Near-Surface Atmospheric Turbulence in the Presence of a Squall Line above a Forested and Deforested Region in the Central Amazon

Valéria L Bezerra,Jose D Fuentes,Marcelo Chamecki,Santiago Botía,Julia C P Cohen,Raoni A Santana,Roseilson S Vale,Hardiney S Martins,Cléo Q Dias-Júnior,Antônio O Manzi

doi:10.3390/atmos12040461

Abstract

Squall lines (SLs) are convective systems that cause heavy precipitation and consequently modify the atmospheric thermodynamic structure near the surface. SLs generated along the northern coast of Brazil and their effect upon atmospheric structure during their westward displacement into the Amazon are studied. Satellite imagery was employed to identify an SL above two experimental sites in the central Amazon and to characterize differences in the near-surface turbulent and ozone exchange during the passage of the SLs. The two sites, which are separated by about 100 km, feature contrasting vegetation. One site is tall canopy rainforest and the other is deforested. From our case study, it is noted that: equivalent potential temperature significantly drops, principally in the forested region; the average near-surface wind speed increases 5 fold; the skewness of vertical wind velocity becomes considerably negative; significant increases in turbulence intensity are observed. These changes suggest the presence of strong downdrafts generated by the SL. Shear production and dissipation rate of turbulent kinetic energy are considerably larger during the SL when compared to periods with absence of SL. In this study, we show that SLs are capable of modifying the vertical organization of the turbulence over forested and deforested areas, leading to changes in certain chemical processes that occur near the surface. To the best of our knowledge, this study represents a first in demonstrating that near-surface turbulent flow in the Amazon region is modified by the presence of SLs.

Highlights

Two-thirds of the global precipitation occurs in tropical regions, primarily caused by Mesoscale Convective Systems (MCSs) ([1,2,3], among others)
These months are during the rainy season of the central Amazon region, when the intertropical convergence zone is well established over the N-NE coast of Brazil [41]
The main reason for using only one case, is that for a better understanding of the Squall lines (SLs) role in organizing turbulence close to the surface we needed a profile of sonic anemometers working reasonably well during the occurrence of these events

Summary

Introduction

Two-thirds of the global precipitation occurs in tropical regions, primarily caused by Mesoscale Convective Systems (MCSs) ([1,2,3], among others). Squall lines (SLs) are a common type of MCSs, in which a series of storms are arranged in a linear manner, at scales greater than 100 km [4,5]. Such SLs can be identified using satellite images and their displacement can be tracked. In the Amazon, SLs often originate along the northern Atlantic coast These storms may either propagate very large distances (greater than 1000 km) from the region of origin or they may dissipate close to the coast [6,7,8]

Methods

Results

Conclusion