共查询到10条相似文献，搜索用时 625 毫秒
1.
Zhang Banglin 《大气科学进展》1994,11(4):447-458
The Tahiti-Darwin Southern Oscillation index provided by Climate Analysis Center of USA has been used in numerous studies. But, it has some deficiency. It contains noise mainly due to high month-to-month variability. In order to reduce the level of noise in the SO index, this paper introduces a fully data-adaptive filter based on singular spectrum analysis. Another interesting aspect of the filter is that it can be used to fill data gaps of the SO index by an iterative process. Eventually, a noiseless long-period data series without any gaps is obtained. 相似文献
2.
Simulation of state-dependent high-frequency atmospheric variability associated with ENSO 总被引：1，自引：1，他引：0
Jong-Seong Kug K. P. Sooraj Daehyun Kim In-Sik Kang Fei-Fei Jin Yukari N. Takayabu Masahide Kimoto 《Climate Dynamics》2009,32(5):635-648
High-frequency atmospheric variability depends on the phase of El Nino/Southern Oscillation (ENSO). Recently, there is increasing
evidence that state-dependent high-frequency atmospheric variability significantly modulates ENSO characteristics. Hence,
in this study, we examine the model simulations of high-frequency atmospheric variability and, further, its dependency on
the El Nino phase, using atmospheric and coupled GCMs (AGCM and CGCM). We use two versions of physical packages here—with
and without convective momentum transport (CMT)—in both models. We found that the CMT simulation gives rise to a large climatological
zonal wind difference over the Pacific. Also, both the climate models show a significantly improved performance in simulating
the state-dependent noise when the CMT parameterization is implemented. We demonstrate that the better simulation of the state-dependent
noise results from a better representation of anomalous, as well as climatological, zonal wind. Our further comparisons between
the simulations, demonstrates that low-frequency wind is a crucial factor in determining the state-dependency of high-frequency
wind variability. Therefore, it is suggested that the so-called state-dependent noise is directly induced by the low-frequency
wind anomaly, which is caused by SST associated with ENSO. 相似文献
3.
I. Matyasovszky 《Theoretical and Applied Climatology》2003,74(1-2):69-75
Summary ?Homogenized monthly and annual mean temperatures for ten locations in Hungary from 1901 to 1999 are analyzed. A principal
component analysis was performed and the first new component containing 94.5% of the total variance has been retained. A linear
regression of this variable on a sea level pressure NAO index results in relatively weak correlations. In order to consider
the trends in both data series, a polynomial of years is added to the regression. After a selection of the optimal polynomial
orders by Akaike’s criteria the correlation coefficients are significantly increased. The Southern Oscillation Index (SO index)
characterizing the El Ni?o – Southern Oscillation (ENSO) is then incorporated in the relationship via a nonlinear, threshold
model. The threshold model consists of the above linear regressions but is conditioned on the SO index threshold variable.
The rationale behind this approach is to allow a change of model performance according to ENSO phase. The thresholds are not
pre-specified but are estimated from the data, while the number of thresholds is chosen by Akaike’s criteria. A likelihood
ratio test shows an improvement of these models over the linear model with very strong significance levels, except in June.
Received March 25, 2002; revised June 20, 2002; accepted June 23, 2002 相似文献
4.
Lazar Lazić 《Meteorology and Atmospheric Physics》2000,75(1-2):121-130
Summary Following a recent approach of Fox-Rabinovitz an iterative Matsuno or a “Super-Matsuno” style scheme is applied as a filter
in the Eta Model. In contrast to Fox-Rabinovitz, we however apply the scheme not for all of the model’s time-differencing
but for its adjustment terms only. These distinctions compared to the original Fox-Rabinovitz’-method are made easy to implement
by the split time differencing approach of the Eta, and at the same time would appear clearly appropriate for the “initialization”
purpose. In addition, while Fox-Rabinovitz emphasizes the use of the method within a long time-scale data assimilation framework,
we are focusing on the impact of the method in a short-range forecasting environment/time-scale.
After a short one hour “initialization” procedure is completed, standard model integration is continued, now very much free
of noise. The Super-Matsuno style scheme is found to balance initially unbalanced external and internal modes and to significantly
reduce the high-frequency noise during the first 6 time steps. In a control case noise also reduces in amplitude as integration
proceeds, but at a much slower rate. The model integration results with and without “initialization” after 6 hours are however
very similar. Even so, it is to be expected that small differences, given that they have resulted from the removal of spurious
initial noise, have to be beneficial.
Received July 5, 1999/Revised January 11, 2000 相似文献
5.
Some features associated with Eastern China Precipitation (ECP), in terms of mean climatology, sea-sonal cycle, interannual
variability are studied based on monthly rainfall data. The rainfall behavior over Eastern China has fine spatial structure
in the seasonal variation and interannual variability. The revealed characteristics of ECP motivate us dividing Eastern China
into four sub—regions to quantify significant lag—correlations of the rainfalls with global sea surface temperatures (SSTs)
and to study the ocean’s pre-dominant role in forcing the eastern China summer monsoon rainfalls. Lagged correlations between
the mid—eastern China summer monsoon rainfalls (MECSMRs) and the global SSTs, with SST leading to rain-fall, are investigated.
The most important key SST regions and leading times, in which SSTs are highly corre-lated with the MECSMRs, are selected.
Part of the results confirms previous studies that show links between the MECSMRs and SSTs in the eastern equatorial Pacific
associated with the El Nino — Southern Oscillation (ENSO) phenomenon. Other findings include the high lag correlations between
the MECSMRs and the SSTs in the high and middle latitude Pacific Ocean and the Indian Ocean, even the SSTs over the Atlantic
Ocean, with SST leading—time up to 4 years. Based on the selected SST regions, regression equa-tions are developed by using
the SSTs in these regions in respective leading time. The correlation coefficient between the observed rainfalls and regressed
rainfalls is over 0.85. The root mean square error (RMSE) for regressed rainfall is around 65% of the standard deviation and
about 15% of the mean rainfall. The regression equation has also been evaluated in a forecasting mode by using independent
data. Discussion on the consistence of the SST—rainfall correlation with circulation field is also presented.
This work was jointed supported by Chinese Academy of Sciences under Grant “Hundred Talents” for “Validation of Coupled Climate
models” and by U.S. Department of Energy under Grant DEFG0285ER 60314 to SUNY at Stony Brook. The authors are grateful to
Professor R. D. Cess at SUNY, Stony Brook for his supports. 相似文献
6.
Two land surface schemes, one the standard Biosphere / Atmosphere Transfer Scheme Version le (B0Z) and the other B1Z based on B0Z and heterogeneously-treated by ‘combined approach’ , were coupled to the meso-scale model MM4, respectively. Through the calculations of equations from the companion paper, parameters representing land surface heterogeneity and suitable for the coupling models were found out. Three cases were simulated for heavy rainfalls during 36 hours, and the sensitivity of short-term weath-er modeling to the land surface heterogeneity was tested. Through the analysis of the simulations of the three heavy rainfalls, it was demonstrated that B1Z, compared with B0Z, could more realistically reflect the features of the land surface heterogeneity, therefore could more realistically reproduce the circulation and precipitation amount in the heavy rainfall processes of the three cases. This shows that even short-term weather is sensitive to the land surface heterogeneity, which is more obvious with time passing, and whose influence is more pronounced in the lower layer and gradually extends to the middle and upper layer. Through the analysis of these simulations with B1Z, it is suggested that the bulk effect of smaller-scale fluxes (i.e., the momentum, water vapor and sensible heat fluxes) near the significantly-heterogeneous Land surface is to change the larger-scale (i.e., meso-scale) circulation, and then to influence the development of the low-level jets and precipitation. And also, the complexity of the land-atmosphere interaction was shown in these simulations. 相似文献
7.
8.
一个压力坐标下的海洋环流模式 总被引：5，自引：0，他引：5
A new oceanic general circulation model in pressure coordinates is formulated. Since the bottom pressure changes with time, the vertical coordinate is actually a pressure-σ coordinate. The numerical solution of the model is based on an energy-conservation scheme of finite difference. The most important new feature of the model is that it is a truly compressible ocean model and it is free of the Boussinesq approxima tions. Thus, the new model is quite different from many existing models in the following ways: 1) the exact form of mass conservation, 2) the in-situ instantaneous pressure and the UNESCO equation of state to calculate density, 3) the in-situ density in the momentum equations, 4) finite difference schemes that conserve the total energy. Initial tests showed that the model code runs smoothly, and it is quite stable. The quasi-steady circulation patterns generated by the new model compare well with existing models, but the time evolution of the new model seems different from some existing models. Thus, the non-Boussinesq models may provide more accurate information for climate study and satellite observations. 相似文献
9.
Tianjun Zhou Stefan Brönnimann Thomas Griesser Andreas M. Fischer Liwei Zou 《Climate Dynamics》2010,34(4):573-585
The authors present a reconstruction of summer (June–July–August) mean dynamic Indian monsoon index (DIMI) back to 1880 based
on a large number of historical surface observation data as well as information from the upper air data. The reconstruction
shows a satisfying skill in terms of both the value of reduction of error and an evaluation against other independent monsoon
indices. The skill of reconstruction increases over time with more predictor data (in particular upper-level data) becoming
available. A comparison with the observed all Indian summer monsoon rainfall index (AIRI) shows a high consistence in both
inter-decadal and inter-annual variability. The reconstruction shows stronger than normal monsoon during the 1880s, 1915–1925
(around 1920) and 1930–1945 (around 1940) as the AIRI. The El Nino/Southern Oscillation (ENSO)—monsoon relationship is reasonably
captured in the reconstruction. Powers concentrating within quasi-biennial band stand out in the reconstruction as well as
in the AIRI. A comparison of the reconstruction against an atmospheric general circulation model simulation with specified
SST and external forcing agents spanning 1901–1999 indicates a slightly higher reproducibility of monsoon circulation than
monsoon rainfall in terms of interannual variability. The relationship between the Asian continent warming and the ENSO–monsoon
connection is also discussed by using the new dynamic index. 相似文献
10.
Recently large quantities of data from many different field experiments have become available to facilitate the examination of various proposed models of atmospheric dispersion. However, these data sets are invariably corrupted by some form of random noise and, also, significant baseline drift is often recorded. Consequently, these problems require careful consideration and treatment before the data can be used in model testing. In many papers, the noise is simply treated by thresholding but this is unacceptable since many valid readings are discarded. This paper examines the performance of two different noise removal methods that are more soundly based, both physically and mathematically. The first is a Wiener filter with certain modifications, and the second is a maximum entropy inversion technique. A comparison of the results of applying these methods is presented, with the emphasis on the practical treatment of the numerical and computational problems that arise. The problem of baseline drift is treated initially by applying a number of subjective fits. Subsequently the noise removal methods are applied. In general, it is found that the maximum entropy method performs better than the Wiener filter for the data sets examined here. 相似文献