Our primary research interests revolve around mountains and tropical clouds. This includes dynamical studies of orographic precipitation, and microphysical studies of aerosol impacts on clouds, either from giant sea-salt nuclei, or accumulation mode aerosols.
A running theme in our work is the inclusion of aircraft in-situ measurements and numerical models including fully coupled models like WRF, and manually written models from a set of equations for droplet growth or the development of buoyancy.
See below for a brief overview of our past research projects.
DOMEX: Dynamics of Orographic Convection
Orographic convection refers to a developing buoyant flow that is initiated by a mountain or raised topography. In this case, the buoyant flow results in beautiful tropical clouds, and the raised topography is the island of Dominica in the Caribbean. The dynamics of orographic convection varies from thermally forced to mechanically forced convection, strongly dependant on the strength of the low level wind speed.
Watson, C. D., R. B. Smith, and A. D. Nugent, 2015: Processes controlling precipitation in shallow, orographic, trade-wind convection. J. Atmos. Sci., 72, 3051–3072. (doi: http://dx.doi.org/10.1175/JAS-D-14-0333.1)
Nugent, A. D., and R. B. Smith, 2014: Initiating convection in an inhomogeneous layer by uniform ascent. J. Atmos. Sci., 71, 4597–4610. (doi: http://dx.doi.org/10.1175/JAS-D-14-0089.1)
Nugent, A. D., J. R. Minder, and R. B. Smith, 2014: Wind speed control of tropical orographic convection. J. Atmos. Sci., 71, 2695-2712. (doi: http://dx.doi.org/10.1175/JAS-D-13-0399.1)
Minder, J. R., R. B. Smith, and A. D. Nugent, 2013: The dynamics of ascent-forced orographic convection in the tropics: results from Dominica. J. Atmos. Sci., 70, 4067–4088. (doi: http://dx.doi.org/10.1175/JAS-D-13-016.1)
Smith, R. B., J. R. Minder, A. D. Nugent, T. Storelvmo, D. J. Kirshbaum, R. Warren, N. Lareau, P. Palany, A. James, and J. French, 2012: Orographic Precipitation in the Tropics: The Dominica Experiment. Bull. Amer. Meteor. Soc., 93, 1567–1579. (doi: http://dx.doi.org/10.1175/BAMS-D-11-00194.1)
Aerosols in Orographic Convection
Tiny airbourne particles can have an impact on the orographic clouds. The number of particles affects the number of cloud droplets that form, in addition to their size, and their ability to form precipitation. Observations from DOMEX show a clear signal of aerosols getting up into clouds and having an impact there. A subsequent model study shows that the impact of aerosols on precipitation is less clear.
Nugent, A., C. Watson, G. Thompson, and R. Smith, 2016: Aerosol Impacts on Thermally Driven Orographic Convection. J. Atmos. Sci., 73, 3115–3132, doi: 10.1175/JAS-D-15-0320.1. (doi: http://dx.doi.org/10.1175/JAS-D-15-0320.1)
Growth of Giant Sea Salt Nuclei
Over the ocean, sea salt particles are constantly emitted from the ocean surface from breaking waves and bursting bubbles. Sometimes these particles are able to make it to cloud base where they grow rapidly by condensation because of their hygroscopicity. This rapid growth gives them a particular advantage when considering their impact on precipitation formation.
Jensen, J. and A. Nugent, 2017: Condensational Growth of Drops Formed on Giant Sea-Salt Aerosol Particles. J. Atmos. Sci., 74, 679–697, doi: 10.1175/JAS-D-15-0370.1. (doi: http://dx.doi.org/10.1175/JAS-D-15-0370.1)
DEEPWAVE: Gravity Wave Energy Fluxes
The field campaign title "DEEPWAVE" refers to the deep propagation of gravity waves into the upper atmosphere over New Zealand. Gravity waves are waves with gravity being the restoring force; therefore they only exist in stabily stratified fluid. They are often caused by airflow over topography, just as ripples on the surface of a pond can be caused by a dropped pebble. Using aircraft measurements, the amount of energy carried by these waves can be quantified.