a
a
b
b Figure 17 Geopotential surface m
2
s
-2
in the level of 200 hPa a and 850 hPa b.
200 hPa. The contours of geopotential also represent the pressure system in the
atmosphere where the horizontal pressure gradient force becomes so strong when the
contours are close together and grow weaker as the contours farther apart.
4.5 Horizontal Wind Profile
Wind develops as a result of spatial differences in atmospheric pressure due to the
variation of heating on the Earth’s surface. As pressure gradient occurs, the air flows from an
area of high toward an area of low pressure. Similarly, it is equivalent for pressure
gradients measured at a constant altitude to gradients of geopotential measured on a
surface of constant pressure. Wind propagates in all direction both horizontally and
vertically. However, the occurrence of vertical winds are much less than the horizontal ones
as the pressure gradient force that flowing upward is balanced by gravity force in the
opposite direction. Since vertical motion is an exceptional case, the focus of this study is on
the horizontal motion that is respectively defined in zonal and meridional direction. The
movement of wind in isobaric coordinate is affected by gradients of geopotential. The
masses of air are moving from low geopotential areas toward high geopotential
m
2
s
2
m
2
s
2
areas as a gradient vector always points in the direction of greater values. Both components
of horizontal winds has its positive and negative velocities; positive and negative
zonal velocities represents the easterly and westerly winds, while positive and negative
meridional velocities represents northerly and southerly winds. The results indicate that wind
magnitudes in the level of 200 hPa are greater than the ones in the level of 850 hPa due to
differences in geopotential value. However, both in the level of 200 hPa and 850 hPa, the
wind movements went in the same direction as it is assumed that the factors of turbulence
flow and friction near the Earth’s surface is negligible in this study.
a
a
b Figure 18 The acceleration of zonal wind ms
-2
in the level of 200 hPa a and 850 hPa b.
b Figure 18 The acceleration of zonal wind ms
-2
in the level of 200 hPa a and 850 hPa b.
ms
2
ms
2
