HAO 2010 PROFILES IN SCIENCE: Chihoko Yamashita

Contact

303-497-2195
yamashic@ucar.edu

Dr. Chihoko Yamashita is a Graduate Research Assistant at the High Altitude Observatory at NCAR. She studies gravity wave impacts on the atmospheric coupling during stratospheric sudden warming.

Publication:

(1) Responses of mesosphere and lower thermosphere temperatures to gravity wave forcing during stratospheric sudden warming
Yamashita, C., H.-L. Liu, and X. Chu (2010), Geophys. Res. Lett., 37, L09803, doi:10.1029/2009GL042351.

Abstract:

Chihoko Yamahsita, Han-Li Liu, and Xinzhao Chu examined how gravity waves (GWs) affect the temperature in the mesosphere and the lower thermosphere (MLT) during a stratospheric sudden warming (SSW) through modifying GW parameters in the NCAR Thermosphere-Ionosphere-Mesosphere-Electrodynamics General-Circulation Model. They confirmed that the characteristics of GW forcing are dependent on the specifications of GW parameters: the height of GW forcing region is mainly determined by GW amplitudes and wavelengths, and their vertical depths are closely tied to the spectral width of GW phase speed. These GW forcings generate planetary waves (PWs) in-situ in the MLT at high latitudes, and the characteristics of these PW forcings vary with the different GW forcing characteristics. The MLT cooling and warming agree with the location and strength of up/downward circulation induced by both GW and the in-situ generated PWs in the MLT. Therefore, the mechanisms of GW controlling the MLT temperature during a SSW are directly through GW forcing and indirectly through the in-situ generation of PWs.

The zonal-mean (top; a,b,c) temperature changes from January 18 over-plotted with residual circulation changes, (2nd column; d,e,f) parameterized gravity wave (GW) forcing changes (m/s/day), (3rd column; g,h,i) resolved planetary wave forcing changes (m/s/day), and (bottom; j,k,l) planetary scale perturbation on zonal wind (m/s) at 64ºN on January 25 for three different cases (left: base case, middle: case 1, and right: case 2). The residual circulation vectors are normalized. Large black arrows (in d-i) represent Coriolis force induced by the corresponding forcing changes. Negative/positive value represents the westward/eastward forcing and zonal wind. Compared with the base case, case 1 uses the narrower spectral width and case 2 uses the longer horizontal wavelength and larger amplitude GWs
Figure: The zonal-mean (top; a,b,c) temperature changes from January 18 over-plotted with residual circulation changes, (2nd column; d,e,f) parameterized gravity wave (GW) forcing changes (m/s/day), (3rd column; g,h,i) resolved planetary wave forcing changes (m/s/day), and (bottom; j,k,l) planetary scale perturbation on zonal wind (m/s) at 64°N on January 25 for three different cases (left: base case, middle: case 1, and right: case 2). The residual circulation vectors are normalized. Large black arrows (in d-i) represent Coriolis force induced by the corresponding forcing changes. Negative/positive value represents the westward/eastward forcing and zonal wind. Compared with the base case, case 1 uses the narrower spectral width and case 2 uses the longer horizontal wavelength and larger amplitude GWs.