Surface Temperature of Earth – making connections

By Chris Merchant

“Surface temperature” might seem to be a straightforward concept at first, but look more carefully, and things soon become rather complex.

The temperatures quoted in the weather forecast are intended to represent the air temperature a metre or two above the ground. This temperature only accounts for part of our subjective sensation of warmth, which is modified by wind, radiation from the Sun, and the radiation of energy at infra-red wavelengths by our surrounding environment. Infra-red imagers on Earth-observing satellites can be used to infer the radiative temperature of Earth’s surface (where not obscured by cloud). The relationship between this “land surface temperature” from space and meteorological surface air temperature is complex and changes rapidly. This is not least because the satellite “sees” the temperature of the first solid or liquid surface along its line of sight, raising, for example, the issue of how the temperature of the uppermost leaves in a forest relates to the air temperature near the ground. And then … well, perhaps those examples are enough to illustrate the point that it is complex.

In short, surface temperature is a key aspect of weather and climate, but the generic term refers to a number distinct quantities, that are observed by different means, and which play interconnected roles within the environment.

Despite the complexity, there are good reasons to learn how to make connections between the various “surface temperatures” that can be observed both at the surface and from space – Figure 1.

2014-06-19 Chris Merchant Fig 1

Figure 1. Different surface temperatures. SST: sea surface temperature, either at depth, measured in situ, or of the skin layer, measured by radiometers on ships or in space; MAT: marine air temperature; LST: land surface temperature, LSAT: land surface air temperature; LSWT: lake surface water temperature; IST: ice surface temperature.1

 

Making those scientific connections in practice also means making human connections, linking domains of expertise. The importance (and challenge) of forging fruitful networks of people is an aspect of doing science that is not always obvious when studying science. Which brings me to what I am doing this week: leading a workshop of the EarthTemp Network2 in Germany, hosted by the Karlsruhe Institute of Technology. (Like all good projects, we have an amateurish logo created in Powerpoint – Figure 2. Can you decode the symbolism?)

 

2014-06-19 Chris Merchant Fig 2

Figure 2. Logo of the NERC-funded EarthTemp Network.

The EarthTemp week is a highlight of my year, in which we gather experts in all forms of surface temperature observation and exploitation. We not only to listen to scientific progress in the form of talks, but also have copious discussion of outstanding problems, and hot-house new ideas in “collaboration incubator” sessions. It is good fun. (Honestly!)

This year’s theme is “Joint exploitation of in situ and satellite surface temperatures in key land regions (focus on Africa)”. Learning to synthesize coherent data on surface temperature variations from diverse in situ and satellite measurements is particularly important in areas where in situ data are sparse, including much of Africa.

In the programme of talks, we have “Satellite Land Surface Temperatures”, “Measuring and Interpreting Land Surface Air Temperatures”, “African Climate and Surface Temperature”, “Coastal Waters”, “Lake Surface Water Temperatures”, “Southern Annular Mode and Diurnal Temperature Range Shifts”, and “Surface Temperature Extremes in Zimbabwe”. We will all learn a lot.

REFERENCES

1. Merchant C J, S Matthiesen, N A Rayner and others (2013). The surface temperatures of Earth: steps towards integrated understanding of variability and change. Geosci. Instrum. Method. Data Syst., 2, 305–321, doi:10.5194/gi-2-305-2013.

2. http://www.earthtemp.net

 

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