Comparison of QSCAT and NCEP Average Wind Directions
The average wind directions for QSCAT and NCEP are compared. Wind directions are computed on
a 2° x 2° grid by averaging u and v components of unit length vectors; and then computing
the direction of the average u and v. The averaging was done for the years 2000 and 2001,
using the northern hemisphere winter (DJFM) and summer (JJAS) seasons. The NCEP data comes from
the Reanalysis on a T62 grid (1.875° x ca. 1.9°).
The computations were motivated by results from drifter derived surface currents and collocated NCEP
surface wind directions by Peter Niiler and Nicolai Maximenko. Maximenko's figure is shown below.
Click on the images for enlarged versions of plots.
Fig. 1. Longterm average surface currents and winds (courtesy of Nicolai Maximenko).
QSCAT and NCEP derived wind directions follow.
Fig. 2. Average wind directions in DJFM of 2000 (Dec1999-Mar2000), for (a) NCEP, and (b) QSCAT.
The colors in Fig. 1 are chosen to emphasize the circular nature of directions: N = red, E = yellow, S = green,
and W = blue. NE directions are orange-to-yellow, SE are light green, SW are greenish, and NW directions are
purple and darkred. The contour program, however, cannot handle the transition from -180° to +180° correctly:
the sharp line with rainbow colors, depicting wind due south, is an artifact of the contour-coloring program (e.g. off the coast of California).
In the following figures the wind direction differences of NCEP - QSCAT are depicted.
The largest differences appear at latitudes where the winds transition from westerlies to easterlies
(e.g. around 30° N), and along the equator.
Fig. 3. Wind direction difference NCEP-QSCAT in 2000, for (a) DJFM, and (b) JJAS.
The zonal average of the above global maps can be computed, and then the difference of the two seasons
(DJFM-JJAS) can be plotted as well.
Fig. 4. Zonal average of wind direction differences NCEP-QSCAT, in (a) 2000, and in (b) 2001.
DJFM differences are in black, JJAS differences are in red.
Fig. 5. DJFM-JJAS differences of zonal averages of NCEP-QSCAT, in (a) 2000, and in (b) 2000
and 2001 (red).
last modified on April 6, 2004
Go
Back
)
)
)
)
)
)
)
)
)