The cause of the spring strengthening of the Antarctic polar vortex

Зуев, В. В.; Savelieva, Ekaterina S.

doi:10.1016/j.dynatmoce.2019.101097

Cited by 28 publications

(10 citation statements)

References 24 publications

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“…This is one factor that explains the higher SDCD values observed in GEO differences in the SH extratropics, as AMV uncertainties tend to increase with increasing wind speed (Posselt et al, 2019) and high wind shear (Bormann et al, 2002;Cordoba et al, 2017). In the Antarctic polar region, the general strengthening of the polar vortex aloft in late winter/early spring (i.e., during the study period) is related to a stronger equator-pole temperature gradient brought about by gradually increasing subtropical lower stratospheric temperatures from March to September (Zuev and Savelieva, 2019). A stronger Antarctic polar vortex is associated with stronger zonal winds aloft (and thus stronger wind shear) which would limit accurate AMV and Aeolus wind retrievals, thereby increasing the corresponding SDCD values on both accounts.…”

Section: Amv-aeolus Comparison Resultsmentioning

confidence: 89%

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2021

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Section: Amv-aeolus Comparison Resultsmentioning

confidence: 89%

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2021

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“…differences in the SH extratropics, as AMV uncertainties tend to increase with increasing wind speed (Posselt et al, 2019) and high wind shear (Bormann et al, 2002;Cordoba et al, 2017). In the Antarctic polar region, the general strengthening of the polar vortex aloft in late winter/early spring (i.e., during the study period) is related to a stronger equator-pole temperature gradient brought about by gradually increasing subtropical lower stratospheric temperatures from March to September (Zuev and Savelieva, 2019). A stronger Antarctic polar vortex is associated with stronger zonal winds aloft (and thus stronger wind shear) which would limit accurate AMV and Aeolus wind retrievals, thereby increasing the corresponding SDCD values on both accounts.…”

Section: Amv-aeolus Comparison Resultsmentioning

confidence: 96%

“…MCD are small, and SDCD and mean collocation distances are smaller for MIE compared to RAY collocations, reflecting the higher accuracy of MIE winds and of AMVs in cloudy scenes and possibly larger collocation errors for the RAY winds which tend to have larger collocation distances with AMVs relative to MIE. Larger SDCD are evident in the SH where wind shear is enhanced especially in winter due to the strengthening of the Antarctic polar vortex (Zuev and Savelieva, 2019), which can affect the representativeness of both AMVs and Aeolus winds. In the Arctic, MIE comparisons exhibit small MCD and SDCD consistent with known LEO AMV characteristics, while Antarctic RAY and MIE comparisons show generally larger SDCD.…”

Section: Discussionmentioning

confidence: 99%

Exploiting Aeolus Level-2B Winds to Better Characterize Atmospheric Motion Vector Bias and Uncertainty

Lukens

Ide

Garrett

et al. 2021

Preprint

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Abstract. The need for highly accurate atmospheric wind observations is a high priority in the science community, and in particular numerical weather prediction (NWP). To address this requirement, this study leverages Aeolus wind LIDAR Level-2B data provided by the European Space Agency (ESA) to better characterize atmospheric motion vector (AMV) bias and uncertainty, with the eventual goal of potentially improving AMV algorithms. AMV products from geostationary (GEO) and low-Earth polar orbiting (LEO) satellites are compared with reprocessed Aeolus horizontal line-of-sight (HLOS) global winds observed in August and September 2019. Winds from two of the four Aeolus observing modes are utilized for comparison with AMVs: Rayleigh-clear (derived from the molecular scattering signal) and Mie-cloudy (derived from particle scattering). For the most direct comparison, quality controlled (QC’d) Aeolus winds are collocated with quality controlled AMVs in space and time, and the AMVs are projected onto the Aeolus HLOS direction. Mean collocation differences (MCD) and standard deviation (SD) of those differences (SDCD) are determined from comparisons based on a number of conditions, and their relation to known AMV bias and uncertainty estimates is discussed. GOES-16 and LEO AMV characterizations based on Aeolus winds are described in more detail. Overall, QC’d AMVs correspond well with QC’d Aeolus HLOS wind velocities (HLOSV) for both Rayleigh-clear and Mie-cloudy observing modes, despite remaining biases in Aeolus winds after reprocessing. Comparisons with Aeolus HLOSV are consistent with known AMV bias and uncertainty in the tropics, NH extratropics, and in the Arctic, and at mid- to upper-levels in both clear and cloudy scenes. SH comparisons generally exhibit larger than expected SDCD, which could be attributed to height assignment errors in regions of high winds and enhanced vertical wind shear. GOES-16 water vapor clear-sky AMVs perform best relative to Rayleigh-clear winds, with small MCD (-0.6 m s-1 to 0.1 m s-1) and SDCD (5.4–5.6 m s-1) in the NH and tropics that fall within the accepted range of AMV error values relative to radiosonde winds. Compared to Mie-cloudy winds, AMVs exhibit similar MCD and smaller SDCD (~4.4–4.8 m s-1) throughout the troposphere. In polar regions, Mie-cloudy comparisons have smaller SDCD (5.2 m s-1 in the Arctic, 6.7 m s-1 in the Antarctic) relative to Rayleigh-clear comparisons, which are larger by 1–2 m s-1. The level of agreement between AMVs and Aeolus winds varies per combination of conditions including the Aeolus observing mode coupled with AMV derivation method, geographic region, and height of the collocated winds. It is advised that these stratifications be considered in future comparison studies and impact assessments involving 3D winds. Additional bias corrections to the Aeolus dataset are anticipated to further refine the results.

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“…Later, this boundary increases again, along with a strengthening of the polar vortex, which is attributed to rising temperatures for given PV values. It is worth mentioning that this strength- ening of the polar vortex in late winter and spring in the Southern Hemisphere (SH) has been attributed to a coincidental seasonal temperature increase in the subtropics (Zuev and Savelieva, 2019), which keeps zonal temperature gradients large, sustaining the development of the polar vortex. The maximum OClO SCDs increase till the end of June and mostly stay constant during July.…”

Section: Winter 2018mentioning

confidence: 99%

OClO as observed by TROPOMI: a comparison with meteorological parameters and polar stratospheric cloud observations

et al. 2022

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Abstract. Chlorine dioxide (OClO) is a by-product of the ozone-depleting halogen chemistry in the stratosphere. Although it is rapidly photolysed at low solar zenith angles (SZAs), it plays an important role as an indicator of the chlorine activation in polar regions during polar winter and spring at twilight conditions because of the nearly linear dependence of its formation on chlorine oxide (ClO). Here, we compare slant column densities (SCDs) of chlorine dioxide (OClO) retrieved by means of differential optical absorption spectroscopy (DOAS) from spectra measured by the TROPOspheric Monitoring Instrument (TROPOMI) with meteorological data for both Antarctic and Arctic regions for the first three winters in each of the hemispheres (November 2017–October 2020). TROPOMI, a UV–Vis–NIR–SWIR instrument on board of the Sentinel-5P satellite, monitors the Earth's atmosphere in a near-polar orbit at an unprecedented spatial resolution and signal-to-noise ratio and provides daily global coverage at the Equator and thus even more frequent observations at polar regions. The observed OClO SCDs are generally well correlated with the meteorological conditions in the polar winter stratosphere; for example, the chlorine activation signal appears as a sharp gradient in the time series of the OClO SCDs once the temperature drops to values well below the nitric acid trihydrate (NAT) existence temperature (TNAT). Also a relation of enhanced OClO values at lee sides of mountains can be observed at the beginning of the winters, indicating a possible effect of lee waves on chlorine activation. The dataset is also compared with CALIPSO Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) polar stratospheric cloud (PSC) observations. In general, OClO SCDs coincide well with CALIOP measurements for which PSCs are detected. Very high OClO levels are observed for the northern hemispheric winter 2019/20, with an extraordinarily long period with a stable polar vortex being even close to the values found for southern hemispheric winters. An extraordinary winter in the Southern Hemisphere was also observed in 2019, with a minor sudden stratospheric warming at the beginning of September. In this winter, similar OClO values were measured in comparison to the previous (usual) winter till that event but with a OClO deactivation that was 1–2 weeks earlier.

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The cause of the spring strengthening of the Antarctic polar vortex

Cited by 28 publications

References 24 publications

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Exploiting Aeolus Level-2B Winds to Better Characterize Atmospheric Motion Vector Bias and Uncertainty

OClO as observed by TROPOMI: a comparison with meteorological parameters and polar stratospheric cloud observations

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