The EFFECT OF LAND WIDTH ON LAND-SEA BREEZE
By Using WRF.4.0.3 & NCL
The Point of Collision of Sea Breezes
“The narrower the land width, the more a collision of the sea breeze occurs”
For finding the collision of sea breeze, we analyzed the change and development of each wind component and also temperature changes additionally.
<Analysis criteria for the sea-breeze collision: U-wind>
In U-wind graph, the red area means the west wind and the blue area means the east wind. In this situation, it can be the sea breeze collision, if those two opposing areas meet with a clear boundary without turbulence.
<Analysis criteria for ascending air current caused by the sea-breeze collision: W-wind>
Originally, the vertical impact range of the sea breeze is 350-1000 meters. However, since we use ideal model in which the input soundings are not given, the sea breeze can affect the higher altitudes. Therefore, when the wind reaches an altitude of 1-2km, it is purely by sea breeze collision and this mean a strong ascending air current by collision.
Then the vortex of breeze was generated again along the coastal line and enlarged its buffer zone with the increase in temperature and pressure differences between the land and sea surfaces. The vortex depth of 350 m was obtained in the early morning and about 1 000 m around 3 p.m. for the modeling period. (R. Pokhrel and H. Lee, 2011)
Unlike the repeated rising and falling currents in land, if the rising air flow’s grid width is greater than 0.5 grid which means about 10km, we also conclude this is a strong ascending air current.
Additionally, if there is penetration into the upper circulation by strong ascending air flow within the range of the sea breeze (less than 2km), we analysis that this is the strong upward current caused by sea breezes' collision.
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Case1 : Sea breeze collide on 3 p.m.
KST: 2018-06-01_14:00:00
KST: 2018-06-01_15:00:00
KST: 2018-06-01_16:00:00
[ U-wind and W-wind ]
At 14kst, the wind of + component and – component does not meet and there is a region of weak wind expressed in white in the middle of the land. But at 15kst, you can see two different colored areas bumping into each other and forming clear boundary line. This means collision of sea breeze.
If you look at the W-wind at the time of 15kst, where the sea breeze overlaps, you will see the rising current, thick and vertical, forming high. At 16kst, an hour later, strong ascending air currents can be seen entering the upper layer of circulation beyond the impact of the sea breeze height. The altitude at which the rising air flow rises is higher than other cases because the land receives the highest heat energy between 3 p.m. and 4 p.m. when the sea breeze collide in case 1. Due to the large amount of heat energy, the upward air flow strengthens, causing interpenetration to higher altitudes.
[ Temperature ]
Before sea breezes’ colliding, the isothermal air column is formed on the center of land mass. The center of air column rises flat and it seems unstable in terms of energy balance.
But after sea breezes’ colliding, the energy imbalance is resolved and the air temperature seems little more stable than the former.
It means that sea-breeze circulations reduce the thermal energy imbalance between land and sea by collision.
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Case2 : Sea breeze collide on 5 - 6 p.m.
KST: 2018-06-01_17:00:00
KST: 2018-06-01_18:00:00
[ U-wind and W-wind ]
In the second case, by the same analysis as in the first case, sea breeze collision occurs between 17kst and 18kst. If you look at the collision time, 18kst is the time when the temperature of land starts to drop, the heat energy of land becomes relatively lower than case 1. Therefore, the interpenetration of the ascending air toward the upper layer by the collision of the sea breeze is located at a lower altitude than the case1.
[ Temperature ]
It has same result as Case 1
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Case3 : No Sea breeze collision
KST: 2018-06-01_19:00:00
KST: 2018-06-01_20:00:00
[ U-wind and W-wind ]
For case3, which is Default, no graph appeared that met all the criteria given above. The sea breeze seems to collide at 19kst, but winds in two opposite direction are not perfectly touching each other.
Also, if you look at the w-wind graph, you can't see the powerful rising air currents caused by the sea breeze collision. Even we can find a downward current that separates the ascending air flow at 20kst.
[ Temperature ]
Before sea breezes’ colliding, the isothermal air column is formed on the center of land mass.
But before the sea-breezes collide each other, the center of the land cools down because of the broader land width.