 240 W/m^2 Table: globally and annually averaged TOA radiation budget Table: globally and annually averaged atmosphere energy budget Energy and moisture budgets of the surface and atmosphere The planetary radiation budget has already been briefly discussed. We now consider the energy and moisture budgets of the Earth’s surface and the atmosphere. It is a shocking fact that we do not know enough about the globally averaged surface energy budget to do more than sketch rough annual mean values, as shown in Table 2.2. None of the numbers in the table is known to better than 20% accuracy. Of the 240 W m-2 that is absorbed by the Earth-atmosphere system, 176 W m-2 is absorbed by the Earth’s surface. Thus only about 240 - 176 = 64 W m-2 of solar radiation is absorbed by the atmosphere. That is only about 1/4 of the total solar radiation absorbed by the Earth-atmosphere system. It should be noted, however, that the partitioning of the absorbed solar radiation between the atmosphere and the Earth’s surface is currently a matter of some controversy. The surface receives a total (LW! + SW; see notation defined in Table 2.2) of 488 W m-2, which is given back in the form of LW", LH and SH. By far the largest of these is LW". Keep in mind that the oceans can transport energy from one place to another, so that the energy absorbed by the oceans is not necessarily given back in the same place where it is absorbed. Also, the large heat capacity of the upper ocean allows energy storage on seasonal time scales. In contrast, the continents cannot transport energy internally at a significant rate, and their limited heat capacity forces near energy balance, everywhere, on time scales longer than a few days (at most). Note that the net radiative heating of the surface, which amounts to 103 W m-2, is balanced primarily by evaporative cooling of the surface at the rate of 79 W m-2. As discussed below, moisture is of comparable importance in the energy budget of the atmosphere. The globally averaged energy budget of the atmosphere is shown in Table 2.3. Again, most of the numbers in Table 2.2 and Table 2.3 are only rough estimates. One interpretation of Table 2.3 is that the atmosphere sheds energy through infrared radiation at the rate required to Absorbed solar (SW) Downward infrared (LW!) Upward infrared (LW") Net longwave (LW) Net radiation (SW + LW) Latent heat (LH) Sensible heat (SH) 176 W m-2 312 W m-2 -385 W m-2 -73 W m-2 103 W m-2 -79 W m-2 -24 W m-2 Table 2.2: Components of the globally and annually averaged surface energy budget. A positive sign means that the surface is warmed. Revised Tuesday, February 10, 2009 18 An Introduction to the General Circulation of the Atmosphere Table: globally and annually averaged surface energy budget

南京大学：《大气环流》课程教学资源（课件讲稿）第二章 大气环流的外部强迫（1/3）

南京大学：《大气环流》课程教学资源（课件讲稿）第二章大气环流的外部强迫（1/3）