scholarly journals Decoding the dynamics of poleward shifting climate zones using aqua-planet model simulations

2022 ◽  
Author(s):  
Hu Yang ◽  
Jian Lu ◽  
Qiang Wang ◽  
Xiaoxu Shi ◽  
Gerrit Lohmann

AbstractGrowing evidence indicates that the atmospheric and oceanic circulation experiences a systematic poleward shift in a warming climate. However, the complexity of the climate system, including the coupling between the ocean and the atmosphere, natural climate variability and land-sea distribution, tends to obfuscate the causal mechanism underlying the circulation shift. Here, using an idealised coupled aqua-planet model, we explore the mechanism of the shifting circulation, by isolating the contributing factors from the direct CO$$_2$$ 2 forcing, the indirect ocean surface warming, and the wind-stress feedback from the ocean dynamics. We find that, in contrast to the direct CO$$_2$$ 2 forcing, ocean surface warming, in particular an enhanced subtropical ocean warming, plays an important role in driving the circulation shift. This enhanced subtropical ocean warming emerges from the background Ekman convergence of surface anomalous heat in the absence of the ocean dynamical change. It expands the tropical warm water zone, causes a poleward shift of the mid-latitude temperature gradient, hence forces a corresponding shift in the atmospheric circulation and the associated wind pattern. The shift in wind, in turn drives a shift in the ocean circulation. Our simulations, despite being idealised, capture the main features of the observed climate changes, for example, the enhanced subtropical ocean warming, poleward shift of the patterns of near-surface wind, sea level pressure, storm tracks, precipitation and large-scale ocean circulation, implying that increase in greenhouse gas concentrations not only raises the temperature, but can also systematically shift the climate zones poleward.

2021 ◽  
Author(s):  
Hu Yang ◽  
Jian Lu ◽  
Xiaoxu Shi ◽  
Qiang Wang ◽  
Gerrit Lohmann

Abstract Growing evidence implies that the atmospheric and oceanic circulation experiences a systematic poleward shift in a warming climate. However, the complexity of climate system, including the coupling between the ocean and the atmosphere, natural climate variability and land-sea distribution, tends to obfuscate the causal mechanism underlying the circulation shift. Here, using an idealized coupled aqua-planet model, we explore the mechanism of the shifting circulation, by isolating the contributing factors from the direct CO2 forcing, the indirect ocean surface warming, and the wind-stress feedback from the ocean dynamics. We find that, in contrast to direct CO2 forcing, an enhanced subtropical ocean warming plays a leading role in driving the circulation shift. This enhanced subtropical ocean warming emerges from the background Ekman convergence of surface anomalous heat in the absence of the ocean dynamical change. It expands the tropical warm water zone, causes a poleward shift of the meridional temperature gradients, hence forces a corresponding shift in the atmospheric circulation. The shift in the atmospheric circulation in turn drives a shift in the ocean circulation. Our simulations, despite being idealized, capture the main features of observed climate changes, for example, the enhanced subtropical ocean warming, poleward shift of the patterns of near-surface wind, sea level pressure, storm tracks, precipitation and large-scale ocean circulation, implying that increase in greenhouse gas concentrations not only raises the temperature, but can also systematically shift the climate zones poleward.


2021 ◽  
Author(s):  
Hu Yang ◽  
Jian Lu ◽  
Xiaoxu Shi ◽  
Qiang Wang ◽  
Gerrit Lohmann

<p>Growing evidence suggests that the oceanic and atmospheric circulation experiences a systematic poleward shift under climate change. However, due to the complexity of climate system, such as, the coupling between the ocean and the atmosphere, natural climate variability and land-sea distribution, the dynamical mechanism of such shift is still not fully understood. Here, using an idealized partially coupled ocean and atmosphere aqua-planet model, we explore the mechanism of the shifting oceanic and atmospheric circulation. We find that, in contrast to the rising GHG concentration, the subtropical ocean warming plays a dominant role in driving the shift in the circulation system. More specifically, due to background ocean dynamics, a relatively faster warming over the subtropical ocean drives a poleward shift in the atmospheric circulation. The shift in the atmospheric circulation in turn drives a shift in the oceanic circulation. Our simulations, despite being idealized, capture the main features of observed climate changes, for example, the enhanced subtropical ocean warming, poleward shift of the patterns of near-surface wind, sea level pressure, cloud, precipitation, storm tracks and large-scale ocean circulation, implying that global warming not only raises the temperature, but also systematically shifts the climate zones.​</p>


Author(s):  
Adil Rasheed ◽  
Jakob Kristoffer Süld ◽  
Mandar Tabib

Accurate prediction of near surface wind and wave height are important for many offshore activities like fishing, boating, surfing, installation and maintenance of marine structures. The current work investigates the use of different methodologies to make accurate predictions of significant wave height and local wind. The methodology consists of coupling an atmospheric code HARMONIE and a wave model WAM. Two different kinds of coupling methodologies: unidirectional and bidirectional coupling are tested. While in Unidirectional coupling only the effects of atmosphere on ocean surface are taken into account, in bidirectional coupling the effects of ocean surface on the atmosphere are also accounted for. The predicted values of wave height and local wind at 10m above the ocean surface using both the methodologies are compared against observation data. The results show that during windy conditions, a bidirectional coupling methodology has better prediction capability.


2020 ◽  
Author(s):  
Artem Moiseev ◽  
Harald Johnsen ◽  
Johnny Johannessen

<p>The Doppler Centroid Anomaly (DCA) registered by microwave Synthetic Aperture Radar (SAR) contains information about ocean surface motion in the radar line-of-sight direction. The recorded signal is associated with the motion induced by the total wavefield (i.e., both wind waves and swell) and underlying ocean surface currents. Hence, accurate estimates of the wave-induced contribution to the observed DCA is required in order to obtain reliable information about underlying ocean surface current. In this study, we develop an empirical geophysical model function for the estimation of the wave-induced DCA. The study is based on two months of Sentinel-1 SAR Wave mode (WV) DCA observations collocated with wind field at 10m height from the ECMWF model and sea state information from the WAVEWATCH III model.</p><p>Analysis of two months of observations acquired over land showed that thanks to the novel Sentinel-1 DCA calibration, the uncertainty in the data does not exceed 3Hz (corresponding to a radial velocity of 0.21/014 m/s in the near/far range. The relationship between the DCA and the near-surface wind is in agreement with previously reported findings under the assumption of fully developed seas; the DCA is about 24% of the range wind speed at 23° incidence angle and decreasing (up to 50%) with increasing incidence angle from 23° to 36°. However, the difference between upwind (i.e., the wind blows towards antenna) and downwind (i.e., wind blows away from the antenna) configurations is inconsistent from study to study. Reliable information about the wave field indeed helps to describe the spread in the DCA, especially at low and moderate wind speeds, and when the ocean surface is dominated by the remotely generated swell.</p><p>The CDOP model is used as a baseline for estimating the wind-wave-induced Doppler shift. Retraining of the CDOP model for the Sentinel-1 SAR observations (CDOP-S) yielded a significantly better fit. Then, we extended the GMF with parameters of the wavefield (significant wave height, mean wave period and direction) in the moment of SAR acquisition. Combining information about near-surface wind and ocean surface wave fields also considerably improves the accuracy of the wave-induced Doppler shift estimates. In turn,  the accuracy of the ocean surface current retrievals are improved as demonstrated by the promising agreement with the near-surface ocean surface current climatology based on multiyear drifter observations.</p>


2015 ◽  
Vol 9 (2) ◽  
pp. 2355-2371
Author(s):  
Dr J Brian Matthews

Anthropogenic global warming (AGW) heat is trapped by the greenhouse gas (GHG) blanket, and the ocean surface layer. It is 93% in the ocean and drives atmospheric warming. The 111-year mean daily surface temperatures are 10.5±0.5°C at Port Erin (PE) Isle of Man compared with 9.6±4.8°C in Central England (CET) air. The Port Erin 5½-year max-min heat cycle synchronizes to the 11-year solar heat pump sunspot cycle. Tropical heat arrives 2 years after a solar maximum on wind-driven currents in the stratified sea surface. Runoff from bottom-up melted Arctic icesheets arrives 3½ year later at solar minimum. These warm and cold waters are the biodiversity source. PE is unique with seasonal meltwaters of Pacific and Atlantic origin. The North Pacific warms twice as fast as other oceans. All ocean near-surface gyre currents harmonize with sunspot cycles. Net cooling by polar icemelt masks catastrophic exponential ocean warming and icemelt. Eleven counter-rotating surface gyres carry heat and nutrients globally in verified ocean surface circulation system.Exponential growth is unsustainable in a finite system. It trends to infinity. Double-exponential gets there twice as quickly. The GHG blanket, grown double-exponentially for 250 years, is now in control. Ocean heat absorption takes 150-250 years. Arctic icemelt increases double-exponentially. The Arctic long-term annual freeze-melt volume cycle is 16.8±1.3 thousand cubic km per year. Polar land icemelt adds ~500 km3 per year. Freeze-brine of salinity >40‰ and temperature –1°C, sinks to the bottom. Equatorial evaporative-brine of salinity >36.4‰ and >28°C floats subsurface under fresh warm layers thickening westwards in tropical meridional cells to ~75m depth. This is consistent with observed extreme weather.Heat imbalance forced Pacific Ocean temperatures above proposed limits of +2°C in 1993, to +3°C in 2014, and is on track for +4°C for 2016. Century-long daily records confirm processes ongoing for 300 years. Coast locations are where impacts are felt and real-time data collected. Corporate governance degraded physics teaching in only 60 years. Individual discovery and data collection was lost. Big science is unnecessary. Satellites cannot do plankton tows. Computer models are governed by the rule of ‘garbage-in garbage-out’. They must be verified by in situ data that cannot be collected retrospectively. Continuous timeseries surface profile data from fixed ocean station locations on a global variable-boundary network are essential. Scientists, if well-trained in ocean experimental physics, can do the hard work.Time-poor scientists, stripped of their intellectual property rights, under rewarded, poorly educated, and ruthlessly exploited by growth-obsessed commercial interests, missed catastrophic global warming and multiple extreme consequences. Climate scientists abandoned classical physics and Newton-Hooke field verification in favor of unverified beliefs, models, and apps. Climate studies confuse heat with temperature, do not include basal icemelt, density temperature-salinity function, Clausius-Clapeyron evaporation exponential skin temperature function, asymmetric brine-heat sequestration, solar and tidal pumping, infra-red GHG heat trap, vertical tropical cells, freshwater warm pools; or wind-driven surface currents at 3 percent of windspeed. Climate model mistaken assumptions lead to the absurd conclusion that evaporation in the Labrador Sea at midnight in midwinter is greater than at the midday Equator.The Isle of Man provides an ideal location for continued monitoring and mitigation research, teaching and public service in a dedicated non-commercial independent multidisciplinary university-type setting. Quality teaching is the major priority. Commercial monopoly rights need replacement with free, fully open discussions and publications. Quality not quantity should be paramount. Internationally competitive academics should control subservient lower paid support staff.Every day without ocean surface data means vital scientific truth lost of interest and concern to all populations. Predictions are groundless without accurate continuous ocean surface data. Skeptics, politicians, statisticians, those with stakes in the status quo, and established research censors obstructing scientific progress squabble in ignorance while the globe burns.


2020 ◽  
Author(s):  
Frank Siegismund ◽  
Xanthi Oikonomidou ◽  
Philipp Zingerle

<p>The Dynamic ocean Topography (DT) describes the deviation of the true ocean surface from a hypothetical equilibrium state ocean at rest forced by gravity alone. With the geostrophic surface currents obtained from its gradients the DT is an essential parameter for describing the ocean dynamics. Observation-based global temporal Mean geodetic DTs (MDTs) are obtained from the difference of altimetric Mean Sea Surface (MSS) and the geoid height, that equipotential surface of gravity closest to the ocean surface.</p><p>The geoid is provided either as a satellite-only, or a combined model including in addition gravity anomalies derived from satellite altimetry and ground data. In recent years the focus was on satellite-only models, produced from new space-born observations obtained from the Gravity Recovery and Climate Experiment (GRACE) and Gravity field and Ocean Circulation Explorer (GOCE) satellite missions. Moreover, combined geoid models are only cautiously used for MDT calculation, since it is still in question to what extent the gravity information obtained from altimetry is distorted by the MDT information included therein and how this translates into errors of the MDT.</p><p>Here we want to concentrate on MDT models based on recent combined geoid models. An assessment is provided based on comparisons to near-surface drifter data from the Global Drifter Program (GDP). Besides providing a general, global assessment, we focus on signal content on small scales, addressing mainly two questions: 1) Do MDTs obtained from combined geoid models contain signal for scales smaller than resolvable by the<br>satellite-only models? 2) Is there a maximum resolution beyond which no signal is detectable?</p><p>Until recently, these questions couldn't be answered since low resolution MDTs usually contained strong wavy-structured errors and thus needed a strong spatial filtering thereby killing the smallest scales resolved in the MDT. These errors, which worsen with lower resolution, are caused by Gibbs effects provoked by imperfections in bringing the high resolution ocean-only MSS models into spectral consistency with the much lower resolved global geoid model. A new methodology, however, improves the necessary globalization of the MSS. After subtraction of the geoid model, subsequent cutting-off the signal beyond a specific spherical harmonic degree and order (d/o) results in an MDT without any Gibbs effects, also for low resolution models.</p><p>To answer the questions posed above applying the new methodology, the scale-dependent signal in MDTs for different geoid models is presented for a list of cut off d/os. To minimize the influence of noise on the results we concentrate on strong signal Western Boundary Currents like the Gulf Stream and the Kuroshio. For the Gulf Stream results of a high resolution hydrodynamic model are available and presented as an independent method to estimate the scale dependent signal.</p>


2020 ◽  
Author(s):  
Yavor Kostov ◽  
Helen L. Johnson ◽  
David P. Marshall ◽  
Gael Forget ◽  
Patrick Heimbach ◽  
...  

<p><strong>The Atlantic meridional overturning circulation (AMOC) is pivotal for regional and global climate due to its key role in the uptake and redistribution of heat, carbon and other tracers. Establishing the causes of historical variability in the AMOC can tell us how the circulation responds to natural and anthropogenic changes at the ocean surface. However, attributing observed AMOC variability and inferring causal relationships is challenging because the circulation is influenced by multiple factors which co-vary and whose overlapping impacts can persist for years.  Here we reconstruct and unambiguously attribute variability in the AMOC at the latitudes of two observational arrays to the recent history of surface wind stress, temperature and salinity. We use a state-of-the-art technique that computes space- and time-varying sensitivity patterns of the AMOC strength with respect to multiple surface properties from a numerical ocean circulation model constrained by observations. While on inter-annual timescales, AMOC variability at 26°N is overwhelmingly dominated by a linear response to local wind stress, in contrast, AMOC variability at subpolar latitudes is generated by both wind stress and surface temperature and salinity anomalies. Our analysis allows us to obtain the first-ever reconstruction of subpolar AMOC from forcing anomalies at the ocean surface.</strong></p>


Author(s):  
D. A. Petrov

The frequency properties of the ocean surface temperature anomalies (SST) and near-surface air (SAT) spectra are analyzed on the basis of a simple energy balance model of the climate, taking into account the fluctuations of the radiation balance, the latent and sensible heat flux and the velocity of the near-surface wind in two particular cases when the statistical properties of the model parameters are the white noise (small-scale-mesoscale subintervals) and the combined case when the properties of the synoptic subinterval of this parameters are taken into account in the SAT block. It was found that in the first case, the spectra have no features, and in the second they contain selected frequencies in the synoptic and low- frequency intervals. The dependent of their frequencies on model parameters are analyzed. The properties of standard deviations of SST and SAT are investigated.


2021 ◽  
Vol 8 ◽  
Author(s):  
Hauke Blanken ◽  
Caterina Valeo ◽  
Charles Hannah ◽  
Usman T. Khan ◽  
Tamás Juhász

This paper proposes a fuzzy number—based framework for quantifying and propagating uncertainties through a model for the trajectories of objects drifting at the ocean surface. Various sources of uncertainty that should be considered are discussed. This model is used to explore the effect of parameterizing direct wind drag on the drifting object based on its geometry, and using measured winds to parameterize shear and rotational dynamics in the ocean surface currents along with wave-driven circulation and near-surface wind shear. Parameterizations are formulated in a deterministic manner that avoids the commonly required specification of empirical leeway coefficients. Observations of ocean currents and winds at Ocean Station Papa in the northeast Pacific are used to force the trajectory model in order to focus on uncertainties arising from physical processes, rather than uncertainties introduced by the use of atmospheric and hydrodynamic models. Computed trajectories are compared against observed trajectories from five different types of surface drifters, and optimal combinations of forcing parameterizations are identified for each type of drifter. The model performance is assessed using a novel skill metric that combines traditional assessment of trajectory accuracy with penalties for overestimation of uncertainty. Comparison to the more commonly used leeway method shows similar performance, without requiring the specification of empirical coefficients. When using optimal parameterizations, the model is shown to correctly identify the area in which drifters are expected to be found for the duration of a seven day simulation.


2020 ◽  
Author(s):  
Hyacinth Nnamchi ◽  
Mojib Latif ◽  
Noel Keenlyside ◽  
Wonsun Park

<p>Although the globally averaged surface temperature of the Earth has considerably warmed since the beginning of global satellite measurements in 1979, a warming hole, with hardly any surface warming that is most pronounced in boreal summer, has been observed in the equatorial Atlantic region during this period. The warming hole occurs in an extended area of the equatorial Atlantic that includes the cold tongue, the region of locally cooler ocean surface waters that develops just south of the equator in boreal summer, partly reflecting the upwelling of deep cold waters by the action of the southeasterly trade winds. This lack of surface warming of the cold tongue denotes an 11% amplification of the mean annual cycle of the sea surface temperature during the satellite era. The warming hole is driven by an intensification of the equatorial upwelling of cold waters into the ocean surface layers and damped by the surface heat flux. In observations, the tendency for surface cooling appears to reflect intrinsic variability of the climate system and is not unusual during the instrumental period. The warming hole is associated with wind-induced ocean circulation changes to the south and north of the northward of the equator. Coupled model ensembles forced by the observed varying concentrations of atmospheric greenhouse gases and natural aerosols as well as unforced runs were analyzed. The ensembles suggest a strong role for atmospheric aerosols in the warming hole. However, although aerosols can cause a cooling of the cold tongue, intrinsic climate variability as represented in the unforced experiment can potentially cause larger cooling than has been observed during the satellite era. This study highlights the difficulty in reconciling observations and the climate models for the attribution of the warming hole.</p>


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