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gfdl on-line bibliography > 2006 citations
Why do temperatures vary vertically (from the surface to the stratosphere) and what do we understand about why they might vary and change over time?
| Ramaswamy, V., J. W. Hurrell, G. A. Meehl, A. Phillips, B. D. Santer, M. D. Schwarzkopf, D. J. Seidel, S. C. Sherwood, and P. W. Thorne, 2006: Why do temperatures vary vertically (from the surface to the stratosphere) and what do we understand about why they might vary and change over time? In, Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences, T. R. Karl, S. J. Hassol, C. D. Miller, W. L. Murray, eds., A Report by the Climate Change Science Program and the Subcommittee on Global Change Research, Washington, DC, 15-28. |
| Summary: The global temperature profile of the Earth's atmosphere reflects a balance between the radiative, convective and dynamical heating/cooling of the surface-atmosphere system. Radiation from the Sun is the source of energy for the Earth's climate, with most of it absorbed at the surface. Combined with the physical properties of the atmosphere and dynamical processes, the heat is mixed vertically and horizontally, yielding the highest temperatures, on average, at the surface, with marked seasonal and spatial variations. In the atmosphere, the distribution of moisture and the lower air pressure at progressively higher altitudes result in decreasing temperatures with height up to the tropopause, with the rate of decrease depending on geographical factors and meteorological conditions. The tropopause marks the top of the troposphere, i.e., the lower 8 to 16 km of the atmosphere (see Preface, Fig. 2), and varies with latitude and longitude. Above this altitude, the physical properties of the air produce a warming with height through the stratosphere (extending from the tropopause to ~50 km). |
| Temperature trends at the surface can be expected to be
different from temperature trends higher in the atmosphere because: • Surface types (sea, snow, ice, and different vegetative covers of land) differ considerably in their physical properties. Near the surface, these differing conditions can produce strong horizontal variations in temperature. Above the surface layer, these contrasts are quickly smoothed out by the atmospheric motions, contributing to varying tempeature trends with height at different locations. • Changes in atmospheric circulation or modes of atmospheric variability (e.g., El Nińo-Southern Oscillation [ENSO]) can produce different temperature trends at the surface and aloft. • Under some circumstances, temperatures may increase with height near the surface or higher in the troposphere, producing a "temperature inversion." Such inversions are more common at night; over continents, sea ice and snow during winter; and in the trade wind regions. Since the air in inversion layers is resistant to vertical mixing, temperatures trends can differ between inversion layers and adjacent layers. • Forcing factors, either natural (e.g., volcanoes and solar) or human-induced (e.g., greenhouse gas, aerosols, ozone, and land use) can result in differing temperature trends at different altitudes, and these vertical variations may change over time. This can arise due to spatial and temporal changes in the concentrations or properties of the forcing agents. |
| This Chapter describes the temperature profile of the layers of the atmosphere from the surface through the stratosphere and discusses the basic reasons for this profile. We also use results from global climate model simulations to show how changes in natural and human-induced factors can produce different temperature trends in the various layers of the atmosphere. This discussion provides the background for the presentation of the observed changes (Chapters 2-4), and for the understanding of their causes (Chapter 5). We also describe temperature changes in the stratosphere in recent decades and the influences of these changes on the troposphere. Finally, making use of surface and satellite observations, we examine the physical processes that can result in different temperature trends at the surface and in the troposphere. |