Atmospheric basics Flashcards
wind is a
vector quantity
wind has
speed and direction
the wind speed is measured in
m/s or knots
1 knot =
0.51 m/s
The wind direction is measured in ………………. from ……………………………
degree angle north (0 degrees / 360 degrees)
Wind direction indicates the direction
from which the wind blows.
wind velocity is a ……………. component
scalar
The three scalar components of wind in Cartesian (x, y and z) coordinate system
are expressed as
The horizontal wind vector can be expressed in terms of scalars as:
The two scalar wind components (u and v) can be obtained from
wind speed and direction
The two scalar wind components (u and v) can be obtained from the wind speed and direction as follows
Synoptic scale motions have a size of approximately
1000 km
for synoptic scale motions friction ……
can be neglected above the lowest few km
scale analysis for the ………………………………. for ……………………………………. shows that ……………………………………………………….. are in exact balance
horizontal momentum equations
mid-latitude synoptic scale disturbance
the horizontal components of coriolis force and pressure gradient force
geostrophic approximation for the x and y direction
define Rossby number
nondimensional number which gives a measure of the magnitude of the acceleration compared to the Coriolis force
how can you obtain the Rossby numbre?
by forming the ratio of the characteristic scales of acceleration and the coriolis force terms
equation of Rossby number
the smallness of the Rossby number is
a measure of the validity of the geostrophic approximation
if Ro<1
the coriolis force is a dominant force, and the flow tends to become geostrophic
if Ro>1
the flow tends to be non-geostophic
you can neglect acceleration term in
mid latitude
geostrophic wind always
blows parallel to the isobars with low pressure to the left
as density is nearly constant at a given height, …………………………..
the geostrophic wind is linearly proportional to the pressure gradient
as f—-> 0 near the ………………….., the geostrophic balance is not valid at …………………..
equator
low latitudes
the vertical momentum equation indicated that
the vertical pressure gradient force is in exact balance with the gravity force
define hydrostatic equilibrium
the pressure at any point is simply equal to the weight of a unit cross-section column of air above that point
the hydrostatic approximation may be expressed as
the higher the PGF the
stronger the wind
vertical PGF =
gravity force
