The boreal summer zonal wavenumber-3 trend pattern and its connection with surface enhanced warming

Abstract The Northern Hemisphere warms faster under global warming and suffers from more frequent heatwaves, causing considerable social and economic damage. The Northern Hemisphere surface warming exhibits strong regionality, with multiple “hotspots” (enhanced warming), but the relations among them remain unclear. This study finds a dominating zonal wavenumber-3 (ZW3) trend pattern in the upper-level geopotential heights during the boreal summer. The summer geopotential heights show significant increasing trends along the latitudinal circle around 60°N, with three centers located over northeastern America, western Eurasia, and eastern Siberia. The regionally enhanced surface warming trends are closely linked to the increased geopotential through the reduced cloud cover, exhibiting a consistent ZW3 pattern. The model simulations forced by sea surface temperature (SST) and Arctic sea ice (SIC) indicate that the SST forcing plays an important role in generating the ZW3 pattern, while the contribution of the SIC is minimal. A theoretical barotropic model can fairly reproduce the observed ZW3 structure forced by a heating source located over the subtropical North Atlantic, where the SSTs show prominent warming trends and a close relationship with the ZW3 pattern. Our results indicate that the “hotspots” may be interconnected and are related to a Rossby wave train with a ZW3 structure. It highlights a vital role of tropical/subtropical SSTs on the atmospheric circulation and the associated surface enhanced warming over the mid-high latitudes, which may have great implications in the coordinated heatwave events and tropical-extratropical teleconnections.

Download Full-text

The Recent Increase in the Occurrence of a Boreal Summer Teleconnection and Its Relationship with Temperature Extremes

Journal of Climate ◽

10.1175/jcli-d-16-0094.1 ◽

2017 ◽

Vol 30 (18) ◽

pp. 7493-7504 ◽

Cited By ~ 21

Author(s):

Min-Hee Lee ◽

Sukyoung Lee ◽

Hyo-Jong Song ◽

Chang-Hoi Ho

Keyword(s):

High Pressure ◽

Northern Hemisphere ◽

Wave Train ◽

Teleconnection Pattern ◽

Extreme Weather Events ◽

Boreal Summer ◽

Temperature Extremes ◽

Self Organizing Map ◽

Eastern United States ◽

Zonal Wavenumber

Abstract This study has investigated the relationship between temperature extremes and a subseasonal hemispheric teleconnection pattern over the Northern Hemisphere during boreal summer. By applying self-organizing map (SOM) analysis to 200-hPa geopotential fields from the European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) for the period 1979–2012, a teleconnection pattern is identified that increased dramatically in its occurrence after the late 1990s. This pattern is characterized by a zonal wavenumber-5 pattern with anomalous high pressure cores over eastern Europe, northeastern Asia, the eastern North Pacific, the eastern United States, and Greenland. These high pressure centers coincide with regions of increasingly frequent temperature extremes in recent decades. To investigate the temporal evolution of the identified SOM pattern, time-lagged composites were performed relative to the days in which the 200-hPa geopotential field most closely resembled the SOM pattern. From day −10 to day 0, a wave train propagated from the central tropical Pacific to the Canadian Arctic Archipelago and Greenland. This poleward wave propagation was followed by the establishment of quasi-stationary high pressure centers over Greenland, Europe, and Asia. This study suggests that more frequent occurrence of the hemispheric teleconnection is linked to more severe and longer extreme weather events over the Northern Hemisphere since the late 1990s.

Download Full-text

The Interaction between Two Separate Propagations of Rossby Waves

Monthly Weather Review ◽

10.1175/mwr3486.1 ◽

2007 ◽

Vol 135 (10) ◽

pp. 3521-3540 ◽

Cited By ~ 15

Author(s):

Yafei Wang ◽

Koji Yamazaki ◽

Yasushi Fujiyoshi

Keyword(s):

Caspian Sea ◽

Wave Train ◽

Deep Convection ◽

Longwave Radiation ◽

Stationary Wave ◽

The Philippines ◽

Boreal Summer ◽

The Caspian Sea ◽

Wave Ray ◽

Zonal Wavenumber

Abstract This study deals with two teleconnection patterns and the subsequent wave train propagations during an East Asian summer. Diagnostic results are as follows: 1) a stationary wave ray with zonal wavenumber 5 approximates the arc path linking the correlation centers originating from the Caspian Sea via Lake Baikal to the sea off the southeast coast of Japan (i.e., the OKJ arc path as a focus area) in a pentad correlation map between 500-hPa geopotential height (Z500) and outgoing longwave radiation (OLR) at 30°N, 150°E in June 1979–98. Ray tracing shows that it took 8–10 days for this stationary wave to propagate from an initial position around the Caspian Sea to the focus area, which roughly coincides with the observed case in July 1998. 2) A wave train pattern (P-Ja) observed in the boreal summer propagated along the arc line in the same way as the normal poleward Rossby wave train originating from the Philippines across the North Pacific (P-J), but with a phase shift northeastward of about 90°. 3) Further correlation analyses showed that the P-J-like waves belong mainly to intraseasonal propagating ones while OKJ waves belong mainly to intraseasonal stationary ones. 4) Propagation of the newly observed wave train pattern (P-Ja) occurred following another wave train along the OKJ arc path in mid-July 1998. Both northeastward and southeastward wave propagations merged off the east coast of Japan. 5) The northeastward-propagating wave train observed in mid-July 1998 was triggered by the southeastward-propagating (OKJ) wave train that produced a deep cyclonic circulation and a strong convective activity in the focus area. The link of wave forcing and deep convection was made solely because of a strong upper-level divergence in the focus area.

Download Full-text

Possible impacts of December Laptev sea ice on Indian Ocean Dipole conditions during spring

Journal of Climate ◽

10.1175/jcli-d-20-0980.1 ◽

2021 ◽

pp. 1-45

Author(s):

Ping Chen ◽

Bo Sun ◽

Huijun Wang ◽

Baoyan Zhu

Keyword(s):

Indian Ocean ◽

Sea Ice ◽

Indian Ocean Dipole ◽

Wave Train ◽

Arctic Sea Ice ◽

North India ◽

Height Anomaly ◽

Laptev Sea ◽

Wave Source ◽

Zonal Wavenumber

AbstractThis study investigates the relationship and underlying mechanisms between the Indian Ocean Dipole (IOD) and Arctic sea ice. The results reveal that the preceding December sea ice over the Laptev Sea plays an important role in the formation of positive IOD conditions during April–June (AMJ). In years with positive December Laptev sea ice anomalies, the zonal wavenumber-1 (ZWN1) planetary wave component is stimulated at middle and high latitudes. The high-latitude ZWN1 propagates upward to the stratosphere and downward to the troposphere in December, affects the atmospheric circulation over the North Atlantic, and further leads to a warm sea surface temperature anomaly (SSTA) that persists until the following February. The mid-latitude ZWN1 propagates upward to the stratosphere in January and downward to the troposphere in February, contributing to the positive 200-hPa geopotential height anomaly (GPHA) in the subtropical Atlantic. The ascending anomaly induced by the warm SSTA and the positive 200-hPa GPHA in the subtropical Atlantic in February are favorable for effective Rossby wave source formation and stimulate an atmospheric wave train that forms an anomalous cyclone over the northern Arabian Sea, which contributes to enhanced convection over North India, stimulating an anomalous anticyclone over East India and leading to reduced convection over the northeastern Indian Ocean in March. The reduced convection over the northeastern Indian Ocean may lead to strengthened equatorial easterly winds and further contribute to positive IOD conditions in AMJ. These findings indicate that December Laptev sea ice may contribute to AMJ IOD conditions.

Download Full-text

Dynamical mechanisms linking Indian monsoon precipitation and the circumglobal teleconnection

Climate Dynamics ◽

10.1007/s00382-021-05825-6 ◽

2021 ◽

Author(s):

Jonathan D. Beverley ◽

Steven J. Woolnough ◽

Laura H. Baker ◽

Stephanie J. Johnson ◽

Antje Weisheimer ◽

...

Keyword(s):

North America ◽

Northern Hemisphere ◽

Rossby Waves ◽

Wave Train ◽

Forecast Model ◽

Seasonal Forecast ◽

The North ◽

Circumglobal Teleconnection ◽

Rossby Wave Train ◽

Ecmwf Model

AbstractThe circumglobal teleconnection (CGT) is an important mode of circulation variability, with an influence across many parts of the northern hemisphere. Here, we examine the excitation mechanisms of the CGT in the ECMWF seasonal forecast model, and the relationship between the Indian summer monsoon (ISM), the CGT and the extratropical northern hemisphere circulation. Results from relaxation experiments, in which the model is corrected to reanalysis in specific regions, suggest that errors over northwest Europe are more important in inhibiting the model skill at representing the CGT, in addition to northern hemisphere skill more widely, than west-central Asia and the ISM region, although the link between ISM precipitation and the extratropical circulation is weak in all experiments. Thermal forcing experiments in the ECMWF model, in which a heating is applied over India, suggest that the ISM does force an extratropical Rossby wave train, with upper tropospheric anticyclonic anomalies over east Asia, the North Pacific and North America associated with increased ISM heating. However, this eastward-propagating branch of the wave train does not project into Europe, and the response there occurs largely through westward-propagating Rossby waves. Results from barotropic model experiments show a response that is highly consistent with the seasonal forecast model, with similar eastward- and westward-propagating Rossby waves. This westward-propagating response is shown to be important in the downstream reinforcement of the wave train between Asia and North America.

Download Full-text

Dynamical Processes Related to the Appearance of Quasi-Stationary Waves on the Subtropical Jet in the Midsummer Northern Hemisphere

Journal of Climate ◽

10.1175/jcli3697.1 ◽

2006 ◽

Vol 19 (8) ◽

pp. 1531-1544 ◽

Cited By ~ 66

Author(s):

Naoki Sato ◽

Masaaki Takahashi

Keyword(s):

Middle East ◽

Northern Hemisphere ◽

Wave Train ◽

Stationary Wave ◽

Stationary Waves ◽

Statistical Features ◽

Basic Field ◽

Subtropical Jet ◽

Anomaly Pattern ◽

Highly Correlated

Abstract Statistical features of quasi-stationary planetary waves were examined on the subtropical jet in the midsummer Northern Hemisphere by using objectively analyzed data and satellite data. As a result, a quasi-stationary wave train that is highly correlated with the midsummer climate over Japan was identified. A clear phase dependency of the appearance of waves was also confirmed. An analysis of temporal evolution and wave activity flux revealed that the eastward propagation of the wave packet starts in the Middle East, passes over East Asia, and reaches North America. The anomaly pattern is strengthened through kinetic energy conversion near the entrance of the Asian jet over the Middle East. The interaction between the anomaly pattern and the basic field contributes to the appearance of the anomalous wavelike pattern. Although the wave train is correlated with the anomaly of convective activity over the western North Pacific and the Indian Ocean, it is implied that internal dynamics are important in determining the statistical features of the appearance of anomalous quasi-stationary waves on the subtropical jet.

Download Full-text

Interdecadal Variations of the Silk Road Pattern

Journal of Climate ◽

10.1175/jcli-d-17-0340.1 ◽

2017 ◽

Vol 30 (24) ◽

pp. 9915-9932 ◽

Cited By ~ 52

Author(s):

Lin Wang ◽

Peiqiang Xu ◽

Wen Chen ◽

Yong Liu

Keyword(s):

Wave Train ◽

Atlantic Multidecadal Oscillation ◽

Teleconnection Pattern ◽

Silk Road ◽

Boreal Summer ◽

Northeastern Asia ◽

Western Asia ◽

Silk Road Pattern ◽

Decadal Climate ◽

The Silk Road

Based on several reanalysis and observational datasets, this study suggests that the Silk Road pattern (SRP), a major teleconnection pattern stretching across Eurasia in the boreal summer, shows clear interdecadal variations that explain approximately 50% of its total variance. The interdecadal SRP features a strong barotropic wave train along the Asian subtropical jet, resembling its interannual counterpart. Additionally, it features a second weak wave train over the northern part of Eurasia, leading to larger meridional scale than its interannual counterpart. The interdecadal SRP contributes approximately 40% of the summer surface air temperature’s variance with little uncertainty and 10%–20% of the summer precipitation’s variance with greater uncertainty over large domains of Eurasia. The interdecadal SRP shows two regime shifts in 1972 and 1997. The latter shift explains over 40% of the observed rainfall reduction over northeastern Asia and over 40% of the observed warming over eastern Europe, western Asia, and northeastern Asia, highlighting its importance to the recent decadal climate variations over Eurasia. The Atlantic multidecadal oscillation (AMO) does not show a significant linear relationship with the interdecadal SRP. However, the Monte Carlo bootstrapping resampling analysis suggests that the positive (negative) phases of the spring and summer AMO significantly facilitate the occurrence of negative (positive) phases of the interdecadal SRP, implying plausible prediction potentials for the interdecadal variations of the SRP. The reported results are insensitive to the long-term trends in datasets and thereby have little relevance to externally forced climate change.

Download Full-text

Intra-interglacial climate variability: model simulations of Marine Isotope Stages 1, 5, 11, 13, and 15

Climate of the Past ◽

10.5194/cp-12-677-2016 ◽

2016 ◽

Vol 12 (3) ◽

pp. 677-695 ◽

Cited By ~ 11

Author(s):

Rima Rachmayani ◽

Matthias Prange ◽

Michael Schulz

Keyword(s):

Climate Variability ◽

Surface Temperature ◽

Northern Hemisphere ◽

High Latitude ◽

West African ◽

Boreal Summer ◽

The West ◽

Temperature Anomalies ◽

Astronomical Forcing

Abstract. Using the Community Climate System Model version 3 (CCSM3) including a dynamic global vegetation model, a set of 13 time slice experiments was carried out to study global climate variability between and within the Quaternary interglacials of Marine Isotope Stages (MISs) 1, 5, 11, 13, and 15. The selection of interglacial time slices was based on different aspects of inter- and intra-interglacial variability and associated astronomical forcing. The different effects of obliquity, precession, and greenhouse gas (GHG) forcing on global surface temperature and precipitation fields are illuminated. In most regions seasonal surface temperature anomalies can largely be explained by local insolation anomalies induced by the astronomical forcing. Climate feedbacks, however, may modify the surface temperature response in specific regions, most pronounced in the monsoon domains and the polar oceans. GHG forcing may also play an important role for seasonal temperature anomalies, especially at high latitudes and early Brunhes interglacials (MIS 13 and 15) when GHG concentrations were much lower than during the later interglacials. High- versus low-obliquity climates are generally characterized by strong warming over the Northern Hemisphere extratropics and slight cooling in the tropics during boreal summer. During boreal winter, a moderate cooling over large portions of the Northern Hemisphere continents and a strong warming at high southern latitudes is found. Beside the well-known role of precession, a significant role of obliquity in forcing the West African monsoon is identified. Other regional monsoon systems are less sensitive or not sensitive at all to obliquity variations during interglacials. Moreover, based on two specific time slices (394 and 615 ka), it is explicitly shown that the West African and Indian monsoon systems do not always vary in concert, challenging the concept of a global monsoon system on astronomical timescales. High obliquity can also explain relatively warm Northern Hemisphere high-latitude summer temperatures despite maximum precession around 495 ka (MIS 13). It is hypothesized that this obliquity-induced high-latitude warming may have prevented a glacial inception at that time.

Download Full-text

Atmosphere similarity patterns in boreal summer show an increase of persistent weather conditions connected to hydro-climatic risks

Scientific Reports ◽

10.1038/s41598-021-01808-z ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Peter Hoffmann ◽

Jascha Lehmann ◽

Bijan H. Fallah ◽

Fred F. Hattermann

Keyword(s):

Northern Hemisphere ◽

Climate Models ◽

Weather Conditions ◽

Boreal Summer ◽

Climatic Extremes ◽

Weather Patterns ◽

Dry Conditions ◽

Climatic Risks ◽

Long Term Trend

AbstractRecent studies have shown that hydro-climatic extremes have increased significantly in number and intensity in the last decades. In the Northern Hemisphere such events were often associated with long lasting persistent weather patterns. In 2018, hot and dry conditions prevailed for several months over Central Europe leading to record-breaking temperatures and severe harvest losses. The underlying circulation processes are still not fully understood and there is a need for improved methodologies to detect and quantify persistent weather conditions. Here, we propose a new method to detect, compare and quantify persistence through atmosphere similarity patterns by applying established image recognition methods to day to day atmospheric fields. We find that persistent weather patterns have increased in number and intensity over the last decades in Northern Hemisphere mid-latitude summer, link this to hydro-climatic risks and evaluate the extreme summers of 2010 (Russian heat wave) and of 2018 (European drought). We further evaluate the ability of climate models to reproduce long-term trend patterns of weather persistence and the result is a notable discrepancy to observed developments.

Download Full-text

Climatology of migrating and non-migrating tides observed by three meteor radars in the southern equatorial region

10.5194/acp-2021-33 ◽

2021 ◽

Author(s):

Jianyuan Wang ◽

Wen Yi ◽

Jianfei Wu ◽

Tingdi Chen ◽

Xianghui Xue ◽

...

Keyword(s):

Harmonic Analysis ◽

Northern Hemisphere ◽

Climate Model ◽

Equatorial Region ◽

Stratospheric Sudden Warming ◽

Tidal Model ◽

Community Climate Model ◽

Zonal Wavenumber ◽

Climatic Features ◽

Community Climate

Abstract. We present a study of migrating and non-migrating tidal winds observed simultaneously by three meteor radars situated in the southern equatorial region. The radars are located at Cariri (7.4° S, 36.5° W), Brazil, Kototabang (0.2° S, 100.3° E), Indonesia and Darwin (12.3° S, 130.8° E), Australia. Harmonic analysis was used to obtain amplitudes and phases for diurnal and semidiurnal solar migrating and non-migrating tides between 80 and 100 km altitude during the period 2005 to 2008. They include the important tidal components of diurnal westward-propagating zonal wavenumber 1 (DW1), diurnal eastward-propagating zonal wavenumber 3 (DE3), semidiurnal westward-propagating zonal wavenumber 2 (SW2), and semidiurnal eastward-propagating zonal wavenumber 2 (SE2). In addition, we also present a climatology of these wind tides and analyze the reliability of the fitting through the reference to Whole Atmosphere Community Climate Model (WACCM) winds. The analysis suggests that the migrating tides could be well fitted by the three different radars, but the non-migrating tides might be overestimated. The results based on observations were also compared with the Climatological Tidal Model of the Thermosphere (CTMT). In general, climatic features between observations and model migrating tides were satisfactory in both wind components. However, the features of the DW1, DE3 and SW2 amplitudes in both wind components were slightly different from the results of the CTMT models. This result is probably because tides could be enhanced by the 2006 northern hemisphere stratospheric sudden warming (NH-SSW) event.

Download Full-text