Do the Amazon and Orinoco freshwater plumes really matter for hurricane‐induced ocean surface cooling?

Abstract

Recent studies suggested that the plume of low‐saline waters formed by the discharge of the Amazon and Orinoco rivers could favor Atlantic Tropical Cyclone (TC) intensification by weakening the cool wake and its impact on the hurricane growth potential. The main objective of this study is to quantify the effects of the Amazon‐Orinoco river discharges in modulating the amplitude of TC‐induced cooling in the western Tropical Atlantic. Our approach is based on the analysis of TC cool wake statistics obtained from an ocean regional numerical simulation with ¼º horizontal resolution over the 1998–2012 period, forced with realistic TC winds. In both model and observations, the amplitude of TC‐induced cooling in plume waters (0.3–0.4ºC) is reduced significantly by around 50–60% compared to the cooling in open ocean waters out of the plume (0.6–0.7ºC). A twin simulation without river runoff shows that TC‐induced cooling over the plume region (defined from the reference experiment) is almost unchanged (∼0.03ºC) despite strong differences in salinity stratification and the absence of barrier layers. This argues for a weaker than thought cooling inhibition effect of salinity stratification and barrier layers in this region. Indeed, results suggest that haline stratification and barrier layers caused by the river runoff may explain only ∼10% of the cooling difference between plume waters and open ocean waters. Instead, the analysis of the background oceanic conditions suggests that the regional distribution of the thermal stratification is the main factor controlling the amplitude of cooling in the plume region.

Benguela Niños and Benguela Niñas in Forced Ocean Simulation From 1958 to 2015

“…This may participate to counterbalance model biases in reproducing the Benguela upwelling variability. There is also no restoring toward observed or climatological sea surface salinity (Hernandez et al, ). A monthly climatological runoff based on the data set of Dai and Trenberth () is prescribed near the river mouths as a surface freshwater flux with increased vertical mixing in the upper 10 m. The OGCM has been integrated over the period 1958–2015 (Hernandez et al, ) and monthly averages were analyzed in this work.…”

Importance of the Equatorial Undercurrent on the sea surface salinity in the eastern equatorial Atlantic in boreal spring

“…The numerical setup is fully described in Hernandez et al . [], together with some comparisons with observations. The regional configuration extends from 35°S to 35°N and from 100°W to 15°E with a quarter degree horizontal resolution.…”

“…A regional numerical simulation of the tropical Atlantic based on NEMO3.6 (Nucleus for European Modeling of the Ocean) [Madec and the NEMO Team, 2016] is analyzed in this study. The numerical setup is fully described in Hernandez et al [2016], together with some comparisons with observations. The regional configuration extends from 358S to 358N and from 1008W to 158E with a quarter degree horizontal resolution.…”

Modification of sea surface temperature by chlorophyll concentration in the Atlantic upwelling systems

“…It has 75 levels in the vertical, with 12 levels in the upper 20 m and 24 levels in the upper 100 m. Such a configuration has already been described in full details in Hernandez et al . [], a study in which it is shown that the model successfully reproduces the Tropical Atlantic mean state and the sea surface cooling in the wake of tropical storms and hurricanes of the western Tropical Atlantic.…”