Abstract
We present a simplified overview of land-atmosphere feedbacks at interannual timescales over tropical South America as structural sets of linkages among surface air temperature (T), specific humidity at 925 hPa (q925), volumetric soil water content (Θ), precipitation (P), and evaporation (E), at monthly scale during 1979–2010. Applying a Maximum Covariance Analysis (MCA), we identify the modes of greatest interannual covariability in the datasets. Time series extracted from the MCAs were used to quantify linear and non-linear metrics at up to six-month lags to establish connections among variables. All sets of metrics were summarized as graphs (Graph Theory) grouped according to their highest ENSO-degree association. The core of ENSO-activated interactions is located in the Amazon River basin and in the Magdalena-Cauca River basin in Colombia. Within the identified multivariate structure, Θ enhances the interannual connectivity since it often exhibits two-way feedbacks with the whole set of variables. That is, Θ is a key variable in defining the spatiotemporal patterns of P and E at interannual time-scales. For both the simultaneous and lagged analysis, T activates non-linear associations with q925 and Θ. Under the ENSO influence, T is a key variable to diagnose the dynamics of interannual feedbacks of the lower troposphere and soil interfaces over tropical South America. ENSO increases the interannual connectivity and memory of the feedback mechanisms.
Highlights
The humid tropics receive a large amount of net radiation and water vapor, and intense heat and humidity fluxes dominate the interactions between soil and the lower atmosphere [1].The excess of net radiation is balanced through latent and sensible heat fluxes [2,3,4]
We focus our study on tropical South America (15◦ N–20◦ S and 82◦ W–40◦ W, Figure 2) taking some of the variables proposed by Brubaker and Entekhabi [48] to the study of land-atmosphere feedbacks (LAFs)
The physical mechanisms of the LAFs over Tropical South America at interannual time scales for oneto three lag-months are clearly modulated by the dynamics of soil moisture to produce the anomalies of precipitation
Summary
The humid tropics receive a large amount of net radiation and water vapor, and intense heat and humidity fluxes dominate the interactions between soil and the lower atmosphere [1].The excess of net radiation is balanced through latent and sensible heat fluxes [2,3,4]. The humid tropics receive a large amount of net radiation and water vapor, and intense heat and humidity fluxes dominate the interactions between soil and the lower atmosphere [1]. By controlling the partition of these fluxes, soil moisture modulates diverse land-atmosphere feedbacks (LAFs); the rates of change between dry and wet conditions in the soil necessarily impact surface temperatures [5,6]. An important body of literature has focused on the role of vegetation and land uses in the dynamics of LAFs [20,21,22,23,24], and the conditions under which LAFs determine the stability of the lower atmosphere [25,26,27].
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