Partial Wavelet Coherence Research Articles

Analysis of the dynamic characteristics of seawater intrusion using partial wavelet coherence: a case study at Nakaura Watergate, Japan

Lake Shinji and Lake Nakaumi are coupled brackish lakes on the Japan Sea coast of Japan. Seawater from the Japan Sea frequently intrudes into Lake Nakaumi through the bottom. Salinity flux at Nakaura Watergate was analysed. Effects of river discharge, tide level, and meteorological forcing variables makes the seawater intrusion non-linear. To account for the non-linear characteristics, partial wavelet coherence (PWC) was used to analyse the impact of river discharge, tide level, and meteorological forcing variables on salinity flux after controlling the effect of all other forcing variables. PWC results show that tide level has impact on salinity flux over short cycles (limited to less than 4 days) throughout the analysis period with an average time lag of about 2 days. This suggests that astronomical tides are the dominant factor in the salinity intrusion processes. The river discharge largely influences salinity flux over medium cycles (5–16 days) during the months of June and July with an average time lag of 0.3 days. Atmospheric pressure occasional affect tide level, indirectly driving salinity transport. The study findings provide guidance for factors affecting salinity intrusion processes and further research.

Demographic impact of climate change on northwestern China in the late imperial era

A growing body of quantitative (large-N) studies examines the climate–man nexus in historical agrarian China. Their dominant approach is to take the whole of China as a spatial aggregate, without taking into account the role of regional context. Furthermore, quantitative investigations of the climate–man nexus in northwestern (NW) China remain scarce. This study seeks to address the above issues. We focused on the extent to which periodic fluctuation of precipitation and temperature affected positive checks (famine, epidemics, nomadic invasion, and rebellion) and subsequently population growth dynamics in Sha'anxi, Gansu, and Ningxia, NW China in AD 1500–1911. Multiple Wavelet Coherence and Partial Wavelet Coherence analyses were applied to handle the non-linear and non-stationary nature of the climate–man nexus. Our results show that drought was the common stressor of various positive checks in NW China at the multi-decadal (32–64 year) time-scale. In addition, there was a coherence break of the relationship in AD 1700–1820, owing to the tremendous increase of subsistence brought about by land reclamation policy and the introduction of foreign food crops. Yet, the coherence resumed afterwards, resulting in more disastrous demographic consequences. We highlighted that the climate–man nexus is not entirely deterministic in nature, even in environmentally-fragile NW China. The relationship is mediated by social factors, particularly government policies. Still, if those measures are made at the expense of the environment, although humans might be able to win over nature in the short-term, the final outcome could be catastrophic in the long-term. This study substantiates the above notion with empirical quantitative evidence.

WHAT CAUSES THE INTER-SOLAR-CYCLE VARIATION OF TOTAL SOLAR IRRADIANCE?

The Physikalisch Meteorologisches Observatorium Davos total solar irradiance (TSI), Active Cavity Radiometer Irradiance Monitoring TSI, and Royal Meteorological Institute of Belgium TSI are three typical TSI composites. Magnetic Plage Strength Index (MPSI) and Mount Wilson Sunspot Index (MWSI) should indicate the weak and strong magnetic field activity on the solar full disk, respectively. Cross-correlation (CC) analysis of MWSI with three TSI composites shows that TSI should be weakly correlated with MWSI, and not be in phase with MWSI at timescales of solar cycles. The wavelet coherence (WTC) and partial wavelet coherence (PWC) of TSI with MWSI indicate that the inter-solar-cycle variation of TSI is also not related to solar strong magnetic field activity, which is represented by MWSI. However, CC analysis of MPSI with three TSI composites indicates that TSI should be moderately correlated and accurately in phase with MPSI at timescales of solar cycles, and that the statistical. significance. test indicates that the correlation coefficient of three TSI composites with MPSI is statistically significantly higher than that of three TSI composites with MWSI. Furthermore, the cross wavelet transform (XWT) and WTC of TSI with MPSI show that the TSI is highly related and actually in phase with MPSI at a timescale of a solar cycle as well. Consequently, the CC analysis, XWT, and WTC indicate that the solar weak magnetic activity on the full disk, which is represented by MPSI, dominates the inter-solar-cycle variation of TSI.

Comovements of ethanol‐related prices: evidence from Brazil and the USA

AbstractWe use the wavelet coherence methodology to investigate the relations between prices of ethanol and its feedstocks. Our continuous wavelet framework allows for discovering price connections and their evolution in both time and frequency domain in the most important ethanol markets – Brazil and the USA. For both of these markets, we show that the long‐run relationship between prices of ethanol and corn (in the USA) or sugar (in Brazil) is positive, strong and stable in time. Importantly, we show that the prices of feedstock lead the prices of ethanol and not the other way around. The price lead of feedstock is documented for both short‐ and long‐run horizons. Our qualitative results hold true even when the influence of crude oil prices is accounted for by utilizing partial wavelet coherence approach.

Co-Movements of Ethanol Related Prices: Evidence from Brazil and the USA

We use the wavelet coherence methodology to investigate relations between prices of ethanol and its feedstocks. Our continuous wavelet framework allows for discovering price connections and their evolution in both time and frequency domain in the most important ethanol markets – Brazil and the USA. For both of these markets we show that the long-run relationship between prices of ethanol and corn (in USA) or sugar (in Brazil) is positive, strong and stable in time. Importantly, we show that the prices of feedstock lead the prices of ethanol and not the other way around. The price lead of feedstock is documented for both short and long run horizons. Our qualitative results hold true even when the influence of crude oil prices is accounted for by utilizing partial wavelet coherence approach.

Disentangling the confounding effects of PAR and air temperature on net ecosystem exchange at multiple time scales

Net ecosystem exchange of CO2 (NEE) in temperate forests is modulated by multiple microclimatic factors. The effects of these factors vary across time scales, with some correlated to produce confounding effects. Photosynthetically active radiation (PAR) and air temperature (Ta) are among the two most important drivers of NEE in temperate forests and are highly correlated because of their similar diel and annual cycles. In this study, we attempted to disentangle the confounding effects of them on NEE at multiple time scales. We applied innovative spectral analysis techniques, including the continuous wavelet transformation (CWT), cross wavelet transformation (XWT), wavelet coherent (WTC), and partial wavelet coherence (PWC), on a seven-year time series (2004–2010) of PAR, Ta, and NEE from the Ohio Oak Openings Ameriflux site (N 41.5545°, W 83.8438°), USA. We found that PAR was the primary driver at short time scales (e.g., multi-hour and daily), while Ta dominated NEE at long time scales (e.g., seasonal to annual). At the daily scale, PAR co-varied with NEE without time lag, while Ta lagged PAR for 2–3h during growing seasons, which could be explained by the strong dependence of NEE on photosynthesis, which has a similar time lag of 2–3h of Ta to PAR. At the daily scale, during the non-growing seasons, NEE varied little and co-varied with Ta and PAR with no high common power. At the annual scale, Ta co-varied with NEE with no time delay, but PAR led NEE by about one month. This can be explained by the strong dependence of leaf area index (LAI) on Ta as well as the lag between the LAI/biomass development and the progress of sunlight. We also found that NEE distributes most of its variation at seasonal and annual scales, suggesting that Ta is more important than PAR in determining the annual and long-term carbon budget.

Geophysical Applications of Partial Wavelet Coherence and Multiple Wavelet Coherence

Abstract In this paper, the application of partial wavelet coherence (PWC) and multiple wavelet coherence (MWC) to geophysics is demonstrated. PWC is a technique similar to partial correlation that helps identify the resulting wavelet coherence (WTC) between two time series after eliminating the influence of their common dependence. MWC, akin to multiple correlation, is, however, useful in seeking the resulting WTC of multiple independent variables on a dependent one. The possible El Niño–Southern Oscillation–related impact of the large-scale atmospheric factors on tropical cyclone activity over the western North Pacific is used as an example. A software package for PWC and MWC has been developed. It also includes modified software that rectified the bias in the wavelet power spectrum and wavelet cross-spectrum. The package is available online (see http://www.cityu.edu.hk/gcacic/wavelet).