&lt;strong&gt;New insights on land surface-atmosphere feedbacks over tropical South America at interannual timescales&lt;/strong&gt;

Germán Poveda,Juan Mauricio Bedoya-Soto

doi:10.3390/chycle-2017-04875

Abstract

Using monthly data for the period 1979-2010, we study the dynamics and strength of land surface-atmosphere feedbacks (LAFs) among variables involved in the heat and moisture fluxes, at interannual timescales for Tropical South America (TropSA). The variables include precipitation, surface air temperature, specific humidity at 925 hPa, evaporation, and estimates of volumetric soil water content. Using a dimensional reduction, we apply a Maximum Covariance Analysis (MCA) to rank the relative contributions to LAFs and group the time series into Maximum Covariance States (MCS) with common mechanisms among variables. We estimate linear (Pearson correlations) and non-linear (information transfer and causality) coupling metrics among pairs of variables to configure the structure of linkages. The main MCS associated with LAFs over TropSA are strongly influenced by ENSO, and the meridional and equatorial SSTs modes over the Atlantic and Indian Oceans. ENSO favors a unimodal behavior, with center of action in the Amazon River basin, while SSTs over the Tropical North Atlantic result in a dipole between northern and southern TropSA. Results show that soil moisture plays a leading role in regulating heat and water anomalies, and provides the memory of the atmosphere-driven processes and their subsequent influence. Thus, soil moisture is fundamental and leads up to 9 month-lags whereby ENSO enhances the interannual connectivity and memory of LAFs in 25% with respect to the mode influenced by TNA. Within the identified multivariate structure, evaporation and soil moisture enhance the interannual connectivity of the whole set of variables since both variables exhibit more frequent two-way feedbacks with the remaining variables.

Highlights

The humid tropics concentrate a large amount of net radiation and water vapor, and intense heat and humidity fluxes dominate the interactions between the soil and the lower atmosphere [1]
The aim of this paper is to explore new ideas and tools to advance our understanding of land surface-atmospheric feedbacks in Tropical South America (TropSA) at interannual timescales, in by studying the connectivity between state and process variables involved in dynamical land-atmosphere feedbacks (LAFs) over TropSA
The pair EVP and PRC exhibits the lower correlation with N3.4 among the set of MCS1 (Table 5, red entries in column MCS1), which implies that the interactions between those process variables at interannual time scales are not completely due to ENSO as we show for the state variables Specific Humidity at 925 hPa (SH925) and Surface Temperature SH925 (T2m)

Summary

Introduction

The humid tropics concentrate a large amount of net radiation and water vapor, and intense heat and humidity fluxes dominate the interactions between the soil and the lower atmosphere [1]. The 1st International Electronic Conference on Hydrological Cycle (CHyCle-2017), 19 Noveber – 1 December 2017; Sciforum Electronic Conference Series, Vol 1, 2017 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]. [31] describe a recycling pattern in South America that regionally connects evapotranspiration in the Amazon with precipitation in La Plata River basin [36,37,38,39] These authors discuss the recycling east of the Andes in TropSA owing to the blocking orographic effect on moisture transport at low levels [40,41]. Several studies have identified the ways in which LAFs are associated with the South American Monsoon (SAM) [36,42,43], and the important role of LAFs over TropSA in connecting the Tropical Pacific with the Tropical North Atlantic SSTs anomalies at interannual timescales [44,45,46]

Objectives

Results

Discussion

Conclusion