Positive Sea Level Pressure Anomalies Research Articles

Effects of Arctic ozone on the stratospheric spring onset and its surface impact

Abstract. Ozone in the Arctic stratosphere is subject to large interannual variability, driven by both chemical ozone depletion and dynamical variability. Anomalies in Arctic stratospheric ozone become particularly important in spring, when returning sunlight allows them to alter stratospheric temperatures via shortwave heating, thus modifying atmospheric dynamics. At the same time, the stratospheric circulation undergoes a transition in spring with the final stratospheric warming (FSW), which marks the end of winter. A causal link between stratospheric ozone anomalies and FSWs is plausible and might increase the predictability of stratospheric and tropospheric responses on sub-seasonal to seasonal timescales. However, it remains to be fully understood how ozone influences the timing and evolution of the springtime vortex breakdown. Here, we contrast results from chemistry climate models with and without interactive ozone chemistry to quantify the impact of ozone anomalies on the timing of the FSW and its effects on surface climate. We find that ozone feedbacks increase the variability in the timing of the FSW, especially in the lower stratosphere. In ozone-deficient springs, a persistent strong polar vortex and a delayed FSW in the lower stratosphere are partly due to the lack of heating by ozone in that region. High-ozone anomalies, on the other hand, result in additional shortwave heating in the lower stratosphere, where the FSW therefore occurs earlier. We further show that FSWs in high-ozone springs are predominantly followed by a negative phase of the Arctic Oscillation (AO) with positive sea level pressure anomalies over the Arctic and cold anomalies over Eurasia and Europe. These conditions are to a significant extent (at least 50 %) driven by ozone. In contrast, FSWs in low-ozone springs are not associated with a discernible surface climate response. These results highlight the importance of ozone–circulation coupling in the climate system and the potential value of interactive ozone chemistry for sub-seasonal to seasonal predictability.

Strengthening of the relationship between West China Autumn Rain and arctic oscillation in the mid-1980s

“West China Autumn Rain” (WCAR), as the last rainy season in China, is inclined to flooding and secondary disasters which often cause severe damages to the development of socio-economy and safety of people's lives. It is thus crucial to explore influential factors and associated physical processes for the anomalies in WCAR. In this study, based on the gridded precipitation data and reanalysis data during 1961–2013, we presented that the WCAR-AO relationship has strengthened in the mid-1980s, which varies from an insignificant correlation to a significant positive one. During the latter period (the significant period), the positive AO phase corresponds to a strong anticyclonic circulation anomaly over the region from northeast Asia extending to the North Pacific in the middle and lower troposphere, concurrent with a northward displacement of the East Asian jet (EAJ) in the upper troposphere. These atmospheric circulation situations favor the increase of WCAR, through their influences on the moisture and dynamical conditions. During the former period (the insignificant period), however, the association of the AO with above atmospheric circulations is weakened, thus diluting the WCAR-AO linkage. The unstable relationship between the AO and aforementioned atmospheric circulations may be due to the change in the AO structure. In the latter period, associated with the positive AO phase is a typical seesaw pattern featured by negative sea level pressure (SLP) anomalies in the Arctic and positive SLP anomalies in the North Atlantic and the North Pacific, whereas the anomalous center in the North Pacific becomes less pronounced in the former period. This discrepancy may be attributed to stronger wave activity arising from the SST warming from the former period to the latter period over the North Pacific.

Comparison of the influence of two types of cold surge on haze dispersion in eastern China

Abstract. Cold surge (CS) is considered a favorable weather process to improve air quality and is widely recognized. However, there is no detailed study on the differences in the dispersion ability of different types of CSs in relation to haze days in eastern China (HDEC). This paper uses the hierarchical clustering algorithm to classify the cool-season (November to February of the following year) CSs across eastern China into blocking CSs and wave-train CSs and compares their influences on the number of HDEC from 1980 to 2017. Results show that the wave-train CSs can significantly improve the visibility in eastern China and generally improve air quality for about 2 d longer than the blocking CSs, which indicates that the blocking CSs have a weaker ability to dissipate HDEC compared with the wave-train CSs. The CSs affect the HDEC by changing meteorological elements like thermal inversion potential, horizontal surface wind, sea level pressure (SLP), and surface air temperature (SAT). A period of 4 d after the outbreak of CSs, the variations of thermal inversion potential and horizontal surface wind of two types of CSs tend to be consistent. However, the negative SAT anomalies and the positive SLP anomalies caused by the blocking CSs lasted shorter than those caused by the wave-train CSs, forming favorable conditions for the rapid growth of HDEC. Furthermore, results show that in recent years, especially after the 1990s, the frequency of wave-train CSs has decreased significantly, while the frequency of blocking CSs has slightly increased, indicating that the overall ability of CSs to dissipate HDEC has weakened in general. This work may provide reference for the future formulation of haze control policies in East Asia.

Cold surge invading the Beijing 2022 Winter Olympic Competition Zones and the predictability in BCC‐AGCM model

AbstractThe 24th Olympic and Paralympic Winter Games will be held at three competition zones in North China. The cold surge is considered as the most dominant weather affecting the game schedule by the Organizing Committee of Beijing Olympic Games. In this article, both the frequency of 124 cold surge cases invading the competition zones and the corresponding atmospheric circulation during the winters of 1985–2020 are first analyzed. The results show that the frequency has not been reduced by the global warming. On the contrary, it has been increasing slightly in recent decade. By verifying the forecast skill of temperature drop at the zones in Beijing Climate Center‐Atmospheric General Circulation Model (version 2.2), it is found that the average efficient forecast leading time with persistent temperature drop exceeding 1°C is about 7 days, but significant differences exist among the individual cases. The 20 best forecasts and the 20 worst forecasts were selected for further analysis. In the 20 worst forecasts, the cold surge processes cannot be forecasted even 1 day in advance. It is mainly due to the great deviation of the simulated circulation from the observation, especially the failure to forecast the enhancement of the Siberian High especially in its southeast part before the cold surge occurrence. While in the 20 best forecasts, the model can capture the cold surges 9 days before the occurrence, owing to its skill in forecasting the positive sea level pressure anomalies from the southern Barents Sea and the Kara Sea to eastern China. Above evaluations can provide useful information to the forecast of cold surge invading the competition zones beyond 1 week.

Decadal changes of East Asian jet streams and their relationship with the Mid-high Latitude Circulations

This study investigates the concurrent location and intensity changes of the East Asian polar front jet (EAPJ) and subtropical jet (EASJ) on decadal time scale using NCEP/NCAR, ERA5 and JRA-55 reanalysis data, along with the relationship with the mid-high latitude circulation changes. Results show that EAPJ was intensified accompanied by the weakening of EASJ after 1985, and shifted equatorward in conjunction with the poleward migration of EASJ after 1999. The three-dimensional structures of the atmospheric circulation over East Asia exhibited distinct changes corresponding to the two regime shifts. Dipole anomalous sea level pressure (SLP) between the Arctic and the North Pacific, a NAM-like geopotential height anomalous pattern, and a deepened polar vortex occurred after 1985, accompanied with the out-of-phase intensity changes of the two jets. In comparison, dipole SLP anomalies between the mid-high latitudes and Tibetan Plateau, a zonal wave train over Eurasia accompanied with a meridional wave train over East Asia, and a polar vortex shifting toward the Siberia were observed after 1999, when the two jets approached each other. These circulation changes exerted pronounced effects on the East Asian climate anomalies. After the mid-1980s, the positive SLP anomaly over the northern North Pacific led to decreased land-sea SLP contrast, and the positive mid-tropospheric geopotential height center near Lake Baikal implied weakened East Asian trough (EAT). Such changes favored the warming of southern East Asia and the weakening of the southern mode of East Asian winter monsoon (EAWM). In contrast, the high latitude positive SLP anomalies denoted enhanced Siberian high (SH) and the East Asian meridional wave train resulted in tilted EAT after the late 1990s, benefitting the cold anomalies over northern Eurasia with the northern mode of EAWM intensified. Possible mechanisms for the decadal changes of the jets are discussed from the perspective of the dynamic forcing of the synoptic-scale transient eddy activities (STEA), and the thermal forcings from the East Asian landmass, the North Pacific sea surface and the Arctic sea ice cover.

Surface warming reacceleration in offshore China and its interdecadal effects on the East Asia\u2013Pacific climate

Since the late 1970s, sea surface temperatures (SSTs) have exhibited greater responses to global warming in the offshore area of China and adjacent seas (offshore China) than in the global ocean. This study identified a surface warming reacceleration in offshore China since 2011, following a well-known interdecadal shift from offshore surface warming to cooling in 1998. During the warming reacceleration period, the rate of increase in offshore China SSTs was twice the mean rate of global ocean surface warming, and the significantly warming area was primarily in the north, especially in the East China Sea. Concurrent with the ascending phase of the Interdecadal Pacific Oscillation, a large area of positive sea level pressure anomalies developed over the tropical Pacific. Accordingly, the surface southerly wind anomalies contributed to the recent surface warming in offshore China, especially in the East China Sea. With greater changes in the warming rate, the spatial mode of the circulation anomalies over East Asia and the western Pacific has shifted westward and has exerted more inshore influence during the recent warming reacceleration period than during the previous periods.

Two Distinct Types of Extratropical Circulation Anomalies Associated with Cold Surges over the South China Sea

Abstract This study investigated the extratropical circulation anomalies responsible for cold surges over the South China Sea in winter. The surge events were identified by the intensity of northerly winds over 110°–117.5°E along 15°N at 925 hPa. Two distinct patterns of sea level pressure (SLP) anomalies in East Asia were found to have a crucial role in inducing cold surges over the South China Sea. Accordingly, the cold surge events were classified into two types. The first type of cold surge is characterized by a pair of SLP anomalies with positive and negative ones centered over China and Japan, respectively, whereas the second type of cold surge is characterized by widespread and persistent positive SLP anomalies over East Asia. Furthermore, the first type of cold surge is accompanied by a deepened East Asian trough and precursory Rossby wave trains across the Eurasian continent in the mid- and upper troposphere, but the latter is not. Prior to both types of the cold surges, the Siberian high is significantly intensified. However, diagnosis of the SLP tendency indicates that the intensification is related to different physical processes. In the first type of cold surge, the Rossby wave trains favor negative vorticity advection and cold advection, inducing intensification of the Siberian high. By contrast, in the second type of cold surge, vorticity advection can be ignored due to the lack of Rossby wave trains, and only the lower-tropospheric cold advection induced by anomalous northerly winds, resulting from the anomalous Siberian high, contributes to the further intensification of the Siberian high.

Recent Reoccurrence of Large Open‐Ocean Polynya on the Maud Rise Seamount

AbstractSatellite observations have shown that the largest and most prolonged Maud Rise open‐ocean polynya since the 1970s appeared on 14 September 2017 (~9.3 × 103 km2) within the seasonal sea‐ice cover which expanded maximum on 1 December 2017 (~298.1 × 103 km2) and existed for 79 days. Record negative anomalies of sea‐ice concentration were observed in and around the polynya. The occurrence of the polynya was associated with a large cyclonic eddy and negative wind stress curl that facilitated melting of sea‐ice. Concurrently, a region of positive sea level pressure anomalies extended over the entire northern Weddell Sea accompanied by record low negative anomalies (deep depressions) over the southwest Weddell Sea and the Maud Rise. The atmospheric circulation anomalies advected moist‐warm air from the midlatitudes, resulted a record atmospheric warming (~11.5 °C) in the Maud Rise that favored this rare event as one of the largest open‐ocean polynyas.

Recent Strengthened Impact of the Winter Arctic Oscillation on the Southeast Asian Surface Air Temperature Variation

A previous study indicated that the Arctic Oscillation (AO) and Siberian High (SH) are two important drivers for the interannual variation of winter surface air temperature (SAT) over southeast Asia. This study reveals that the impact of the winter SH on the southeast Asian SAT was stable. By contrast, the connection between the winter AO and southeast Asian SAT displays a pronounced interdecadal change around the late-1990s. Significant impact of the winter AO on the southeast Asian SAT can only be detected after the late-1990s. The result shows that change in the impact of the winter AO on southeast Asian SAT was mainly attributed to change in the spatial structure of the AO. Before the late-1990s, significant atmospheric signals related to the winter AO were confined to the North Atlantic region and the atmospheric anomalies over Eurasia were weak. As such, impact of the winter AO on the southeast Asian SAT was weak. By contrast, after the late-1990s, winter AO displays a more zonally symmetric structure, with significant negative sea level pressure (SLP) anomalies over the Arctic, and positive anomalies over mid-latitudes. Specifically, the positive SLP anomalies over East China induce clear northerly wind anomalies over southeast Asia, which lead to negative SAT anomalies there via wind-induced temperature advection. Hence, the winter AO has a significant impact on the southeast Asian SAT after the late-1990s. Further analysis shows that after the late-1990s, hindcast skill of the winter southeast Asian SAT anomalies was enhanced when taking both the winter AO and SH into account.

Record-low coastal sea levels in the Northeast Pacific during the winter of 2013\u20132014

During the winter of 2013–2014, the averaged tide gauge (TG) coastal sea level (CSL) anomaly north of 40°N was a record low of −107 mm for the period of 1948–2016. Statistical analysis indicates that this large drop was a once-in-a-century event and closely related to an unusual ocean warming event known as “The Blob”. The Blob developed in the NE Pacific during the winter of 2013–2014. Both the Blob and record-low CSL can be attributed to wind changes associated with an unusually high sea level pressure (SLP) pattern over the NE Pacific. The anomalous local longshore winds induced by the positive SLP anomalies caused strong offshore Ekman transport along the coast of NE Pacific, thereby leading to the record-low CSL. In addition, the steric sea level changes also contributed a significant part (17%) to the record-low CSL. The Pacific Decadal Oscillation (PDO), as the primary variability mode in the NE Pacific on decadal time scales, did not contribute to the emergence of this extreme CSL event.

Strong heat and cold waves in Poland in relation with the large-scale atmospheric circulation

Occurrence of heat and cold waves in Poland in the years 1966–2015 (1966/1967–2015/2016) was described, and their circulation conditions were determined in this study. A heat wave is defined as a period of at least 3 days with Tmax > 30.0 °C and a cold wave as a period of at least 3 days with Tmax <− 10.0 °C. Heat waves occurred most often in central and southern Poland and cold waves in north-eastern Poland. The occurrence of both heat and cold waves is related to high pressure systems. Anticyclonic blocking patterns both in winter and summer inhibit the zonal flow of air masses and intensify the meridional flow. Positive sea level pressure anomalies occurred over the study area, in the case of heat waves up to 3 hPa and in the case of cold waves up to 11 hPa. Perpendicular profiles showing geopotential height and air temperature anomalies in the troposphere were identified for the selected cases of extreme temperature episodes. Centres of geopotential height positive/negative anomalies were detected at the level of 300–250 hPa geopotential height, right over the area of the positive/negative surface temperature extremes.

Responses and mechanisms of East Asian winter and summer monsoons to weakened Atlantic meridional overturning circulation using the FGOALS‐g2 model

ABSTRACTThis study investigates the responses and mechanisms of East Asian winter monsoon (EAWM) and East Asian summer monsoon (EASM) to weakened Atlantic meridional overturning circulation (AMOC) through three perturbation experiments with different intensities of freshwater hosing in the North Atlantic, using the Flexible Global Ocean – Atmosphere – Land System Model, Grid‐point Version 2. These experiments show that a subtle weakening of AMOC does not significantly influence either the EAWM or the EASM. When AMOC weakens more substantially, northerly wind anomalies emerge in East Asia throughout the year, strengthening the EAWM and weakening the EASM. The northerly wind anomalies result from an anomalous westward sea level pressure (SLP) gradient, namely positive SLP anomalies across Eurasia and negative anomalies in the western North Pacific (WNP). In winter, negative WNP SLP anomalies are found in mid‐high latitudes. They are caused by anomalous stationary wave activity, which is associated with the Aleutian Iceland seesaw teleconnection. In summer, negative WNP SLP anomalies are present in the subtropics, and are linked with an anomalous cyclonic circulation over the north of the Philippian Sea. This cyclonic circulation anomaly is induced by the anomalous warm water in the subsurface of the South China Sea and Philippian Sea through the Gill mechanism.

Storm-Track Response to SST Fronts in the Northwestern Pacific Region in an AGCM

Abstract The storm-track response to sea surface temperature (SST) fronts in the northwestern Pacific region is investigated using an atmospheric general circulation model with a 50-km horizontal resolution. The following two experiments are conducted: one with 0.25° daily SST data (CNTL) and the other with smoothed SSTs over an area covering SST fronts associated with the Kuroshio, the Kuroshio Extension, the Oyashio, and the subpolar front (SMTHK). The storm track estimated from the local deepening rate of surface pressure (LDR) exhibits a prominent peak in this region in CNTL in January, whereas the storm-track peak weakens and moves eastward in SMTHK. Storm-track differences between CNTL and SMTHK are only found in explosive deepening events with LDR larger than 1 hPa h−1. A diagnostic equation of LDR suggests that latent heat release associated with large-scale condensation contributes to the storm-track enhancement. The SST fronts also affect the large-scale atmospheric circulation over the northeastern Pacific Ocean. The jet stream in the upper troposphere tends to meander northward, which is associated with positive sea level pressure (SLP) anomalies in CNTL, whereas the jet stream flows zonally in SMTHK. A composite analysis for the northwestern Pacific SLP anomaly suggests that frequent explosive cyclone development in the northwestern Pacific in CNTL causes downstream positive SLP anomalies over the Gulf of Alaska. Cyclones in SMTHK developing over the northeastern Pacific enhance the moisture flux along the west coast of North America, increasing precipitation in that region.

Decadal variability of tropical tropopause temperature and its relationship to the Pacific Decadal Oscillation.

Tropopause temperatures (TPTs) control the amount of stratospheric water vapour, which influences chemistry, radiation and circulation in the stratosphere, and is also an important driver of surface climate. Decadal variability and long-term trends in tropical TPTs as well as stratospheric water vapour are largely unknown. Here, we present for the first time evidence, from reanalysis and state-of-the-art climate model simulations, of a link between decadal variability in tropical TPTs and the Pacific Decadal Oscillation (PDO). The negative phase of the PDO is associated with anomalously cold sea surface temperatures (SSTs) in the tropical east and central Pacific, which enhance the zonal SST gradient across the equatorial Pacific. The latter drives a stronger Walker Circulation and a weaker Hadley Circulation, which leads to less convection and subsequently a warmer tropopause over the central equatorial Pacific. Over the North Pacific, positive sea level pressure anomalies occur, which damp vertical wave propagation into the stratosphere. This in turn slows the Brewer-Dobson circulation, and hence warms the tropical tropopause, enabling more water vapour to enter the stratosphere. The reverse chain of events holds for the positive phase of the PDO. Such ocean-troposphere-stratosphere interactions may provide an important feedback on the Earth’s global surface temperature.

Effects of stratospheric variability on El Niño teleconnections

The effects of the tropical Pacific El Niño Southern Oscillation (ENSO) phenomenon are communicated to the rest of the globe via atmospheric teleconnections. Traditionally, ENSO teleconnections have been viewed as tropospheric phenomena, propagating to higher latitudes as Rossby waves. Recent studies, however, suggest an influence of the stratosphere on extra-tropical ENSO teleconnections. The stratosphere is highly variable: in the tropics, the primary mode of variability is the quasi-biennial oscillation (QBO), and in the extra-tropics sudden stratospheric warmings (SSWs) regularly perturb the mean state. Here, we conduct a 10-member ensemble of simulations with a stratosphere-resolving atmospheric general circulation model forced with the observed evolution of sea surface temperatures during 1952–2001 to examine the effects of the QBO and SSWs on the zonal-mean circulation and temperature response to El Niño, with a focus on the northern extra-tropics during winter. We find that SSWs have a larger impact than the QBO on the composite El Niño responses. During El Niño winters with SSWs, the polar stratosphere shows positive temperature anomalies that propagate downward to the surface where they are associated with increased sea-level pressure over the Arctic. During El Niño winters without SSWs, the stratosphere and upper troposphere show negative temperature anomalies but these do not reach the surface. The QBO modulates the El Niño teleconnection primarily in winters without SSWs: the negative temperature anomalies in the polar stratosphere and upper troposphere are twice as large during QBO West compared to QBO East years. In addition, El Niño winters that coincide with the QBO West phase show stronger positive sea-level pressure anomalies over the eastern Atlantic and Northern Europe than those in the QBO East phase. The results imply that the stratosphere imparts considerable variability to ENSO teleconnections.

Global land vegetation and marine fishery responses to atmospheric and oceanic decadal variability

The decadal variability of sea surface temperature (SST) and sea level pressure (SLP) anomalies, as well as the response of global land vegetation and marine fisheries, are investigated for three periods: 1982–1988, 1989–1998, and 1999–2008, separated by the 1988–89 and 1998–99 regime shifts. The goal is to develop a global-scale ecosystem concept to support an improved understanding of the corresponding changes in atmospheric, oceanic, and biological responses. The analysis is based on global SST, SLP, precipitable water content (PWC), land vegetation condition index (VCI), and the United Nations Food and Agriculture Organization’s (FAO) fish capture data. The results show that SST and SLP displayed significant decadal variability. The decadal variability of sea surface temperature anomalies (SSTA) associated with sea level pressure anomalies (SLPA) has an influence on the land vegetation moisture condition (VCI). Positive SSTA tends to be associated with negative SLPA, and vice versa, in the corresponding ocean areas and most land areas. Consequently, clearly opposing distributions of SSTA and SLPA are observed in the periods 1982–1988 and 1999–2008. With positive SSTA and negative SLPA, VCI tends to increase in value representing more favourable vegetation conditions. Negative SSTA and positive SLPA is generally unfavourable for global vegetation development. The decadal variability of SSTA is closely related to the number of fish species (NFS) doing better or worse based on normalized fish landing data. However, the fishery responses show different yet consistent trends in the three ocean basins. When SSTA is negative, it appears more beneficial for the number of fish species with improved landings in the Atlantic Ocean. However, positive SSTA leads to more fish species with improved landings in the Indian and Pacific Oceans.

November seesaw in northern extratropical sea level pressure and its linkage to the preceding wintertime Arctic Oscillation

ABSTRACTThis paper examines the impact of the wintertime Arctic Oscillation (AO) on the following November circulation. The application of a set of statistical methods shows that a response of November sea level pressure (SLP) to the preceding wintertime AO operates on a hemispheric scale. At high and middle latitudes, this response is a well‐pronounced seesaw in SLP between the Eastern and Western Hemispheres. Winters of the positive AO polarity tend to be followed by positive SLP anomalies spanning the whole Northern Eurasia and negative SLP anomalies extending from the Bering Sea through the Western North Atlantic. Opposite SLP anomalies prevail after winters of the negative AO polarity. The response of November SLP to the preceding wintertime AO closely resembles the first empirical orthogonal function of November SLP. That is, the polarity of the wintertime AO precedes the polarity of the leading mode of variability of November SLP over the Northern Hemisphere. The wintertime AO exerts a 9‐month lag impact on November circulation due to the re‐emergence of a sea surface temperature anomaly over the western North Atlantic.

A connection between the tropical Pacific Ocean and the winter climate in the Asian‐Pacific region

AbstractThe impact of the tropical Pacific sea surface temperature (SST) anomaly on the winter mean surface air temperature (SAT) in the Asian‐Pacific region is investigated during the period from 1948 to 2008 using both observations and a linear baroclinic model (LBM). A singular value decomposition (SVD) analysis is conducted between the 500 hPa geopotential height (Z500) over the Northern Hemisphere and the SST over the tropical Pacific Ocean to obtain the large‐scale atmospheric patterns related to tropical Pacific SST. Focus is given to the second pair of SVD mode (SVD2) which bears some similarities in the Z500 field to the Arctic Oscillation over the North Atlantic sector and can impact the SAT over a larger area of Asian‐Pacific. In the winter of a positive SVD2 the SAT over the midlatitude to high‐latitude Asian continent, the Arctic Ocean, the Indian Ocean, and the western subtropical Pacific Ocean tends to be warmer than normal, while the North Pacific Ocean around the Bering Strait is abnormally cold, and vice versa. Examination of the associated surface general circulation shows that a positive SVD2 tends to shift the Siberian High southward and the Aleutian Low eastward resulting in anomalous weak pressure gradient between the Asian continent the North Pacific. Anomalous positive sea level pressure anomalies around Japan and southerly wind along the east coast of the Asian continent are observed. At the same time, the East Asian trough at midtroposphere becomes weaker than normal and the East Asian westerly jet stream is increased in magnitudes and shifted northward. The analysis of the wave activity flux and result of idealized numerical experiments show a possible influence of the western tropical Pacific SST forcing on the SVD2.

Interactions between externally forced climate signals from sunspot peaks and the internally generated Pacific Decadal and North Atlantic Oscillations

AbstractWhen the Pacific Decadal Oscillation is in phase with the 11 year sunspot cycle, there are positive sea level pressure (SLP) anomalies in the Gulf of Alaska, nearly no anomalous zonal SLP gradient across the equatorial Pacific, and a mix of small positive and negative sea surface temperature (SST) anomalies there. When the two indices are out of phase, positive SLP anomalies extend farther south in the Gulf of Alaska and west into eastern Russia, with a strengthened anomalous zonal equatorial Pacific SLP gradient and larger magnitude and more extensive negative SST anomalies along the equatorial Pacific. In the North Atlantic, when the North Atlantic Oscillation (NAO) is in phase with the sunspot peaks, there is an intensified positive NAO SLP pattern. When the NAO is out of phase with the peaks, there is the opposite pattern (negative NAO). The relationships are physically consistent with previously identified processes and mechanisms and point the way to further research.

Heavy snow in Polish–German lowlands – Large-scale synoptic reasons and economic impacts

Large-scale synoptic conditions and economic impact of heavy snow in Polish–German lowlands were analysed. During intense snowfalls, negative anomalies of sea level pressure (SLP) and 500hPa level appear over central Europe, resulting in a low pressure system. Snow cover persistence is possible under positive anomalies of SLP over the majority of the continent, except for its south western part where weak negative anomalies are observed.