地球大氣緯向風系、副熱帶高壓和太陽較差自轉的形成機制
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Formation Mechanism of Earth Atmospheric Zonal Winds, Subtropical High and Solar Differential Rotation
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    摘要:

    利用NS(NavierStokes)方程和一個基本假設推導出星體大氣平均緯向風和平均氣壓公式,根據公式討論了地球大氣緯向風系和平均氣壓以及副熱帶高壓的成因并進行了數值模擬。結果發現,地球大氣緯向風是大氣微團密度與基準大氣密度存在差異而形成的,大氣微團的密度大于(小于)基準密度,則為西風(東風);密度的差距越大,風速越強。在中高緯度地區大氣微團吸收的太陽輻射少而向空間輻射多,導致其密度變大,因此在中高緯度盛行西風;而在低緯度地區,因為吸收的太陽輻射多使大氣微團密度變小而盛行東風。夏季(冬季)太陽輻射增強(減弱)使得大氣微團密度變小(增大),進而導致中高緯度地區西風減弱(增強)和低緯度地區的東風加強(減弱)。風速的大小還與緯度的余弦成正比,這就使得最大西風帶位于中緯度地區而不是大氣微團密度最大的極地附近;也使得最大的東風不是發生在太陽直射點附近而是靠近赤道一側。根據氣壓公式和大氣密度的經向差異可以得出中高緯度區域氣壓隨緯度的升高而減小的分布特征,而太陽輻射所造成低緯地區密度的減小是該區域氣壓大于中高緯度的主要原因;在赤道上緯度的正弦為零,使得氣壓在赤道上存在極小值,導致了赤道槽和副熱帶高壓的形成,且太陽輻射越強、副熱帶高壓越強。因為緯度正弦因子的存在,使得副高脊線總是位于太陽直射點的向極一側。在假定太陽大氣為理想氣體的情況下,由NS方程推導出太陽大氣自轉角速度隨緯度的變化公式,由此解釋了太陽較差自轉的成因在于低緯地區的大氣微團密度大于高緯度,并且在赤道上大氣微團的密度最大。該公式與觀測得到的經驗公式在略去高階小項后一致。由此認為,太陽大氣的運動在形成機制上與地球大氣沒有區別,不同的是在太陽表面沒有象地球表面那樣受太陽輻射的影響,NS方程是所有星體(包括恒星、行星)大氣共同遵守的動力方程。

    Abstract:

    By using the NS equation and a basic hypothesis, the stellar atmospheric mean zonal wind and mean pressure formulas are derived. Based on these equations, the causes of earth atmospheric zonal wind system, mean pressure and subtropical high are discussed and numerically simulated. The results show that earth atmospheric zonal wind is formed by the density difference between atmospheric microcells and benchmark atmosphere. When the density of atmospheric microcells is greater (less) than benchmark atmospheric density, the direction of wind is westerly (easterly); the greater the density difference is, the stronger the wind will be. In middle and high latitude regions, the solar radiation absorbed by atmospheric microcell is less than their radiation into the space, which makes the density increase, so the west wind prevails in middle and high latitude regions; in the low latitude region, east wind prevails because the solar radiation absorbed by atmospheric microcell is more than their radiation. In summer (winter), the solar radiation strengthens (weakens), which makes the density of atmospheric microcells increase (decrease) and leads to the west wind in middle and high latitude areas weakening (strengthening) and east wind in the low latitude areas strengthening (weakening). The wind speed is proportional to cosine of latitude, which makes the strongest westerly belt located in the middle latitude region but not polar region where the density of atmospheric microcells is the biggest, and it also makes the strongest east wind appears not around the direct sunlight point but near the equator side. According to the pressure formula and the meridional difference of atmospheric density, the distribution feature that the pressure decreases as latitude increases in the middle and high latitude regions can be gained. The decreasing of density caused by solar radiation in the low latitude region is the main reason to make the pressure higher in this region than in middle and high latitude areas. The sine of latitude on equator is zero, so there exists a minimum of pressure on the equator, which leads to the formation of the equatorial trough and subtropical high, and the stronger the solar radiation is, the stronger the subtropical high will be. Because of the existence of latitude sine factor, the axis of ridge is always on the polar side of the direct sunlight point. Based on assumption that the solar atmosphere is ideal gas, the formula of the solar atmospheric rotation angular velocity with latitude is derived by using the NS equation, which explains the cause of the solar differential rotation; that is, the micelle density at low latitudes is larger than that at high latitudes and it is largest at the equator. The formula is fully consistent with the empirical formula by observation in omitted higher order small items. These results indicate that the movement of the solar atmosphere has no difference with the earth atmosphere in formation mechanisms; the difference is that there is no solar radiation on the surface of the sun as the earth surface; the NS equation is suitable for all stars.

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葉更新.地球大氣緯向風系、副熱帶高壓和太陽較差自轉的形成機制[J].氣象科技,2015,43(5):849~857

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  • 收稿日期:2014-10-09
  • 定稿日期:2015-04-20
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  • 在線發布日期: 2015-11-02
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