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1997 Vol. 14, No. 3

Display Method:
Impacts of Land Surface on Climate of July and Onset of Summer Monsoon: A Study with an AGCM plus SSiB
Liu Hui, Wu Guoxiong
1997, 14(3): 289-308. doi: 10.1007/s00376-997-0051-8
To get more insight into the impacts of land surface processes on climate, a simplified biosphere model (SSiB) developed by Sellers and Xue et al. is implemented into the LASG / IAP spectral climate AGCM (R15L9). The new model has been integrated for more than twenty years. The diagnoses of the integration show that the implementing of the land surface processes has greatly improved the simulation of July climate. It is also shown that the seasonal variations of land surface characteristics have great impacts on the onset of summer monsoon, especially the seasonal march of wind at 850 hPa and precipitation over the regions of summer monsoon.
Relationships between Atmospheric Circulation Patterns and CO2 Greenhouse-Gas Concentration Levels in the Alpine Troposphere
A. Longhetto, S. Ferrarese, C. Cassardo, C. Giraud, F. Apadttla, P. Bacci, P. Bonelli, A. Marzorati
1997, 14(3): 309-322. doi: 10.1007/s00376-997-0052-7
Middle tropospheric CO2 air concentrations, measured during a four year observation period at an Alpine Sta-tion (Plateau Rosa , Italian North-West Alps, 3480 m a.s.l.), have been correlated with the relevant synoptic air tra?jectories crossing the observation site Meaningful relationships have been found among average curvature, altitude and potential temperature of clus?ters of homogeneous trajectories and their related CO2 concentrations measured at Plateau Rosa, allowing an objec?tive identification of weather conditions giving rise to fully mixed air masses corresponding to background atmos?pheric CO2 levels. Air trajectories were calculated by using the wind speed fields provided by the ECMWF objective analysis. As during the analysis period a change of the ECMWF model resolution occurred (from T106 to T213), the study was al?so carried out in the sub-periods respectively preceding and following this change (in September 1991). Even if some features of the wind field turned out to be statistically different in the two sub-periods, nevertheless the differences on the trajectory patterns were small enough to keep almost unchanged all conclusions drawn for the whole four-year period.
Development and Propagation of Equatorial Waves
Xiaofan Li, Han-Ru Cho
1997, 14(3): 323-338. doi: 10.1007/s00376-997-0053-6
Development and propagation of equatorial waves are investigated with the model which includes convection -wave convergence feedback and convection-frictional convergence feedback. Two experiments with an initial Kelvin wave (Exp. K) and with an initial Rossby wave (Exp. R) are carried out. The equatorial waves in Exp. R grow much faster than those in Exp. K. The equatorial waves in both experiments follow zonal (eastward / westward) and meridional (poleward) propagation. The equatorial waves can be partitioned into two meridional modes using Parabolic Cylinder Function. An equa?tor mode denotes a wave component with a positive precipitation center at the equator and an off-equator mode rep?resents a wave component with positive precipitation centers off the equator. The equator mode dominates in Exp. K whereeas the off-equator mode dominates in Exp. R. The rapid wave growth in Exp. R is interpreted by analyzing the eddy available potential energy (EAPE) generation. Stronger off-equator mode in Exp. R obtains more EAPE through convection-frictional convergence feedback which results in more rapid wave growth. The relative vorticity tendency is determined by interactions between Earth’s vorticity and lower-troposphere convergence (divergence effect) and between the meridional gradient and lower-troposphere circulation (beta effect). The eastward and poleward propagation of equatorial waves is a result of the divergence effect, and the westward movement is caused by the beta effect.
Influences of the Extratropical Pacific SST on the Precipitation of the North China Region
Geng Quanzhen, Ding Yihui, Huang Chaoying
1997, 14(3): 339-349. doi: 10.1007/s00376-997-0054-5
The influences of the extratropical Pacific SST on the precipitation of the North China region are reexamined with the observational data and studied with numerical simulations by using NCAR CCM2. It is found that there ex-ist high positive correlations between the annual precipitation of the North China region and the extratropical Pacific SST in late spring, especially in two regions, e.g., the Kuroshio Current region and the midlatitude central Pacific re-gion. The numerical simulations with NCAR CCM2 show that the warmer SSTs in the Kuroshio Current region and the midlatitude central Pacific in late spring can generate a large-scale circulation pattern over the Asia-Pacific re-gion that is favorable to the precipitation of the North China region.
Particle Size Truncation Effect on the Inference of Effective Particle Diameter
Liu Chunlei, Yao Keya
1997, 14(3): 350-354. doi: 10.1007/s00376-997-0055-4
The effective ice crystal particle diameter (De) of cirrus clouds can be inferred by comparing the measured radar / lidar backscattering ratio with the theoretically calculated one. The calculated ratios are based upon assump-tions of ice crystal particle density and size distribution, and it will be affected by the artificially assumed particle size ranges. This size truncation effect on the inference of effective particle diameter will be investigated theoretically by assuming the cirrus ice particle spherical and particle density of 0.9g / cm3. Results show that the truncation at large particle end has very small effect on the inference of De , but the truncation at the small particle end will have some ef-fect on the inference of De.
A Finite-Mode Model of Ideal Fluid Dynamics on the 2-Sphere
Wei Mozheng
1997, 14(3): 355-368. doi: 10.1007/s00376-997-0056-3
We develop the finite-mode model for a two-dimensional Euler system on the sphere based on Hopped’s discovery in group theory. This model strives to keep as many invariants of the original Euler equation as possible. Theoretically, the number of invariants in this model is limited only by computing power. At present, almost all the popular numerical models in weather and climate researches such as numerical weather prediction models and general circulation models (GCMs) use spectral method. However all these spectrally truncated models do not keep all the invariants except for the energy and the enstrophy. By using this model one is able to study the influence from some other lost invariants. The result from this model is expected to be closer to that of the original Euler equations than from ordinary spectrally truncated models. The relevant fundamental equations and important formulas for this model are given explicitly.
On the Unified Theory of Atmospheric Particle Systems Part II: Self-affine Particles
Liu Yangang
1997, 14(3): 369-388. doi: 10.1007/s00376-997-0057-2
As the second attempt at unifying treatment of atmospheric particle systems, this paper further examines shape characterization of atmospheric particles. First, to support the theoretical framework developed in Part I, methods for studying non-spherical particles are reviewed. It is argued that these different methods can be unified under fractal geometry through the generalized power laws given in Part I. Empirical power-laws for hydrometeors scat-tered in literature since 1935 are summarized and reevaluated in terms of fractals. Second, generalization from self-similar to self-affine particles is discussed. Self-affinity of atmospheric particles is exemplified by examining the exponents in the power laws between the length along a- and c-axis of ice crystals. It is argued that unlike Euclidean and self-similar particles, self-affine particles do not have a simple dimensional relation between original particles and their projections; the relation for projection of self-similar particles and Mandelbrot’ thumb rules for intersection respectively set the lower and upper bound. Using published data, self-affine particles are shown to exist in the at-mosphere. The existence of self-affine particles in turn calls for instruments that can simultaneously measure mass, area and maximum diameter (or their equivalents).
Man-Computer Interactive Method on Cloud Classification Based on Bispectral Satellite Imagery
Yu Fan, Liu Changsheng, Chen Weimin
1997, 14(3): 389-398. doi: 10.1007/s00376-997-0058-1
A bispectral cloud classification method based on man-computer interactive way, i.e. a unit feature space clasification method (UFSCM), has been presented in this paper. Apart from land and water, six types of clouds including cumulonimbus, multilayer cloud system, thin / think cirrus, middle and low level clouds are recognized. The method has been tested by using more than two hundred samples, with total accuracy reaching 87.1%.
Turbulent Fluxes over Inhomogeneous Landscape
Ye Zhuojia, Li Jun, Fan Sihong
1997, 14(3): 399-408. doi: 10.1007/s00376-997-0059-0
Mesoscale surface turbulent fluxes over a complex terrain surrounded by oceans have been investigated using a 3-D numerical mesoscale model, under conditions with and without synoptic flows. The study indicated that under synoptically calm condition, the allocation and intensity of mesoscale surface turbulent fluxes (MSTFs) were greatly impacted by the thermally forced mesoscale circulation (TFMC) over mesoscale heterogeneous landscape. The max-imum values of sensible (Hs) and latent (LE) heat fluxes were located over the convergent zones and considerably im-pacted by the soil wetness (M), but did not depend strongly on the atmospheric background thermal stability (β0). The simulated results suggested that the sensible heat flux was closely proportional to the square of wind speed in the surface layer. By the action of synoptic flow, the allocation of LE was shifted to downwind, its intensity increased.
The African Climate as Predicted by the IAP Grid-Point Nine-Layer Atmospheric General Circulation Model (IAP-9L-AGCM)
Chineke Theo Chidiezie, Bi Xunqiang, Wang Huijun, Xue Feng
1997, 14(3): 409-416. doi: 10.1007/s00376-997-0060-7
A brief introduction is given of the Grid-point 9-layer Atmospheric General Circulation Model (AGCM) de-veloped at the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences. The results of the 1980-1989 Atmospheric Model Inter-Comparison Program (AMIP) run were compared with observed European Centre for Medium-Range weather Forecasts (ECMWF) temperature data for the same period. The statistical analysis, and Grids Analysis and Display System (GrADS) results have shown that the model holds a great promise in predicting the African climate with considerable accuracy, within and across the seasons. This is a great hope for climate re-search in Africa which is data-sparse region.
Solar Multi-Spectral Radiometric Observations of Atmospheric Optical Thickness over Pasarlapudi Gas Well Blow-Out Site in India
G. Pandithurai, P.C.S. Devara
1997, 14(3): 417-424. doi: 10.1007/s00376-997-0061-6
Multi-spectrai observations of solar radiation using a Volz sun-photometer have been carried out during February 24-March 2, 1995 in the vicinity of the blow-out of the gas well at Pasarlapudi, Andhra Pradesh, India. These unique and special observations have been utilized to study the aerosol, Rayleigh molecular and gaseous optical thicknesses. The re-sults of the analysis of the observations indicated, besides low gas concentrations well below their background values, sig-nificant variations in aerosol optical thickness (AOT) at visible and neat-infrared wavelength regions. The wavelength de-pendence of AOT revealed wide variations in the Junge aerosol size exponent from 0.98 to 6.70 indicating the presence of both sub-micron and coarse-mode aerosol particles over the observational site. A close correspondence between AOT and surface-level meteorological parameters during the period of observations was also noticed.
Seasonal Variations in the Vertical Structure of Water Vapor Optical Depth in the Lower Troposphere over a Tropical Station
P. Ernest Raj, P.C.S. Devara
1997, 14(3): 425-432. doi: 10.1007/s00376-997-0049-2
Spatio-temporal variations of water vapor optical depth in the lower troposphere (450-3850 m) over Punt (18o32’N, 73o51’E, 559 m Above Mean Sea Level), India have been studied over a period of five years. The mean ver-tical structure showed that the moisture content is greatest at the lowest level and decreases with increasing altitude, except in the south-west monsoon season (June to September) where an increase upto 950 m has been found. Optical depths are maximum in the monsoon season. The increase from pre-monsoon (March-May) to monsoon season in moisture content on an average is by about 58% in the above altitude range. The temporal variations in surface Rela-tive Humidity and optical depth at 450 m show positive correlation. The amplitude of seasonal oscillation is the larg-est at 1465 m altitude. The time-height cross-sections of water vapor optical depths in the lower troposphere showed a contrast between years of good and bad monsoon.