This study examines the response of the tropical atmospheric and oceanic circulation to increasing greenhouse gases using a coordinated set of twenty-first-century climate model experiments performed for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). The strength of the atmospheric overturning circulation decreases as the climate warms in all IPCC AR4 models, in a manner consistent with the thermodynamic scaling arguments of Held and Soden. The weakening occurs preferentially in the zonally asymmetric (i.e., Walker) rather than zonal-mean (i.e., Hadley) component of the tropical circulation and is shown to induce substantial changes to the thermal structure and circulation of the tropical oceans. Evidence suggests that the overall circulation weakens by decreasing the frequency of strong updrafts and increasing the frequency of weak updrafts, although the robustness of this behavior across all models cannot be confirmed because of the lack of data. As the cli...

https://www.gfdl.noaa.gov/bibliography/related_files/gav0704.pdf

Global Warming and the Weakening of the Tropical Circulation

Since the mid-nineteenth century the Earth's surface has warmed, and models indicate that human activities have caused part of the warming by altering the radiative balance of the atmosphere. Simple theories suggest that global warming will reduce the strength of the mean tropical atmospheric circulation. An important aspect of this tropical circulation is a large-scale zonal (east-west) overturning of air across the equatorial Pacific Ocean--driven by convection to the west and subsidence to the east--known as the Walker circulation. Here we explore changes in tropical Pacific circulation since the mid-nineteenth century using observations and a suite of global climate model experiments. Observed Indo-Pacific sea level pressure reveals a weakening of the Walker circulation. The size of this trend is consistent with theoretical predictions, is accurately reproduced by climate model simulations and, within the climate models, is largely due to anthropogenic forcing. The climate model indicates that the weakened surface winds have altered the thermal structure and circulation of the tropical Pacific Ocean. These results support model projections of further weakening of tropical atmospheric circulation during the twenty-first century.

/pdf/weakening-of-tropical-pacific-atmospheric-circulation-due-to-3p4u9sqrf3.pdf

Weakening of tropical Pacific atmospheric circulation due to anthropogenic forcing

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 Nino–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.

The Forcing of the Pacific Decadal Oscillation

[1] We review teleconnections within the atmosphere and ocean, their dynamics and their role in coupled climate variability. We concentrate on teleconnections in the latitudinal direction, notably tropical-extratropical and interhemispheric interactions, and discuss the timescales of several teleconnection processes. The tropical impact on extratropical climate is accomplished mainly through the atmosphere. In particular, tropical Pacific sea surface temperature anomalies impact extratropical climate variability through stationary atmospheric waves and their interactions with midlatitude storm tracks. Changes in the extratropics can also impact the tropical climate through upper ocean subtropical cells at decadal and longer timescales. On the global scale the tropics and subtropics interact through the atmospheric Hadley circulation and the oceanic subtropical cell. The thermohaline circulation can provide an effective oceanic teleconnection for interhemispheric climate interactions.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005RG000172

Atmospheric bridge, oceanic tunnel, and global climatic teleconnections

A spring ‘predictability barrier’ exists in both data and models of the El Nino/Southern Oscillation (ENSO) phenomenon. In statistical analyses this barrier manifests itself as a drop-off in monthly persistence (lagged correlation) while in coupled ocean-atmosphere models it appears as a decrease in forecast skill.



The ‘persistence barrier’ for ENSO indices is investigated using historical sea surface temperature and sealevel pressure data. Simple statistical models are used to show that the persistence barrier occurs because the boreal spring is the transition time from one climate state to another, when the ‘signal-to-noise’ of the system is lowest and the system is most susceptible to perturbations. The strength of the persistence barrier is shown to depend on the degree of phase locking of the ENSO to the annual cycle.



The phase locking of the ENSO to the annual cycle, as well as the ENSO variance, is shown to vary on interdecadal time-scales. During 1871–1920 and 1960–90 the ENSO variance was high, while during 1920–50 it was low. Using wavelet analysis, this interdecadal variability in ENSO is shown to be correlated with changes in Indian summer monsoon strength. Finally, the change in persistence-barrier strength between 1960–79 and 1980–95 is related to changes in the phase locking of ENSO to the annual cycle. These changes in persistence and phase locking appear to be related to the increased forecast skill seen from recent coupled ocean-atmosphere models.

The annual cycle of persistence in the El Nño/Southern Oscillation

Past work has shown that surface zonal equatorial wind stress, zonally integrated from one side of the Pacific to the other, is the key variable for estimating long-term El Nino behavior in the eastern Pacific. The long-term behavior of this key variable is difficult to determine directly because of the paucity of the equatorial wind observations and because of false trends in the wind data introduced by gradual changes in the methods of wind measurement. However, surface pressure data generally does not suffer from these false trends and theory suggests that this key wind variable is linearly related to the difference (Δp) of surface atmospheric pressure between the eastern and western equatorial Pacific. Detrended COADS pressure in the eastern and western equatorial Pacific and post 1960 detrended equatorial wind stress zonally averaged across the Pacific were used to verify this relationship. Pressure difference and zonally averaged equatorial zonal windstress (τ) were highly correlated (r = −...

Long-Term Changes in the Equatorial Pacific Trade Winds

Previous work has shown that near-surface ocean temperature off southern California increased during the 1970s and 1980s. This increase is probably not due to anthropogenic effects since measurements at three California coastal stations show that decadal and longer sea surface warming and cooling has also occurred earlier this century as part of a “natural” decadal and longer varying climate signal. The changes are mainly driven remotely by decadal and longer weakening and strengthening of the equatorial Pacific trade winds, which lower and raise the thermocline and affect ecosystems along thousands of kilometers of the western coastline of the Americas.

Remotely Driven Decadal and Longer Changes in the Coastal Pacific Waters of the Americas

Recently, Clarke and Lebedev showed that τ, the low-frequency eastward equatorial wind stress zonally averaged along the equator, can, in the case of the Pacific Ocean winds, be linearly estimated by Δp, the surface atmospheric pressure difference between the eastern and western ocean boundaries. The authors find that detrended interannual τ calculated from monthly winds is similarly linearly correlated with detrended Δp in the equatorial Atlantic and Indian Oceans since 1964 when enough wind data are available. The regression coefficient between τ and Δp enables the authors to estimate the turbulent stress atmospheric boundary layer height as being about 240 m for the equatorial Atlantic Ocean and 320 m for the equatorial Indian Ocean. Using a central Pacific pressure observation at 168°W, the authors similarly estimate the western and eastern Pacific turbulent stress atmospheric boundary layer heights as about 665 and 630 m, respectively. Unlike the wind data, the pressure data do not contain s...

Interannual and Decadal Changes in Equatorial Wind Stress in the Atlantic, Indian, and Pacific Oceans and the Eastern Ocean Coastal Response

Previous work has shown that near-surface ocean temperature off southern California increased during the 1970s and 1980s. This increase is probably not due to anthropogenic effects since measurements at three California coastal stations show that decadal and longer sea surface warming and cooling has also occurred earlier this century as part of a ‘‘natural’’ decadal and longer varying climate signal. The changes are mainly driven remotely by decadal and longer weakening and strengthening of the equatorial Pacific trade winds, which lower and raise the thermocline and affect ecosystems along thousands of kilometers of the western coastline of the Americas.

https://journals.ametsoc.org/doi/pdf/10.1175/1520-0485%281999%29029%3C0828%3ARDDALC%3E2.0.CO%3B2

NOTES AND CORRESPONDENCE Remotely Driven Decadal and Longer Changes in the Coastal Pacific Waters of the Americas

Modern changes in the Earth&rsquo;s crust take place under the joint influence of the natural tectonic forces and the progressive anthropogenic activity. The induced type of seismicity prevails in the territory of Karelia, which mainly includes active blasting operations. The study of blasting-induced seismicity is relevant considering numerous industrial facilities present in the territory of Karelia (construction and operation of large structures, roads, pipelines, hydroelectric power plants, etc.). Based on the seismic data obtained in 2018&ndash;2019, the induced seismicity map is built and the time characteristics of the blasting operations performed are analyzed. The purpose of the study is to assess the level of seismicity induced by blasting operations in Karelia. In the early 2000s, the seismological network was created in the territory of the Republic by the Institute of Geology, Karelia Science Center RAS. The network is equipped with modern digital equipment that allows seismic monitoring of the whole territory of Karelia. The layout of epicenters of the induced events recorded in Karelia is presented. A brief description of the mining activity is given together with its reflections in the seismic record for each region. The time profiles of the blasting operations were built. The studied seismicity comes out at 4:00-18:00 (UTC). Most blasting operations in Karelia are carried out at 9:00-11:00 (UTC). A fewer seismic events are recorded in summer than in winter, and the number of seismic events exceeds 300 per year. The observations show that the blasting-induced seismicity is recorded in many regions of Karelia. The western part of the region is characterized by more frequent and stronger events than the eastern part.The study was carried out within the framework of Topic No. 213: 3D Model of the Lithosphere of Karelia&nbsp;Based on the Geological and Geophysical Data, No. АААА-А18-118020290086-1. 

Seismicity of blasting operations in Karelia

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