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2001 Vol. 18, No. 6

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Meridional Wind Stress Anomalies over the Tropical Pacific and the Onset of El Ni?o Part Ⅱ: Dynamical Analysis
Zhang Renhe, Zhao Gang
2001, 18(6): 1053-1065. doi: 10.1007/s00376-001-0022-4
The data analyses in the first part of this study have shown that the sea surface temperature anomalies (SSTA) in the eastern equatorial Pacific are significantly correlated with the preceding anomalous convergence of the meridional wind stress near the equator. In order to understand the dynamical role of the convergent meridional wind stress anomalies in the El Nino occurring, an ideal wind stress which converges about the equator is set up based on the observations revealed in the first part. A simple dynamical model of tropical ocean is used to study the response of the tropical ocean to the convergent meridional wind stress. The results show that the convergent wind stress in the eastern equatorial Pacific is favorable for the occurrence of El Nino. When the convergent wind stress exerts on the tropical ocean, the westward propagating Rossby wave is excited, which, on the one hand, makes the mixed layer near the equator become thicker. On the other hand, the westward oceanic currents associated with the Rossby wave appear in the vicinity of the equator. The oceanic currents can drive the upper layer sea water to transfer to the west, which is favorable for the sea water to pile up in the western equatorial Pacific and to accumulate energy for the upcoming warm event.
Associations with the Interannual Variations of Onset and Withdrawal of the Changma
Lu Riyu, Huang Ronghui, Hee-Jeong Baek, Jai-Ho Oh, Baek-Jo Kim
2001, 18(6): 1066-1080. doi: 10.1007/s00376-001-0023-3
The associations of onset and withdrawal of the rainy season in South Korea (called Changma) have been examined. Composite studies showed that there are significant differences in circulations between extremely early and late onset (or withdrawals) not only over East Asia, but also over remote areas. The in situ significant differences include the upper-level jet over East Asia and the subtropical anticyclone over the western North Pacific at lower levels. The significant remote associations include the Indian monsoon and ENSO. The Indian summer monsoon is related to both onset and withdrawal of the Changma, while ENSO has a significant relation only to onset, but not to withdrawal.
Theoretical Aspect of Suitable Spatial Boundary Condition Specified for Adjoint Model on Limited Area
Wang Yuan, Wu Rongsheng
2001, 18(6): 1081-1089. doi: 10.1007/s00376-001-0024-2
Theoretical argumentation for so-called suitable spatial condition is conducted by the aid of homotopy framework to demonstrate that the proposed boundary condition does guarantee that the over-specification boundary condition resulting from an adjoint model on a limited-area is no longer an issue, and yet preserve its well-poseness and optimal character in the boundary setting. The ill-poseness of over-specified spatial boundary condition is in a sense, inevitable from an adjoint model since data assimilation processes have to adapt prescribed observations that used to be over-specified at the spatial boundaries of the modeling domain.In the view of pragmatic implement, the theoretical framework of our proposed condition for spatial boundaries indeed can be reduced to the hybrid formulation of nudging filter, radiation condition taking account of ambient forcing, together with Dirichlet kind of compatible boundary condition to the observations prescribed in data assimilation procedure. All of these treatments, no doubt, are very familiar to mesoscale modelers.
Comparing Cloud Radiative Properties between the Eastern China and the Indian Monsoon Region
Zhang Minghua, Yu Rucong, Yu Yongqiang
2001, 18(6): 1090-1102. doi: 10.1007/s00376-001-0025-1
Based on the data from International Satellite Cloud Climatology Project (ISCCP) and Earth Radiation Budget Experiment (ERBE), the climatic cloud properties and cloud radiative forcing in the eastern China and the Indian monsoon region are compared. Although both of the Indian monsoon region and the eastern China are included in the Asian monsoon region and the seasonal cycles of rainfall are in phase, the properties of clouds and related cloud radiative forcing are significantly different. All of cloud components in the Indian region have similar phase structure of seasonal cycle. The maximum cloud fractions occur in the summer monsoon period and high clouds dominate the total cloud fraction. However. the seasonal features of clouds in the eastern China are complex. It is the mid-low clouds rather than high clouds dominating the total cloud fraction. The maximum total cloud fraction occurs in spring season. The total cloud and mid-low cloud fractions in winter season are larger than that in summer season. A unique global distinction of clouds in the eastern China is the largest cover of nimbostratus clouds. Reflecting to the cloud properties, the maximums of negative short wave, positive long wave and negative net cloud radiative forcing in the Indian monsoon region are in the summer season. In the eastern China. large negative short wave cloud radiative forcing occurs in early summer. The annual mean negative net cloud radiative forcing in the eastern China is obviously larger than that in the Indian region.
Why Is the Climate Forcing of Sulfate Aerosols So Uncertain?
Hu Rongming, Serge Planton, Michel Déque, Pascal Marquet, Alain Braun
2001, 18(6): 1103-1120. doi: 10.1007/s00376-001-0026-0
Sulfate aerosol particles have strong scattering effect on the solar radiation transfer which results in increasing the planet albedo and, hence, tend to cool the earth-atmosphere system. Also, aerosols can act as the cloud condensation nuclei (CCN) which tend to increase the albedo of clouds and cool the global warming. The ARPEGE-Climat version 3 AGCM with FMR radiation scheme is used to estimate the direct and indirect radiative forcing of sulfate aerosols. For minimizing the uncertainties in assessing this kind of cooling effect, all kinds of factors are analyzed which have been mixed in the assessment process and may lead to the different results of the radiative forcing of aerosols. It is noticed that one of the uncertainties to assess the climate forcing of aerosols by GCM results from the different definition of radiative forcing that was used. In order to clarify this vague idea, the off-line case for considering no feedbacks and on-line case for including all the feedbacks have been used for assessment. The direct forcing of sulfate aerosols in off-line case is -0.57 W/m2 and -0.38 W/m2 for the clear sky and all sky respectively. The value of on-line case appears to be a little larger than that in off-line case chiefly due to the feedback of clouds. The indirect forcing of sulfate aerosols in off-line case is -1.4 W / m2 and -1.0 W / m2 in on-line case. The radiative forcing of sulfate aerosols has obvious regional characteristics. There is a larger negative radiative forcing over North America, Europe and East Asia. If the direct and indirect forcing are added together, it is enough to offset the positive radiative forcing induced by the greenhouse gases in these regions.
Comparison of Field Measurements of CH4 Emission from Rice Cultivation in Nanjing, China and in Texas, USA
Huang Yao, Jiang Jingyan, Zong Lianggang, Ronald L. Sass, Frank M. Fisher
2001, 18(6): 1121-1130. doi: 10.1007/s00376-001-0027-z
Field measurements of methane emission from rice paddies were made in Nanjing, China and in Texas, USA, respectively. Soil temperature at approximately 10 cm depth of the flooded soils was automatically recorded. Aboveground biomass of rice crop was measured approximately every 10 days in Nanjing and every other week in Texas. Seasonal variation of soil temperature in Nanjing was quite wide with a magnitude of 15.3℃ and that in Texas was narrow with a magnitude of 2.9℃. Analysis of methane emission fluxes against soil temperature and rice biomass production demonstrated that the seasonal course of methane emission in Nanjing was mostly attributed to soil temperature changes, while that in Texas was mainly related to rice biomass production. We concluded that under the permanent flooding condition, the seasonal trend of methane emission would be determined by the soil temperature where there was a wide variation of soil temperature, and the seasonal trend would be mainly determined by rice biomass production if there are no additional organic matter inputs and the variation of soil temperature over the rice growing season is small.
On the 4D Variational Data Assimilation with Constraint Conditions
Zhu Keyun
2001, 18(6): 1131-1145. doi: 10.1007/s00376-001-0028-y
An investigation is carried out on the problem involved in 4D variational data assimilation (VDA) with constraint conditions based on a finite-element shallow-water equation model. In the investigation, the adjoint technology, penalty method and augmented Lagrangian method are used in constraint optimization field to minimize the defined constraint objective functions. The results of the numerical experiments show that the optimal solutions are obtained if the functions reach the minima. VDA with constraint conditions controlling the growth of gravity oscillations is efficient to eliminate perturbation and produces optimal initial field. It seems that this method can also be applied to the problem in numerical weather prediction.
Strong/Weak Summer Monsoon Activity over the South China Sea and Atmospheric Intraseasonal Oscillation
Li Chongyin, Long Zhenxia, Zhang Qingyun
2001, 18(6): 1146-1160. doi: 10.1007/s00376-001-0029-x
The circulation pattern corresponding to the strong / weak summer monsoon in the South China Sea (SCS) region and the associated characteristics of the abnormal rainfall in Eastern China have been studied by using the NECP reanalysis data and precipitation data in China. The results show that the climate variations in China caused by the strong/weak summer monsoon are completely different (even in opposite phase). The analyses of atmospheric intraseasonal oscillation (ISO) activity showed that the atmospheric ISO at 850 hPa near the SCS region is strong (weak) corresponding to the strong (weak) SCS summer monsoon. And the analyses of the circulation pattern of the atmospheric ISO showed that the strong / weak SCS summer monsoon circulation (200 hPa and 850 hPa) result mainly from abnormal atmospheric ISO.This study also reveals that the atmospheric ISO variability in the South China Sea region is usually at opposite phase with one in the Jiang-huai River basin. For example, strong (weak) atmospheric ISO in the SCS region corresponds to the weak (strong) atmospheric ISO in the Jiang-huai River basin. As to the intensity of atmospheric ISO, it is generally exhibits the local exciting characteristics, the longitudinal propagation is weak.
Structure of Thunderstorm Gust Fronts with Topographic Effects
A. A. Bidokhti, T. Bani-Hashem
2001, 18(6): 1161-1174. doi: 10.1007/s00376-001-0030-4
Surface meteorological observations, associated with gust fronts produced by thunderstorm outflows over Tehran, an area surrounded by mountains, have been analyzed. Distinctive features are sudden drop in air temperature, up to 10℃, sharp increase in wind speed, up to 30 m s-1, with wind shift, to northwesterly, ressure jump, up to 4 hPa, humidity increase, up to 40%, and rain after some 20 min. Gust fronts which often occur in spring time, have a typical thickness of about 1.5 km and produce vertical wind shear of the order of 10-2s-1. Although these features seem to be common for most of the events, their intensities differ from one event to another, indicating that the gust fronts may occur in different sizes and shapes. Apart from a dominant effect on the formation of the original thunderstorms, topography appears to break up the frontal structure of the gust fronts. The internal Rossby radius of deformation for these flows is small enough (~ 100 km) for rotational effects to be minor.A laboratory model of the gust front (gravity current) also shows that it initially has a distinctive head with a turbulent wake, and can be broken up by topography. It is shown that when the environment is stratified, turbulence due to lobes and clefts instabilities near the nose of the current is suppressed. When the ground is rough, these instabilities are highly amplified and the internal Froude number of the flow is reduced. The bottom slope in the presence of rough topography leads to the break up of the current head and produces a broad and highly non-uniform head, recognized in the density signals.
Performance of a Parallel Finite Difference Atmospheric General Circulation Model
Zhang Xin, Wang Bin, Ji Zhongzhen
2001, 18(6): 1175-1184. doi: 10.1007/s00376-001-0031-3
A new version of the Institute of Atmospheric Physics (IAP) 9-Layer (9L) atmospheric general circulation model (AGCM) suitable for Massively Parallel Processor (MPP) has been developed. This paper presents the principles of the parallel code design and examines its performance on a variety of state-of-the-art parallel computers in China. Domain decomposition strategy is used to achieve parallelism that is implemented by Message Passing Interface (MPI). Only the one dimensional domain decomposition algorithm is shown to scale favorably as the number of processors is increased.
The Parallel Computing of GPS Ray-shooting Model
Li Shuyong, Wang Bin, Zhang Xin
2001, 18(6): 1185-1191. doi: 10.1007/s00376-001-0032-2
The Global Positioning System (GPS) ray-shooting model is a self-sufficient observation operator in GPS MET (Meteorology) data variational assimilation linking up the GPS observation data and the atmospheric state variables. But its huge computations make it impracticable in real data assimilation so far. In order to overcome this default, a parallel version of the GPS ray shooting model has been developed,and has been running successfully on the PC cluster manufactured under the support of the China National Key Development Planning Project for Basic Research: The Large Scale Scientific Computation Research.High speed-up and Efficiency as well as good scalability are obtained. This is an important step for this GPS observation operator to become practicable.
The Climatic-induced Net Carbon Sink by Terrestrial Biosphere over 1901-1995
Yang Xin, Wang Mingxing, Huang Yao
2001, 18(6): 1192-1206. doi: 10.1007/s00376-001-0033-1
The spatial and temporal variability of land carbon flux over the past one hundred years was investigated based on an empirical model directly calculating soil respiration rate. Our model shows that during 1901-1995, about 44-89 PgC (equals to 0.5, 0.9 PgC/yr respectively) were absorbed by terrestrial biosphere. The simulated net ecosystem productivity (NEP) after the 1930s was close to the estimated value of" missing C sink” from deconvolution analysis. Most of the total carbon sink happened during 1951-1985 with the estimated value of 33-50 PgC. Three major sinks were located in the tropics (10°S-10°N), Northern mid-latitudes (30°-60°N) and Southern subtropics (10°-40°S). During 1940s-mid-1970s, carbon sinks by terrestrial ecosystem increased with time, and decreased after the mid-1970s. These may be due to the ch anging of climate condition, as during the 1940s-1970s, temperature decreased and precipitation increased, while after the mid-1970s, an opposite climate situation occurred with evident increasing in temperature and decreasing in precipitation. Usually, warmer and dryer climate condition is not favor for carbon absorption by biosphere and even induces net carbon release from soil, while cooler and wetter condition may induce more carbon sink. Our model results show that the net carbon flux is particularly dependent on moisture / precipitation effect despite of temperature effect. The changing of climate in the past century may be a possible factor inducing increases in carbon sink in addition to CO2 and N fertilizer.
The Effects of Anomalous Snow Cover of the Tibetan Plateau on the Surface Heating
Li Guo ping, Lu Jinghua, Jin Bingling, Bu Nima
2001, 18(6): 1207-1214. doi: 10.1007/s00376-001-0034-0
On the basis of snow data and AWS (Automatic Weather Station) data obtained from the Tibetan Plateau in recent years (1993 to 1999), the features of sensible heat, latent heat and net long-wave radiations are estimated, and their variations in more-snow year (1997/1998) and less-snow year (1996/1997) are analyzed comparatively. The relationships between snow cover of the Tibetan Plateau and plateau's surface heating to the atmospheric heating are also discussed. The difference between more-snow and less-snow year in spring is remarkably larger than that in winter. Therefore, the effect of anomalous snow cover of the Tibetan Plateau in winter on the plateau heating appears more clearly in the following spring of anomalous snow cover.
Analysis of the Surface Temperature on the Tibetan Plateau from Satellite
Jiang Hao, Wang Keli
2001, 18(6): 1215-1223. doi: 10.1007/s00376-001-0035-z
Using surface temperature data set of the ISCCP-C2, spatial features and temporal changes of the surface temperature on the Tibetan Plateau are analyzed through the EOF method. The impact and response between the surface temperature and climatic variation about precipitation and monsoon are discussed. Representativenesses of the meteorological observing stations are investigated and three subregions are compartmentalized for the surface temperature on the Tibetan Plateau.
Climate Change due to Greenhouse Effects in China as Simulated by a Regional Climate Model
Gao Xuejie, Zhao Zongci, Ding Yihui, Huang Ronghui, Filippo Giorgi
2001, 18(6): 1224-1230. doi: 10.1007/s00376-001-0036-y
Impacts of greenhouse effects (2 CO2) upon climate change over China as simulated by a regional climate model over China (RegCM / China) have been investigated. The model was based on RegCM2 and was nested to a global coupled ocean-atmosphere model (CSIRO R21L9 AOGCM model). Results of the control run (1 CO2) indicated that simulations of surface air temperature and precipitation in China by RegCM are much better than that by the global coupled model because of a higher resolution. Results of sen sitive experiment by RegCM with 2 CO2 showed that the surface air temperature over China might increase remarkably due to greenhouse effect, especially in winter season and in North China. Precipitation might also increase in most parts of China due to the CO2 doubling.
A Case Modeling of Sea-Land Breeze in Macao and Its Neighborhood
Lin Wenshi, Wang Anyu, Wu Chisheng, Fong Soi Kun, Ku Chimeng
2001, 18(6): 1231-1240. doi: 10.1007/s00376-001-0037-x
PSU/NCAR MM5 was utilized to simulate the sea-land breeze circulation in Macao and the three-dimensional flow around the Pearl River estuary. Four two-way nested grids having resolution of 1, 3.9. and 27 km were included in the simulation. It was initialized with conventional observational data, and a 30 h simulation and analysis of one sea-land breeze case were performed. It was shown that the model with a finer resolution (1 km) captures the sea breeze and land breeze in Macao with reasonable skill. The sea breeze front and the thermal internal boundary layer (TIBL) were also obviously revealed. However, the coarser horizontal resolution (3 km) could capture the sea breeze but not the land breeze.