Composite Life Cycle of West Pacific Jet-Superposition Events and the Large-Scale Environmental Response over Western North America

2021 ◽  
Author(s):  
Zachary J. Handlos ◽  
Jonathan E. Martiny
Keyword(s):  
Geopotential Height ◽  
General Circulation ◽  
Large Scale ◽  
Cold Season ◽  
Height Anomaly ◽  
Lower Latitude ◽  
Environmental Response ◽  
Jet Streams ◽  
West Pacific ◽  
Asian Winter Monsoon

AbstractVertical alignment of the polar and subtropical jet streams in the west Pacific basin occurs most often during the boreal cold season. Recent work has revealed that the large-scale environment conducive to producing such superpositions involves interaction between East Asian Winter Monsoon cold surge events, lower latitude convection and internal jet dynamics. The evolution of the large-scale environments associated with these events post-superposition as well as the significance of that evolution on aspects of the wintertime Northern Hemisphere general circulation is examined through construction of a 44-case composite. The post-superposition west Pacific jet extends eastward associated with an anomalous positive/negative geopotential height couplet straddling the jet’s exit region. This jet extension results in ridge building over Alaska and northwestern Canada. The large-scale evolutions associated with the composite post-superposition environment occurs consistently amongst the majority of cases considered within this analysis. The positive/negative geopotential height anomaly couplet, enhanced jet entrance circulation, low latitude convection and internal jet dynamics present in the pre-superposition environment weaken post-superposition. As a result, the characteristic vertical PV “wall” associated with the composite vertically superposed jet weakens. Lastly, investigation of the value of using the two most dominant modes of west Pacific jet variability in observing the evolution of the superposed west Pacific jet post-superposition reveals that, while the extension of the jet is exhibited, significant variability exists when analyzing each of the 44 cases of interest individually.

scholarly journals Assessment of CMIP5 Model Simulations of the North American Monsoon System

2013 ◽  
Vol 26 (22) ◽  
pp. 8787-8801 ◽  
Author(s):  
Kerrie L. Geil ◽  
Yolande L. Serra ◽  
Xubin Zeng
Keyword(s):  
North American ◽  
Geopotential Height ◽  
General Circulation ◽  
Large Scale ◽  
North American Monsoon ◽  
Monthly Precipitation ◽  
Large Scale Circulation ◽  
Low Level ◽  
The North ◽  
Monsoon System

Abstract Precipitation, geopotential height, and wind fields from 21 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are examined to determine how well this generation of general circulation models represents the North American monsoon system (NAMS). Results show no improvement since CMIP3 in the magnitude (root-mean-square error and bias) of the mean annual cycle of monthly precipitation over a core monsoon domain, but improvement in the phasing of the seasonal cycle in precipitation is notable. Monsoon onset is early for most models but is clearly visible in daily climatological precipitation, whereas monsoon retreat is highly variable and unclear in daily climatological precipitation. Models that best capture large-scale circulation patterns at a low level usually have realistic representations of the NAMS, but even the best models poorly represent monsoon retreat. Difficulty in reproducing monsoon retreat results from an inaccurate representation of gradients in low-level geopotential height across the larger region, which causes an unrealistic flux of low-level moisture from the tropics into the NAMS region that extends well into the postmonsoon season. Composites of the models with the best and worst representations of the NAMS indicate that adequate representation of the monsoon during the early to midseason can be achieved even with a large-scale circulation pattern bias, as long as the bias is spatially consistent over the larger region influencing monsoon development; in other words, as with monsoon retreat, it is the inaccuracy of the spatial gradients in geopotential height across the larger region that prevents some models from realistic representation of the early and midseason monsoon system.

Potential Arctic connections to eastern North American cold winters

2017 ◽  
Vol 7 (2) ◽  
pp. 232-243 ◽  
Author(s):  
James E. Overland ◽  
Muyin Wang
Keyword(s):  
Sea Ice ◽  
North American ◽  
Geopotential Height ◽  
Large Scale ◽  
Chukchi Sea ◽  
Height Anomaly ◽  
Positive Temperature ◽  
Temperature Anomalies ◽  
Cold Events ◽  
Extreme Cold

Far-field temperature and geopotential height fields associated with eastern North American early winter (DEC-JAN) extreme cold events are documented since 1950. Based on 19 cases of monthly extreme cold events, two large-scale patterns emerge. First, a strong Alaskan Ridge (AR) can develop with higher 700 hPa geopotential heights and positive temperature anomalies from Alaska south along the coastal northeastern Pacific Ocean, and low eastern North American geopotential height anomalies, the well-known North American ridge/trough pattern. A second subset of cases is a Greenland-Baffin Blocking (GBB) pattern that have positive temperature anomalies centered west of Greenland with a cut off tropospheric polar vortex feature over eastern North America; cold temperature anomalies extend from southeastern United States northwestward into central Canada. Both of these historical large-scale patterns associated with eastern North American cold events (AR and GBB) have the potential for future reinforcement by sea ice loss and associated warm Arctic regional temperature anomalies. An example of a GBB case is 15-22 December 2010 and an extreme AR case is in early 4-14 December 2016. In both cases lack of sea ice and warm temperature anomalies were colocated with local maximums in the geopotential height anomaly fields. Future regional delay of fall freeze up in the Chukchi Sea and Baffin Bay regions could reinforce these geopotential height patterns once they occur, but is not likely to initiate AR and GBB type events.

scholarly journals A Simple Kinematic Source of Skewness in Atmospheric Flow Fields

2012 ◽  
Vol 69 (2) ◽  
pp. 578-590 ◽  
Author(s):  
Fay Luxford ◽  
Tim Woollings
Keyword(s):  
Geopotential Height ◽  
General Circulation ◽  
Dynamical Behavior ◽  
Kinematic Model ◽  
Circulation Model ◽  
Jet Stream ◽  
Jet Streams ◽  
Close Link ◽  
Nonlinear Dynamical ◽  
Kinematic Effect

Abstract Geopotential height fields exhibit a well-known pattern of skewness, with distributions that are positively skewed on the poleward side of the midlatitude jets/storm tracks and negatively skewed on the equatorward side. This pattern has often been interpreted as a signature of nonlinear dynamical features, such as blocking highs and cutoff lows, and there is renewed interest in the higher moments of flow variables as indicators of the nature of the underlying dynamics. However, this paper suggests that skewness can arise as a simple kinematic consequence of the presence of jet streams and so may not be a reliable indicator of nonlinear dynamical behavior. In support of this, reanalysis data are analyzed to demonstrate a close link between the jet streams and the skewness patterns. Further evidence is provided by a simple stochastic kinematic model of a jet stream as a Gaussian wind profile. The parameters of this model are fitted to data from the reanalysis and also from an aquaplanet general circulation model. The skewness of the model’s geopotential height and zonal wind fields are then compared to those of the original data. This shows that a fluctuating jet stream can produce patterns of skewness that are qualitatively similar to those observed, although the magnitude of the skewness is significantly overestimated by the kinematic model. These results suggest that this simple kinematic effect does contribute to the observed patterns of skewness but that other processes (such as nonlinear dynamics) likely also play a role.

The Structure and Evolution of Extratropical Cyclones, Fronts, Jet Streams, and the Tropopause in the GEOS General Circulation Model

2001 ◽  
Vol 82 (9) ◽  
pp. 1853-1868 ◽  
Author(s):  
A. L. Conaty ◽  
J. C. Jusem ◽  
L. Takacs ◽  
D. Keyser ◽  
R. Atlas
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Large Scale ◽  
North Atlantic Ocean ◽  
Potential Temperature ◽  
Circulation Model ◽  
Structural Features ◽  
Extratropical Cyclones ◽  
Jet Streams ◽  
The North

The realism of extratropical cyclones, fronts, jet streams, and the tropopause in the Goddard Earth Observing System (GEOS) general circulation model (GCM), implemented in assimilation and simulation modes, is evaluated from climatological and case-study perspectives using the GEOS-1 reanalysis climatology and applicable conceptual models as benchmarks for comparison. The latitude-longitude grid spacing of the datasets derived from the GEOS GCM ranges from 2° × 2.5° to 0.5° × 0.5°. Frontal systems in the higher-resolution datasets are characterized by horizontal potential temperature gradients that are narrower in scale and larger in magnitude than their lower-resolution counterparts, and various structural features in the Shapiro–Keyser cyclone model are replicated with reasonable fidelity at 1° × 1° resolution. The remainder of the evaluation focuses on a 3-month Northern Hemisphere winter simulation of the GEOS GCM at 1° × 1° resolution. The simulation realistically reproduces various large-scale circulation features related to the North Pacific and Atlantic jet streams when compared with the GEOS-1 reanalysis climatology, and conforms closely to a conceptualization of the zonally averaged troposphere and stratosphere proposed originally by Napier Shaw and revised by Hoskins. An extratropical cyclone that developed over the North Atlantic Ocean in the simulation features surface and tropopause evolutions corresponding to the Norwegian cyclone model and to the LC2 life cycle proposed by Thorncroft et al., respectively. These evolutions are related to the position of the developing cyclone with respect to upper-level jets identified in the time-mean and instantaneous flow fields. This article concludes with the enumeration of several research opportunities that may be addressed through the use of state-of-the-art GCMs possessing sufficient resolution to represent mesoscale phenomena and processes explicitly.

scholarly journals Some Atmospheric Processes Governing the Large-Scale Tropical Circulation in Idealized Aquaplanet Simulations

2011 ◽  
Vol 68 (3) ◽  
pp. 553-575 ◽  
Author(s):  
Guillaume Gastineau ◽  
Laurent Li ◽  
Hervé Le Treut
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Moist Static Energy ◽  
Jet Streams ◽  
Atmospheric General Circulation ◽  
Static Energy ◽  
Hadley Cells ◽  
The Walker Circulation

Abstract The large-scale tropical atmospheric circulation is analyzed in idealized aquaplanet simulations using an atmospheric general circulation model. Idealized sea surface temperatures (SSTs) are used as lower-boundary conditions to provoke modifications of the atmospheric general circulation. Results show that 1) an increase in the meridional SST gradients of the tropical region drastically strengthens the Hadley circulation intensity, 2) the presence of equatorial zonal SST anomalies weakens the Hadley cells and reinforces the Walker circulation, and 3) a uniform SST warming causes small and nonsystematic changes of the Hadley and Walker circulations. In all simulations, the jet streams strengthen and move equatorward as the Hadley cells strengthen and become narrower. Some relevant mechanisms are then proposed to interpret the large range of behaviors obtained from the simulations. First, the zonal momentum transport by transient and stationary eddies is shown to modulate the eddy-driven jets, which causes the poleward displacements of the jet streams. Second, it is found that the Hadley circulation adjusts to the changes of the poleward moist static energy flux and gross moist static stability, associated with the geographical distribution of convection and midlatitude eddies. The Walker circulation intensity corresponds to the zonal moist static energy transport induced by the zonal anomalies of the turbulent fluxes and radiative cooling. These experiments provide some hints to understand a few robust changes of the atmospheric circulation simulated by ocean–atmosphere coupled models for future and past climates.

scholarly journals Tree-ring Cellulose δ18O Records Similar Large-scale Climate Influences as Precipitation δ18O in the Northwest Territories of Canada

2021 ◽  
Author(s):  
Robert Field ◽  
Laia Andreu-Hayles ◽  
Rosanne D'Arrigo ◽  
Rose Oelkers ◽  
Brian Luckman ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Northwest Territories ◽  
Tree Ring ◽  
Moisture Transport ◽  
Geopotential Height ◽  
General Circulation ◽  
Large Scale ◽  
Winter Season ◽  
Study Region ◽  
Precipitation Δ18o

Abstract Oxygen stable isotopes measured in tree rings have been useful for reconstructing climate variability and explaining changes in physiological processes occurring in forests, complementing other more widely studied tree-ring parameters such as ring width. Here, we analyzed the relationships between different climate parameters and annually resolved tree-ring δ18O records (d18OTR) from white spruce (Picea glauca [Moench]Voss) trees located near Tungsten, Northwest Territories, Canada, and used the NASA GISS ModelE2 isotopically equipped general circulation model (GCM) to interpret the relationships in an idealized sense. The d18OTR series were primarily related to temperature variations in spring and summer, likely through temperature effects on the precipitation δ18O with a combination of evaporative enrichment at leaf level in summer. The GCM simulations showed significant positive relationships between modelled precipitation δ18O over the study region and surface temperature and geopotential height over northwestern North America, with stronger patterns during fall winter than during spring-summer. The modelled precipitation δ18O was only significantly associated with moisture transport during the fall-winter season. The d18OTR showed similar correlation patterns to modelled precipitation δ18O during spring-summer, with significant positive correlations with surface temperature and geopotential height, but no correlations with moisture transport. Overall, the d18OTR records for northwestern Canada reflect the same significant large-scale climate patterns as precipitation δ18O for spring-summer, and therefore have potential for reconstructions past atmospheric dynamics in addition to temperature variability.

DESIGN AND IMPLEMENTATION OF THE OCEANOGRAPHIC MODELING AND OBSERVATION NETWORK (REMO) FOR PHYSICAL OCEANOGRAPHY STUDIES AND OCEAN FORECASTING

2014 ◽  
Vol 31 (2) ◽  
Author(s):  
Jose Antonio Moreira Lima
Keyword(s):  
Atlantic Ocean ◽  
Large Scale ◽  
North Pacific Ocean ◽  
Integrated Approach ◽  
Sea Surface ◽  
Global Ocean ◽  
Height Anomaly ◽  
The North ◽  
Observation Network ◽  
Ocean Forecasting

This paper is concerned with the planning, implementation and some results of the Oceanographic Modeling and Observation Network, named REMO, for Brazilian regional waters. Ocean forecasting has been an important scientific issue over the last decade due to studies related to climate change as well as applications related to short-range oceanic forecasts. The South Atlantic Ocean has a deficit of oceanographic measurements when compared to other ocean basins such as the North Atlantic Ocean and the North Pacific Ocean. It is a challenge to design an ocean forecasting system for a region with poor observational coverage of in-situ data. Fortunately, most ocean forecasting systems heavily rely on the assimilation of surface fields such as sea surface height anomaly (SSHA) or sea surface temperature (SST), acquired by environmental satellites, that can accurately provide information that constrain major surface current systems and their mesoscale activity. An integrated approach is proposed here in which the large scale circulation in the Atlantic Ocean is modeled in a first step, and gradually nested into higher resolution regional models that are able to resolve important processes such as the Brazil Current and associated mesoscale variability, continental shelf waves, local and remote wind forcing, and others. This article presents the overall strategy to develop the models using a network of Brazilian institutions and their related expertise along with international collaboration. This work has some similarity with goals of the international project Global Ocean Data Assimilation Experiment OceanView (GODAE OceanView).

scholarly journals Relationship between large-scale ionospheric field-aligned currents and electron/ion precipitations: DMSP observations

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Chao Xiong ◽  
Claudia Stolle ◽  
Patrick Alken ◽  
Jan Rauberg
Keyword(s):  
Time Distribution ◽  
Large Scale ◽  
Particle Flux ◽  
Particle Energy ◽  
Lower Latitude ◽  
Particle Precipitation ◽  
Data Set ◽  
The Mean ◽  
Two Parameters ◽  
Meteorological Satellite

Abstract In this study, we have derived field-aligned currents (FACs) from magnetometers onboard the Defense Meteorological Satellite Project (DMSP) satellites. The magnetic latitude versus local time distribution of FACs from DMSP shows comparable dependences with previous findings on the intensity and orientation of interplanetary magnetic field (IMF) By and Bz components, which confirms the reliability of DMSP FAC data set. With simultaneous measurements of precipitating particles from DMSP, we further investigate the relation between large-scale FACs and precipitating particles. Our result shows that precipitation electron and ion fluxes both increase in magnitude and extend to lower latitude for enhanced southward IMF Bz, which is similar to the behavior of FACs. Under weak northward and southward Bz conditions, the locations of the R2 current maxima, at both dusk and dawn sides and in both hemispheres, are found to be close to the maxima of the particle energy fluxes; while for the same IMF conditions, R1 currents are displaced further to the respective particle flux peaks. Largest displacement (about 3.5°) is found between the downward R1 current and ion flux peak at the dawn side. Our results suggest that there exists systematic differences in locations of electron/ion precipitation and large-scale upward/downward FACs. As outlined by the statistical mean of these two parameters, the FAC peaks enclose the particle energy flux peaks in an auroral band at both dusk and dawn sides. Our comparisons also found that particle precipitation at dawn and dusk and in both hemispheres maximizes near the mean R2 current peaks. The particle precipitation flux maxima closer to the R1 current peaks are lower in magnitude. This is opposite to the known feature that R1 currents are on average stronger than R2 currents.

scholarly journals Analog Downscaling of Seasonal Rainfall Forecasts in the Murray Darling Basin

2013 ◽  
Vol 141 (3) ◽  
pp. 1099-1117 ◽  
Author(s):  
Andrew Charles ◽  
Bertrand Timbal ◽  
Elodie Fernandez ◽  
Harry Hendon
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Seasonal Prediction ◽  
General Circulation Models ◽  
Meridional Wind ◽  
Seasonal Forecasts ◽  
Local Climate ◽  
Continental Scale ◽  
Predictive Skill ◽  
Murray Darling Basin

Abstract Seasonal predictions based on coupled atmosphere–ocean general circulation models (GCMs) provide useful predictions of large-scale circulation but lack the conditioning on topography required for locally relevant prediction. In this study a statistical downscaling model based on meteorological analogs was applied to continental-scale GCM-based seasonal forecasts and high quality historical site observations to generate a set of downscaled precipitation hindcasts at 160 sites in the South Murray Darling Basin region of Australia. Large-scale fields from the Predictive Ocean–Atmosphere Model for Australia (POAMA) 1.5b GCM-based seasonal prediction system are used for analog selection. Correlation analysis indicates modest levels of predictability in the target region for the selected predictor fields. A single best-match analog was found using model sea level pressure, meridional wind, and rainfall fields, with the procedure applied to 3-month-long reforecasts, initialized on the first day of each month from 1980 to 2006, for each model day of 10 ensemble members. Assessment of the total accumulated rainfall and number of rainy days in the 3-month reforecasts shows that the downscaling procedure corrects the local climate variability with no mean effect on predictive skill, resulting in a smaller magnitude error. The amount of total rainfall and number of rain days in the downscaled output is significantly improved over the direct GCM output as measured by the difference in median and tercile thresholds between station observations and downscaled rainfall. Confidence in the downscaled output is enhanced by strong consistency between the large-scale mean of the downscaled and direct GCM precipitation.

scholarly journals Can We Infer Diapycnal Mixing Rates from the World Ocean Temperature–Salinity Distribution?

2016 ◽  
Vol 46 (12) ◽  
pp. 3751-3775 ◽  
Author(s):  
Olivier Arzel ◽  
Alain Colin de Verdière
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Water Mass ◽  
World Ocean ◽  
Eddy Diffusivity ◽  
Regional Variability ◽  
Diapycnal Mixing ◽  
Inverse Models ◽  
The World ◽  
The Difference

AbstractThe turbulent diapycnal mixing in the ocean is currently obtained from microstructure and finestructure measurements, dye experiments, and inverse models. This study presents a new method that infers the diapycnal mixing from low-resolution numerical calculations of the World Ocean whose temperatures and salinities are restored to the climatology. At the difference of robust general circulation ocean models, diapycnal diffusion is not prescribed but inferred. At steady state the buoyancy equation shows an equilibrium between the large-scale diapycnal advection and the restoring terms that take the place of the divergence of eddy buoyancy fluxes. The geography of the diapycnal flow reveals a strong regional variability of water mass transformations. Positive values of the diapycnal flow indicate an erosion of a deep-water mass and negative values indicate a creation. When the diapycnal flow is upward, a diffusion law can be fitted in the vertical and the diapycnal eddy diffusivity is obtained throughout the water column. The basin averages of diapycnal diffusivities are small in the first 1500 m [O(10−5) m2 s−1] and increase downward with bottom values of about 2.5 × 10−4 m2 s−1 in all ocean basins, with the exception of the Southern Ocean (50°–30°S), where they reach 12 × 10−4 m2 s−1. This study confirms the small diffusivity in the thermocline and the robustness of the higher canonical Munk’s value in the abyssal ocean. It indicates that the upward dianeutral transport in the Atlantic mostly takes place in the abyss and the upper ocean, supporting the quasi-adiabatic character of the middepth overturning.

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