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Shifeng Hao, Xiaopeng Cui, and Jianping Huang

Abstract

The square conservative exponential integral method (SCEIM) is proposed for transport problems on the sphere. The method is a combination of the square conservation algorithm and the exponential integral method. The main emphasis in the development of SCEIM is on conservation, positive-definite, and reversibility as well as achieving comparable accuracy to other published schemes. The most significant advantage of SCEIM is to change the forward model to the backward model by setting a negative time step, and the backward model can be used to solve the inverse problem. Moreover, the polar problem is significantly improved by using a simple effective central skip-point difference scheme without major penalty on the overall effectiveness of SCEIM. To demonstrate the effectiveness and generality of the SCEIM, this method is evaluated by standard cosine bell tests and deformational flow tests. The numerical results show that SCEIM is a time-convergence method as well as a grid-convergence method, and has a strong shape-preserving ability. In the tests of the inverse problem, the sharp fronts are successfully regressed back into their initial weak fronts and the cosine bells move against the wind direction and return to the initial position with high accuracy. The numerical results of forward simulations are compared with those of published schemes, the total mass conservation, and error norms are competitive in term of accuracy.

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Jian-Ping Huang and Gerald R. North

Abstract

Due to the variety of periodic or quasi-periodic deterministic forcings (e.g., diurnal cycle, seasonal cycle, Milankovitch cycles, etc.), most climate fluctuations may be modeled as cyclostationary processes since their properties are modulated by these cycles. Difficulties in using conventional spectral analysis to explore the seasonal variation of climate fluctuations have indicated the need for some new statistical techniques. It is suggested here that the cyclic spectral analysis he used for interpreting such fluctuations. The technique is adapted from cyclostationarity theory in signal processing. To demonstrate the usefulness of this technique, a very simple cyclostationarity stochastic climate model is constructed. The results show that the seasonal cycle strongly modulates the amplitude of the covariance and spectrum. The seasonal variation of intraseasonal oscillations in the Tropics has also been studied on a zonally symmetric all-land planet in the absence of external forcing. The idealized planet has no ocean no topography. A 15-year length seasonal run of the atmosphere is analyzed with the NCAR Community Climate Model (CCM2, R15). Analysis of the simulation data indicates the presence of intraseaonal oscillations in the Tropics, which are also localized in the time of year.

Both examples suggest that these techniques might be useful for analysis of fluctuations that exhibit locality in both frequency and season.

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Shanshan Wang, Jianping Huang, and Xing Yuan
Open access
Haipeng Yu, Jianping Huang, and Jifan Chou

Abstract

This study further develops the analog-dynamical method and applies it to medium-range weather forecasts. By regarding the forecast field as a small disturbance superimposed on historical analog fields, historical analog errors can be used to estimate and correct forecast errors. This method is applied to 10-day forecasts from the Global and Regional Assimilation and Prediction System (GRAPES). Both the distribution of atmospheric circulation and the pattern of sea surface temperature (SST) are considered in choosing the analog samples from a historical dataset for 2001–10 based on NCEP Final (FNL) data. The results demonstrate that the analog-dynamical method greatly reduces forecast errors and extends the period of validity of the global 500-hPa height field by 0.8 days, which is superior to results obtained using systematic correction. The correction effect at 500 hPa is increasingly significant when the lead time increases. Although the analogs are selected using 500-hPa height fields, the forecast skill at all vertical levels is improved. The average increase of the anomaly correlation coefficient (ACC) is 0.07, and the root-mean-square error (RMSE) is decreased by 10 gpm on average at a lead time of 10 days. The magnitude of errors for most forecast fields, such as height, temperature, and kinetic energy is decreased considerably by inverse correction. The model improvement is primarily a result of improvement for planetary-scale waves, while the correction for synoptic-scale waves does not affect model forecast skill. As this method is easy to operate and transport to other sophisticated models, it could be appropriate for operational use.

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Yongkun Xie, Guoxiong Wu, Yimin Liu, and Jianping Huang

Abstract

The three-dimensional connections between Eurasian cooling and Arctic warming since 1979 were investigated using potential vorticity (PV) dynamics. We found that Eurasian cooling can be regulated by Arctic warming through PV adaptation and PV advection. Here, PV adaptation refers to the adaptation of PV to forcing and coherent dynamic–thermodynamic adaptation to PV change. In a PV perspective, first, the anticyclonic circulation change over the Arctic is produced by a negative PV change through PV adaptation, in which the change means the linear trend from 1979 to 2017. The negative PV change is directly regulated by Arctic warming because the vertical structure of Arctic warming is stronger at lower levels, which generates a negative PV change through the diabatic heating effect. Second, the circulation change produces a change in horizontal PV advection due to the existence of climatological PV gradients. Thus, as a balanced result, both the circulation change and PV change extend to the midlatitudes through horizontal PV advection and PV adaptation. Eventually, Eurasian cooling at the surface and in the lower troposphere is dominated by PV changes at the surface through PV adaptation. Meanwhile, enhanced Eurasian cooling in the middle troposphere is dominated by top-down influences of upper-level PV change through PV adaptation. Nevertheless, the upper-level PV changes are still contributed to by horizontal PV advection associated with Arctic warming. Overall, the general dynamics connecting Eurasian cooling with Arctic warming are demonstrated in a PV view.

Open access
Kwang-Y. Kim, Gerald R. North, and Jianping Huang

Abstract

Many climatic time series seem to be a mixture of unpredictable fluctuations and changes that occur at a known frequency, as in the case of the annual cycle. Such a time series is called a cyclostationary process. The lagged covariance statistics of a cyclostationary process are periodic in time with the frequency of the nested undulations, and the eigenfunctions are no longer Fourier functions. In this study, examination is made of the properties of cyclostationary empirical orthogonal functions (CSEOFs) and a computational algorithm is developed based on Bloch's theorem for the one-dimensional case. Simple examples are discussed to test the algorithm and clarify the nature and interpretation of CSEOFs. Finally, a stochastic model has been constructed, which reasonably reproduces the cyclostationary statistics of a 100-yr series of the globally averaged, observed surface air temperature field. The simulated CSEOFs and the associated eigenvalues compare fairly with those of the observational data.

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Yongli He, Jianping Huang, Herman Henry Shugart, Xiaodan Guan, Bin Wang, and Kailiang Yu

Abstract

Siberia has experienced a pronounced warming over the past several decades, which has induced an increase in the extent of evergreen conifer forest. However, the potential slowing of the trend of increasing surface air temperature (SAT) has produced intense debate since the late 1990s. During this warming hiatus, the Siberian region experienced a significant cooling during the winter season around 10 times that of the Northern Hemisphere (NH) as a whole. This potentially stresses evergreen conifer forests because cooler winters can cause cold-temperature damage and, hence, increase the mortality of young evergreen conifer forests. In this study, the response of Siberian forest composition during the warming hiatus was investigated using satellite observations coupled with model simulations. Observations indicated that from 2001 to 2012, the apparent area of evergreen conifer forest has increased by 10%, while that of the deciduous conifer forest has decreased by 40%. The transition from deciduous to evergreen conifer forest usually occurs through mixed forest or woody savannas as a buffer. To verify the response of evergreen conifer forest, model experiments were performed using an individual-based forest model. Hysteresis of forest change seen in the model simulations indicates that changes in forest composition dynamics under temperature oscillations induced by internal climate variability may not reverse this composition change. As a result, the evergreen conifer forest expansion under climate warming is expected to be a continuing process despite the occurrence of a warming hiatus, exerting far-reaching implications for climate-change-induced albedo shifts in the Siberian forest.

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Jianping Huang, Qiang Fu, Wu Zhang, Xin Wang, Rudong Zhang, Hao Ye, and Stephen G. Warren

Abstract

Snow is the most reflective natural surface on Earth. Its albedo (the fraction of sunlight reflected) can be reduced by small amounts of dark impurities such as dust and black carbon (BC) particles. This effect is significant for climate and the hydrological cycle. BC has previously been measured in Arctic snow, but it now appears that the larger effect may be in the midlatitudes because snow at lower latitudes is exposed to more sunlight and is closer to the sources of BC.

A field campaign was conducted across northern China in January and February 2010. Snow samples were collected at 46 sites in six provinces. The absorbing impurities are principally dust and BC particles in northwestern and northeastern China, respectively. The estimated concentration of BC is only 30–50 ppb in the far north of Heilongjiang Province (51°N), which is not much more than that found along the coast of the Arctic Ocean, 2,000 km farther north, but it increases to several hundred parts per billion in heavily industrialized Liaoning Province, Jilin Province, and the southern part of Heilongjiang. The BC content of snow in northeast China is comparable to values found in Europe (20–800 ppb). The steep drop-off in BC content of snow with latitude may indicate that little BC emitted in China in the winter is exported northward to the Arctic.

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Bida Jian, Jiming Li, Guoyin Wang, Yongli He, Ying Han, Min Zhang, and Jianping Huang

Abstract

Planetary albedo (PA; shortwave broadband albedo) and its long-term variations, which are controlled in a complex way by various atmospheric and surface properties, play a key role in controlling the global and regional energy budget. This study investigates the contributions of different atmospheric and surface properties to the long-term variations of PA based on 13 years (2003–15) of albedo, cloud, and ice coverage datasets from the Clouds and the Earth’s Radiant Energy System (CERES) Single Scanner Footprint edition 4A product, vegetation product from Moderate Resolution Imaging Spectroradiometer (MODIS), and surface albedo product from the Cloud, Albedo, and Radiation dataset, version 2 (CLARA-A2). According to the temporal correlation analysis, statistical results indicate that variations in PA are closely related to the variations of cloud properties (e.g., cloud fraction, ice water path, and liquid water path) and surface parameters (e.g., ice/snow percent coverage and normalized difference vegetation index), but their temporal relationships vary among the different regions. Generally, the stepwise multiple linear regression models can capture the observed PA anomalies for most regions. Based on the contribution calculation, cloud fraction dominates the variability of PA in the mid- and low latitudes while ice/snow percent coverage (or surface albedo) dominates the variability in the mid- and high latitudes. Changes in cloud liquid water path and ice water path are the secondary dominant factor over most regions, whereas change in vegetation cover is the least important factor over land. These results verify the effects of atmospheric and surface factors on planetary albedo changes and thus may be of benefit for improving the parameterization of the PA and determining the climate feedbacks.

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Xi Chen, Luolin Wu, Xiaoyang Chen, Yan Zhang, Jianping Guo, Sarah Safieddine, Fuxiang Huang, and Xuemei Wang

Abstract

Air transport from the troposphere to the stratosphere plays an important role in altering the vertical distribution of pollutants in the upper troposphere and lower stratosphere (UTLS). On 21 July 2012, Beijing was hit by an unprecedented extreme rainfall event. In the present study, the Community Multiscale Air Quality Modeling System (CMAQ) is used to simulate the change in vertical profiles of pollutants during this event. The integrated process rate (IPR) method was applied to quantify the relative contributions from different atmospheric processes to the changes in the vertical profile of pollutants and to estimate the vertical transport flux across the tropopause. The results revealed that, in the tropopause layer, during the torrential rainfall event, the values of O3 decreased by 35% and that of CO increased by 98%, while those of SO2, NO2, and PM2.5 increased slightly. Atmospheric transport was the main cause for the change in O3 values, contributing 32% of the net increase and 99% of the net decrease of O3. The calculations showed that the transport masses of CO, O3, PM2.5, NO2, and SO2 to the stratosphere by this deep convection in 25 h were 6.0 × 107, 2.4 × 107, 7.9 × 105, 2.2 × 105, and 2.7 × 103 kg, respectively, within the ∼300 km × 300 km domain. In the midlatitudes of the Northern Hemisphere, penetrating deep convective activities can transport boundary layer pollutants into the UTLS layer, which will have a significant impact on the climate of this layer.

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