| There exits changes of two aspects while solar radiation pass through atmosphere or ocean water, containing solar radiation value and solar spec-tral characteristic. Based on the previous analysis on Q:W, in paper, a new optical parameter named as principal wavelength was defined, which inherits the physical significance of Q:W and is also endowed with a new property which is the gravity center of solar radiation spectrum at wavelength-axis. Principal wavelength unveils the variation of solar radiation spectrum pen-etrating atmosphere or ocean. As a constant is the only difference between the definitional equations of Q:W and principal wavelength, principal wave-length is able to replace Q:W. Likewise, W:Q can be explained as the total energy of lmol photons at principal wavelength.First, principal wavelength was calculated from the extraterrestrial ir-radiance data directly observed by SORCE from2004to2011. During the seven years, the average value of principal wavelength is543.86nm and the standard deviation is0.011. Principal wavelength as the response of solar spectral variation from400nm to700nm presents an obvious inter-annual variation of increased and decreased after that. Analysed from the climatological extraterrestrial irradiance data provided by Lean, principal wavelength at extraterrestrial atmosphere has been calculated and presents an obvious climatological variation of11years as well as total solar irra-diance(TSI). Principal wavelength has a negative correlation with TSI. A longer timescale change by the removal of11years periodical change is presented that principal wavelength is decreasing from1840to1960and stabilized after that. Comparison with global average temperature, there is a positive correlation in between them. In particular, recently, the syn-chronized movement between them verify that the change of solar spectrum should directly influence the earth-atmosphere system.Principal wavelength arriving at earth surface is influenced by air molecules, aerosol and cloud cover. To explore the variation of principal wavelength on the surface, solar irradiance data observed at different latitude under the different weather are used. The variation of principal wavelength un-der clear-sky is analyzed and presents a general pattern in which principal wavelength is increasing and then decreasing rapidly with increasing solar zenith angle. Under a overcast day, principal wavelength varies very little with increasing solar zenith angle. However, the principal wavelength under clear-sky is more than in a overcast day. In clear-sky, the difference between principal wavelengths is attributed to the different pollutant concentration in atmosphere.To explain the variation of principal wavelength under clear-sky, the SPCTRAL2model is used to simulate the change of principle wavelength observed at Bohai sea. Analysing the simulation results indicates that the pattern of simulation principal wavelength is close to the observational prin-cipal wavelength. Some impact factors, including solar zenith angel, vis-ibility, Angstrom parameter, ozone scale height and a few meteorological parameters had been analyzed by SPCTRAL2. The influence of ozone scale height and meteorological paramters, including wind speed, pressure, tem-perature, humidity at earth’s surface on principal wavelength is negligible. And, Angstrom parameter and visibility is the important impact factors and induces the dramatic change of principal wavelength. In paper, principal wavelength calculated from direct irradiance and principal wavelength cal- culated from diffuse irradiance had been analyzed. Principal wavelength cal-culated from direct irradiance presents a persistent increase with increasing solar zenith angle, and Principal wavelength calculated from diffuse irradi-ance presents a persistent increase first and then a dramatic decrease with increasing solar zenith angle. Principal wavelength obtained from total solar irradiance is between them. It is concluded that the observational principal wavelength has been varied with the ratio of diffuse irradiance to total solar irradiance. In paper, the expression between principal wavelength and the ratio has been built.The variation of principal wavelength under sea water has been analyzed by using the solar irradiance profiles observed at Beaufort Sea in2006and Bering Sea in2007. Principal wavelength in sea water belonging to Type Ⅰ sea water in Beaufort Sea presents a dramatic decrease in upper10m and then the performance of stabilization below10m. Principal wavelength at depth of70m presents a regional property in connection with the total attnuation matter concentration above70m. Principal wavelength in Bering sea water belonging to Type Ⅱ sea water presents a rapid decrease within10m first, and a accelerative increase in10-20m layer, and final a slow decrease beyond20m. It is concluded that the performance of CDOM plays an importance role.It is concluded that the observational principal wavelength at depth of70m is determined in chief by total attenuation matter concentration above70m. Incorpcorating the numerical analysis, a fundamental property of prin-cipal wavelength has been presented that the variation of principal wave-length only change with total attenuation matter concentration in upper layer, and has no connection with the depth of attenuation mater.A new expression of principle wavelength has been built throught deriva- tion of definitional function, and can explain the exponential movement of principal wavelength profile in sea water. The attenuation coefficient of prin-cipal wavelength has been defined and is equivalent to the different between the attenuation coefficient of photosynthetic radiation flux density and the attenuation coefficient of photosynthetic photo flux density, expressing the asynchronization property of the attenuation process of solar spectrum. The deviation ratio of principal wavelength has been solved, formulating the dif-ferent between the observational principal wavelength and ideal principal wavelength in pure sea water. The change of principal wavelength profile in sea water can been perfectly explained by this deviation ratio concept.Based on the deviation ratio concept of principal wavelength, a nu-merical relationship and semi-empirical relationship between principal wave-length and chlorophyll concentration had been built. And the determination coefficient from semi-empirical relationship is more than92%。Principal wavelength, similar with PAR, is an important parameter in study on solar radiation. The only different between them is that PAR expresses the change of solar radiation value, and principal wavelength ex-presses the change of solar spectrum characteristic. In research on solar radiation, both of them are comlementary. There are amounts of potential application of principal wavelength on the study of the extraterrestrial irra-diance, solar radiation arriving on earth surface, solar radiation penetrating into sea water and so on. |
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