scholarly journals A Multifaceted Climatology of Atmospheric Blocking and Its Recent Linear Trend

2007 ◽  
Vol 20 (4) ◽  
pp. 633-649 ◽  
Author(s):  
M. Croci-Maspoli ◽  
C. Schwierz ◽  
H. C. Davies
Keyword(s):  
North Pacific ◽  
Linear Trend ◽  
Age Distribution ◽  
Atmospheric Blocking ◽  
Weather Forecasts ◽  
The North ◽  
Four Seasons ◽  
Medium Range ◽  
The Mean ◽  
The North Pacific

Abstract A dynamically based climatology is derived for Northern Hemisphere atmospheric blocking events. Blocks are viewed as large amplitude, long-lasting, and negative potential vorticity (PV) anomalies located beneath the dynamical tropopause. The derived climatology [based on the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40)] provides a concise, coherent, and illuminating description of the main physical characteristics of blocks and the accompanying linear trends. The latitude–longitude distribution of blocking frequency captures the standard bimodal geographical distribution with major peaks over the North Atlantic and eastern North Pacific in all four seasons. The accompanying pattern for the age distribution, the genesis–lysis regions, and the track of blocks reveals that 1) younger blocks (1–4 days) are more prevalent at lower latitudes whereas significantly older blocks (up to 12 days) are located at higher latitudes; 2) genesis is confined predominantly to the two major ocean basins and in a zonal band between 40° and 50°N latitude, whereas lysis is more dispersed but with clear preference to higher latitudes; and 3) the general northeastward–west-northwest movement of blocks in the genesis–lysis phase also exhibits subtle seasonal and intra- and interbasin differences. Examination of the intensity and spatial-scale changes during the blocking life cycle suggests that in the mean a block’s evolution is independent of the genesis region and its eventual duration. A novel analysis of blocking trends reveals significant negative trends in winter over Greenland and in spring over the North Pacific. It is shown that the changes over Greenland are linked to the number of blocking episodes, whereas a neighboring trend signal to the south is linked to higher-frequency anticyclonic systems. Furthermore, evidence is adduced that changes in blocking frequency contribute seminally to tropopause height trends.

scholarly journals An Examination of Tropical Cyclone Position, Intensity, and Intensity Life Cycle within Atmospheric Reanalysis Datasets

2012 ◽  
Vol 25 (10) ◽  
pp. 3453-3475 ◽  
Author(s):  
Benjamin A. Schenkel ◽  
Robert E. Hart
Keyword(s):  
Life Cycle ◽  
North Pacific ◽  
Strongly Correlated ◽  
Sea Level Pressure ◽  
Climate Forecast System Reanalysis ◽  
Weather Forecasts ◽  
The North ◽  
Medium Range ◽  
The Mean ◽  
Modern Era

Abstract The following study examines the position and intensity differences of tropical cyclones (TCs) among the Best-Track and five atmospheric reanalysis datasets to evaluate the degree to which reanalyses are appropriate for studying TCs. While significant differences are found in both reanalysis TC intensity and position, the representation of TC intensity within reanalyses is found to be most problematic owing to its underestimation beyond what can be attributed solely to the coarse grid resolution. Moreover, the mean life cycle of normalized TC intensity within reanalyses reveals an underestimation of both prepeak intensification rates as well as a delay in peak intensity relative to the Best-Track. These discrepancies between Best-Track and reanalysis TC intensity and position can further be described through correlations with such parameters as Best-Track TC age, Best-Track TC intensity, Best-Track TC location, and the extended Best-Track TC size. Specifically, TC position differences within the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), ECMWF Interim Re-Analysis (ERA-I), and Modern Era Retrospective-Analysis for Research and Applications (MERRA) exhibit statistically significant correlations (0.27 ≤ R ≤ 0.38) with the proximity of TCs to observation dense areas in the North Atlantic (NATL) and western North Pacific (WPAC). Reanalysis TC intensity is found to be most strongly correlated with Best-Track TC size (0.53 ≤ R ≤ 0.70 for maximum 10-m wind speed; −0.71 ≤ R ≤ −0.53 for minimum mean sea level pressure) while exhibiting smaller, yet significant, correlations with Best-Track TC age, Best-Track TC intensity, and Best-Track TC latitude. Of the three basins examined, the eastern North Pacific (EPAC) has the largest reanalysis TC position differences and weakest intensities possibly due to a relative dearth of observations, the strong nearby terrain gradient, and the movement of TCs away from the most observation dense portion of the basin over time. The smaller mean Best-Track size and shorter mean lifespan of Best-Track EPAC TCs may also yield weaker reanalysis TC intensities. Of the five reanalyses, the smaller position differences and stronger intensities found in the Climate Forecast System Reanalysis (CFSR) and Japanese 25-year Reanalysis (JRA-25) are attributed to the use of vortex relocation and TC wind profile retrievals, respectively. The discrepancies in TC position between the Best-Track and reanalyses combined with the muted magnitude of TC intensity and its partially nonphysical life cycle within reanalyses suggests that caution should be exercised when utilizing these datasets for studies that rely either on TC intensity (raw or normalized) or track. Finally, several cases of nonphysical TC structure also argue that further work is needed to improve TC representation while implying that studies focusing solely on TC intensity and track do not necessarily extend to other aspects of TC representation.

scholarly journals The mean meridional circulation and midlatitude ozone buildup

2005 ◽  
Vol 5 (3) ◽  
pp. 4223-4256
Author(s):  
G. Nikulin ◽  
A. Karpechko
Keyword(s):  
Heat Flux ◽  
North Pacific ◽  
Meridional Circulation ◽  
Residual Velocity ◽  
The North ◽  
Eddy Heat Flux ◽  
Mean Meridional Circulation ◽  
The Mean ◽  
Temperature Tendency ◽  
The North Pacific

Abstract. The development of wintertime ozone buildup over the Northern Hemisphere (NH) midlatitudes and its connection with the mean meridional circulation in the stratosphere are examined statistically on a monthly basis from October to March (1980–2002). The ozone buildup begins locally in October with positive ozone tendencies over the North Pacific, which spread eastward and westward in November and finally cover all midlatitudes in December. During October–January a longitudinal distribution of the ozone tendencies mirrors a structure of quasi-stationary planetary waves in the lower stratosphere and has less similarity with this structure in February–March when chemistry begins to play a more important role. From November to March, zonal mean ozone tendencies (50°–60° N) show strong correlation (|r|=0.7) with different parameters used as proxies of the mean meridional circulation, namely: eddy heat flux, the vertical residual velocity (diabatically-derived) and temperature tendency. The correlation patterns between ozone tendency and the vertical residual velocity or temperature tendency are more homogeneous from month to month than ones for eddy heat flux. A partial exception is December when correlation is strong only for the vertical residual velocity. In October zonal mean ozone tendencies have no coupling with the proxies. However, positive tendencies averaged over the North Pacific correlate well, with all of them suggesting that intensification of northward ozone transport starts locally over the Pacific already in October. We show that the NH midlatitude ozone buildup has stable statistical relation with the mean meridional circulation in all months from October to March and half of the interannual variability in monthly ozone tendencies can be explained by applying different proxies of the mean meridional circulation.

scholarly journals Characteristics of the North Pacific Oscillation in CMIP5 Models in Relation to Atmospheric Mean States

2020 ◽  
Vol 33 (9) ◽  
pp. 3809-3825
Author(s):  
Mi-Kyung Sung ◽  
Changhyun Yoo ◽  
Sang-Wook Yeh ◽  
Yu Kosaka ◽  
Soon-Il An
Keyword(s):  
North Pacific ◽  
Climate Models ◽  
Horizontal Wind ◽  
Cmip5 Models ◽  
Systematic Bias ◽  
North Pacific Oscillation ◽  
The West ◽  
The North ◽  
The Mean ◽  
The North Pacific

AbstractThe North Pacific Oscillation (NPO), the second leading atmospheric mode in the North Pacific Ocean, is known to be responsible for climate variability and extremes in adjacent regions. The reproducibility of the NPO in climate models is thus a topic of interest for the more accurate prediction of climate extremes. By investigating the spatial characteristics of the NPO in models from phase 5 of the Coupled Model Intercomparison Project (CMIP5), this study reveals the intimate relationship between the NPO structure and the atmospheric mean states over the North Pacific. The majority of the models reasonably capture the meridional contrast of pressure anomalies, but the detailed horizontal characteristics of the NPO are found to differ among the models. Diagnostic analysis of 30 climate models and long-term observations suggest that systematic bias in the mean atmospheric baroclinicity over the North Pacific crucially affects the horizontal shape and zonal position of the NPO. In the models in which the climatological continental trough over the western North Pacific extends farther to the east, the NPO tends to be simulated farther to the east, strengthening its impact on the downstream climate. In contrast, when the climatological continental trough is reduced in size toward the west, the growth of the NPO is limited to the west, and its influence is weakened downstream. This relationship can be understood via the altered available potential and kinetic energy conversions that feed the total energy of the NPO, primarily stemming from the difference in the mean horizontal temperature gradient and stretching deformation of the mean horizontal wind.

Forcing of Low-Frequency Ocean Variability in the Northeast Pacific*

2009 ◽  
Vol 22 (5) ◽  
pp. 1255-1276 ◽  
Author(s):  
Kettyah C. Chhak ◽  
Emanuele Di Lorenzo ◽  
Niklas Schneider ◽  
Patrick F. Cummins
Keyword(s):  
North Pacific ◽  
Ocean Dynamics ◽  
Sea Surface ◽  
Altimeter Data ◽  
Atmospheric Forcing ◽  
Ocean Variability ◽  
Northeast Pacific ◽  
The North ◽  
The Mean ◽  
The North Pacific

Abstract An ocean model is used to examine and compare the forcing mechanisms and underlying ocean dynamics of two dominant modes of ocean variability in the northeast Pacific (NEP). The first mode is identified with the Pacific decadal oscillation (PDO) and accounts for the most variance in model sea surface temperatures (SSTs) and sea surface heights (SSHs). It is characterized by a monopole structure with a strong coherent signature along the coast. The second mode of variability is termed the North Pacific Gyre Oscillation (NPGO). This mode accounts for the most variance in sea surface salinities (SSSs) in the model and in long-term observations. While the NPGO is related to the second EOF of the North Pacific SST anomalies (the Victoria mode), it is defined here in terms of SSH anomalies. The NPGO is characterized by a pronounced dipole structure corresponding to variations in the strengths of the eastern and central branches of the subpolar and subtropical gyres in the North Pacific. It is found that the PDO and NPGO modes are each tied to a specific atmospheric forcing pattern. The PDO is related to the overlying Aleutian low, while the NPGO is forced by the North Pacific Oscillation. The above-mentioned climate modes captured in the model hindcast are reflected in satellite altimeter data. A budget reconstruction is used to study how the atmospheric forcing drives the SST and SSH anomalies. Results show that the basinwide SST and SSS anomaly patterns associated with each mode are shaped primarily by anomalous horizontal advection of mean surface temperature and salinity gradients (∇ Tand ∇ S) via anomalous surface Ekman currents. This suggests a direct link of these modes with atmospheric forcing and the mean ocean circulation. Smaller-scale patterns in various locations along the coast and in the Gulf of Alaska are, however, not resolved with the budget reconstructions. Vertical profiles of the PDO and NPGO indicate that the modes are strongest mainly in the upper ocean down to 250 m. The shallowness of the modes, the depth of the mean mixed layer, and wintertime temperature profile inversions contribute to the sensitivity of the budget analysis in the regions of reduced reconstruction skill.

Season-Dependent Forecast Skill of the Leading Forced Atmospheric Circulation Pattern over the North Pacific and North American Region*

2012 ◽  
Vol 25 (20) ◽  
pp. 7248-7265 ◽  
Author(s):  
XiaoJing Jia ◽  
Hai Lin ◽  
June-Yi Lee ◽  
Bin Wang
Keyword(s):  
Atmospheric Circulation ◽  
North Pacific ◽  
Circulation Pattern ◽  
Tropical Pacific ◽  
Atmospheric Circulation Pattern ◽  
Potential Predictability ◽  
The North ◽  
The Mean ◽  
The North Pacific ◽  
Mean State

Abstract Multimodel ensemble (MME) seasonal forecasts are analyzed to evaluate numerical model performance in predicting the leading forced atmospheric circulation pattern over the extratropical Northern Hemisphere (NH). Results show that the time evolution of the leading tropical Pacific sea surface temperature (SST)-coupled atmospheric pattern (MCA1), which is obtained by applying a maximum covariance analysis (MCA) between 500-hPa geopotential height (Z500) in the extratropical NH and SST in the tropical Pacific Ocean, can be predicted with a significant skill in March–May (MAM), June–August (JJA), and December–February (DJF) one month ahead. However, most models perform poorly in capturing the time variation of MCA1 in September–November (SON) with 1 August initial condition. Two possible reasons for the models’ low skill in SON are identified. First, the models have the most pronounced errors in the mean state of SST and precipitation along the central equatorial Pacific. Because of the link between the divergent circulation forced by tropical heating and the midlatitude atmospheric circulation, errors in the mean state of tropical SST and precipitation may lead to a degradation of midlatitude forecast skill. Second, examination of the potential predictability of the atmosphere, estimated by the ratio of the total variance to the variance of the model forecasts due to internal dynamics, shows that the atmospheric potential predictability over the North Pacific–North American (NPNA) region is the lowest in SON compared to the other three seasons. The low ratio in SON is due to a low variance associated with external forcing and a high variance related to atmospheric internal processes over this area.

Estimating Bolus Velocities from Data—How Large Must They Be?

2009 ◽  
Vol 39 (1) ◽  
pp. 70-88 ◽  
Author(s):  
Peter D. Killworth
Keyword(s):  
North Pacific ◽  
Density Level ◽  
Eddy Flux ◽  
Mean Flow ◽  
Flux Divergence ◽  
The North ◽  
Resolution Model ◽  
Eddy Fluxes ◽  
The Mean ◽  
The North Pacific

Abstract This paper examines the representation of eddy fluxes by bolus velocities. In particular, it asks the following: 1) Can an arbitrary eddy flux divergence of density be represented accurately by a nondivergent bolus flux that satisfies the condition of no normal flow at boundaries? 2) If not, how close can such a representation come? 3) If such a representation can exist in some circumstances, what is the size of the smallest bolus velocity that fits the data? The author finds, in agreement with earlier authors, that the answer to the first question is no, although under certain conditions, which include a modification to the eddy flux divergence, a bolus representation becomes possible. One such condition is when the eddy flux divergence is required to balance the time-mean flux divergence. The smallest bolus flow is easily found by solving a thickness-weighted Poisson equation on each density level. This problem is solved for the North Pacific using time-mean data from an eddy-permitting model. The minimum bolus flow is found to be very small at depth but larger than is usually assumed near the surface. The magnitude of this minimum flow is of order one-tenth of the mean flow. Similar but larger results are found for a coarse-resolution model.

Influence of Atmospheric Blocking on Storm Track Activity Over the North Pacific During Boreal Winter

2021 ◽  
Vol 48 (17) ◽  
Author(s):  
Minghao Yang ◽  
Dehai Luo ◽  
Chongyin Li ◽  
Yao Yao ◽  
Xin Li ◽  
...  
Keyword(s):  
North Pacific ◽  
Storm Track ◽  
Boreal Winter ◽  
Atmospheric Blocking ◽  
The North ◽  
Storm Track Activity ◽  
The North Pacific

scholarly journals The Effects of Spring and Winter Blocking on PM10 Concentration in Korea

Atmosphere ◽  
2019 ◽  
Vol 10 (7) ◽  
pp. 410 ◽  
Author(s):  
Sug-gyeong Yun ◽  
Changhyun Yoo
Keyword(s):  
Wind Speed ◽  
North Pacific ◽  
Pm10 Concentration ◽  
Positive Pressure ◽  
Atmospheric Blocking ◽  
Pressure System ◽  
The North ◽  
Different Types ◽  
Positive Correlations ◽  
The North Pacific

Atmospheric blocking is known to be related to locally developed abnormal climate of the Korean Peninsula, such as heat and cold waves. However, little attention has been devoted to the effects of blocking on the fine dust concentration over Korea. In this study, we analyze the connection between the monthly frequency of blocking occurrence and high particulate matter smaller than 10 μm in diameter (PM10) concentration events in Korea. Our analyses are limited to winter (DJF) and spring (MAM) when both the blocking and high PM10 events tend to take place most frequently. During winter, significant and positive correlations are found in the North Pacific, while significantly negative values are seen over Ural-Siberia. A high PM10 concentration tends to be accompanied by negative (positive) pressure anomalies over Siberia (North Pacific). However, while examining atmospheric fields associated with the high PM10 events, we find that the high PM10 events show two different types of atmospheric fields depending on the strength of wind speed over Korea. When the local wind speed over Korea is weaker than normal, the connection with the North Pacific blocking is strengthened, whereas, the connection with the Ural-Siberia blocking is enhanced when the wind speed is stronger than normal. However, to increase the occurrence of the high PM10 events, both types feature a strong meridional pressure gradient caused by a high pressure system forming over Siberia. This is accompanied by a strong upper tropospheric zonal wind from China and Mongolia to Korea.

scholarly journals Projection of North Pacific Tropical Upper-Tropospheric Trough in CMIP5 Models: Implications for Changes in Tropical Cyclone Formation Locations

2018 ◽  
Vol 31 (2) ◽  
pp. 761-774 ◽  
Author(s):  
Chao Wang ◽  
Liguang Wu
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Climate Models ◽  
Coupled Model ◽  
Atmospheric Composition ◽  
Cmip5 Models ◽  
The North ◽  
The Mean ◽  
The Impact ◽  
The North Pacific

The strong westerly shear to the south flank of the tropical upper-tropospheric trough (TUTT) limits the eastward extension of tropical cyclone (TC) formation over the western North Pacific (WNP) and thus the zonal shift of the TUTT in warming scenarios has an important implication for the mean formation location of TCs. The impact of global warming on the zonal shift of the TUTT is investigated by using output from phase 5 of the Coupled Model Intercomparison Project (CMIP5) of 36 climate models in this study. It is found that considerable spread exists in the zonal position, orientation, and intensity of the simulated-climatologic TUTT in the historical runs, which is forced by observed conditions such as changes in atmospheric composition, solar forcing, and aerosols. The large spread is closely related to the diversity in the simulated SST biases over the North Pacific. Based on the 15 models with relatively high skill in their historical runs, the near-term (2016–35) projection shows no significant change of the TUTT longitude, while the TUTT experiences an eastward shift of 1.9° and 3.2° longitude in the representative concentration pathway (RCP) 4.5 and 8.5 scenarios in the long-term (2081–2100) projection with considerable intermodel variability. Further examination indicates that the projected changes in the zonal location of the TUTT are also associated with the projected relative SST anomalies over the North Pacific. A stronger (weaker) relative SST warming over the North Pacific favors an eastward (westward) shift of the TUTT, suggesting that the spatial pattern of the future SST change is an important factor for the zonal shift of the mean formation location of TCs.

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