The Shortwave Radiative Flux Response to an Injection of Sea Salt Aerosols in the Gulf of Mexico.

Marine cloud brightening (MCB) has been proposed as a potential means of geoengineering the climate, temporarily providing cooling to offset some of the effects of climate change. Marine sky brightening (MSB), involving the direct scattering of sunlight from sea salt injection into the marine boundary layer, has been proposed as an additional geoengineering method that could work in areas that are not regularly cloudy. Here, we use a regional atmospheric model to simulate MCB and MSB over the Gulf of Mexico and nearby land, a highly populated and economically important region that is not characterized by persistent marine stratocumulus cloud cover. Injection of sea salt in the Aitken mode from a region in the central Gulf of Mexico equivalent to 10.8 Tg yr−1 produces an upwards 8.4 W m−2 radiative flux change across the region at the top of the atmosphere, largely due to cloud property changes. Comparatively, a similar mass injection in the accumulation mode produces a 3.1 W m−2 radiative flux change driven primarily by direct scattering. Injection of even larger particles produces a much smaller radiative flux change. Shortwave flux changes due to clouds are largely driven by an increase in cloud droplet number concentration and an increase in cloud liquid water path (each contributing about 45% to the flux change), with a much lower contribution from cloud fraction changes (10%). Plain Language Summary: In addition to limiting the burning of fuels that causes global temperatures to increase, scientists are investigating methods to reflect sunlight in order to help cool the planet. One option is to brighten clouds over the ocean so that they will reflect more sunlight. This option, called marine cloud brightening (MCB), works by increasing the number of cloud droplets within a cloud so that there are more surfaces for sunlight to hit and be reflected back to space before the sunlight can warm the planet's surface. Previous research has suggested that MCB may work in regions with many clouds that are close to the surface. In the current study, we use computers to test whether MCB may work in the Gulf of Mexico, where the clouds are higher above the surface and less abundant as compared to the regions in previous studies. Our results indicate that clouds can brighten and increase in size in the Gulf of Mexico. Our research suggests that MCB could be used in this region to reduce local temperatures, including the cooling of the Gulf waters which could reduce hurricane strength and benefit the health of local coral reefs. Key Points: The simulations show that marine cloud and sky brightening are effective at reducing shortwave radiation in the Gulf of Mexico regionThe Aitken mode injection results in the largest direct and indirect radiative response during clear‐ and all‐sky conditions, respectivelyThe Aitken mode response is largely due to cloud albedo and liquid water path increases vs. cloud fraction increase or direct scattering [ABSTRACT FROM AUTHOR]