Contrasting extremely warm and long-lasting cold air anomalies in the North Atlantic sector of the Arctic during the HALO-(𝒜 𝒞)3 campaign

<strong class="journal-contentHeaderColor">Abstract.</strong> The airborne field campaign HALO&ndash;(AC)&sup3; took place from 07 March to 12 April 2022 and was designed to observe the transformation of air masses during their meridional transport in the North Atlantic sector of the Arctic. We evaluate the meteorological and sea ice conditions during the campaign based on the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5), satellite data, and atmospheric soundings with respect to climatology and describe special synoptic events. HALO&ndash;(AC)&sup3; started with a warm period (11&ndash;20 March) where strong southerly winds prevailed that caused moist and warm air intrusions (MWAIs). Two MWAIs were detected as Atmospheric Rivers (ARs). Compared to the ERA5 climatology (1979&ndash;2022), record breaking vertically integrated poleward heat and moisture fluxes averaged over 75.0&ndash;81.5&deg; N were found. The related warm and moist air masses reached the central Arctic, causing the highest rainfall rates over the sea ice northwest of Svalbard recorded since the beginning of the ERA5 climatology. Subsequently, the cold period of HALO&ndash;(AC)&sup3; started after the passage of a Shapiro&ndash;Keyser cyclone on 21 March when the wind regime turned to northerlies, advecting colder air into the Fram Strait. Until 08 April, marine cold air outbreaks (MCAOs) prevailed, including two strong MCAO events on 21&ndash;26 March and 01&ndash;02 April. In between, aged subpolar warm air was advected to the Fram Strait with northeasterly and easterly winds. On average, the campaign period was warmer than the climatology, especially due to the exceptionally strong ARs during the warm period. In the Fram Strait, the sea ice concentration (SIC) was within the 10&ndash;90^th percentiles of the climatology over the entire campaign duration. During the warm period, SIC was strongly reduced and an untypically large polynya for this season opened north of Svalbard. During the cold period, the polynya was closed again and above average SICs were found. We describe the environmental conditions of a Polar Low and far north reaching cirrus in detail, which will be subjects of research using HALO's remote sensing suite in the future. We also present the perspective on the HALO&ndash;(AC)&sup3; weather conditions from the research site Ny&ndash;&Aring;lesund, where orographic effects caused by the Svalbard archipelago and temporal shifts of atmospheric signals due to the propagation of synoptic systems must be taken into account. Overall, our study may serve as basis for future analyses of the data collected during HALO&ndash;(AC)&sup3; and to compare synoptic conditions with other field campaigns.

Abstract. Low-level airborne observations of the Arctic surface radiative energy budget are discussed. We focus on the terrestrial part of the budget, quantified by the thermal-infrared net irradiance (TNI). The data were collected in cloudy and cloud-free conditions over and in the vicinity of the marginal sea ice zone (MIZ) close to Svalbard during two aircraft campaigns conducted in the spring of 2019 and in the early summer of 2017. The measurements, complemented by ground-based observations available from the literature and radiative transfer simulations, are used to evaluate the influence of surface type (sea ice, open ocean, MIZ), seasonal characteristics, and synoptically driven meridional air mass transports into and out of the Arctic on the near-surface TNI. The analysis reveals a typical four-mode structure of the frequency distribution of the TNI as a function of surface albedo, the sea ice fraction, and surface brightness temperature. Two modes prevail over sea ice and another two over open ocean, each representing cloud-free and cloudy radiative states. Characteristic shifts and modifications of the TNI modes during the transition from winter to spring and early summer conditions are discussed. Furthermore, the influence of warm air intrusions (WAIs) and marine cold-air outbreaks (MCAOs) on the near-surface downward thermal-infrared irradiances and the TNI is highlighted for several case studies. It is concluded that during WAIs the surface warming depends on cloud properties and evolution. Lifted clouds embedded in warmer air masses over a colder sea ice surface, decoupled from the ground by a surface-based temperature inversion, have the potential to warm the surface more strongly than near-surface fog or thin low-level boundary layer clouds because of a higher cloud base temperature. For MCAOs it is found that the thermodynamic profile of the southward-moving air mass adapts only slowly to the warmer ocean surface.

During marine cold air outbreaks (MCAOs), cold and dry Arctic air masses are transported from the central Arctic southward across the closed sea ice and much warmer open oceans. They experience significant transformations including a rapid heating and moistening, often leading to cloud formation. While intense wintertime MCAOs have been analyzed widely, the air mass transformations during other seasons have been studied sparsely. We address this gap by investigating an MCAO case observed in September 2020. To study the transformation processes, we combine the fifth generation of atmospheric reanalyses of the global climate (ERA5), trajectory calculations, as well as shipborne and airborne measurements. In the central Arctic, observations acquired from aboard the research vessel (RV) Polarstern during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition characterized the initial state of the air mass over closed sea ice. Trajectories indicated the pathway the air mass took from RV Polarstern southward to the Fram Strait. For the first 24 h of the southbound drift, the air masses remained quasi-stationary. Then, still 15 h ahead of the marginal sea ice zone, differential advection across the boundary layer flow introduced humidity and clouds at higher altitudes between 1.5 and 2.5 km. ERA5-derived temperature and humidity tendencies indicated complex vertical interactions. Radiative cloud-top cooling, entrainment, and turbulence were significantly reduced in the lower and enhanced in the upper advected cloud layer. Eventually, the lower cloud deck dissipated. After this confluence of 2 different air masses, observations gathered by Polar 5 in Fram Strait as part of the MOSAiC Airborne observations in the Central Arctic campaign revealed cloudy, moist layers throughout the lowest 3.5 km and an increasing boundary layer height. Comparing the initial with the final state 48 h later, the largest net heating of +8 K was found close to the surface, yet the largest net moistening of +2.5 g kg−1 at an altitude of 1 km, as the initial profile was exceptionally dry here. We conclude that the observed air mass transformations were driven by the surface changes from sea ice to open ocean but additionally strongly impacted by the differential advection of clouds and moisture across the near-surface MCAO flow.

&amp;lt;p&amp;gt;Marine Cold Air Outbreaks (MCAOs) are common features above the open water surfaces of the Nordic Seas. They are characterized by marked vertical temperature gradients, which typically persist over several days, and strongly shape air-sea heat exchanges, convection, weather and boundary layer characteristics in the affected region. Based on the novel ERA-5 reanalysis product, we are analyzing climatological and recent aspects of MCAOs in the Fram Strait region of the North Atlantic, which is a &amp;amp;#8220;hot spot&amp;amp;#8221; particularly during winter and early spring. MCAOs in Fram Strait occur preferably when persistent low pressure systems occupy Northern Scandinavia and the Barents/Kara Sea, which exerts strong zonal pressure gradients across Fram Strait. Based on the vertical gradients of potential temperature, occurrence frequencies of MCAOs of different strengths are investigated.&amp;amp;#160; It is found that MCAOs of moderate strength occur at an average of 7-9 days per month between December and March, while especially strong MCAOs occur at an average of 1-3 days in that time. Regarding the former, March is the only month for which a significant trend of +1.7 days/month/decade was found over the 1979-2020 period. While regional MCAO expression is dependent on both the relative location of the ice edge and on the atmospheric circulation, MCAO increase in Fram Strait in March can be explained mainly with the latter and the associated zonal pressure gradient.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;February and March 2020 serve as examples of particularly strong and persistent MCAOs in Fram Strait. The record-breaking strong polar vortex at that time, which had received global attention in the media and literature, had left its associated footprint in near surface and tropospheric circulation fields, hence providing anomalous northerly flow across the ice edge in Fram Strait. While this clearly shaped MCAOs in Fram Strait, associated anomalies were also observed in the North Atlantic Sea Ice edge, and were even detected in upper air profiles and sea ice conditions on Svalbard.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;For the detailed study of such northerly advection events, atmospheric data gathered during the year-long MOSAiC expedition 2019/2020 in the central Arctic are expected to provide valuable information in the upstream direction of the anomalies in Fram Strait.&amp;lt;/p&amp;gt;

<strong class="journal-contentHeaderColor">Abstract.</strong> Low-level airborne observations of the Arctic surface radiative energy budget are discussed. We focus on the terrestrial part of the budget, quantified by the thermal-infrared net irradiance (TNI). The data have been collected in cloudy and cloud-free conditions over and in the vicinity of the marginal sea ice zone (MIZ) close to Svalbard during two aircraft campaigns in spring of 2019 and in early summer of 2017. The measurements, complemented by ground-based observations available from the literature and radiative transfer simulations, are used to evaluate the influence of surface type (sea ice, open ocean, MIZ), seasonal characteristics, and synoptically driven meridional air mass transports into and out of the Arctic on the near-surface TNI. The analysis reveals a typical four-mode structure of the frequency distribution of the TNI as a function of surface albedo, sea ice fraction, and surface brightness temperature. Two modes prevail over sea ice and another two over open ocean, each representing cloud-free and cloudy radiative states. Characteristic shifts and modifications of the TNI modes during the transition from winter towards early spring and summer conditions are discussed. Furthermore, the influence of warm air intrusions (WAIs) and marine cold air outbreaks (MCAOs) on the near-surface downward thermal-infrared irradiances and the TNI is highlighted for several case studies. It is concluded that during WAIs the surface warming depends on cloud properties and evolution. Lifted clouds embedded in warmer air masses over a colder sea ice surface, decoupled from the ground by a surface-based temperature inversion, have the potential to warm the surface more strongly than near-surface fog or thin low-level boundary layer clouds, because of a higher cloud base temperature. For MCAOs it is found that the thermodynamic profile of the southward moving air mass adapts only slowly to the warmer ocean surface.

Low-level airborne observations of the Arctic surface radiative energy budget are discussed. We focus on the terrestrial part of the budget, quantified by the thermal-infrared net irradiance (TNI). The data have been collected in cloudy and cloud-free conditions over and in the vicinity of the marginal sea ice zone (MIZ) close to Svalbard during two aircraft campaigns in spring of 2019 and in early summer of 2017. The measurements, complemented by ground-based observations available from the literature and radiative transfer simulations, are used to evaluate the influence of surface type (sea ice, open ocean, MIZ), seasonal characteristics, and synoptically driven meridional air mass transports into and out of the Arctic on the near-surface TNI. The analysis reveals a typical four-mode structure of the frequency distribution of the TNI as a function of surface albedo, sea ice fraction, and surface brightness temperature. Two modes prevail over sea ice and another two over open ocean, each representing cloud-free and cloudy radiative states. Characteristic shifts and modifications of the TNI modes during the transition from winter towards early spring and summer conditions are discussed. Furthermore, the influence of warm air intrusions (WAIs) and marine cold air outbreaks (MCAOs) on the near-surface downward thermal-infrared irradiances and the TNI is highlighted for several case studies. It is concluded that during WAIs the surface warming depends on cloud properties and evolution. Lifted clouds embedded in warmer air masses over a colder sea ice surface, decoupled from the ground by a surface-based temperature inversion, have the potential to warm the surface more strongly than near-surface fog or thin low-level boundary layer clouds, because of a higher cloud base temperature. For MCAOs it is found that the thermodynamic profile of the southward moving air mass adapts only slowly to the warmer ocean surface.

Given the high rate of sea ice loss and the Arctic amplification, the dynamical processes responsible for airmass transport into or out of the Arctic, thus affecting the seasonal melt and recovery of sea ice, need to be understood and scrutinized from different observational perspectives. In a classical, rather binary view of transport &amp;#8220;into or out of the Arctic&amp;#8221;, a lot of attention in the recent years has rightfully been given on understanding the role of heat and moisture transport into the Arctic in regulating the sea ice melt. However, the cold and dry Arctic airmasses with long residence times are more than occasionally transported out of the Arctic over the open ocean waters, creating one of the most spectacular air mass transformations: the marine cold air outbreaks (MCAOs). The most tangible manifestation of MCAOs are the convectively rolled, narrow cloud streets formed over open water off the edges of the Arctic sea ice in the Nordic and Barents Seas, seen vividly in visible satellite imageries. MCAOs can also locally influence the onset of sea ice melt as they often happen in spring. &amp;#160;By combining nearly 20 years of remotely sensed data from the hyperspectral Atmospheric Infrared Sounder (AIRS), the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth&amp;#8217;s Radiant Energy System (CERES) instruments onboard NASA&amp;#8217;s Aqua satellite, this study presents a climatological view of the vertical structure of atmosphere and the cloud radiative effects during MCAOs in the northeast Atlantic.

&amp;lt;p&amp;gt;The air temperature over Arctic sea ice can fall strongly below 0&amp;amp;#176;C, while for adjacent areas of open water, sea surface temperature remains close to freezing. This creates a strong temperature gradient across the sea ice edge. Transports of cold air masses from the sea ice toward open ocean water, known as marine cold air outbreaks (MCAOs), modify vertical stability of the atmospheric column and thus can create conditions favorable for the formation of hazardous maritime cyclones (polar lows), which pose risks to marine and coastal infrastructure and society. For marine management, MCAO predictions would be highly beneficial. Previous studies analyze the genesis of MCAOs, while predictability and large-scale drivers of MCAOs remain poorly understood.&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;br&amp;gt;We investigate (i) the ability of the Earth System Model from the Max-Planck Institute for Meteorology (MPI-ESM) to predict MCAOs at a seasonal timescale and (ii) options to improve predictability of MCAOs through their large-scale drivers. To identify MCAO preconditions, we utilize the atmospheric reanalysis ERA-Interim using lagged cross-correlation analysis, composite analysis, and causal effect network (CEN).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;br&amp;gt;Our results show that the MPI-ESM has high prediction skill for MCAOs over the Barents Sea (BS), Greenland-Iceland-Norwegian Seas and the Labrador Sea for about 2-2.5 weeks ahead starting from the November and February initial conditions. This holds for the prediction skill analyzed from daily model output. For MCAO properties such as extreme MCAO values occurring during a month, or the frequency of MCAO events per month, we find high prediction skill for up to a month ahead. Whereas the lagged cross-correlation analysis indicates a relationship between September and October atmospheric circulation and sea ice conditions with November BS-MCAOs, the CEN identifies the causal link only from the Arctic sea ice cover.&amp;lt;/p&amp;gt;

Fram Strait in the northern North Atlantic is a key region for marine cold air outbreaks (MCAOs), southward discharges of polar air under northerly air flow, which have a strong impact on air‐sea heat fluxes, boundary layer processes and severe weather. This study investigates climatologies and decadal trends of Fram Strait MCAOs of different intensity classes based on the ERA5 reanalysis product for 1979–2020. Among striking interannual variability, it is shown that the main MCAO season is December through March, when MCAOs occur around 2/3 of the time. We report on significant decadal MCAO decreases in December and January, and a significant increase in March. While the mid‐winter decrease is mainly related to the different paces of warming between the surface and the lower atmosphere, the increase in March can be related to changes in synoptic circulation patterns. As an explanation for the latter, a possible feedback between retreating Barents Sea sea ice, enhanced cyclonic activity and Fram Strait MCAOs is postulated. Exemplifying the trend toward stronger MCAOs during March, the study details the recordbreaking MCAO season in early 2020, and an observational case study of an extreme MCAO event in March 2020 is conducted. Thereby, radiosonde observations are combined with kinematic air back‐trajectories to provide rare observational evidence for the diabatic cooling and drying during the MCAO preconditioning phase.

The Arctic experiences remarkable changes in environmental parameters that affect fluctuations in the surface energy budget, including radiation and sensible and latent heat fluxes. Cold air masses and cloud transformations during marine cold air outbreaks (MCAOs) substantially influence the radiative fluxes, thereby shaping the link between large-scale dynamics, sea ice conditions, and the surface energy budget. In this study, we investigate various cloud characteristics during intense MCAOs over the Barents Sea from 2000 to 2018 using satellite data. We identify 72 intense MCAO events that propagated southward using reanalysis data of the surface temperature and potential temperature at the 800 hPa level. We investigate the macro- and microphysical parameters and radiative properties of clouds within selected MCAOs, their dependence on sea ice concentration, and their initial air mass properties using satellite data. A significant increase in low-level clouds near the ice edge (up to +25% anomalies) and a smooth transition to upper-level clouds is revealed. The total cloud top height during intense MCAOs is generally 500–700 m lower than under neutral conditions. MCAOs induce a positive net cloud radiative effect, which peaks at +20 W m−2 (100 km from the ice edge) and gradually decreases towards the continent (−2.3 W m−2 per 100 km). Our study provides evidence for the importance of changes in the cloud radiative effect within MCAOs, which should be accurately simulated in regional and global climate models.

Abstract. In Arctic warm-air intrusions, air masses undergo a series of radiative, turbulent, cloud, and precipitation processes, the sum of which constitutes the air mass transformation. During the Arctic air mass transformation, heat and moisture are transferred from the air mass to the Arctic environment, melting the sea ice and potentially reinforcing feedback mechanisms responsible for the amplified Arctic warming. We tackle this complex, poorly understood phenomenon from a Lagrangian perspective using the warm-air intrusion event on 12–14 March captured by the 2022 HALO-(𝒜𝒞)3 campaign. Our trajectory analysis of the event suggests that the intruding air mass can be treated as a cohesive air column, therefore justifying the use of a single-column model. In this study, we test this hypothesis using the Atmosphere–Ocean Single-Column Model (AOSCM). The rates of heat and moisture depletion vary along the advection path due to the changing surface properties and large-scale vertical motion. Cloud radiative cooling and turbulent mixing in the stably stratified boundary layer are constant sinks of heat throughout the air mass transformation. Boundary layer cooling intensifies over the marginal ice zone and forces the development of a low-level cloud underneath the advected one. As the air mass flows past the marginal ice zone, large-scale updrafts dominate the temperature and moisture changes through adiabatic cooling and condensation. The ability of the Lagrangian AOSCM framework to simulate elements of the air mass transformation seen in aircraft observations, reanalysis, and operational forecast data makes it an attractive tool for future model analysis and diagnostics development. Our findings can benefit the understanding of the timescales and driving mechanisms of Arctic air mass transformation and help determine the contribution of warm-air intrusions in Arctic amplification.

Marine cold air outbreaks (MCAOs) are events where cold air flows over a relatively warm sea surface. Such outbreaks are associated with severe mesoscale weather systems that are not generally resolved in global climate models, such as polar lows and boundary-layer fronts. Here, an analysis of winter climatology and variability of MCAOs in the Southern Hemisphere (SH) is presented. Near the sea ice edge, north—south fluctuations of the Southern Annular Mode (SAM) index are key, while further north, large-scale wave disturbances are needed to move air masses far enough away from the Antarctic continent to instigate MCAOs. Unlike in the Northern Hemisphere (NH), the spatial patterns of mean and extreme values of the MCAO index differ considerably. Near 60◦S, both mean and extreme values of the index are similar to those found in the main MCAO regions in the NH. Further north, the mean MCAO index is quite high, but the extreme values are much lower than in the NH. We conclude that MCAOs in the SH are as widespread and can be as strong as in the NH, but severe MCAOs near densely populated regions such as the Tasman Sea are less common than in the Nordic Seas and near Japan.

Abstract. The Arctic has warmed more rapidly than the global mean during the past few decades. The lapse rate feedback (LRF) has been identified as being a large contributor to the Arctic amplification (AA) of climate change. This particular feedback arises from the vertically non-uniform warming of the troposphere, which in the Arctic emerges as strong near-surface and muted free-tropospheric warming. Stable stratification and meridional energy transport are two characteristic processes that are evoked as causes for this vertical warming structure. Our aim is to constrain these governing processes by making use of detailed observations in combination with the large climate model ensemble of the sixth Coupled Model Intercomparison Project (CMIP6). We build on the result that CMIP6 models show a large spread in AA and Arctic LRF, which are positively correlated for the historical period of 1951–2014. Thus, we present process-oriented constraints by linking characteristics of the current climate to historical climate simulations. In particular, we compare a large consortium of present-day observations to co-located model data from subsets that show a weak and strong simulated AA and Arctic LRF in the past. Our analyses suggest that the vertical temperature structure of the Arctic boundary layer is more realistically depicted in climate models with weak (w) AA and Arctic LRF (CMIP6/w) in the past. In particular, CMIP6/w models show stronger inversions in the present climate for boreal autumn and winter and over sea ice, which is more consistent with the observations. These results are based on observations from the year-long Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in the central Arctic, long-term measurements at the Utqiaġvik site in Alaska, USA, and dropsonde temperature profiling from aircraft campaigns in the Fram Strait. In addition, the atmospheric energy transport from lower latitudes that can further mediate the warming structure in the free troposphere is more realistically represented by CMIP6/w models. In particular, CMIP6/w models systemically simulate a weaker Arctic atmospheric energy transport convergence in the present climate for boreal autumn and winter, which is more consistent with fifth generation reanalysis of the European Centre for Medium-Range Weather Forecasts (ERA5). We further show a positive relationship between the magnitude of the present-day transport convergence and the strength of past AA. With respect to the Arctic LRF, we find links between the changes in transport pathways that drive vertical warming structures and local differences in the LRF. This highlights the mediating influence of advection on the Arctic LRF and motivates deeper studies to explicitly link spatial patterns of Arctic feedbacks to changes in the large-scale circulation.

&amp;lt;p&amp;gt;The rapidly transforming Svalbard and Fram Strait region is characterised by strong air-sea exchanges and represents a major gateway of oceanic and atmospheric transport between the Arctic and lower latitudes. In winter, Marine Cold Air Outbreaks (MCAOs) extract large amounts of energy from the ocean in the form of surface sensible and latent heat fluxes. We investigate how the spatiotemporal variability in Fram Strait MCAOs affects the heat fluxes in ERA5 and the novel Arctic reanalysis CARRA over ocean, sea-ice and land during November-March 1991-2020.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;We find that the daily mean heat fluxes are strongly correlated with the MCAO index and that wind speed only plays a large role for the heat fluxes when the MCAO index is positive. The sensible heat flux from the surface to the atmosphere reaches greater values in CARRA than in ERA5 while the opposite is true for the latent heat flux. The difference between the reanalyses scale with the magnitude of the heat fluxes, leading to large disagreement over ice-free ocean, where the fluxes have their highest values. When accounting for the differences in magnitude, we find the largest disagreement between the reanalyses over sea ice.&amp;amp;#160;&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;In addition, we find that although sea ice loss drives positive ocean-to-atmosphere heat flux trends around much of Svalbard, negative trends in the monthly mean heat fluxes are seen in Fram Strait during the winter, especially in January. These negative trends reflect the decline in the surface-atmosphere potential temperature difference which forms the basis for the MCAO index.&amp;amp;#160;&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;Finally, we examine the vertical structure of the atmosphere during MCAOs and find anomalously northerly winds, low temperature and low specific humidity throughout the troposphere. The specific humidity anomalies are strongest at low altitudes over the ice-free ocean in southern Fram Strait, while the temperature anomalies reach their maximum in the vicinity of the ice edge. Over the ice-free ocean, where the heat fluxes warm the air from below, the strongest temperature anomalies are found around the altitude of the 800 hPa level.&amp;lt;/p&amp;gt;

&amp;lt;p&amp;gt;In recent years the surface temperature at high latitudes &amp;amp;#8211; especially in the Arctic region &amp;amp;#8211; warmed faster than the global average. This process called Polar amplification is a key characteristic of anthropogenic global warming. Polar amplification will reduce the equator-to-pole temperature gradient of the lower troposphere, but the consequences to the atmospheric general circulation are not fully understood. Here, we study the effect of the reduced meridional temperature gradient by enhanced Sea Surface Temperatures (SSTs), primarily at the Polar regions, on the atmospheric general circulation by executing idealised aquaplanet simulations with the Open Integrated Forecast System (OpenIFS) from the European Centre for Medium-Range Weather Forecasts (ECMWF).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Firstly, we show the global atmospheric response to Polar amplification by comparing various atmospheric climatologies of the control and Polar amplification simulations. We found that Polar amplification influences the Hadley cell circulation and jet stream: both key features of the atmospheric general circulation are strongly reduced in strength. Secondly, we studied the influence of Polar amplification on jet stream waviness. In this study, waviness is quantified by the Sinuosity Index. Sinuosity decreases in a statistically significant manner under Polar amplification: the jet stream becomes less wavy and the meridional extend of the zonal flow decreases as well. The perturbed SSTs around the Polar edge of the Hadley cell and in the baroclinic zone found to be key. Our result contradicts results found in other studies on the consequences of Polar amplification: potential reasons for this and the implication of our results will be discussed in this study.&amp;lt;/p&amp;gt;