Coral Reef Coupling to the Atmospheric Boundary Layer Through Exchanges of Heat, Moisture, and Momentum: Case Studies From Tropical and Desert Fringing Coral Reefs

Abstract

Coral reefs represent abrupt changes in surface roughness, temperature, and humidity in oceanic and coastal locations. This leads to formation of internal atmospheric boundary layers that grow vertically in response to turbulent mixing which conveys changes in surface properties into the prevailing wind. As a result, coral reefs under favourable conditions couple to the overlying atmosphere. Here we present rare observations of coral reef – atmospheric interactions during summer monsoon conditions on the Great Barrier Reef, Australia, and a desert fringing coral reef in the Gulf of Eilat, Israel. We show that in the hyper-arid location of the Gulf of Eilat where air temperatures are greater than water temperatures, a stable atmospheric boundary inhibits coupling of the reef to the atmosphere. In contrast, under monsoon conditions on the Great Barrier Reef, the coral reef is shown to couple to the overlying atmosphere leading to the formation of a convective internal boundary layer in which convective exchange of heat and moisture influences cloud and possibly precipitation. We conclude that understanding these processes is essential for determining the role of coral reefs in coastal meteorology, and whether through coupling with the overlying atmosphere coral reefs may regulate their meteorology by triggering formation of cloud and/or vertical exchange on aerosols and their precursor gases such as Dimethyl sulphide.

Direct Measurement of CO2 Air‐Sea Exchange Over a Desert Fringing Coral Reef, Gulf of Eilat (Aqaba), Israel

“…Relative humidity reached daily minimums around show mid‐afternoon of 25% associated with hot north‐northeast winds peaking at 9–10 m s −1 (Figure 2). Ambient air temperatures remained higher than the water temperature ( Tw ) throughout the measurement period, being representative of summer conditions (McGowan et al., 2022). Net radiation peaked just prior to midday at approximately 680 Wm −2 with wind speed reaching daily maximums around 0930 hr and then gradually decreasing to 1600 hr before decreasing more rapidly to near 3 m s −1 following sunset.…”

Exploring Meteorological Conditions and Microscale Temperature Inversions above the Great Barrier Reef through Drone-Based Measurements

“…The marine boundary layer can be defined as the lowest part of the troposphere that is directly influenced by the Earth's surface, which responds to surface forcing within one hour or less [12]. Coral reefs influence the surface roughness, temperature, and humidity of the ocean, sometimes leading to a connection of the ocean with the overlying atmosphere, in the form of a convective internal atmospheric boundary layer within the marine boundary layer [1,58,59]. The convective internal atmospheric boundary layer is usually characterised by an interpretation of wind speed, vertical profiles of virtual potential temperature, and mixing ratio [59,60].…”

“…Coral reefs influence the surface roughness, temperature, and humidity of the ocean, sometimes leading to a connection of the ocean with the overlying atmosphere, in the form of a convective internal atmospheric boundary layer within the marine boundary layer [1,58,59]. The convective internal atmospheric boundary layer is usually characterised by an interpretation of wind speed, vertical profiles of virtual potential temperature, and mixing ratio [59,60]. The drone-based vertical profiles measured changes in temperature, relative humidity, atmospheric pressure, and wind parameters multiple times per day.…”

“…The drone-based vertical profiles measured changes in temperature, relative humidity, atmospheric pressure, and wind parameters multiple times per day. Such high-resolution datasets could be applied to providing further insight into the potential coupling of coral reefs with the overlying atmosphere [59,60].…”

Identifying an Evaporative Thermal Refugium for the Preservation of Coral Reefs in a Warming World—The Gulf of Eilat (Aqaba)

“…The proximity of the GoE reef to the arid desert with the terrestrial atmospheric boundary layer above the GoE which is characterized by hot and dry air above colder GoE water leads to a stable atmospheric boundary layer. In comparison, the marine boundary layer above the GBR dictates the flow of humid air above the GBR reef water, resulting in the coupling of the air‐sea exchange with convective exchange to the marine boundary layer in tropical humid coral reefs (McGowan et al., 2022).…”