| 1. |
- Wang, Tongmei, et al.
(författare)
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On the dynamics of the spring seasonal transition in the two hemispheric high-latitude stratosphere
- 2019
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Ingår i: Tellus. Series A, Dynamic meteorology and oceanography. - : Stockholm University Press. - 0280-6495 .- 1600-0870. ; 71:1
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Tidskriftsartikel (refereegranskat)abstract
- The seasonal transition is one of the main features of the atmospheric general circulation and is particularly manifest in the high-latitude stratosphere. To explore the dynamics of stratospheric seasonal transition in both hemispheres, the observational features of the annual cycle and seasonal transition in high-latitude stratosphere are investigated using the 38-year ERA-interim reanalysis. Climatological analysis shows that tropospheric planetary waves propagate to the stratosphere and affect significantly the winter-to-summer stratospheric seasonal transition over both hemispheres, but with a much stronger wave activity in austral spring than its boreal counterpart. The austral spring seasonal transition occurs first at the stratopause then propagates down to the lower stratosphere due to enhanced planetary wave breaking, weakening the westerlies. In boreal spring, the seasonal transition occurs simultaneously across the depth of the stratosphere, mainly due to the solar radiation and weaker planetary wave activity. Interannual variability analysis shows that the timing of stratospheric seasonal transition is closely linked to the intensity of upward propagation of planetary wave activity, i.e. the stronger the upward propagation of planetary wave activity in high-latitudes in spring the earlier the stratospheric seasonal transition. Transition indexes are defined and the probability distributions of the indexes show that there are two types of transition in both hemispheres: synchronous/asynchronous in the Northern Hemisphere (NH), and steep/moderate transitions in the Southern Hemisphere (SH). A composite analysis shows that before the transition, stronger wave activity leads to asynchronous rather than synchronous transition in the NH, which propagates downward from the stratopause. In the SH, a moderate rather than steep transition is obtained, which occurs earlier and takes longer to propagate from the upper to lower stratosphere.
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| 2. |
- Wang, Tongmei, et al.
(författare)
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Response of stratospheric water vapour to CO2 doubling in WACCM
- 2020
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 54, s. 4877-4889
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Tidskriftsartikel (refereegranskat)abstract
- Stratospheric water vapour (SWV), as a greenhouse gas, modulates the radiative energy budget of the climate system. It is sensitive to, and plays a significant role in the climate change. In this study, we investigate the SWV response to CO2 increase with the Whole Atmosphere Community Climate Model (WACCM). In addition, we study its possible feedback on stratospheric temperature and relevant mechanisms. In our model experiments, the CO2 concentration and sea surface temperature (SSTs) are changed at the same time, as well as separately, to enable separating the radiative-photochemical and dynamical response to CO2 doubling scenarios. The model results show that the response of SWV to CO2 doubling is dominated by the changes in the SSTs, with an increase of the SWV concentration by similar to 6 to 10% in most of the stratosphere and more than 10% in the lower stratosphere, except for winter pole in the lower stratosphere, where the CO2 doubling decreases water vapour. The increase of SWV is mostly due to a dynamical response to the warm SSTs. Doubled CO2 induces warm SSTs globally and further leads to moist troposphere and a warmer tropical and subtropical tropopause, resulting in more water vapour entering stratosphere from below. As a greenhouse gas, large increase of SWV in the lower stratosphere, in turn, affects the stratospheric temperature, resulting in a warming of the tropical and subtropical lower stratosphere, offsetting the cooling caused by CO2 doubling.
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| 3. |
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| 4. |
- Wang, Tongmei, 1973-
(författare)
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Seasonality and variability of stratospheric water vapour
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stratospheric water vapour (SWV) plays a critical role in the climate system by modulating the radiation budget and influencing the stratospheric chemistry. Studying changes of SWV on global scale is helpful for our understanding of climate change. This thesis aims to gain an improved understanding of the stratospheric processes and dynamic mechanisms that determine the seasonality and variability of SWV. Water vapour is characterized by its compound, which leaves an isotopic fingerprint in relevant atmospheric and hydrologic processes. The thesis starts with analyzing the global features of three stable water isotopes (SWIs) in the stratosphere by using satellite retrievals from Odin/SMR. The spatial pattern of SWI indicates clear effects of methane oxidation in the upper stratosphere, dehydration at the tropopause and stratospheric transport via the Brewer-Dobson circulation (BDC). In addition to the tropical tape recorder in the lower stratosphere, a pronounced downward propagation of the seasonal signal from the upper to the lower stratosphere is observed in high-latitudes. These observed features are further compared to model outputs to identify possible causes of model deficiencies in reproducing the distribution of SWV.The downward propagation signal of zonal wind has been demonstrated in the high-latitude stratosphere in spring seasonal transition in the Southern Hemisphere, but not in the Northern Hemisphere. This inter-hemispheric difference is due to the stronger stratospheric planetary wave activity in austral spring than in boreal spring. With strong wave activity in spring, the transition is inclined to occur first at the stratopause followed by a downward propagation to the lower stratosphere. In particular, the stronger the upward propagation of planetary waves in high-latitudes in spring the earlier the stratospheric seasonal transition. The new generation reanalysis ERA5 represents climatological distribution and seasonal cycle of SWV better than its predecessor ERA-Interim by assimilating more satellite observations. The variability of SWV in ERA5 is highly consistent with SDI MIM observation. The interannual variability of water vapour in the lower stratosphere is found to be closely linked to the tropical Quasi-Biennial Oscillation (QBO) and QBO-induced residual circulation. On decadal scale, the deficit of SWV in boreal winter is associated with a warm sea surface temperature (SST) anomaly in the North Atlantic, which leads to stronger upward propagation of planetary waves, resulting in a warmer pole in the lower stratosphere, colder tropical tropopause and stronger BDC, hence less water vapour enters the stratosphere through the tropopause and the anomaly extends to the entire stratosphere. Sensitivity experiments for a CO2 doubling scenario are performed with the model WACCM to investigate the SWV response to climate change. The response of SWV is dominated by the warm SST, which is induced by CO2 doubling in a coupled ocean-atmosphere system. The enhanced SST leads to a moist troposphere and warmer tropical and subtropical tropopause, resulting in more water vapour entering the stratosphere from below. A large increase of SWV in the lower stratosphere, in turn, affects stratospheric temperature. It results in a warming in the tropical and subtropical lower stratosphere, offsetting the cooling caused by CO2 doubling in general.
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| 5. |
- Wang, Tongmei, et al.
(författare)
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Stable Water Isotopologues in the Stratosphere Retrieved from Odin/SMR Measurements
- 2018
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Ingår i: Remote Sensing. - : MDPI AG. - 2072-4292. ; 10:2
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Tidskriftsartikel (refereegranskat)abstract
- Stable Water Isotopologues (SWIs) are important diagnostic tracers for understanding processes in the atmosphere and the global hydrological cycle. Using eight years (2002-2009) of retrievals from Odin/SMR (Sub-Millimetre Radiometer), the global climatological features of three SWIs, (H2O)-O-16, HDO and (H2O)-O-18, the isotopic composition D and O-18 in the stratosphere are analysed for the first time. Spatially, SWIs are found to increase with altitude due to stratospheric methane oxidation. In the tropics, highly depleted SWIs in the lower stratosphere indicate the effect of dehydration when the air comes through the cold tropopause, while, at higher latitudes, more enriched SWIs in the upper stratosphere during summer are produced and transported to the other hemisphere via the Brewer-Dobson circulation. Furthermore, we found that more (H2O)-O-16 is produced over summer Northern Hemisphere and more HDO is produced over summer Southern Hemisphere. Temporally, a tape recorder in (H2O)-O-16 is observed in the lower tropical stratosphere, in addition to a pronounced downward propagating seasonal signal in SWIs from the upper to the lower stratosphere over the polar regions. These observed features in SWIs are further compared to SWI-enabled model outputs. This helped to identify possible causes of model deficiencies in reproducing main stratospheric features. For instance, choosing a better advection scheme and including methane oxidation process in a specific model immediately capture the main features of stratospheric water vapor. The representation of other features, such as the observed inter-hemispheric difference of isotopic component, is also discussed.
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| 6. |
- Wang, Tongmei, et al.
(författare)
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Tropical water vapour in the lower stratosphere and its relationship to tropical/extratropical dynamical processes in ERA5
- 2020
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 146:730, s. 2432-2449
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Tidskriftsartikel (refereegranskat)abstract
- Stratospheric water vapour (SWV), in spite of its low concentration in the stratosphere as compared to the troposphere, contributes significantly to the surface energy budget and can have an influence on the surface climate. This study investigates the dynamical processes that determine SWV on interannual to decadal time-scales. First, we evaluate two SWV reanalysis products and show that SWV is better represented in a new-generation reanalysis product, ERA5, than in its predecessor, ERA-Interim. In particular, it is shown that SWV in ERA5 is highly consistent with observational data obtained from the SPARC Data Initiative Multi-Instrument Mean (SDI MIM). Second, we investigate the variability of tropical SWV and its relationship to dynamical stratospheric variables. The analyses show that the interannual variability in the tropical lower-stratospheric water vapour is closely linked to the tropical Quasi-Biennial Oscillation (QBO). When westerlies occupy the middle stratosphere and easterlies the lower stratosphere, a decrease is observed in lower-stratospheric water vapour due to a colder tropical tropopause and a QBO-induced enhanced residual circulation. On decadal time-scales, the composite analysis of the boreal winter in two typical periods shows that less SWV is related to a warm anomaly in the North Atlantic sea-surface temperature, which leads to stronger upward propagation of planetary wave activity at high latitudes, a weaker polar vortex and an enhanced residual circulation. The opposite occurs during periods with higher concentrations of SWV.
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