Predictable Patterns of Wintertime Surface Air Temperature in Northern Hemisphere and Their Predictability Sources in the SEAS5

2020 ◽  
Vol 33 (24) ◽  
pp. 10743-10754
Author(s):  
Hongdou Fan ◽  
Lin Wang ◽  
Yang Zhang ◽  
Youmin Tang ◽  
Wansuo Duan ◽  
...  
Keyword(s):  
North America ◽  
Northern Hemisphere ◽  
Air Temperature ◽  
Southern Oscillation ◽  
Arctic Sea Ice ◽  
Prediction Skill ◽  
The Arctic ◽  
The Tibetan Plateau ◽  
Central Pacific ◽  
The Pacific

AbstractBased on 36-yr hindcasts from the fifth-generation seasonal forecast system of the European Centre for Medium-Range Weather Forecasts (SEAS5), the most predictable patterns of the wintertime 2-m air temperature (T2m) in the extratropical Northern Hemisphere are extracted via the maximum signal-to-noise (MSN) empirical orthogonal function (EOF) analysis, and their associated predictability sources are identified. The MSN EOF1 captures the warming trend that amplifies over the Arctic but misses the associated warm Arctic–cold continent pattern. The MSN EOF2 delineates a wavelike T2m pattern over the Pacific–North America region, which is rooted in the tropical forcing of the eastern Pacific-type El Niño–Southern Oscillation (ENSO). The MSN EOF3 shows a wavelike T2m pattern over the Pacific–North America region, which has an approximately 90° phase difference from that associated with MSN EOF2, and a loading center over midlatitude Eurasia. Its sources of predictability include the central Pacific-type ENSO and Eurasian snow cover. The MSN EOF4 reflects T2m variability surrounding the Tibetan Plateau, which is plausibly linked to the remote forcing of the Arctic sea ice. The information on the leading predictable patterns and their sources of predictability is further used to develop a calibration scheme to improve the prediction skill of T2m. The calibrated prediction skill in terms of the anomaly correlation coefficient improves significantly over midlatitude Eurasia in a leave-one-out cross-validation, implying a possible way to improve the wintertime T2m prediction in the SEAS5.

scholarly journals Unraveling the Teleconnection Mechanisms that Induce Wintertime Temperature Anomalies over the Northern Hemisphere Continents in Response to the MJO

2016 ◽  
Vol 73 (9) ◽  
pp. 3557-3571 ◽  
Author(s):  
Kyong-Hwan Seo ◽  
Hyun-Ju Lee ◽  
Dargan M. W. Frierson
Keyword(s):  
North America ◽  
Eastern Europe ◽  
Northern Hemisphere ◽  
Air Temperature ◽  
Surface Air Temperature ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Temperature Variations ◽  
Temperature Anomalies ◽  
Air Temperature Variations

Abstract Significant extratropical surface air temperature variations arise as a result of teleconnections induced by the Madden–Julian oscillation (MJO). The authors elucidate the detailed physical processes responsible for the development of temperature anomalies over Northern Hemisphere continents in response to MJO-induced heating using an intraseasonal perturbation thermodynamic equation and a wave activity tracing technique. A quantitative assessment demonstrates that surface air temperature variations are due to dynamical processes associated with a meridionally propagating Rossby wave train. Over East Asia, a local Hadley circulation causes adiabatic subsidence following MJO phase 3 to be a main driver for the warming. Meanwhile, for North America and eastern Europe, horizontal temperature advection by northerlies or southerlies is the key process for warming or cooling. A ray-tracing analysis illustrates that Rossby waves with zonal wavenumbers 2 and 3 influence the surface warming over North America and a faster wavenumber 4 affects surface temperature over eastern Europe. Although recent studies demonstrate the impacts of the Arctic Oscillation, Arctic sea ice melting, and Eurasian snow cover variations on extremely cold wintertime episodes over the NH extratropics, the weather and climate there are still considerably modulated through teleconnections induced by the tropical heat forcing. In addition, the authors show that the MJO is a real source of predictability for strong warm/cold events over these continents, suggesting a higher possibility of making a skillful forecast of temperature extremes with over 1 month of lead time.

Variability of Arctic Sea Ice Based on Quantile Regression and the Teleconnection with Large-Scale Climate Patterns

2020 ◽  
Vol 33 (10) ◽  
pp. 4009-4025
Author(s):  
Shuyu Zhang ◽  
Thian Yew Gan ◽  
Andrew B. G. Bush
Keyword(s):  
Sea Ice ◽  
Quantile Regression ◽  
Large Scale ◽  
Southern Oscillation ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Climate Indices ◽  
The Pacific ◽  
Arctic Sea ◽  
Climate Patterns

AbstractUnder global warming, Arctic sea ice has declined significantly in recent decades, with years of extremely low sea ice occurring more frequently. Recent studies suggest that teleconnections with large-scale climate patterns could induce the observed extreme sea ice loss. In this study, a probabilistic analysis of Arctic sea ice was conducted using quantile regression analysis with covariates, including time and climate indices. From temporal trends at quantile levels from 0.01 to 0.99, Arctic sea ice shows statistically significant decreases over all quantile levels, although of different magnitudes at different quantiles. At the representative extreme quantile levels of the 5th and 95th percentiles, the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO), and the Pacific–North American pattern (PNA) have more significant influence on Arctic sea ice than El Niño–Southern Oscillation (ENSO), the Pacific decadal oscillation (PDO), and the Atlantic multidecadal oscillation (AMO). Positive AO as well as positive NAO contribute to low winter sea ice, and a positive PNA contributes to low summer Arctic sea ice. If, in addition to these conditions, there is concurrently positive AMO and PDO, the sea ice decrease is amplified. Teleconnections between Arctic sea ice and the climate patterns were demonstrated through a composite analysis of the climate variables. The anomalously strong anticyclonic circulation during the years of positive AO, NAO, and PNA promotes more sea ice export through Fram Strait, resulting in excessive sea ice loss. The probabilistic analyses of the teleconnections between the Arctic sea ice and climate patterns confirm the crucial role that the climate patterns and their combinations play in overall sea ice reduction, but particularly for the low and high quantiles of sea ice concentration.

scholarly journals Seasonal Variation and Spatial Patterns of the Atmospheric Component of the Pacific Decadal Oscillation

2013 ◽  
Vol 26 (5) ◽  
pp. 1575-1594 ◽  
Author(s):  
Catrin M. Mills ◽  
John E. Walsh
Keyword(s):  
United States ◽  
North America ◽  
Air Temperature ◽  
Pacific Decadal Oscillation ◽  
Southern Oscillation ◽  
Grid Point ◽  
Southeastern United States ◽  
Surface Air Temperature ◽  
The Pacific ◽  
Difference Fields

Abstract The Pacific decadal oscillation (PDO) is an El Niño–Southern Oscillation (ENSO)-like climate oscillation that varies on multidecadal and higher-frequency scales, with a sea surface temperature (SST) dipole in the Pacific. This study addresses the seasonality, vertical structure, and across-variable relationships of the local North Pacific and downstream North American atmospheric signal of the PDO. The PDO-based composite difference fields of 500-mb geopotential height, surface air temperature, sea level pressure, and precipitation vary not only across seasons, but also from one calendar month to another within a season, although month-to-month continuity is apparent. The most significant signals occur in western North America and in the southeastern United States, where a positive PDO is associated with negative heights, consistent with underlying temperatures in the winter. In summer, a negative precipitation signal in the southeastern United States associated with a positive PDO phase is consistent with a ridge over the region. When an annual harmonic is fit to the 12 monthly surface air temperature differences at each grid point, the PDO temperature signal peaks in winter in most of North America, while a peak in summer occurs in the southeastern United States. Approximately 25% of the variance of the PDO index is accounted for by ENSO. Atmospheric composite differences based on a residual (ENSO linearly removed) PDO index have many similarities to those of the full PDO signal.

scholarly journals Subseasonal Midlatitude Prediction Skill Following QBO-MJO Activity

2019 ◽  
Author(s):  
Kirsten J. Mayer ◽  
Elizabeth A. Barnes
Keyword(s):  
Spatial Distribution ◽  
North America ◽  
Northern Hemisphere ◽  
Rossby Waves ◽  
Prediction Skill ◽  
Height Field ◽  
Madden Julian Oscillation ◽  
Quasi Biennial Oscillation ◽  
The Pacific ◽  
Biennial Oscillation

Abstract. The Madden-Julian Oscillation (MJO) is known to force extratropical weather days-to-weeks following an MJO event through excitation of stationary Rossby waves, tropical-extratropical teleconnections. Prior research has demonstrated that this tropically forced midlatitude response leads to increased prediction skill on subseasonal to seasonal (S2S) timescales. Furthermore, the Quasi-Biennial Oscillation (QBO) has been shown to possibly alter these teleconnections through modulation of the MJO itself and the atmospheric basic state upon which the Rossby waves propagate. This implies that the MJO-QBO relationship may affect midlatitude circulation prediction skill on S2S timescales. In this study, we quantify midlatitude circulation sensitivity and prediction skill following active MJOs and QBOs across the Northern Hemisphere on S2S timescales through an examination of the 500 hPa geopotential height field. First, a comparison of the spatial distribution of Northern Hemisphere sensitivity to the MJO during different QBO phases is performed for ERA-Interim reanalysis and ECMWF and NCEP hindcasts. Secondly, differences in prediction skill in ECMWF and NCEP hindcasts are quantified following MJO-QBO activity. We find that regions across the Pacific, North America and the Atlantic exhibit increased prediction skill following MJO-QBO activity, but these regions are not always collocated with the locations most sensitive to the MJO under a particular QBO state. Both hindcast systems demonstrate enhanced prediction skill 7–14 days following active MJO events during strong QBO periods compared to MJO events during neutral QBO periods.

scholarly journals Impact of Reduced Arctic Sea Ice on Northern Hemisphere Climate and Weather in Autumn and Winter

2021 ◽  
pp. 1-61
Author(s):  
Svenya Chripko ◽  
Rym Msadek ◽  
Emilia Sanchez-Gomez ◽  
Laurent Terray ◽  
Laurent Bessières ◽  
...  
Keyword(s):  
North America ◽  
Sea Ice ◽  
Central Asia ◽  
Northern Hemisphere ◽  
Climate Model ◽  
Polar Vortex ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Arctic Sea ◽  
Autumn And Winter

AbstractThe Northern Hemisphere transient atmospheric response to Arctic sea decline is investigated in autumn and winter, using sensitivity experiments performed with the CNRMCM6-1 high-top climate model. Arctic sea ice albedo is reduced to the ocean value, yielding ice-free conditions during summer and a more moderate sea ice reduction during the following months. A strong ampli_cation of temperatures over the Arctic is induced by sea ice loss, with values reaching up to 25°C near the surface in autumn. Signi_cant surface temperature anomalies are also found over the mid-latitudes, with a warming reaching 1°C over North America and Europe, and a cooling reaching 1°C over central Asia. Using a dynamical adjustment method based on a regional reconstruction of circulation analogs, we show that the warming over North America and Europe can be explained both by changes in the atmospheric circulation and by the advection of warmer oceanic air by the climatological ow. In contrast, we demonstrate that the sea-ice induced cooling over central Asia is solely due to dynamical changes, involving an intensi_cation of the Siberian High and a cyclonic anomaly over the Sea of Okhotsk. In the troposphere, the abrupt Arctic sea ice decline favours a narrowing of the subtropical jet stream and a slight weakening of the lower part of the polar vortex that is explained by a weak enhancement of upward wave activity toward the stratosphere. We further show that reduced Arctic sea ice in our experiments is mainly associated with less severe cold extremes in the mid-latitudes.

Different Climatic Effects of the Arctic and Antarctic ice Covers on Land Surface Temperature in the Northern Hemisphere: Application of Liang-Kleeman Information Flow Method and CAM4.0

2021 ◽  
Author(s):  
Shunyu Jiang ◽  
Haibo HU ◽  
William Perrie ◽  
Ning Zhang ◽  
Haokun Bai ◽  
...  
Keyword(s):  
North America ◽  
East Asia ◽  
Atmospheric Circulation ◽  
Northern Hemisphere ◽  
Information Flow ◽  
Air Temperature ◽  
The Arctic ◽  
High Latitudes ◽  
Flow Method ◽  
The Antarctic

Abstract Ice covers in high latitudes play important role in the global atmospheric circulation and abnormal temperature distribution. The observations have revealed the differences in the interannual variability of the Arctic and Antarctic ice covers, but their respective climate effect is not clear. The Liang-Kleeman information flow method is used to reveal the causal relationships from the sea ices of the Arctic and Antarctic to the global air temperature. The results point out that changes of the Arctic or Antarctic sea ices both have significant impacts on the global air temperature. Especially for the air temperature in East Asia and North America, the interannual variation of the Antarctic sea ice has an even stronger impact than the Arctic ice covers. This causality is further proved by the General Atmospheric Circulation Model (CAM4.0). In the numerical experiments, the ice covers in Arctic and Antarctic are changed individually or simultaneously as the forcing fields, and then the respective climate effects are analyzed. The results show that both the Arctic and Antarctic ice cover variations can change the intensity of atmospheric baroclinic disturbance in mid-high latitudes of individual hemisphere, generating wave energy transmission across the equator in the meridional direction, and eventually causing air temperature anomalies in both hemispheres. Furthermore, the Antarctic ice covers are closer to the mid-high latitude atmospheric jets in the southern hemisphere. Therefore, the changes of Antarctic ice covers lead to a larger atmospheric wave-activity flux response, and quickly spread to the northern hemisphere, causing more significant temperature anomalies over the East Asia and North America.

Comparisons of different definitions of the western Pacific pattern and associated winter climate anomalies in Eurasia and North America

2020 ◽  
Author(s):  
Hasi Aru
Keyword(s):  
North America ◽  
Air Temperature ◽  
Southern Oscillation ◽  
Surface Air Temperature ◽  
Western Pacific ◽  
The Arctic ◽  
Temperature Anomalies ◽  
The Western Pacific ◽  
Air Temperature Anomalies ◽  
Western Pacific Pattern

<p>The western Pacific pattern (WP) is one of the most prominent teleconnection patterns over the Northern Hemisphere (NH) in boreal winter. There exist several methods employed to identify the WP in the literature. This study compares eight WPs defined by different methods. Correlation coefficients among the eight WP indices (WPIs) show considerable spreads, though most of them are statistically significant. The meridional dipole structure of WP can be captured by all of the WPIs, but it shows large spreads in the locations of the centers. Several WPIs produce a significant correlation with the winter Arctic Oscillation, with marked signals of atmospheric anomalies over the Arctic region. Connections of the WPs with the simultaneous winter El Niño-Southern Oscillation (ENSO) depend largely upon their definitions. Impacts of the WPs on the surface air temperature over many parts of Eurasia and North America are also sensitive to their definitions. Differences in the surface air temperature anomalies are closely related to differences in the spatial structure of the WPs. Finally, we define a new WP index as differences in the area-average 500-hPa geopotential height anomalies between subtropics and mid-latitude of northwestern Pacific. This newly defined WP index has a close relation with the above eight WPIs, the tropical Pacific sea surface temperature and surface air temperature anomalies over Eurasia and North America.</p>

Seismic surface waves and the crustal structure of the Pacific region*

1934 ◽  
Vol 24 (3) ◽  
pp. 231-302
Author(s):  
Dean S. Carder
Keyword(s):  
North America ◽  
Surface Waves ◽  
Pacific Islands ◽  
Long Waves ◽  
The Arctic ◽  
Focal Region ◽  
Western North America ◽  
Central Pacific ◽  
Natural Period ◽  
The Pacific

summary The favorable location of Berkeley on the eastern margin of the Pacific makes possible a comparative study of surface waves coming directly from the epicenter to that station over paths that are purely Pacific or purely continental. Records of 378 earthquakes dating from November, 1910, to May, 1934, have been used in this study. Speeds and period of the initial impulses of Love waves have been measured and associated with wave-velocity. These waves show normal dispersion, the long waves having the greater speeds. Speeds over oceanic paths are higher than over continental paths, the difference diminishing with an increase in the wave-length. For short or long waves, they are about the same over all Pacific paths, but waves having intermediate periods (30 or 40 seconds) cross under the Aleutian deep faster than under the Polynesian Pacific. The data indicate for the crustal thicknesses under western North America and the Pacific the following approximate values: granite 20 kilometers, gabbro 40 kilometers, under western North America; basalt 25 kilometers, dunite 20 kilometers, under the Aleutian deep; basalt 30 kilometers, dunite 25 kilometers under Polynesia; and intermediate values under the remainder of the Pacific. A third discontinuity under the continent at depths somewhat greater than 60 kilometers is indicated. If the sub-Pacific is assumed to be single-layered, thicknesses of 35 to 45 kilometers form the best fit to the data. The thickness of the crust underlying the Pacific Islands is probably about 10 kilometers greater than that underlying the deeps of the North Pacific. Movements associated with Rayleigh waves apparently have their closest approach to theoretical conditions over central Pacific paths. The dominant periods in the coda are 8 to 9, 10, 13, and 16 seconds. The longer periods are dominant at the greater distances. The increase in period with distance is a discontinuous, step-like function. The structure underlying the Aleutian deep apparently is opaque to 13-second periods in the Rayleigh wave, and the central Pacific and possibly the Atlantic structure seems to be unfavorable in the transmission of waves having this period. Vibrations in the natural period or overtones thereof set up in the focal region being eventually transmitted as sympathetic vibrations to the region of the station seems to be a logical explanation for the dominant groupings in the coda. Should any section of the path be out of sympathy with a given period, this period would probably become subordinate if not lost. The natural period of a portion of the Arctic region, including Alaska, seems to be different from other parts of the world. The natural period of the San Francisco Bay region, or its dominant overtone, is observed to be about eight seconds.

Assessing the climate response to regional sea ice change across all Arctic regions.

2020 ◽  
Author(s):  
Xavier Levine ◽  
Ivana Cvijanovic ◽  
Pablo Ortega ◽  
Markus Donat
Keyword(s):  
Climate Change ◽  
North America ◽  
Sea Ice ◽  
Northern Hemisphere ◽  
Ice Cover ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Climate Response ◽  
Arctic Sea ◽  
Arctic Sea Ice Loss

<p>Climate models predict that sea ice cover will shrink--even disappear-- in most regions of the Arctic basin by the end of the century, triggering local and remote responses in the surface climate via atmospheric and oceanic circulation changes. In particular, it has been suggested that seasonal anomalies over Europe and North America in recent years could have been caused by record low Arctic sea ice cover. Despite an intense research effort toward quantifying its effect, the contribution of regional sea ice loss to climate change and its mechanisms of action remain controversial. </p><p>In this study, we prescribe sea ice loss in individual sectors of the Arctic within a climate model, and study its effect on climatic anomalies in the Northern Hemisphere. Using the EC-EARTH3.3 model in its atmospheric-only and fully coupled configuration, and following the PAMIP protocol, sea ice cover is set to either its present day state, or a hypothetical future distribution of reduced sea ice cover in the Arctic. This pan-Arctic sea ice loss experiment is then complemented by 8 regional sea ice loss experiments.</p><p>Comparing those experiments, we assess the contribution of sea ice loss in each region of the Arctic to climate change over Europe, Siberia and North America. We find that sea ice loss in some sectors of the Arctic appears to matter more for Northern Hemisphere climate change than others, even after normalizing for differences in surface cover. Furthermore, the climatic effect of regional sea ice loss is compared to that of a pan-Arctic sea ice loss, whose associated climate anomalies are found to be strikingly different from that expected from a simple linear response to regional sea ice loss. We propose a mechanism for this nonlinear climate response to regional sea ice loss, which considers regional differences in the strength of the thermal inversion over the Arctic, as well as the relative proximity of each Arctic region to features critical for stationary wave genesis (e.g. the Tibetan plateau).</p>

Variability in the Position and Strength of Winter Jet Stream Cores Related to Northern Hemisphere Teleconnections

2008 ◽  
Vol 21 (3) ◽  
pp. 584-592 ◽  
Author(s):  
Courtenay Strong ◽  
Robert E. Davis
Keyword(s):  
North America ◽  
Northern Hemisphere ◽  
Three Dimensional ◽  
Analysis Data ◽  
The Arctic ◽  
Jet Stream ◽  
Arctic Oscillation Index ◽  
The Pacific ◽  
Height Fields ◽  
The Arctic Oscillation

Abstract Numerous teleconnections have been identified based upon spatial variability in sea level pressure or lower-tropospheric geopotential height fields. These teleconnections, which are commonly strongest in winter when the mean meridional temperature gradient is large, typically are neither derived from nor linked to changes in the jet stream. Here, winter tropospheric jet stream cores over the Northern Hemisphere (NH) are recovered from 6-hourly gridded data and interannual variability in winter jet core position, speed, and pressure are investigated in the context of NH teleconnections. Common methods for researching jet stream speed and position variability may yield unrepresentative results because jet core pressure variability is ignored (only one isobaric surface is evaluated) or pressure variability effects are smoothed (values are vertically averaged across several isobaric surfaces). In this analysis, data are extracted at the surface of maximum wind, thus controlling for jet core pressure variability and allowing for a more representative tracking of three-dimensional jet core variations. In the extratropics, the leading pattern of variability in jet core frequency is correlated with the Arctic Oscillation index (AOI) and appears as an oscillation about the spiral-shaped mean configuration of the winter jet stream. In contrast to previous research, the authors find no evidence of Pacific jet deceleration during positive AOI. The second leading mode of variability appears as a split (merged) winter-mean jet stream in the east Pacific together with a merged (split) winter-mean jet stream over North America, a pattern of change that correlates with the Pacific–North American pattern and is reflected in the amplitude of the long-wave ridge over western North America.

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