scholarly journals Variability of multi-site decadal running means arising from year-to-year fluctuations

2020 ◽  
pp. 1-41
Author(s):  
Xiaogu Zheng ◽  
Carsten S. Frederiksen
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Pacific Decadal Oscillation ◽  
Geopotential Height ◽  
Radiative Forcing ◽  
Decadal Variability ◽  
Sea Surface ◽  
Annular Mode ◽  
Northern Annular Mode ◽  
The Pacific

AbstractDecadal mean variables are frequently used to characterise decadal climate variabilities. Decadal means are often calculated using yearly data which can represent variability at time scales from annual to centennial. Residuals from interannual fluctuations may contribute to the variability in decadal time series. Such variability is more difficult to be predicted at the long range. Removing it from the decadal variability means that the remaining variability is more likely to arise from slowly varying multi-decadal or longer time scale external forcing and internal climate dynamics which are more likely to be predicted.Here, a new approach is proposed to understand the uncertainty, potential predictability and drivers of decadal mean variables. The covariance matrix of multivariate decadal running means is decomposed into unpredictable fast decadal variability and the potentially predictable slow decadal variability. EOF analysis is then applied to the decomposed matrices to find the dominant modes which may be related to the drivers of the two types of variabilities in the multivariate decadal means.The methodology has been applied to 140 year datasets of North Pacific sea surface temperature and the Northern Hemisphere 1000hPa geopotential height. For sea surface temperature, the Pacific Decadal Oscillation is the major driver of the fast decadal variability, while the radiative forcing and the Atlantic Multi-decadal Oscillation are major drivers of the slow decadal variability. For the 1000hPa geopotential height, fast decadal variability is associated with the Northern Annular Mode, the East Atlantic Mode and the Pacific Decadal Oscillation. Slow decadal variability is associated with the Northern Annular Mode and the Atlantic Multi-decadal Oscillation.

The Forcing of the Pacific Decadal Oscillation*

2005 ◽  
Vol 18 (21) ◽  
pp. 4355-4373 ◽  
Author(s):  
Niklas Schneider ◽  
Bruce D. Cornuelle
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Pacific Decadal Oscillation ◽  
North Pacific ◽  
Sea Surface ◽  
Aleutian Low ◽  
The Pacific ◽  
Sea Surface Temperature Anomalies ◽  
Zonal Advection ◽  
The Kuroshio

Abstract The Pacific decadal oscillation (PDO), defined as the leading empirical orthogonal function of North Pacific sea surface temperature anomalies, is a widely used index for decadal variability. It is shown that the PDO can be recovered from a reconstruction of North Pacific sea surface temperature anomalies based on a first-order autoregressive model and forcing by variability of the Aleutian low, El Niño–Southern Oscillation (ENSO), and oceanic zonal advection anomalies in the Kuroshio–Oyashio Extension. The latter results from oceanic Rossby waves that are forced by North Pacific Ekman pumping. The SST response patterns to these processes are not orthogonal, and they determine the spatial characteristics of the PDO. The importance of the different forcing processes is frequency dependent. At interannual time scales, forcing from ENSO and the Aleutian low determines the response in equal parts. At decadal time scales, zonal advection in the Kuroshio–Oyashio Extension, ENSO, and anomalies of the Aleutian low each account for similar amounts of the PDO variance. These results support the hypothesis that the PDO is not a dynamical mode, but arises from the superposition of sea surface temperature fluctuations with different dynamical origins.

scholarly journals The Role of Tropospheric Rossby Wave Breaking in the Pacific Decadal Oscillation

2009 ◽  
Vol 22 (7) ◽  
pp. 1819-1833 ◽  
Author(s):  
Courtenay Strong ◽  
Gudrun Magnusdottir
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Rossby Wave ◽  
Pacific Decadal Oscillation ◽  
Wave Breaking ◽  
El Nino ◽  
Sea Surface ◽  
Rossby Wave Breaking ◽  
The Pacific ◽  
Circulation Patterns

Abstract The leading pattern of extratropical Pacific sea surface temperature variability [the Pacific decadal oscillation (PDO)] is shown to depend on observed variability in the spatiotemporal distribution of tropospheric Rossby wave breaking (RWB), where RWB is the irreversible overturning of potential vorticity on isentropic surfaces. Composite analyses based on hundreds of RWB cases show that anticyclonic (cyclonic) RWB is associated with a warm, moist (cool, dry) column that extends down to a surface anticyclonic (cyclonic) circulation, and that the moisture and temperature advection associated with the surface circulation patterns force turbulent heat flux anomalies that project onto the spatial pattern of the PDO. The RWB patterns that are relevant to the PDO are closely tied to El Niño–Southern Oscillation, the Pacific–North American pattern, and the northern annular mode. These results explain the free troposphere-to-surface segment of the atmospheric bridge concept wherein El Niño anomalies emerge in summer and modify circulation patterns that act over several months to force sea surface temperature anomalies in the extratropical Pacific during late winter or early spring. Leading patterns of RWB account for a significant fraction of PDO interannual variability for any month of the year. A multilinear model is developed in which the January mean PDO index for 1958–2006 is regressed upon the leading principal components of cyclonic and anticyclonic RWB from the immediately preceding winter and summer months (four indexes in all), accounting for more than two-thirds of the variance.

scholarly journals Análise da Variabilidade Climática dos Oceanos Atlântico e Pacífico

2021 ◽  
Vol 14 (4) ◽  
pp. 1861-1879
Author(s):  
Pedro Fernandes de Souza Neto ◽  
Djane Fonseca Da Silva ◽  
Henrique Ravi Rocha de Carvalho Almeida
Keyword(s):  
Wavelet Analysis ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Pacific Decadal Oscillation ◽  
Temperature Anomaly ◽  
Sea Surface ◽  
Sea Surface Temperature Anomaly ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Northern Sector

The sea surface temperature is one of the main variables for analyzing the global climate, and with that, it is essential to know its behavior. Thus, the objective of this study is to understand the best temperature variability of the sea surface of the Atlantic and Pacific oceans, through information on the causes of its variability using Wavelet analysis, and also using the climatic trends of the TSM of the oceans. Sea surface temperature anomaly data obtained through the National Oceanic and Atmospheric Administration with period of 1955-2018, for the Atlantic and Pacific Oceans, divided into sectors and some statistical analyzes were used. Using the wavelet analysis method, it was possible to observe the phenomena El Niño South Oscillation, Atlantic Dipole, sunspots and Pacific Decadal Oscillation, acting on the studied time series; however, the Pacific Decadal Oscillation, which occurs in the Pacific Ocean, proved to be a phenomenon of dominant time scale in the Atlantic and Pacific Oceans. The Mann-Kendall trend test showed a linear increase in the sea surface temperature anomaly for the two studied Oceans, and in both, the South sector has a greater increase than the North sector. Climate trends indicate that the Pacific Ocean is warming more than the Atlantic Ocean. It is also possible to conclude that the Southern sector of the two Oceans is heating up more than the Northern sector. The signs of the limit ranges for the averages of the southern sectors demonstrate greater variability of the anomalies at the South Atlantic and South Pacific. The Northern sector was more similar to the general basin, both in the Atlantic and the Pacific, proving the importance of continental areas for warming the oceans. These results were strengthened with those found by box plots and frequency distribution. The warming of the Pacific was also reinforced in all statistics mad.

scholarly journals Impact of Desert Dust Radiative Forcing on Sahel Precipitation: Relative Importance of Dust Compared to Sea Surface Temperature Variations, Vegetation Changes, and Greenhouse Gas Warming

2007 ◽  
Vol 20 (8) ◽  
pp. 1445-1467 ◽  
Author(s):  
Masaru Yoshioka ◽  
Natalie M. Mahowald ◽  
Andrew J. Conley ◽  
William D. Collins ◽  
David W. Fillmore ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Africa ◽  
Radiative Forcing ◽  
Sea Surface ◽  
Desert Dust ◽  
Direct Radiative Forcing ◽  
Sahel Region ◽  
Precipitation Reduction ◽  
Sahel Precipitation

Abstract The role of direct radiative forcing of desert dust aerosol in the change from wet to dry climate observed in the African Sahel region in the last half of the twentieth century is investigated using simulations with an atmospheric general circulation model. The model simulations are conducted either forced by the observed sea surface temperature (SST) or coupled with the interactive SST using the Slab Ocean Model (SOM). The simulation model uses dust that is less absorbing in the solar wavelengths and has larger particle sizes than other simulation studies. As a result, simulations show less shortwave absorption within the atmosphere and larger longwave radiative forcing by dust. Simulations using SOM show reduced precipitation over the intertropical convergence zone (ITCZ) including the Sahel region and increased precipitation south of the ITCZ when dust radiative forcing is included. In SST-forced simulations, on the other hand, significant precipitation changes are restricted to over North Africa. These changes are considered to be due to the cooling of global tropical oceans as well as the cooling of the troposphere over North Africa in response to dust radiative forcing. The model simulation of dust cannot capture the magnitude of the observed increase of desert dust when allowing dust to respond to changes in simulated climate, even including changes in vegetation, similar to previous studies. If the model is forced to capture observed changes in desert dust, the direct radiative forcing by the increase of North African dust can explain up to 30% of the observed precipitation reduction in the Sahel between wet and dry periods. A large part of this effect comes through atmospheric forcing of dust, and dust forcing on the Atlantic Ocean SST appears to have a smaller impact. The changes in the North and South Atlantic SSTs may account for up to 50% of the Sahel precipitation reduction. Vegetation loss in the Sahel region may explain about 10% of the observed drying, but this effect is statistically insignificant because of the small number of years in the simulation. Greenhouse gas warming seems to have an impact to increase Sahel precipitation that is opposite to the observed change. Although the estimated values of impacts are likely to be model dependent, analyses suggest the importance of direct radiative forcing of dust and feedbacks in modulating Sahel precipitation.

scholarly journals Role of sea surface temperature responses in simulation of the climatic effect of mineral dust aerosol

2011 ◽  
Vol 11 (12) ◽  
pp. 6049-6062 ◽  
Author(s):  
X. Yue ◽  
H. Liao ◽  
H. J. Wang ◽  
S. L. Li ◽  
J. P. Tang
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Radiative Forcing ◽  
Mineral Dust ◽  
Dust Aerosol ◽  
Sea Surface ◽  
Climatic Effect ◽  
Radiative Effects ◽  
Climate Simulations

Abstract. Mineral dust aerosol can be transported over the nearby oceans and influence the energy balance at the sea surface. The role of dust-induced sea surface temperature (SST) responses in simulations of the climatic effect of dust is examined by using a general circulation model with online simulation of mineral dust and a coupled mixed-layer ocean model. Both the longwave and shortwave radiative effects of mineral dust aerosol are considered in climate simulations. The SST responses are found to be very influential on simulated dust-induced climate change, especially when climate simulations consider the two-way dust-climate coupling to account for the feedbacks. With prescribed SSTs and dust concentrations, we obtain an increase of 0.02 K in the global and annual mean surface air temperature (SAT) in response to dust radiative effects. In contrast, when SSTs are allowed to respond to radiative forcing of dust in the presence of the dust cycle-climate interactions, we obtain a global and annual mean cooling of 0.09 K in SAT by dust. The extra cooling simulated with the SST responses can be attributed to the following two factors: (1) The negative net (shortwave plus longwave) radiative forcing of dust at the surface reduces SST, which decreases latent heat fluxes and upward transport of water vapor, resulting in less warming in the atmosphere; (2) The positive feedback between SST responses and dust cycle. The dust-induced reductions in SST lead to reductions in precipitation (or wet deposition of dust) and hence increase the global burden of small dust particles. These small particles have strong scattering effects, which enhance the dust cooling at the surface and further reduce SSTs.

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