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Qiang Wang

Abstract

The author has attempted to detect the presence of low-dimensional deterministic chaos in temperature data by estimating the correlation dimension with the Hill estimate that has been recently developed by Mikosch and Wang. There is no convincing evidence of low dimensionality with either global dataset (Southern Hemisphere monthly average temperatures from 1858 to 1984) or local temperature dataset (daily minimums at Auckland, New Zealand). Any apparent reduction in the dimension estimates appears to be due large1y, if not entirely, to effects of statistical bias, but neither is it a purely random stochastic process. The dimension of the climatic attractor may be significantly larger than 10.

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Qiang Wang

Abstract

The Arctic Beaufort Gyre plays a critical role in climate and marine ecosystems. This study investigates the response of the liquid freshwater in the Beaufort Gyre to various wind perturbations using numerical simulations. A new diagnostic called “freshwater renewal” is introduced, which quantifies the amount of freshwater that has entered the Beaufort Gyre since a specific point in time. The findings reveal that the process of freshwater renewal is persistently efficient in the Beaufort Gyre region, occurring irrespective of the gyre’s status. The spatial distribution of freshwater renewal varies, influenced by factors such as wind forcing and gyre circulation patterns. Cyclonic wind perturbation associated with a negative Beaufort high sea level pressure anomaly triggers freshwater release from the Beaufort Gyre, with freshwater export and renewal dependent on wind-perturbation locations and time scales. While some released Beaufort Gyre freshwater exits the Arctic Ocean through the Davis and Fram Straits, a considerable portion could remain within the Arctic Ocean for many years under specific conditions. Wind perturbation associated with the positive Arctic Oscillation enhances the Arctic export of Beaufort Gyre freshwater, mainly through the Fram Strait. The Arctic export of total freshwater and the Arctic export of the portion originating from the Beaufort Gyre have different time scales and magnitudes. Hence, it is essential to collectively examine different freshwater components in order to assess the role of Arctic export in the climate system.

Open access
Qiang Wang
and
Stefano Pierini

Abstract

The eddy kinetic energy (EKE) in the Kuroshio Extension (KE) region may be affected by two factors: EKE in the Kuroshio large meander (KLM) region and the North Pacific Gyre Oscillation (NPGO). Previous studies reported that the Kuroshio path variations south of Japan may affect the low-frequency variability of the KE jet and related EKE, but the linear correlation between these phenomena derived from long time series is low and not significant, implying that the linkage between EKE in the KLM and KE regions is still unclear. Besides, whether NPGO has a causal effect on the KE EKE remains under debate. In this study, we investigate the causal forcing of the KLM EKE and NPGO on the KE EKE using the convergent cross mapping (CCM) approach based on satellite sea surface height observations. The analysis shows that the KLM EKE affects the EKE only in the KE upstream area (west of 146°E), with no significant causal effect on the EKE in the downstream area; the NPGO plays, instead, a remarkable role on the EKE in both areas. The effect of the KLM EKE on the KE EKE is found to depend on the Kuroshio latitudinal position over the Izu Ridge. Changes in the KLM EKE affect the downstream advection of eddies and induce changes in the Kuroshio position over the ridge, which cause different EKE levels in the KE upstream region. The NPGO affects the KE EKE through the westward propagation of sea surface height anomalies remotely forced by wind stress anomalies associated with the North Pacific Oscillation.

Free access
Suqi Peng
and
Qiang Wang

Abstract

Indian Ocean (IO) stratification has important effects on the air–sea interaction, ocean dynamics, and ecology. It is, therefore, of significance to investigate the changes in IO stratification. In this study, we use ensemble empirical mode decomposition (EEMD) to extract the nonlinear long-term trend in the upper IO stratification quantified by potential energy anomalies. The results show that the strengthening of the stratification is spatially and temporally nonuniform. Specifically, the trend of stratification intensified gradually before 1996, but accelerated rapidly after 1996. Temperature and salinity changes play a crucial role in the fast enhancement of stratification and its regional differences. Temperature variations dominate the stratification trend in ∼90% of the IO area, while the contributions of salinity changes are mainly in the southeast Indian Ocean (SEIO). Vertically, the rapid enhancement of stratification is caused by the trend of temperature and salt in the upper 400 m. We further perform temperature budget analysis and find that the warming trend in the upper 400 m south of the IO is mainly modulated by vertical advection and meridional advection, while the warming in the north of the IO is mainly induced by air–sea heat fluxes. Salinity budget analysis shows that ocean advection has played a primary role in modulating SEIO salinity over the past 20 years.

Restricted access
Xia Liu
,
Mu Mu
, and
Qiang Wang

Abstract

Based on the Regional Ocean Modeling System (ROMS) and the conditional nonlinear optimal perturbation (CNOP) method, we explore the nonlinear optimal triggering perturbation of the Kuroshio large meander (LM) and its evolution, and reveal the role of nonlinear physical processes in the formation of the LM path. The results show that the large amplitudes of the perturbations are mainly located in the upper 2000 m in the southeastern area of Kyushu (29°–32°N, 131°–134°E), where the eastward propagation of the cold anomaly is vital to the formation of the LM path. By analyzing the depth-integrated vorticity equation of the perturbation, we find that linear advection, namely, the interaction between the perturbation and the reference field, tends to move the cyclonic eddy induced by the optimal triggering perturbation eastward, while the nonlinear advection associated with the interaction of perturbations tends to move the cyclonic eddy westward. The opposing effects of the nonlinear advection and the linear advection slow the eastward movement of the cyclonic eddy so that the eddy has a chance to effectively develop, eventually leading to the formation of the Kuroshio LM path.

Open access
Zunya Wang
,
Qiang Zhang
,
Shao Sun
, and
Pengling Wang

Abstract

Based on the standardized precipitation evapotranspiration index (SPEI), a significant increase after the mid-1990s is detected in the annual number of days with drought in the zonal belt from southern Xinjiang to southern Northeast China and North China. This change features the predominant mode of the annual number of days with drought in China. Meanwhile, two significant breakpoints in 1981 and 2001 indicate a continuous increase of days with drought in the meridional belt from eastern Northwest China to eastern Southwest China. The increase in days with drought is closely related to the significant warming in the zonal belt but is attributed to both the increase of temperature and the decrease of precipitation in the meridional belt. The typical circulation patterns responsible for the increase of days with drought comprise a wave train stretching from North Atlantic to East Asia, the generally anomalous high pressure over China, the northerly anomalies prevailing over northern and central China, and the suppressed convection in most of the zonal and meridional belt. Both the AMO and the PDO after the 1980s have a close relationship with the interdecadal variation of the number of days with drought. On one hand, either a positive AMO phase or negative PDO phase motivates the typical circulation patterns favorable for the occurrence of drought. On the other hand, both the AMO and PDO affect the warming in the zonal and meridional belt, and the PDO is also closely connected with the precipitation in the meridional belt.

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Qiang Zhang
,
Wenyu Wang
,
Sheng Wang
, and
Liang Zhang

Abstract

In most parts of the world, pan evaporation decreases with increased air temperature rather than increases, which is known as the “evaporation paradox.” The semiarid Loess Plateau, which is sensitive to global climate change and ecological variations, has a unique warming and drying climate. The authors of this study consider whether pan evaporation shows the same decreasing trend in this unique environment. Meteorological observations of the typical semiarid Dingxi in the Loess Plateau from 1960 to 2010 were used to analyze the variation in pan evaporation and its responses to climatic factors. It was found that the pan evaporation has increased considerably over the past 50 yr, which does not support the evaporation paradox proposed in previous studies. A multifactor model developed to simulate the independent impacts of climate factors on pan evaporation indicated that the temperature, humidity, wind speed, and low cloud cover variations contributed to pan evaporation by 46.18%, 25.90%, 2.48%, and 25.44%, respectively. The increased temperature, decreased relative humidity, and decreased low cloud cover all caused an increase in pan evaporation, unlike many parts of the world where increased low cloud cover offsets the effects of increased temperature and decreased relative humidity on pan evaporation. This may explain why the evaporation paradox occurs. If all relevant factors affecting pan evaporation are considered, it is possible the paradox will not occur. Thus in warm and drying regions, the increased pan evaporation will lead to increasingly arid conditions, which may exacerbate drought and flood disaster occurrences worldwide.

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Zunya Wang
,
Yanju Liu
,
Guofu Wang
, and
Qiang Zhang

Abstract

It is argued that the occurrence of cold events decreases under the background of global warming. However, from the mid-1990s to the early 2010s, northern China experienced a period of increasing occurrence of low temperature extremes (LTE). Factors responsible for this increase of LTE are investigated in this analysis. The results show that the interdecadal variation of the winter mean temperature over mid- and high-latitude Eurasia acts as an important thermal background. It is characterized by two dominant modes, the “consistent cooling” pattern and the “warm high-latitude Eurasia and cold midlatitude Eurasia” pattern, from the mid-1990s to the early 2010s. The two patterns jointly provide a cooling background for the increase of LTE in northern China. Meanwhile, though the interdecadal variation of the Arctic Oscillation (AO), Ural blocking (UB), and Siberian high (SH) are all highly correlated with the occurrence of LTE in northern China, the AO is found to play a dominant role. On one hand, the AO directly affects the occurrence of LTE because of its dynamic structure; on the other hand, it takes an indirect effect by affecting the intensity of UB and SH. Further analyses show that the winter temperature in mid- and high-latitude Eurasia and the AO are independent factors that influence the increase of LTE in northern China from the mid-1990s to the early 2010s.

Full access
Jiacheng Wang
,
Qiang Zhao
,
Shengcheng Cui
, and
Chengjie Zhu

Abstract

Coastal and island Aerosol Robotic Network (AERONET) sites are used to determine characteristic aerosol modes over marine environments. They are compared with the assumed modes used in the operational Moderate Resolution Imaging Spectroradiometer (MODIS) ocean aerosol algorithm, and the results show that 1) the standard deviation values of three fine aerosol modes (0.6) and one dustlike aerosol mode (0.8) are much higher than the corresponding statistical AERONET modal values (0.45 and 0.6, respectively). The values of three sea salt aerosol modes (0.6) are somewhat lower than the corresponding statistical AERONET modal value (0.675). 2) The number median radius of the current fine and dustlike aerosol modes cannot span the dynamic range of corresponding aerosol distribution properly. 3) AERONET products show that the standard deviation and the number median radius exhibit an obvious negative correlation, especially for sea salt and dustlike aerosol modes. According to this, a refinement of the current aerosol modes is made. These revised modes are used in a version of the MODIS retrieval over ocean. Compared with the current aerosol modes: 1) more retrieved aerosol optical depths (AODs) from the revised aerosol modes lie within the expected error bars and 2) the linear regression lines of the retrievals from the revised aerosol modes and AERONET are closer to the 1:1 line.

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Qiang Wang
,
Youmin Tang
,
Stefano Pierini
, and
Mu Mu

Abstract

The effects of optimal initial error on the short-range prediction of transition processes between the Kuroshio Extension (KE) bimodalities are analyzed using a reduced-gravity shallow-water model and the singular vector (SV) approach. Emphasis is placed on the spatial structures, growing processes, and effects of the SVs. The results show that the large values of the SVs are mainly located in the first crest region of the KE (around 35°N, 144°E) and in the Kuroshio large meander (KLM) region south of Japan (around 32°N, 139.5°E). The fast growths of the SVs have important impacts on the prediction of transition of the KE bimodality. The initial error with +SV pattern (with positive anomalies in the first crest region of the KE and negative anomalies in the KLM region) tends to strengthen the KE and shift it toward the high-energy state, while the error with −SV pattern is prone to weaken the KE and shift it toward the low-energy state. In addition, the SV-type initial errors grow more quickly in the transition phase of the KE from the high-energy to the low-energy state than in the opposite transition phase. A perturbation energy analysis illustrates that different physical processes are responsible for the error growth in the KE region for different transition phases of the KE; barotropic instability plays a dominant role in the error growth in the low-to-high (LH) energy phase, while the error evolution in the high-to-low (HL) energy phase is mainly caused by advection processes.

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