Understanding Local Diurnal
Winds
• Sea Breezes and Land Breezes dependent on the
differences in heating and cooling between land and
water.
• Upslope and downslope winds forced by the
differences in heating and cooling between terrain
and lowlands.
Diurnal Local Winds
Diurnal Winds 101
Why?
Sea and Land Breezes Influence Clouds!
The Peninsula Effect with
colliding sea breezes
Can enhance convection and
precipitation during the day
Stepped Art
Fig. 7-6, p. 175
Summer
Diurnal
Winds
The Sound Breeze
Viewed Using
Ferry Data
Picture take in Sequim looking N
Strong Regional Sea Breeze
Winds During the Summer
Sea Breeze Winds Along the
Southern Oregon Coast
• Gusts frequently reach 30-35 knots during
the summer during the afternoon.
• Very painful to stay on the beach!
• Strong pressure gradient normal to the coast
between the warm land areas and the cold
upwelling water.
Southern Oregon Coast Near Brookings
Average Summer Wind Speeds
18
16
14
Wind Speed (knots)
12
10
8
6
Hoquiam
4
Newport
North Bend
Gold Beach
2
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Hour (LDT)
2-minute average July-August winds along the Northwest coast.
Land Breezes Tend to Be Weak
in the Northwest
• Why? Because the land rarely cools down
more than the water.
• Local minimum temperatures generally in
the low to mid-50s…similar to the
temperature of the Sound and the Pacific
Ocean.
• But it can happen in winter during
unusually cold periods.
Stepped Art
Fig. 7-5, p. 174
Land Breeze
example during a
cold period.
Slope Winds
Upslope Flow on Heated Slopes
Downslope Flow on Cooled Slopes
Fig. 7-11, p. 178
Fig. 7-12, p. 179
Low temperatures are generally cooler
in low spots on cold, cloud-free nights.
The Columbia River Gorge
An Example of Diurnal Gap
Flows
35
Columbia Gorge Winds: August 25, 2002
30
Dales Mean Wind
Dales Gusts
25
Carson M ean Wi nd
Wind Speed (kts)
T routdale
20
15
10
5
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Hour
14
15
16
17
18
19
20
21
22
23
24
Regional Diurnal Circulations
Total Diurnal Wind Pattern Can
Be a Superposition of Many
Diurnal Circulations
• Sea breezes and land breezes along coasts
and between inland areas and oceans/bodies
of water
• Upslope and downslope flows, both in
valleys and between higher elevations and
lowlands.
The End
Fovell (UCLA) Sea Breeze
Simulations
• http://www.atmos.ucla.edu/~fovell/ASother
/mm5/LA_seabreeze.html