M. Joan Alexander Sr. Research Scientist

Publications - Research - Field Campaigns - Vitae - Miscellaneous - Contact

In order to better predict the weather and better understand climate change, many atmospheric scientists are involved in developing computer simulations that describe the global circulation of the atmosphere. These global circulation models (GCMs) cannot explicitly resolve all of the scales of phenomena important in the atmosphere, so they use parameterizations of some of the smaller-scale processes, such as clouds, precipitation, and many others including the effects of small-scale atmospheric waves on the circulation.

My research focuses on atmospheric waves of all scales ranging from global scale to small-scale atmospheric gravity waves that have horizontal wavelengths in the range of about 10 to 1000s of km. These waves are poorly described in GCMs, yet they can have dramatic effects on the global-scale circulation, so they must be parameterized.


Observations: The small scales of gravity waves have made global observations of their properties and occurence difficult. Our understanding of them is therefore relatively new, and therefore still very incomplete. My research focuses on developing the needed understanding through observations and observational analyses, and through computer modeling of gravity wave sources, their propagation through the atmosphere, and their interaction with regional and global circulations.



Global Models: Increases in computing power over time permit us to directly simulate gravity waves in some global models. The image at left shows vertical motion in the atmosphere near the tropopause allowing visualization of the gravity waves resolved in a 7-km resolution NASA GEOS-5 model run by the Global Modelling and Assimilation Office. The circular features near the equator show waves generated by storms in the atmosphere below. Waves are also prominent over the northern (winter in this image from January) mountain ranges and storm tracks. Studying the waves in these models permits investigation into the nature of the sources of the waves and how the waves dynamically interact with the larger-scale circulation. Click on Global Modeling Studies to learn more.


Regional Models: Limited-area regional models with a range of complexity permit studies of the properties of gravity waves generated by convection in varied environmental conditions. The models range from full-physics simulations with models like the Weather Research and Forecasting (WRF) model to very idealized models forced by localized, time-varying heating. An example at right shows radar-observed rain at the ground (colors) and vertical velocities caused by the waves (gray shading) near the tropopause. Click on Gravity Wave Generation by Storms to learn more.


Research Projects:

• Observing Gravity Waves from Space


1. Global Positioning System Radio-occultation with COSMIC: Constellation Observing System for Meteorology, Ionosphere, and Climate
2. AIRS: Atmospheric Infrared Sounder
3. MLS: Microwave Limb Sounder
4. CRISTA: Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere
5. HIRDLS: High Resolution Dynamics Limb Sounder
6. Waves Explorer: A space science proposal to observe atmospheric gravity waves and their effects on the middle and upper atmosphere


• Gravity Wave Effects in Global Circulation Models


1. Parameterization of Gravity Wave Mean-Flow Forcing
2. Global Modeling Studies


• Gravity Wave Generation by Storms



• Atmospheric Waves Observed with High Altitude Aircraft and Balloon-Borne Instruments