scholarly journals Stratospheric influence on the predictability of cold spells

2021 ◽  
Author(s):  
Irina Statnaia ◽  
Alexey Karpechko ◽  
Heikki Järvinen
Keyword(s):  
Chaotic Behavior ◽  
Weather Conditions ◽  
Forecast Model ◽  
Northern Eurasia ◽  
Normal Surface ◽  
Cold Air ◽  
Downward Influence ◽  
Stratospheric Circulation ◽  
Circulation Anomalies ◽  
Cold Air Outbreaks

<p>The weather-dependent planning and decision-making benefit greatly from subseasonal to seasonal (S2S) weather predictions made for up to six weeks ahead. At this timescale anomalies in the extratropical stratospheric circulation, which can last for several weeks in the Northern Hemisphere during winter, are known to affect climate at the surface and can extend the predictability of tropospheric weather conditions. The downward influence of the stratospheric circulation anomalies on the troposphere is projected by the Northern Annular Mode (NAM). Because of the long persistence of stratospheric anomalies beyond typical weather timescale, the increase in forecast skill is possible for the regions influenced by the atmospheric circulation variability associated with NAM based on the stratospheric predictor.</p><p>In this study, we investigate the predictability of the Eurasian severe and persistent cold spells during winter and its dependence on the state of the stratosphere. We first detected the below-normal surface temperature events over northern Eurasia (cold spells) in the ERA5 re-analysis. Then, to assess the predictability of these cold spells and to evaluate the skill in the probabilistic re-forecasts we divided them into groups associated with different stratospheric circulation anomalies which took place prior to the below-normal temperature events. When the stratospheric vortex is strong it is not expected to favor cold air outbreaks in this region. Therefore, in these cases, the cold air outbreaks result from internal tropospheric dynamics and their predictability is limited by the chaotic behavior of the weather systems. On the other hand, the weakening of the vortex is characterized by a more negative NAM index. This weakening is often followed by an equatorward shift of the tropospheric jets, an increase in the frequency of occurrence of tropospheric blocking, and cold air outbreaks over northern Eurasia. In these cases, the stratospheric vortex weakening can lead to the statistically significant improvement of the skill of cold air outbreak forecasts in case if the forecast model is capable of properly representing the coupling between the stratosphere and the troposphere. We show that the predictability of cold spells in the European Centre for Medium-range Weather Forecasts (ECMWF) model is enhanced under weak vortex conditions starting from week 3 before the event. We also evaluate how the surface predictability is affected by model imperfections by comparing the predictability across different S2S models.</p>

scholarly journals Eurasian Cold Air Outbreaks under Different Arctic Stratospheric Polar Vortex Strengths

2019 ◽  
Vol 76 (5) ◽  
pp. 1245-1264 ◽  
Author(s):  
Jinlong Huang ◽  
Wenshou Tian
Keyword(s):  
Climate Models ◽  
Sensible Heat Flux ◽  
Coupled Model ◽  
Surface Air Temperature ◽  
Polar Vortex ◽  
Northern Eurasia ◽  
Reanalysis Dataset ◽  
Stratospheric Polar Vortex ◽  
Cold Air ◽  
Cold Air Outbreaks

Abstract This study analyzes the differences and similarities of Eurasian cold air outbreaks (CAOs) under the weak (CAOW), strong (CAOS), and neutral (CAON) stratospheric polar vortex states and examines the potential links between the polar vortex and Eurasian CAOs. The results indicate that the colder surface air temperature (SAT) over Europe in the earlier stages of CAOW events is likely because the amplitude of the preexisting negative North Atlantic Oscillation pattern is larger in CAOW events than in CAON and CAOS events. Marked by the considerably negative stratospheric Arctic Oscillation signals entering the troposphere, the SAT at midlatitudes over eastern Eurasia in CAOW events is colder than in CAON events. A larger diabatic heating rate related to a positive sensible heat flux anomaly in CAOW events likely offsets, to some degree, the cooling effect caused by the stronger cold advection and makes the differences in area-averaged SAT anomalies over northern Eurasia between the CAOW and CAON events look insignificant in most stages. Massive anomalous waves from the low-latitude western Pacific merge over northeastern Eurasia, then weaken the westerly wind over this region to create favorable conditions for southward advection of cold air masses in the earlier stages of all three types of CAOs. This study further analyzes the interannual relationship between the stratospheric polar vortex strength and the intensity of Eurasian CAOs and finds that climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) relative to the reanalysis dataset tend to underestimate the correlation between them. The relationship between them is strengthening under representative concentration pathway 4.5 (RCP4.5) and 8.5 (RCP8.5) scenarios over the period 2006–60. In addition, the intensity of Eurasian CAOs exhibits a decreasing trend in the past and in the future.

Relationship between extensive and persistent extreme cold events in China and stratospheric circulation anomalies

2016 ◽  
Vol 1 (1) ◽  
Author(s):  
Hui Yang ◽  
Xinrong Chen ◽  
Gui-Ying Yang
Keyword(s):  
Atmospheric Circulation ◽  
The Arctic ◽  
Height Anomaly ◽  
Composite Analysis ◽  
Cold Air ◽  
Atmospheric Circulations ◽  
Cold Events ◽  
Extreme Cold ◽  
Stratospheric Circulation ◽  
Circulation Anomalies

This study examines the relationship between the extensive and persistent extreme cold events (EPECEs) in China and geopotential height anomalies in the stratosphere using daily mean fields of outgoing long wave radiation (OLR) produced by the NCAR and daily atmospheric circulations produced by the NCEP/NCAR. The OLR composite analysis for the EPECE in China demonstrates that the negative OLR height anomalies (cold air) originated from Siberia influence China progressively from north to south. The largest negative OLR height anomaly (cooling event) occurs in the region to the north of the Nanling Mountains. This suggests that the OLR height anomalies can be used to represent the temporal and spatial characteristics of extreme low temperatures and cold air activities in winter in China. The composite analysis of large-scale atmospheric circulations during the EPECE reveals characteristic evolutions of stratospheric and tropospheric circulations during the extreme cold event. We demonstrate the important role of atmospheric circulation anomalies in the outbreak and dissipation of the EPECE in China. We also demonstrate that significant perturbations in the stratospheric circulation occur more than 10 days prior to the outbreak of the EPECE, with positive height anomalies in the Arctic stratosphere. These positive anomalies propagate downward from the stratosphere and affect the formation and development of the high pressure ridge in the middle troposphere over the Ural Mountains. Significant changes also occur in the atmospheric circulation in the mid-latitude stratosphere. These changes propagate downward from the stratosphere and strengthen the low pressure trough in the troposphere in the region to the east of Lake Balkhash and Lake Baikal. Therefore, the changes in the stratospheric circulation during the EPECE in China occur prior to changes in the tropospheric circulation and are very useful for predicting extreme wintertime cold temperatures in China.

scholarly journals Tropical–Extratropical Interactions Associated with East Asian Cold Air Outbreaks. Part I: Interannual Variability

2017 ◽  
Vol 30 (8) ◽  
pp. 2989-3007 ◽  
Author(s):  
Muhammad Rais Abdillah ◽  
Yuki Kanno ◽  
Toshiki Iwasaki
Keyword(s):  
Interannual Variability ◽  
North Pacific ◽  
Western North Pacific ◽  
East Asian ◽  
Potential Temperature ◽  
Northern Eurasia ◽  
Maritime Continent ◽  
Central Pacific ◽  
Cold Air ◽  
Cold Air Outbreaks

Interannual variability of winter-mean East Asian cold air outbreaks (CAOs) and its relationship with the tropical climate system during 56 boreal winters (DJF) are investigated. The magnitude of CAO is quantified as winter-mean equatorward cold airmass (CAM) flux below 280-K potential temperature across the 45°N latitude. EOF analysis shows that the interannual variation of East Asian CAOs is attributed mainly to the contributions from western and eastern CAOs. In particular, the western and eastern CAOs tend to be remotely forced by La Niña and El Niño events, respectively. The western and eastern CAOs have distinct climate variability. The western CAO, which is enhanced under the climatic anomalies of high pressure over northern Eurasia and low pressure over the western North Pacific, causes negative CAM anomalies over northern Eurasia and positive ones over midlatitude East Asia. In the tropical region, the western CAO negatively correlates with the eastern Pacific and Indian Ocean SST, both of which enhance precipitation over the Maritime Continent. On the other hand, the eastern CAO is enhanced by the strong Aleutian low and results in positive CAM anomalies in the western North Pacific and substantial negative anomalies in western North America. The eastern CAO positively correlates with the tropical SST anomalies and accordingly precipitation anomalies over the central Pacific. ENSO influences western and eastern CAOs through upper and poleward Rossby wave trains excited by convective anomalies over the Maritime Continent and central Pacific, respectively.

scholarly journals On the Relationship between Winter Sea Ice and Summer Atmospheric Circulation over Eurasia

2013 ◽  
Vol 26 (15) ◽  
pp. 5523-5536 ◽  
Author(s):  
Bingyi Wu ◽  
Renhe Zhang ◽  
Rosanne D'Arrigo ◽  
Jingzhi Su
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Rainfall Variability ◽  
Summer Rainfall ◽  
Eastern Coast ◽  
Northern Eurasia ◽  
Sea Ice Concentration ◽  
The North ◽  
Circulation Anomalies ◽  
Atmospheric Circulation Anomalies

Abstract Using NCEP–NCAR reanalysis and Japanese 25-yr Reanalysis (JRA-25) data, this paper investigates the association between winter sea ice concentration (SIC) in Baffin Bay southward to the eastern coast of Newfoundland, and the ensuing summer atmospheric circulation over the mid- to high latitudes of Eurasia. It is found that winter SIC anomalies are significantly correlated with the ensuing summer 500-hPa height anomalies that dynamically correspond to the Eurasian pattern of 850-hPa wind variability and significantly influence summer rainfall variability over northern Eurasia. Spring atmospheric circulation anomalies south of Newfoundland, associated with persistent winter–spring SIC and a horseshoe-like pattern of sea surface temperature (SST) anomalies in the North Atlantic, act as a bridge linking winter SIC and the ensuing summer atmospheric circulation anomalies over northern Eurasia. Indeed, this study only reveals the association based on observations and simple simulation experiments with SIC forcing. The more precise mechanism for this linkage needs to be addressed in future work using numerical simulations with SIC and SST as the external forcings. The results herein have the following implication: Winter SIC west of Greenland is a possible precursor for summer atmospheric circulation and rainfall anomalies over northern Eurasia.

Local identification of persistent cold air pool conditions in the Great Hungarian Plain

Időjárás ◽  
2021 ◽  
Vol 125 (2) ◽  
pp. 167-192
Author(s):  
Karolina Szabóné André ◽  
Judit Bartholy ◽  
Rita Pongrácz ◽  
József Bór
Keyword(s):  
Meteorological Data ◽  
Weather Conditions ◽  
Reanalysis Data ◽  
Weather Event ◽  
Cold Air ◽  
Great Hungarian Plain ◽  
Winter Time ◽  
Heat Deficit ◽  
Local Detection ◽  
Hungarian Plain

Cold air pool (CAP) is a winter-time, anticyclonic weather event: a cold air layer confined by the topography and warm air aloft. If its duration is more than one day, then it is called persistent cold air pool (PCAP). CAPs are mainly examined in small basins and valleys. Fewer studies pay attention to PCAPs in much larger basins (with an area of more than 50 000 km2), and it is not evident how effective the existing numerical definitions are in cases of extensive PCAP events. A possible method of identifying PCAPs in a large basin is to identify PCAP weather conditions at different measuring sites across the basin. If there are PCAP weather conditions at most of the sites, then it is likely to be an extensive PCAP. In this work, we examine which of the documented CAP definitions can be used for reliable local detection of CAP conditions. Daily weather reports and meteorological data from two locations in the 52 000 km2 sized Great Hungarian Plain have been used to obtain a reference set of days with PCAP weather conditions during two consecutive winter months. Several numerical CAP definitions were compared for their performance in recognizing the presence of PCAP weather conditions using radiosonde measurements and reanalysis data. The lowest error was produced by using the heat deficit (HD) method. So this is considered the most suitable method for local identification of PCAPs in the Great Hungarian Plain.

scholarly journals Projections of Cold Air Outbreaks In CMIP6 Earth System Models

2021 ◽  
Author(s):  
Erik T. Smith ◽  
Scott Sheridan
Keyword(s):  
North Atlantic ◽  
Climate Models ◽  
Coupled Model ◽  
Meridional Overturning Circulation ◽  
Cold Air ◽  
Complex Processes ◽  
The North ◽  
Meridional Overturning ◽  
Earth System Models ◽  
Cold Air Outbreaks

Abstract Historical and future simulated temperature data from five climate models in the Coupled Model Intercomparing Project Phase 6 (CMIP6) are used to understand how climate change might alter cold air outbreaks (CAOs) in the future. Three different Shared Socioeconomic Pathways (SSPs), SSP 1 – 2.6, SSP 2 – 4.5, and SSP 5 – 8.5 are examined to identify potential fluctuations in CAOs across the globe between 2015 and 2054. Though CAOs may remain persistent or even increase in some regions through 2040, all five climate models show CAOs disappearing by 2054 based on current climate percentiles. Climate models were able to accurately simulate the spatial distribution and trends of historical CAOs, but there were large errors in the simulated interannual frequency of CAOs in the North Atlantic and North Pacific. Fluctuations in complex processes, such as Atlantic Meridional Overturning Circulation, may be contributing to each model’s inability to simulate historical CAOs in these regions.

The Climatology, Meteorology, and Boundary Layer Structure of Marine Cold Air Outbreaks in Both Hemispheres*

2016 ◽  
Vol 29 (6) ◽  
pp. 1999-2014 ◽  
Author(s):  
Jennifer Fletcher ◽  
Shannon Mason ◽  
Christian Jakob
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Zonal Flow ◽  
Heat Fluxes ◽  
Pressure Gradients ◽  
Cold Air ◽  
Surface Heat Fluxes ◽  
Cold Air Outbreak ◽  
Wide Range ◽  
Cold Air Outbreaks

Abstract A comparison of marine cold air outbreaks (MCAOs) in the Northern and Southern Hemispheres is presented, with attention to their seasonality, frequency of occurrence, and strength as measured by a cold air outbreak index. When considered on a gridpoint-by-gridpoint basis, MCAOs are more severe and more frequent in the Northern Hemisphere (NH) than the Southern Hemisphere (SH) in winter. However, when MCAOs are viewed as individual events regardless of horizontal extent, they occur more frequently in the SH. This is fundamentally because NH MCAOs are larger and stronger than those in the SH. MCAOs occur throughout the year, but in warm seasons and in the SH they are smaller and weaker than in cold seasons and in the NH. In both hemispheres, strong MCAOs occupy the cold air sector of midlatitude cyclones, which generally appear to be in their growth phase. Weak MCAOs in the SH occur under generally zonal flow with a slight northward component associated with weak zonal pressure gradients, while weak NH MCAOs occur under such a wide range of conditions that no characteristic synoptic pattern emerges from compositing. Strong boundary layer deepening, warming, and moistening occur as a result of the surface heat fluxes within MCAOs.

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