Qa-Qz

QBO

Acronym for Quasi-Biennial Oscillation.

Quasi-Biennial Oscillation

The alternation of easterly and westerly winds in the equatorial stratosphere with an interval between successive corresponding maxima of 20 to 36 months. The regimes start at about 30 km and propagate downwards at about one kilometer per month.

quasi-geostrophic approximation

A set of filtered equations to the equations of motion governing atmospheric or oceanic flow, the chief of which is the vorticity equation. In this, the horizontal wind is replaced by the geostrophic wind in the term representing the vorticity but not in the term representing the divergence.

quasi-geostrophic equations

A set of equations developed using the quasi-geostrophic approximation. These are formally valid only when the planetary vorticity is large compared to the relative vorticity of the fluid, when the variation in the Coriolis parameter over the domain is small compared to its mean value, and when free surface and topographic fluctuations are both much smaller than the average fluid depth. See Pedlosky (1987).

quantum meter

An instrument used to measure PAR.

QuikSCAT

Acronym for the NASA Quick Scatterometer Mission, a satellite launched from Vandenberg Air Force base aboard a Titan II vehicle on June 19, 1999. QuikSCAT was a quick recovery mission to fill the gap created by the loss of data from the ADEOS-1 satellite, which lost power in June 1997. It was launched into a sun-synchronous, 803 km, circular orbit with a local equator crossing time at the ascending node of 6:00 AM $\pm$ 30 minutes. The recurrent period is 4 days (57 obits), the orbit period 101 minutes (14.25 orbits per day) and the inclination 98.616$^\circ$. QuikSCAT consists of two major systems, the spaceborne observatory and the ground data processing system.

The main sensor on QuikSCAT is the SeaWinds scatterometer, an active microwave radar designed to measure winds over the oceans. It is a conically scanning pencil-beam scatterometer, which provides a higher SNR, is smaller, and provides better coverage than a fan-beam scatterometer. It measures near-surface wind speed and direction under all weather and cloud conditions over the oceans.

[http://podaac.jpl.nasa.gov/quikscat/]

Q-vector method

A method for diagnosing vertical motion from measured data in the atmosphere or ocean. The Q-vector method is similar to the quasigeostrophic equations, except it introduces an ageostrophic component neglected by the latter. In the ocean, the vertical velocity is estimated from the following Q-vector equation:

$$\left({\nabla^2}\,+\,{ {f_0^2} \over {N^2} } { {\partial^2} \over {\partial {z^2}} }\right)\,w\, = \, {2\over{N^2}}\,\nabla\cdot\mathbf{Q}$$

$$\mathbf{Q}\,=\,{g\over{\rho_0}} \left( { {\partial{u_g}} \over {\... ...partial{v_g}} \over {\partial y} } { {\partial\rho} \over {\partial y} }\right)$$

where $f$ is the Coriolis force, $N$ is the buoyancy frequency, $g$ is gravitational acceleration, $\rho_0$ is a reference density, $\rho$ is the density, and ${(u,v)}_g$ are the horizontal geostrophic velocities. A detailed derivation and discussion can be found in Pollard and Regier (1992). See also Wang and Ikeda (1997).