In this lecture we will discuss the following topics:
Weather, Witterung, Climate
Modern definition of climate by AMS (Link)
The slowly varying aspects of the atmosphere–hydrosphere–land surface system.
It is typically characterized in terms of suitable averages of the climate system over periods of a month or more, taking into consideration the variability in time of these averaged quantities. Climatic classifications include the spatial variation of these time-averaged variables. Beginning with the view of local climate as little more than the annual course of long-term averages of surface temperature and precipitation, the concept of climate has broadened and evolved in recent decades in response to the increased understanding of the underlying processes that determine climate and its variability.
One way to appreciate the complexity of the climate system is through a visualization provided by NASA, available at https://svs.gsfc.nasa.gov/31139.
Figure 1: Components of the climate system. Source: NASA.
Figure 2: From Schönwiese (2020).
Figure 3: From Schönwiese (2020).
Figure 4: Sources: ECMWF (left), ECMWF (middle), Bildungsserver (right).
Figure 5: Essential Climate Variables. Source: GCOS.
Figure 6: Source: NASA Visible Earth.
Climate classifications aim to provide a typification of the characteristic geographical differences of climate, and are typically presented in the form of global maps. There are several types of climate classifications.
Climate classifications
Figure 7: Köppen-Geiger classification. Fig. 1 from Kottek et al. (2006).
In climate science, the “top of the atmosphere” (TOA) is defined as the upper boundary of the atmosphere. At the TOA, the atmosphere becomes so thin that mass transport is negligible and the vertical exchange of energy is exclusively by radiation. The energy budget of Earth as a whole is hence determined by the radiative fluxes at the TOA.
TOA energy budget
\[ dE/dt = N = I - R - L \]
Figure 8: A CERES instrument on the left and onboard the NOAA-20 satellite on the right. Sources: NASA and NOAA.
Global-mean time-mean Earth’s energy budget for July 2005 – June 2015
| Contribution by clouds | |||
|---|---|---|---|
| Incoming shortwave radiation | \(I\) | 340 | 0 |
| Reflected shortwave radiation | \(R\) | 99 | 46 |
| Outgoing longwave radiation | \(L\) | 240 | -28 |
| Net radiation | \(N\) | 1 | -18 |
Figure 9: Fig. 3.1 of Trenberth (2022).
\[ \alpha_p = \frac{R}{I} = \frac{99}{340} \approx 0.3. \]
\[ \alpha_p^{\text{clear-sky}} = \frac{R}{I} = \frac{53}{340} \approx 0.15. \]
Table 2: Tab. 3.1 of Brönnimann (2018).
Figure 10: Global map of annual-mean planetary albedo derived from CERES. Fig. 2.9 of Hartmann (2016).
Figure 11: Global map of absorbed shortwave radiation derived from CERES. Fig. 5.8 of Trenberth (2022).
Figure 12: Global map of annual-mean outgoing longwave radiation derived from CERES. Fig. 2.10 of Hartmann (2016).
Figure 13: Global map of annual-mean net radiation derived from CERES. Fig. 2.11 of Hartmann (2016).
Figure 14: Zonal-mean annual-mean radiative fluxes at the TOA. Fig. 2.12 of Hartmann (2016).
The relation between Earth’s energy budget and meridional energy transports is captured by the following budget equation that expresses the conservation of energy:
\[ \frac{dE(\varphi)}{dt} = N(\varphi) - \text{div} F(\varphi). \]
Figure 15: Fig. 6.5 of Brönnimann (2018).
Aiko Voigt