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1、2011,PHYSICS OF THE MIDDLE AND UPPER ATMOSPHERE 中高层大气物理学 Solar Irradiance,Absorption of ultraviolet radiation by ozone (O3),surface,particles and magnetic fields,photons,core,convection zone,radiative zone,surface,atmosphere,magnetosphere,sunspot,plage,coronal mass ejection,bow shock,plasmasphere,no
2、t to scale,solar wind,heliosphere,atmosphere,Sun-Earth System: Energy Coupling,Radiation,All molecules with a temperature above zero Kelvin (-273.15 ) emit radiant energy. Energy of a photonAbsorption: electron excitation from low to high orbit Emission: electron de-excitation from high to low orbit
3、 Lyman series, L = 1216 Balmer series, H = 6563 ,Irradiance,对每一特定的频率间隔，如果每单位时间物体发射的光子与吸收的一样多，就说这个物体和它的环境处于辐射平衡。 物体每单位面积和单位时间内发射的总辐射能，称为辐射度(Irradiance)或发射功率E。 一定波长的辐射度E称为光谱辐射度。表示每单位波长间隔（即波长和 + d之间）的辐射度。E和E指的半球上的单位面积在任何方向的总的发射。 单位立体角内的强度I称为辐射强度(Radiance)。 在各向同性辐射时，与辐射度之间的关系为 E=I。,Blackbody,A blackbody
4、 is a hypothetical object composed of a sufficient number of molecules absorbing and emitting radiant energy in all parts of the electromagnetic spectrum. 如果频率为的各向同性辐射投射在物体的表面上，一部分辐射被吸收，一部分被反射，一部分将透射。 把物体吸收辐射的百分率称为吸收率k。k的大小取决于物体的性质及温度。定义对所有频率的吸收率都等于1的物体为黑体。 黑体的辐射是各向同性的，只与物体的温度有关。黑体发射的光谱辐射强度I 称为黑体的特征
5、辐射，用B(, T)表示。,Blackbody Irradiance,Stephan-Boltzmann定律：积分辐射度EB与温度的四次方成正比Stephan-Boltzmann常数对于温度为T的黑体，定义B为一定频率处的辐射强度 由Planck辐射定律导出也可以用波长表示,Blackbody Irradiance,辐射强度最大对应的波长是m维恩位移定律 (Wien displacement law) 黑体的最大辐射度所在的波长与黑体的温度成反比。,课后习题,物体每单位面积和单位时间内发射的总辐射能，称为辐射度(Irradiance)或发射功率E。 E指的半球上的单位面积在任何方向的总的发射。
6、 单位立体角内的强度I称为辐射强度(Radiance)。 试证明在各向同性辐射时，与辐射度之间的关系为 E=I。,Solar Radiation Spectrum,Blackbody of 5000-6000K Continuum blackbody radiation in visible light and longer wavelength Absorption bands by vapor and carbon dioxide Of solar radiation: 7% is in the ultraviolet 44 % is in the visible 49 % is in t
7、he infrared,Solar Total Irradiance,Radiant flux (辐射通量) is the rate of radiant energy transfer has units of J.s-1, 1 J.s-1 = 1 Watt (W) radiant flux of the sun is 3.9x1026 WIrradiance (辐照度) is the radiant flux per unit area has units of W.m-2The solar constant (太阳常数) is the irradiance passing through
8、 an area perpendicular to the direction that the electromagnetic waves are traveling at the top of the Earths atmosphere. The mean value of solar constant is 1366 W.m-2.,Visible part of the radiation,According to the Stephan-Boltzmanns law When T=5780K, in the visible part of the spectrum the radiat
9、ed power per unit area is Since the solar radium is R= 7 108m, the total radiated power from the Sun will be As a distance from the Sun corresponding to the average position of the Earth, from the conservation of energy Ee is the radiation per unit are hitting the Earth The radiation density from Su
10、n will vary at the position of the Earth give by:,Solar constant variation,The solar constant varies over about 6.9% during a year from a low of 1321 W/m in early July when Earth is farthest from the Sun to 1412 W/m in early January when Earth is closest to the Sun. If the annual variation due to Su
11、n-Earth distance is removed, during a full sunspot solar cycle the value varies by only by 0.1% from maximum and minimum.,Short Wavelength Radiation,There is a maximum close to 500 nm in the solar spectrum 1.5W m-2 nm according to the Wien displacement law, T = 5780K For a temperature of the order o
12、f 2106 K, the radiation maximum is at,UV radiation,Excessive continuum and line emission in EUV and X-ray from corona and transition region Near Ultraviolet (NUV) 300 - 400 nm Middle Ultraviolet (MUV)200 - 300 nm Far Ultraviolet (FUV) 100 - 200 nm Extreme Ultraviolet (EUV) 10 - 100 nm Soft X-ray 1 -
13、 10 nm,UV/EUV radiation,Far UV region between 0.1 and 0.2 m Originates from the uppermost layer of the photosphere, with effective blackbody temperature of 4500 K Completely absorbed by molecular oxygen at altitude between 80 and 120 km EUV between 0.01 and 0.1 m Originates in the chromosphere There
14、 is a number of strong emission lines such as the hydrogen lines at 121.6 nm (Ly-), 102.5 nm (Ly-) Emission lines from multi-ionized Si, Fe, Mg, N and O The strong atomic emission lines are all originating in the low temperature region of the chromosphere, while the ionic lines are emitted from the
15、high temperature region near the coronal base.,UV/EUV Radiation,While the solar spectrum between 0.2 and 3.2 m is rather constant during a solar cycle, the UV lines and X-ray emission are more variable. The emissions in the EUV and X-ray regimes (50 nm) are often connected to sunspots and other visi
16、ble phenomena on the solar surface. The estimated emission curves for temperatures vary between 5105 K and 4106 K. The estimated peak intensity is about 10-4 W m-2 nm,Variations of UV and X-ray,At wavelengths shorter than about 300 nm (EUV and X-ray), there is relatively large variation (greater than 100%).,Solarterrestrial Energy Source,22 year magnetic cycle 11 year sunspot number cycle,
