By analyzing the total ozone data from TOMS and ground-based observations, it is found that a large area with extremely low ozone occurred over the Tibetan Plateau during December 14-17, 2003. After correcting the bias in TOMS data, the area with the total ozone < 220 DU is found to be over 2500000 km2, and the minimum value is only 190 DU. It is the first time that an ozone mini-hole or an extremely low ozone event is found to occur over the Tibetan Plateau.
This paper uses SHDOM (Spherical Harmonics Discrete Ordinate Method) to calculate the nadir bidi-rectional reflectance distribution function (BRDF) of the cumulus and stratocumulus fields at the wave-lengths of 0.67 μm and 2.13μm, and discusses the impact of cloud inhomogeneity on BRDF. The cloud fields are adopted from I3RC Phase II, which are used to compare 3D radiative transfer models. The simulation results show that the cu field has 6% abnormal BRDF values (BRDF>1) with the increase of solar zenith angle. Further analyses show that grid cells whose BRDF is greater than one gather to-gether at the local trough of the top of cloud. These regions can receive not only the direct incident solar beam, but also the beam scattered by the higher cloud of its neighborhood. Hence, the BRDF of those regions is enhanced. The abnormal BRDF phenomenon shows that the cloud inhomogeneity can result in inconsistency between satellite observation and plane parallel theory, implying that the re-flectance observed by high resolution satellite is maybe enhanced by the cloud 3D effects. Thus one should take this fact into account when using the product retrieved by these data. The dominant solar zenith angles are quite large in the mid-high altitude area, and the impact of cloud inhomogeneity on these areas may be more significant.
