Differences between soil and air temperatures: Implications for geological reconstructions of past climate
Differences between soil and air temperatures: Implications for geological reconstructions of past climate
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土壤温度和气温之间的差异：对过去气候地质重建的影响
DOI：
10.1130/ges02448.1
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发表时间：
2022
期刊：
影响因子：
2.5
通讯作者：
Molnar, Peter
中科院分区：
文献类型：
--
作者：
Molnar, Peter
在对古气候感兴趣的数量中，地表正上方的年平均气温 T a 尤为突出。然而，大多数对大陆地区过去温度的地质估计都量化了地表以下土壤或其他物质的温度 T s ，并且一般来说 T a < T s 。地面能量平衡 FLUXNET2015 数据集的理论和数据都表明，温差 ΔT= T s− T a 以及鲍文比（从地表到大气的感热与潜热通量之比）对陆地表面覆盖性质的系统依赖性。在寒冷地区，年平均气温≥5℃，潜热通量往往较小，ΔT值可能较大，为3-5℃或更大。在潮湿的表面上，潜热通量主导着感热通量，并且 ΔT 和鲍文比的值通常都很小。相比之下，在仅向上层大气提供有限水分的干旱表面上，情况恰恰相反。理论和观察都表明，ΔT 年平均值如下（尽管是近似值）：湿地为 1 C；森林，1±1℃；灌木丛，3–4 C；稀树草原，3.5 C< ΔT< 5.5 C；草原，湿润地区 1 摄氏度，干旱地区 3 摄氏度；和沙漠，4-6 C。随着推断过去陆地表面条件的地质工具的改进，这些 ΔT 的近似值将允许将过去年平均地表温度 T s 的地质估计值转化为过去年平均气温 T a 的估计值。
Among quantities of interest in paleoclimate, the mean annual air temperature, T a, directly over the surface looms prominently. Most geologic estimates of past temperatures from continental regions, however, quantify temperatures of the soil or other material below the surface, T s, and in general T a< T s. Both theory and data from the FLUXNET2015 data set of surface energy balance indicate systematic dependences of temperature differences ΔT= T s− T a and also of Bowen ratios—ratios of sensible to latent heat fluxes from surface to the atmosphere—on the nature of the land-surface cover. In cold regions, with mean annual temperatures≲ 5 C, latent heat flux tends to be small, and values of ΔT can be large, 3–5 C or larger. Over wet surfaces, latent heat fluxes dominate sensible heat fluxes, and values of both ΔT and Bowen ratios commonly are small. By contrast, over arid surfaces that provide only limited moisture to the overlying atmosphere, the opposite holds. Both theory and observation suggest the following, albeit approximate, mean annual values of ΔT: for wetlands, 1 C; forests, 1±1 C; shrublands, 3–4 C; savannas, 3.5 C< ΔT< 5.5 C; grasslands, 1 C where wet to 3 C where arid; and deserts, 4–6 C. As geological tools for inferring past land-surface conditions improve, these approximate values of ΔT will allow geologic estimates of past mean annual surface temperatures, T s, to be translated into estimates of past mean annual air temperatures, T a.