scholarly journals Structure of the Pacific Walker Circulation Depicted by the Reanalysis and CMIP6

Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1219
Author(s):  
Emmanuel Olaoluwa Eresanya ◽  
Yuping Guan
Keyword(s):  
Large Scale ◽  
Structural Changes ◽  
Numerical Models ◽  
Walker Circulation ◽  
Future Climate Change ◽  
Western Boundary ◽  
Extreme Caution ◽  
The Pacific ◽  
Mean State

The Pacific Walker circulation (PWC) is one of the most important components of large-scale tropical atmospheric circulations. The PWC and its influences have been studied extensively by numerical models and reanalysis. The newly released ERA5 and NCEP2 are the most widely used reanalysis datasets and serve as benchmarks for evaluation of model simulations. If the results of these datasets differ significantly, this could lead to a bias in projected long-term climate knowledge. For better understanding of future climate change, it is necessary to evaluate PWC reanalysis productions. As a result, we compared the PWC structures between the ERA5 and NCEP2 datasets from month to seasonal time scales. We used the zonal mass streamfunction (ZMS) over the equatorial Pacific to indicate the strength of the PWC. The PWC’s average monthly or seasonal cycle peaks around July. From February to June, the NCEP2 shows a higher PWC intensity, whereas the ERA5 shows greater intensity from July to December. The circulation center in the NCEP2 is generally stronger and wider than in the ERA5. The ERA5, however, revealed that the PWC’s west edge (zero line of ZMS over the western Pacific) had moved 10 degrees westward in comparison to the NCEP2. In addition, we compared the PWC mean state in the reanalysis and CMIP6 models; the mean state vertical structures of the tropical PWC in the CMIP6 multi-model ensemble (MME) are similar to those of the reanalyses in structure but weaker and wider than in the two reanalysis datasets. The PWC is broader in CMIP6, and the western boundary is 7 and 17 degrees farther west than in the ERA5 and NCEP2, respectively. This study suggests that, when using reanalysis datasets to evaluate PWC structural changes in intensity and western edge, extreme caution should be exercised.

Pacific Walker circulation variability during the last millennium reconstructed from a network of water isotope proxy records

2021 ◽  
Author(s):  
Georgina Falster ◽  
Bronwen Konecky ◽  
Sloan Coats ◽  
Samantha Stevenson ◽  
Midhun Madhavan
Keyword(s):  
Walker Circulation ◽  
Future Climate ◽  
Extreme Weather Events ◽  
Future Climate Change ◽  
Specific Information ◽  
Last Millennium ◽  
Climate Signal ◽  
The Past ◽  
The Pacific ◽  
Global Precipitation

<p>Changes in the strength of the Pacific Walker circulation (PWC) can have a significant impact on global mean surface temperatures, as well as regional temperature, precipitation, and extreme weather events far beyond the tropical Pacific. Understanding PWC variability is therefore important for constraining future climate. But observational records of the PWC are short, and single-site proxy records for changes in the strength of the PWC during the last millennium offer contrasting interpretations. This leaves a critical gap in our understanding of PWC variability on the decadal to centennial timescales relevant to future climate change.</p><p>Falster et al. (in prep.) demonstrated that the PWC is strongly imprinted in modern global precipitation δ<sup>18</sup>O (δ<sup>18</sup>O<sub>P</sub>). This relationship arises via multiple complementary mechanisms, including but not limited to ENSO dynamics. We exploit this relationship to reconstruct changes in the strength of the PWC over the past millennium, using six different statistical and machine learning reconstruction methods in conjunction with a globally-distributed network of palaeo-δ<sup>18</sup>O<sub>P</sub> records (Konecky et al. 2020). Although δ<sup>18</sup>O<sub>P</sub> from a relatively small number of locations explains a large proportion of PWC variance in the calibration interval, we use a larger network of sites because larger networks are less susceptible to non-stationary teleconnections or non-signal biases than individual sites or smaller networks. </p><p>Preliminary results indicate that reconstructed PWC variability is coherent across methods, particularly for the past 400 years. Our reconstructions are also robust to both the calibration window used, and the particular palaeo-δ<sup>18</sup>O<sub>P</sub> records included in the reconstruction. This provides confidence that our network comprises sufficient proxy timeseries i.e. that we successfully extracted the common underlying climate signal (the PWC) from site-specific information inherent in individual palaeo-δ<sup>18</sup>O<sub>P</sub> records. Thus, we are confident that our reconstruction of changes in the strength of the PWC through the last millennium is robust, and it will therefore help to constrain the PWC’s long-term internal variability and sensitivity to external forcing.</p><p><br><strong>References:</strong></p><p>Falster, G. M., B. Konecky, M. Madhavan, S. Coats, S. Stevenson. 2021. “Imprint of the Pacific Walker circulation in global precipitation δ<sup>18</sup>O”. In preparation for <em>Journal of Climate</em>. </p><p>Konecky, B. L., N. P. McKay, O. V. Churakova (Sidorova), L. Comas-Bru, E. P. Dassié, K. L. DeLong, G. M. Falster, et al. 2020. “The Iso2k Database: A Global Compilation of Paleo-δ<sup>18</sup>O and δ<sup>2</sup>H Records to Aid Understanding of Common Era Climate.” <em>ESSD</em>. https://doi.org/10.5194/essd-2020-5.</p>

Modelling creep deformation in floating ice

2003 ◽  
Vol 30 (1) ◽  
pp. 28-41 ◽  
Author(s):  
K van Steenis ◽  
F E Hicks ◽  
T M Hrudey ◽  
S Beltaos
Keyword(s):  
Large Scale ◽  
Field Experiments ◽  
Numerical Models ◽  
Ice Sheet ◽  
Transversely Isotropic ◽  
Element Model ◽  
Ice Cover ◽  
Load Test ◽  
Drilling Rig

The ability to predict the response of an ice sheet to long-term loading is important in many situations. In northern regions, ice sheets have been used as construction platforms, drilling rig platforms, airfields, parking lots, and festival platforms. Numerical models can be used to predict the deflection of an ice sheet over time and, together with a failure criterion based on allowable deflection, can facilitate the safe use of an ice cover under long-term loading situations. In this study, a two-dimensional axisymmetric finite element model was developed to model the behaviour of a homogeneous, transversely isotropic, infinite ice cover under long-term loading. The model was validated using 33 sets of long-term load test data from large-scale field experiments performed on lake, bay, and reservoir ice and was shown to be capable of reliably predicting deflections under a variety of loading scenarios.Key words: bearing capacity of ice, long-term loading, ice platforms.

scholarly journals Evaluating the large-scale hydrological cycle response within the PlioMIP2 ensemble

2021 ◽  
Author(s):  
Zixuan Han ◽  
Qiong Zhang ◽  
Qiang Li ◽  
Ran Feng ◽  
Alan M. Haywood ◽  
...  
Keyword(s):  
Large Scale ◽  
Hydrological Cycle ◽  
Atmospheric Transport ◽  
Hadley Circulation ◽  
Dynamic Effect ◽  
Walker Circulation ◽  
Future Climate Change ◽  
Atmospheric Energy ◽  
Budget Analysis ◽  
Thermodynamic Effect

Abstract. The mid-Pliocene (~ 3 million years ago) is one of the most recent warm periods with high CO2 concentrations in the atmosphere and resulting high temperatures and is often cited as an analog for near-term future climate change. Here, we apply a moisture budget analysis to investigate the response of the large-scale hydrological cycle at low latitudes within a 13-model ensemble from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The results show that increased atmospheric moisture content within the mid-Pliocene ensemble (the thermodynamic effect) results in wetter conditions over the deep tropics, i.e., the Pacific intertropical convergence zone (ITCZ) and the Maritime Continent, and drier conditions over the subtropics. The thermodynamic effect is to some extent offset by a dynamic effect involving a northward shift of the Hadley circulation that dries the deep tropics and moistens the subtropics in the Northern Hemisphere (i.e., the subtropical Pacific). From the perspective of Earth’s energy budget, the enhanced southward cross-equatorial atmospheric transport (0.22 PW), induced by the hemispheric asymmetries of the atmospheric energy, favors an approximately 1° northward shift of the ITCZ. The shift of the ITCZ reorganizes atmospheric circulation, favoring a northward shift of the Hadley circulation. In addition, the Walker circulation consistently shifts westward within PlioMIP2 models, leading to wetter conditions over the northern Indian Ocean. The PlioMIP2 ensemble highlights that an imbalance of interhemispheric atmospheric energy during the mid-Pliocene could have led to changes in the dynamic effect, offsetting the thermodynamic effect and hence altering mid-Pliocene hydroclimate cycling.

scholarly journals MODELLING LONG TERM IMPLICATION OF CLIMATE CHANGE PROJECTION ON SHORE MORPHOLOGY OF NORTH NORFOLK, UK, COMBINING TOMAWAC AND SCAPE

2011 ◽  
Vol 1 (32) ◽  
pp. 61 ◽  
Author(s):  
Nicolas Chini ◽  
Peter Stansby ◽  
Mike Walkden ◽  
Jim Hall ◽  
Judith Wolf ◽  
...  
Keyword(s):  
Climate Change ◽  
Global Climate Change ◽  
Large Scale ◽  
Numerical Models ◽  
Global Climate ◽  
Stationary Processes ◽  
Climate Change Projections ◽  
Future Evolution ◽  
The Future

Assessment of nearshore response to climatic change is an important issue for coastal management. To predict potential effects of climate change, a framework of numerical models has been implemented which enables the downscaling of global projections to an eroding coastline, based on TOMAWAC for inshore wave propagation input into SCAPE for shoreline modelling. With this framework, components of which have already been calibrated and validated, a set of consistent global climate change projections is used to estimate the future evolution of an un-engineered coastline. The response of the shoreline is sensitive to the future scenarios, underlying the need for long term large scale offshore conditions to be included in the prediction of non-stationary processes.

scholarly journals Comparison of the Far-Eastern Seas and North-West Pacific by integral characteristics of pelagic and benthic trawled macrofaun

2014 ◽  
Vol 178 (3) ◽  
pp. 58-67
Author(s):  
Igor V. Volvenko
Keyword(s):  
Bering Sea ◽  
Large Scale ◽  
North West ◽  
The Pacific ◽  
Integral Characteristics ◽  
The Pacific Ocean ◽  
Far Eastern ◽  
Far Eastern Seas ◽  
The Bering Sea

The Bering Sea, ​​Okhotsk Sea, Japan/East Sea and adjacent waters of the Pacific Ocean (mainly within EEZ of Russia) are compared by abundance of pelagic and benthic macrofauna, its species richness, evenness, diversity, and mean weight of animals using the data of long-term large-scale pelagic and bottom trawl surveys conducted by Pacific Fish. Res. Center (TINRO) in 1977-2010.

Precipitation–Radiation–Circulation Feedback Processes Associated with Structural Changes of the ITCZ in a Warming Climate during 1980–2014: An Observational Portrayal

2020 ◽  
Vol 33 (20) ◽  
pp. 8737-8749 ◽  
Author(s):  
William K. M. Lau ◽  
Weichen Tao
Keyword(s):  
Relative Humidity ◽  
Large Scale ◽  
Structural Changes ◽  
Climate Model ◽  
Longwave Radiation ◽  
Hadley Circulation ◽  
Specific Humidity ◽  
Necessary Condition ◽  
Multiple Sources

AbstractIn this study, long-term structural changes in the intertropical convergence zone (ITCZ) and associated precipitation–radiation–circulation feedback processes are examined using multiple sources of reanalysis data for temperature, winds, moisture, and observed precipitation and outgoing longwave radiation (OLR) during 1980–2014. Consistent with CMIP5 climate model projections of the “deep tropical squeeze” under greenhouse warming, this period witnessed a warming and wetting (increased specific humidity) global trend, characterized by a narrowing of the ITCZ core with increased precipitation, coupled to widespread tropospheric drying (deficient relative humidity), increased OLR in the subtropics and midlatitudes, a widening of the descending branches of the Hadley circulation, and a poleward shift of the jet streams in both hemispheres. The widespread tropospheric drying stems from 1) a faster rate of increased saturated water vapor with warming, relative to the increase in ambient moisture due to convective and large-scale transport, and 2) enhanced anomalous subsidence, and low-level moisture divergence in the subtropics and midlatitudes. The long-term trend in enhanced precipitation (latent heating) in the ITCZ core region is strongly coupled to increasing OLR (radiative cooling to space) in the expanding dry zones, particularly over land regions in the subtropics and midlatitudes, arguably as a necessary condition for global thermodynamic energy balance. Analyses of the trend patterns in vertical profiles of p velocity, temperature, and relative humidity with respect to ITCZ precipitation rate and OLR reveal that the contrast between the wet and dry regions in the troposphere has been increasing globally, with the ITCZ core getting wetter and contracting, while the marginal convective and dry zones are getting drier and expanding.

Influence of river pattern and sediment input on estuary morphology

2020 ◽  
Author(s):  
Anne Baar ◽  
Elena Bastianon ◽  
Lisanne Braat ◽  
Daniel Parsons
Keyword(s):  
River Discharge ◽  
Large Scale ◽  
Numerical Models ◽  
Sediment Supply ◽  
Tidal Amplitude ◽  
Model Studies ◽  
Braiding Index ◽  
Sediment Input ◽  
River Pattern

<p>Alluvial estuaries are dynamic landscapes that are very sensitive to changes in boundary conditions such as river discharge and sediment supply. A better understanding of the influence of upstream river discharge and sediment input on the development of estuaries under various scenarios requires long-term morphodynamic models, to both predict future changes and improve geological interpretations by storing the stratigraphy. Past 1D model studies have shown that upstream river discharge has a significant effect on the equilibrium bed profile of estuaries, but these studies ignore the effect of 2D bar and channel formation. Using 2D numerical models to predict the development of these systems on the scale of millennia proved to be difficult, since the modelled morphology is very sensitive to the choice in e.g. sediment transport predictor and bed slope effect. In this study, we use the knowledge of previous research that determined best parameter settings for realistic river and bar patterns to model long-term and large-scale estuary morphodynamics in Delft3D. Our objective is to quantify the effects of river discharge and sediment supply on the shape of estuaries and its deposits. Firstly, we systematically varied upstream river width and tidal amplitude to examine the relation between upstream river pattern and estuary dimensions. We quantified e.g. braiding index, bar dimensions, and tidal excursion length. Results show that flood flow velocities and tidal prism are less influenced by river discharge than suggested by 1D models, and are significantly influenced by the braiding index of the river. With relatively high tides, estuary bar patterns depend on tidal amplitude, while with lower tides estuary depth and braiding index are related to upstream river width and discharge. Next steps will include varying discharge to study the effect on the rate of adaptation of the river and estuary, and varying the grain size of the sediment input at the upstream boundary. We will input coarse sediment to explore differences between fluvial deposits and tidal currents, and fine sediment to use the model for research related to biofilm.</p>

scholarly journals The 1912 Douglas-Fir Heredity Study: Long-Term Effects of Climatic Transfer Distance on Growth and Survival

2019 ◽  
Vol 118 (1) ◽  
pp. 1-13 ◽  
Author(s):  
J Bradley St. Clair ◽  
Glenn T Howe ◽  
Jennifer G Kling
Keyword(s):  
Pacific Northwest ◽  
Douglas Fir ◽  
Future Climate Change ◽  
Long Term Effects ◽  
Term Survival ◽  
Growth And Survival ◽  
Seed Sources ◽  
The Pacific ◽  
Near Term

Abstract The 1912 Douglas-Fir Heredity Study is one of the first studies undertaken by the US Forest Service, and one of the first forest genetics studies in North America. The study considers provenance variation of 120 parent trees from 13 seed sources planted at five test sites in the Pacific Northwest. The unique, long-term nature of the study makes it valuable to revisit and consider its biological and historical significance. This analysis considers how far climatically Douglas-fir populations may be moved without incurring unacceptable declines in growth and survival. Results indicate that Douglas-fir seed sources may be moved at least 2° C cooler or warmer and still retain good long-term survival and productivity. However, projected future climate change beyond 2° C may lead to lower survival and productivity. One option to address these concerns is assisted migration; however, if seed sources are moved beyond 2–3° C to a cooler climate in anticipation of warming, or from a more continental to a maritime climate, we are likely to see increased mortality and associated losses in productivity in the near-term. Lessons from this study include: (1) pay attention to good experimental design; we were able to overcome limitations from the design by using new statistical approaches; (2) maladaptation may take time to develop; poorer survival was not evident until more than two decades after planting; and (3) long-term studies may have value for addressing new, unforeseen issues in the future.

scholarly journals Tropical Cyclone Footprints in Long-Term Mean State and Multiscale Climate Variability in the Western North Pacific as Seen in the JRA-55 Reanalysis

2021 ◽  
pp. 1-46
Author(s):  
Sho Arakane ◽  
Huang-Hsiung Hsu
Keyword(s):  
Climate Variability ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Lower Troposphere ◽  
Monsoon Trough ◽  
Climate Projections ◽  
Anticyclonic Circulation ◽  
Mean State

AbstractThe monsoon trough and subtropical high have long been acknowledged to exert a substantial modulating effect on the genesis and development of TCs in the western North Pacific (WNP). However, the potential upscaling effect of TCs on large-scale circulation remains poorly understood. This study revealed the considerable contributions of TCs to the climate mean state and variability in the WNP between 1958 and 2019, characterized by a strengthened monsoon trough and weakened subtropical anticyclonic circulation in the lower troposphere, enhanced anticyclonic circulation in the upper troposphere, and warming throughout the troposphere. TCs constituted distinct footprints in the long-term mean states of the WNP summer monsoon, and their contributions increased intraseasonal and interannual variance by 50%–70%. The interdecadal variations and long-term trends in intraseasonal variance were mainly due to the year-to-year fluctuations in TC activity. The size of TC footprints was positively correlated with the magnitude of TC activity.Our findings suggest that the full understanding of climate variability and changes cannot be achieved simply on the basis of low-frequency, large-scale circulations. Rather, TCs must be regarded as a crucial component in the climate system, and their interactions with large-scale circulations require thorough exploration. The long-term dataset created in this study provides an opportunity to study the interaction between TCs and TC-free large-scale circulations to advance our understanding of climate variability in the WNP. Our findings also indicate that realistic climate projections must involve the accurate simulations of TCs.

scholarly journals Imprint of the Pacific Walker Circulation in global precipitation δ18O

2021 ◽  
pp. 1-55
Author(s):  
Georgina Falster ◽  
Bronwen Konecky ◽  
Midhun Madhavan ◽  
Samantha Stevenson ◽  
Sloan Coats
Keyword(s):  
Data Processing ◽  
Water Cycle ◽  
Southern Oscillation ◽  
Walker Circulation ◽  
Future Climate Change ◽  
Moisture Source ◽  
Global Water Cycle ◽  
The Pacific ◽  
Global Water

AbstractCharacterising variability in the global water cycle is fundamental to predicting impacts of future climate change; understanding the role of the Pacific Walker circulation (PWC) in the regional expression of global water cycle changes is critical to understanding this variability. Water isotopes are ideal tracers of the role of the PWC in global water cycling, because they retain information about circulation-dependent processes including moisture source, transport, and delivery. We collated publicly-available measurements of precipitation δ18O (δ18OP), and used novel data processing techniques to synthesise long (34-year), globally-distributed composite records from temporally discontinuous δ18OP measurements. We investigated relationships between global-scale δ18OP variability and PWC strength, as well as other possible drivers of global δ18OP variability—including the El Niño Southern Oscillation (ENSO) and global mean temperature—and used isotope-enabled climate model simulations to assess potential biases arising from uneven geographical distribution of the observations or our data processing methodology. Co-variability underlying the δ18OP composites is more strongly correlated with the PWC (r = 0.74) than any other index of climate variability tested. We propose that the PWC imprint in global δ18OP arises from multiple complementary processes, including PWC-related changes in moisture source and transport length, and a PWC- or ENSO-driven ‘amount effect’ in tropical regions. The clear PWC imprint in global δ18OP implies a strong PWC influence on the regional expression of global water cycle variability on interannual to decadal timescales, and hence that uncertainty in the future state of the PWC translates to uncertainties in future changes in the global water cycle.

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