Oceanic fronts shape hemispheric contrasts in polar stratospheric extremes

Omrani, Nour-Eddine [Univ. of Bergen (Norway)] (ORCID:0000000265474456); Ogawa, Fumiaki [Mie Univ. (Japan)] (ORCID:0000000340799518); Nakamura, Hisashi [Univ. of Tokyo (Japan); Japan Agency for Marine-Earth Science and Technology, Yokohama (Japan)] (ORCID:0000000317916325); Lubis, Sandro W. [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)] (ORCID:0000000166159880); Keenlyside, Noel S. [Univ. of Bergen (Norway); Nansen Environmental and Remote Sensing Center, Bergen (Norway)] (ORCID:0000000287086868); Paolini, Luca Famooss [Univ. of Bologna (Italy); Euro-Mediterranean Center on Climate Change (Italy)]

doi:10.1038/s41467-026-71998-5

DOE OSTI · 3383094

Oceanic fronts shape hemispheric contrasts in polar stratospheric extremes

Omrani, Nour-Eddine [Univ. of Bergen (Norway)] (ORCID:0000000265474456)·Ogawa, Fumiaki [Mie Univ. (Japan)] (ORCID:0000000340799518)·Nakamura, Hisashi [Univ. of Tokyo (Japan); Japan Agency for Marine-Earth Science and Technology, Yokohama (Japan)] (ORCID:0000000317916325)·Lubis, Sandro W. [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)] (ORCID:0000000166159880)·Keenlyside, Noel S. [Univ. of Bergen (Norway); Nansen Environmental and Remote Sensing Center, Bergen (Norway)] (ORCID:0000000287086868)·Paolini, Luca Famooss [Univ. of Bologna (Italy); Euro-Mediterranean Center on Climate Change (Italy)]

View original source ↗Read source document ↗Export metadata ↓

Abstract

Sudden Stratospheric Warmings (SSWs) and Polar Stratospheric Clouds (PSCs) exhibit striking inter-hemispheric asymmetries: SSWs are frequent in the Arctic but rare in the Antarctic, while PSCs are more persistent in the Antarctic. Although land–sea thermal contrast and orography (LSCO) have been traditionally invoked to explain these asymmetries, here we show using semi-idealized model experiments that even though LSCO strongly impacts the mean state of SSWs and PSCs, it alone cannot fully account for the observed differences. Using model experiments, we reveal that midlatitude oceanic sea surface temperature (SST) fronts represent a crucial supporting additional driver of the hemispheric stratospheric differences. Like LSCO, SST fronts enhance stratospheric convergence of resolved waves, strengthening the Brewer–Dobson Circulation and inducing high-latitude adiabatic warming. This warming significantly enhances Arctic SSW frequency and strongly suppresses PSC formation. Sub-grid-scale non–resolved wave forcing modulates the stratospheric resolved waves effect. The oceanic impact is dominated by North Pacific SST fronts. Our results highlight the indispensable role of SST fronts in shaping Arctic–Antarctic asymmetries in stratospheric dynamics and associated extremes.

Keep this discovery

BibTeX RIS

Omrani, Nour-Eddine [Univ. of Bergen (Norway)] (ORCID:0000000265474456), Ogawa, Fumiaki [Mie Univ. (Japan)] (ORCID:0000000340799518), Nakamura, Hisashi [Univ. of Tokyo (Japan); Japan Agency for Marine-Earth Science and Technology, Yokohama (Japan)] (ORCID:0000000317916325), Lubis, Sandro W. [Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)] (ORCID:0000000166159880), Keenlyside, Noel S. [Univ. of Bergen (Norway); Nansen Environmental and Remote Sensing Center, Bergen (Norway)] (ORCID:0000000287086868), Paolini, Luca Famooss [Univ. of Bologna (Italy); Euro-Mediterranean Center on Climate Change (Italy)]. 2026-04-20. Oceanic fronts shape hemispheric contrasts in polar stratospheric extremes. https://doi.org/10.1038/s41467-026-71998-5

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related discoveries

DOE OSTI2026

Upper ocean mixing, surface heat fluxes, and heat content variability in the upper 150 m during Hurricane Laura (2020)

Observations (from thermistor sensors and a hurricane glider) and model-based temperature were used to answer questions including the following: 1) What physical and environmental conditions explain the rapid intensification of Hurricane Laura? 2) How did the pre-existing warm mixed layer at Stone mooring (StM) influence the degree of cooling in the mixed layer? 3) How did vertical mixing, surface heat fluxes, and advective processes collectively shape the mixed layer heat evolution at StM? Observations measured by thermistor sensors showed that Hurricane Laura induced a cooling of -1.2oC in the mixed layer when Hurricane Laura’s wind speed increased to 47 m/s on 26 August. This contrasts with the -1.04oC mixed layer temperature change estimated from model-based temperature. At StM, the presence of a 31oC warm mixed layer and elevated heat content (60-80kJ/cm2) effectively preconditioned the upper ocean ahead of Hurricane Laura’s passage. After Hurricane Laura passed, turbulent mixing associated with the storm transported the heat anomalies downward into subsurface layers. In addition, this study shows that a surface heat flux of 5.04 kJ/cm2 supported the intensity of Hurricane Laura as it traversed over the StM. Using a mixed layer heat balance model, this study shows that entrainment flux and surface flux mostly contributed to the observed change in the mixed layer temperature.

Tsai, Senam↗

DOE OSTI2026

Topographic effects on reflected acoustic waves from the OSIRIS-REx reentry observed from stratospheric balloons

During long-distance sound propagation in planetary atmospheres, acoustic waves may reflect off the air/surface interface one or more times. For low sound frequencies and flat interfaces, the incident and reflected wave tend to be nearly identical. However, this may not be the case when the downgoing acoustic wave encounters topography. Here, we describe a set of direct and reflected acoustic signals recorded on free-flying balloons during the hypersonic entry of the OSIRIS-REx sample return capsule (SRC). In two of the three cases presented here, an impulsive reflected arrival similar in form to the direct sonic boom of the SRC is observed, followed by a diffuse coda. In contrast, one of the floating stations lacked an impulsive reflection entirely, with only the coda present. We use full waveform modeling to show how reflection in the presence of complex topography can explain coda seen in all three examples as well as the lack of impulsive arrival on the third. Our results indicate that the complex signals often observed in long range acoustic propagation could be due, in part, to interactions with topography during transmission.

Lees, Jonathan M. [University of North Carolina, C↗

NASA NTRS1985

NASA Scatterometer Oceanic Wind Measurement System

Satellite scatterometers are active microwave radars designed to yield measurements of near surface horizontal wind velocity over the ocean. Scatterometers are unique in that they are the only existing microwave remote sensing instruments that allow measurements of both wind speed and wind direction. NASA will fly a scatterometer, NSCAT, aboard the Navy Ocean Remote Sensing System (N-ROSS) mission starting in late 1990. N-ROSS is a spaceborne ocean remote sensing system with a planned mission life of three years. In addition to the NSCAT, N-ROSS will have three other microwave instruments mounted on a single satellite flying in a near polar orbit: an altimeter; a special sensor microwave/imager (SSM/I); and a low frequency microwave radiometer. The NSCAT to be flown on N-ROSS is described.

M Freilich↗