It has been noted that when the convective Richardson number Ri* is used to characterize the depth of the entrainment zone, various parameterization schemes can be obtained. This situation is often attributed to the i...It has been noted that when the convective Richardson number Ri* is used to characterize the depth of the entrainment zone, various parameterization schemes can be obtained. This situation is often attributed to the invalidity of parcel theory. However, evidence shows that the convective Richardson number Ri* might be an improper characteristic scaling parameter for the entrainment process. An attempt to use an innovative parameter to parameterize the entrainment-zone thickness has been made in this paper. Based on the examination of the data of water-tank experiments and atmospheric measurements, it is found that the total lapse rate of potential temperature across the entrainment zone is proportional to that of the capping inversion layer. Inserting this relationship into the so-called parcel theory, it thus gives a new parameterization scheme for the depth of the entrainment zone. This scheme includes the lapse rate of the capping inversion layer that plays an important role in the entrainment process. Its physical representation is reasonable. The new scheme gives a better ordering of the data measured in both water-tank and atmosphere as compared with the traditional method using Ri*. These indicate that the parcel theory can describe the entrainment process suitably and that the new parameter is better than Ri*.展开更多
There exists great uncertainty in parameterizing snow cover fraction in most general circulation models (GCMs) using various empirical formulae, which has great influence on the performance of GCMs. This work reviews ...There exists great uncertainty in parameterizing snow cover fraction in most general circulation models (GCMs) using various empirical formulae, which has great influence on the performance of GCMs. This work reviews the commonly used relationships between region-averaged snow depth (or snow water equivalent) and snow cover extent (or fraction) and suggests a new empirical formula to compute snow cover fraction, which only depends on the domain-averaged snow depth, for GCMs with different horizontal resolution. The new empirical formula is deduced based on the 10-yr (1978-1987) 0.5°× 0.5° weekly snow depth data of the scanning multichannel microwave radiometer (SMMR) driven from the Nimbus-7 Satellite. Its validation to estimate snow cover for various GCM resolutions was tested using the climatology of NOAA satellite-observed snow cover.展开更多
Based on the two-stream approximation a broad-band parameterization scheme for solar radiative flux calculation is presented.The whole solar spectral region from 0.2 to 3.58 μm is divided into three broad spectral in...Based on the two-stream approximation a broad-band parameterization scheme for solar radiative flux calculation is presented.The whole solar spectral region from 0.2 to 3.58 μm is divided into three broad spectral intervals.The effec- tive broad-band optical depths and single scattering albedos in the atmosphere in each spectral interval can be obtained using parameterized formulae from known atmospheric parameters.The overlapping scattering and/or absorption ef- fects of two atmospheric constituents are considered properly.In the consideration of radiative effect of clouds in the atmosphere the single scattering albedos and backscattering parameters of clouds in each broad spectral interval are giv- en preliminarily and the cloud optical depths are determined according to the cloud liquid water content.展开更多
基金This paper was supported by the National Natural Science Foundation of China under Grant Nos.40105002 and 40333027.
文摘It has been noted that when the convective Richardson number Ri* is used to characterize the depth of the entrainment zone, various parameterization schemes can be obtained. This situation is often attributed to the invalidity of parcel theory. However, evidence shows that the convective Richardson number Ri* might be an improper characteristic scaling parameter for the entrainment process. An attempt to use an innovative parameter to parameterize the entrainment-zone thickness has been made in this paper. Based on the examination of the data of water-tank experiments and atmospheric measurements, it is found that the total lapse rate of potential temperature across the entrainment zone is proportional to that of the capping inversion layer. Inserting this relationship into the so-called parcel theory, it thus gives a new parameterization scheme for the depth of the entrainment zone. This scheme includes the lapse rate of the capping inversion layer that plays an important role in the entrainment process. Its physical representation is reasonable. The new scheme gives a better ordering of the data measured in both water-tank and atmosphere as compared with the traditional method using Ri*. These indicate that the parcel theory can describe the entrainment process suitably and that the new parameter is better than Ri*.
基金This work was conducted unlder the joint support of the National Natural Sciences Foundation of China under Grant Nos.40005008 and 40135020the Chinese Academy Project ZKCX2-SW-210.
文摘There exists great uncertainty in parameterizing snow cover fraction in most general circulation models (GCMs) using various empirical formulae, which has great influence on the performance of GCMs. This work reviews the commonly used relationships between region-averaged snow depth (or snow water equivalent) and snow cover extent (or fraction) and suggests a new empirical formula to compute snow cover fraction, which only depends on the domain-averaged snow depth, for GCMs with different horizontal resolution. The new empirical formula is deduced based on the 10-yr (1978-1987) 0.5°× 0.5° weekly snow depth data of the scanning multichannel microwave radiometer (SMMR) driven from the Nimbus-7 Satellite. Its validation to estimate snow cover for various GCM resolutions was tested using the climatology of NOAA satellite-observed snow cover.
文摘Based on the two-stream approximation a broad-band parameterization scheme for solar radiative flux calculation is presented.The whole solar spectral region from 0.2 to 3.58 μm is divided into three broad spectral intervals.The effec- tive broad-band optical depths and single scattering albedos in the atmosphere in each spectral interval can be obtained using parameterized formulae from known atmospheric parameters.The overlapping scattering and/or absorption ef- fects of two atmospheric constituents are considered properly.In the consideration of radiative effect of clouds in the atmosphere the single scattering albedos and backscattering parameters of clouds in each broad spectral interval are giv- en preliminarily and the cloud optical depths are determined according to the cloud liquid water content.
