scholarly journals Climatological impact of the Brewer–Dobson circulation on the N<sub>2</sub>O budget in WACCM, a chemical reanalysis and a CTM driven by four dynamical reanalyses

2020 ◽  
Vol 20 (21) ◽  
pp. 12609-12631
Author(s):  
Daniele Minganti ◽  
Simon Chabrillat ◽  
Yves Christophe ◽  
Quentin Errera ◽  
Marta Abalos ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Rate Of Change ◽  
Polar Regions ◽  
Antarctic Region ◽  
Vertical Advection ◽  
Advection Term ◽  
Horizontal Mixing ◽  
The Mean ◽  
The Tropics ◽  
The Antarctic

Abstract. The Brewer–Dobson circulation (BDC) is a stratospheric circulation characterized by upwelling of tropospheric air in the tropics, poleward flow in the stratosphere, and downwelling at mid and high latitudes, with important implications for chemical tracer distributions, stratospheric heat and momentum budgets, and mass exchange with the troposphere. As the photochemical losses of nitrous oxide (N2O) are well known, model differences in its rate of change are due to transport processes that can be separated into the mean residual advection and the isentropic mixing terms in the transformed Eulerian mean (TEM) framework. Here, the climatological impact of the stratospheric BDC on the long-lived tracer N2O is evaluated through a comparison of its TEM budget in the Whole Atmosphere Community Climate Model (WACCM), in a chemical reanalysis of the Aura Microwave Limb Sounder version 2 (BRAM2) and in a chemistry transport model (CTM) driven by four modern reanalyses: the European Centre for Medium-Range Weather Forecasts Interim reanalysis (ERA-Interim; Dee et al., 2011), the Japanese 55-year Reanalysis (JRA-55; Kobayashi et al., 2015), and the Modern-Era Retrospective analysis for Research and Applications version 1 (MERRA; Rienecker et al., 2011) and version 2 (MERRA-2; Gelaro et al., 2017). The effects of stratospheric transport on the N2O rate of change, as depicted in this study, have not been compared before across this variety of datasets and have never been investigated in a modern chemical reanalysis. We focus on the seasonal means and climatological annual cycles of the two main contributions to the N2O TEM budget: the vertical residual advection and the horizontal mixing terms. The N2O mixing ratio in the CTM experiments has a spread of approximately ∼20 % in the middle stratosphere, reflecting the large diversity in the mean age of air obtained with the same CTM experiments in a previous study. In all datasets, the TEM budget is closed well; the agreement between the vertical advection terms is qualitatively very good in the Northern Hemisphere, and it is good in the Southern Hemisphere except above the Antarctic region. The datasets do not agree as well with respect to the horizontal mixing term, especially in the Northern Hemisphere where horizontal mixing has a smaller contribution in WACCM than in the reanalyses. WACCM is investigated through three model realizations and a sensitivity test using the previous version of the gravity wave parameterization. The internal variability of the horizontal mixing in WACCM is large in the polar regions and is comparable to the differences between the dynamical reanalyses. The sensitivity test has a relatively small impact on the horizontal mixing term, but it significantly changes the vertical advection term and produces a less realistic N2O annual cycle above the Antarctic. In this region, all reanalyses show a large wintertime N2O decrease, which is mainly due to horizontal mixing. This is not seen with WACCM, where the horizontal mixing term barely contributes to the TEM budget. While we must use caution in the interpretation of the differences in this region (where the reanalyses show large residuals of the TEM budget), they could be due to the fact that the polar jet is stronger and is not tilted equatorward in WACCM compared with the reanalyses. We also compare the interannual variability in the horizontal mixing and the vertical advection terms between the different datasets. As expected, the horizontal mixing term presents a large variability during austral fall and boreal winter in the polar regions. In the tropics, the interannual variability of the vertical advection term is much smaller in WACCM and JRA-55 than in the other experiments. The large residual in the reanalyses and the disagreement between WACCM and the reanalyses in the Antarctic region highlight the need for further investigations on the modeling of transport in this region of the stratosphere.

scholarly journals Climatological impact of the Brewer–Dobson Circulation on the N<sub>2</sub>O budget in WACCM, a chemical reanalysis and a CTM driven by four dynamical reanalyses

2020 ◽  
Author(s):  
Daniele Minganti ◽  
Simon Chabrillat ◽  
Yves Christophe ◽  
Quentin Errera ◽  
Marta Abalos ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Rate Of Change ◽  
Polar Regions ◽  
Antarctic Region ◽  
Vertical Advection ◽  
Advection Term ◽  
Horizontal Mixing ◽  
The Mean ◽  
The Antarctic

Abstract. The Brewer–Dobson Circulation (BDC) transports chemical tracers from the well-mixed tropical troposphere to the polar stratosphere, with many important implications for climate, chemistry, ozone distribution and recovery. Since the photochemical losses of nitrous oxide (N2O) are well-known, model differences in its rate of change are due to transport processes that can be separated in the mean residual advection and the isentropic mixing terms in the Transformed Eulerian Mean (TEM) framework. Here the climatological impact of the stratospheric BDC on the long-lived tracer N2O is evaluated through a comparison of its TEM budget in the Whole Atmosphere Community Climate Model (WACCM), a chemical reanalysis of the Aura Microwave Limb Sounder version 2 (BRAM2) and in a Chemistry-Transport Model (CTM) driven by four modern reanalyses (ERA-Interim, JRA-55, MERRA and MERRA2). The effects of stratospheric transport on the N2O rate of change, as depicted in this study, have not been compared across this variety of datasets and never investigated in a chemical reanalysis. We focus on the seasonal means and climatological annual cycles of the two main contributions to the N2O TEM budget: the vertical residual advection and the horizontal mixing terms. The N2O mixing ratio in the CTM experiments has a spread of approximately ~ 20 % in the middle stratosphere, reflecting the large diversity in the mean Age of Air obtained with the same experiments. In all datasets the TEM budget is well-closed and the agreement between the vertical advection terms is qualitatively very good in the Northern Hemisphere, and good in the Southern Hemisphere except above the Antarctic region. The datasets do not agree as well with respect to the horizontal mixing term, especially in the Northern Hemisphere where horizontal mixing has a smaller contribution in WACCM than in the reanalyses. WACCM is investigated through three model realizations and a sensitivity test where gravity waves are forced differently in the Southern Hemisphere. The internal variability of the horizontal mixing in WACCM is large in the polar regions, and comparable to the differences between the dynamical reanalyses. The sensitivity test has a relatively small impact on the horizontal mixing term, but significantly changes the vertical advection term and produces a less realistic N2O annual cycle above the Antarctic. In this region, all reanalyses show a large wintertime N2O decrease, which is mainly due to horizontal mixing. This is not seen with WACCM, where the horizontal mixing term barely contributes to the TEM budget. While we must use caution in the interpretation of the differences in this region, where the reanalyses show large residuals of the TEM budget, they could be due to the fact that the polar jet is stronger and not tilted equatorward in WACCM compared with the reanalyses. We also compare the inter-annual variability in the horizontal mixing and the vertical advection terms. As expected, the horizontal mixing term presents a large variability during austral fall and boreal winter in the polar regions. In the Tropics, the inter-annual variability of the vertical advection term is much smaller in WACCM and JRA-55 than in the other experiments. The large residual in the reanalyses and the disagreement between WACCM and the reanalyses in the Antarctic region highlight the need for further investigations on the modeling of transport in this region of the stratosphere.

scholarly journals N2O-based climatology of the Brewer-Dobson Circulation in WACCM, a chemical reanalysis and a CTM driven by four dynamical reanalyses

2020 ◽  
Author(s):  
Daniele Minganti ◽  
Simon Chabrillat ◽  
Yves Christophe ◽  
Quentin Errrera ◽  
Marta Abalos ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Arctic Region ◽  
The Arctic ◽  
Antarctic Region ◽  
Tem Analysis ◽  
Large Variability ◽  
Residual Term ◽  
Vertical Advection ◽  
Advection Term ◽  
Horizontal Mixing

&lt;p&gt;The Brewer-Dobson Circulation (BDC) plays a major role in the stratospheric dynamics in terms of tracer transport through the mean residual meridional advection and the isentropic 2-way mixing. &lt;br&gt;The climatological BDC in the Whole Atmosphere Community Climate Model (WACCM) is separated in its components and evaluated through a comparison with a chemical reanalysis of the Aura Microwave Limb Sounder version 2 (BRAM2) and with a chemistry-transport model driven by four modern reanalyses (ERA-Interim, JRA-55, MERRA and MERRA2). The BDC seasonal means and climatological annual cycle are addressed using the Transformed Eulerian Mean (TEM) analysis of the long-lived tracer N2O. The N2O TEM budget terms considered in this study are the vertical residual advection and the horizontal two-way mixing terms.&lt;br&gt;WACCM presents a general underestimation of the horizontal mixing term in the wintertime Northern Hemisphere with respect to the reanalyses throughout the stratosphere.In the wintertime antarctic region the mid-low stratospheric horizontal mixing term in WACCM does not agree with the reanalyses: it shows near-zero positive values, while all the reanalyses show a consistent negative contribution. This disagreement between WACCM and the reanalyses is located in the region and period of the polar vortex development, and can be related to a different representation of the polar jet. In this region the reanalyses are nevertheless affected by large uncertanties of the TEM analysis: the residual term of the budget has the same magnitude as the horizontal mixing term.Even though the residual term can be interpreted as the effect of sub-grid mixing processes, caution must be exerted when considering these regions because the N2O TEM budget is not completetely closed.&lt;br&gt;The mid-stratospheric arctic region are characterized by smaller uncertanties of the TEM budget together with large differences among the datasets during winter: the WACCM realizations, characterized by a large internal variability, show a smaller horizontal mixing contribution with respect to the reanalyses. &lt;br&gt;The agreement among datasets is generally improved when considering the middle and low latitudes, especially in the Northern Hemisphere: those regions are characterized by smaller differences among datasets and a well-closed TEM budget.&lt;br&gt;The inter-annual variability of the horizontal mixing term and the vertical advection term is highly latitude-dependent: the horizontal mixing term presents a large variability, together with a large dataset spread, in the antarctic region in the austral fall and during boreal winter in the Arctic; the vertical advection shows large variability in the arctic region and large model spread in the Tropical regions.&lt;/p&gt;

scholarly journals Investigation of Changes of the Kinematic Parameters of Antarctic Tectonic Plate Using Data Observations of Permanent GNSS Stations

2017 ◽  
Vol 103 (1) ◽  
pp. 119-135 ◽  
Author(s):  
Kornylii Tretyak ◽  
Al-Alusi Forat ◽  
Yurii Holubinka
Keyword(s):  
Angular Velocity ◽  
Kinematic Parameters ◽  
Antarctic Region ◽  
Tectonic Plate ◽  
Euler Pole ◽  
The Mean ◽  
Using Data ◽  
Gnss Permanent Stations ◽  
The Antarctic

Abstract The paper describes a modified algorithm of determination of the Euler pole coordinates and angular velocity of the tectonic plate, considering the continuous and uneven distribution of daily measurements of GNSS permanent stations. Using developed algorithm were determined the mean position of Euler pole and angular velocity of Antarctic tectonic plate and their annual changes. As the input data, we used the results of observations, collected on 28 permanent stations of the Antarctic region, within the period from 1996 to 2014.

scholarly journals Spatial and temporal variability of interhemispheric transport times

2018 ◽  
Vol 18 (10) ◽  
pp. 7439-7452 ◽  
Author(s):  
Xiaokang Wu ◽  
Huang Yang ◽  
Darryn W. Waugh ◽  
Clara Orbe ◽  
Simone Tilmes ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Mean Transit Time ◽  
Intertropical Convergence Zone ◽  
Spatial And Temporal Variability ◽  
Rapid Loss ◽  
Seasonal And Interannual Variability ◽  
Transit Times ◽  
The Mean ◽  
The Tropics ◽  
Interhemispheric Transport

Abstract. The seasonal and interannual variability of transport times from the northern midlatitude surface into the Southern Hemisphere is examined using simulations of three idealized “age” tracers: an ideal age tracer that yields the mean transit time from northern midlatitudes and two tracers with uniform 50- and 5-day decay. For all tracers the largest seasonal and interannual variability occurs near the surface within the tropics and is generally closely coupled to movement of the Intertropical Convergence Zone (ITCZ). There are, however, notable differences in variability between the different tracers. The largest seasonal and interannual variability in the mean age is generally confined to latitudes spanning the ITCZ, with very weak variability in the southern extratropics. In contrast, for tracers subject to spatially uniform exponential loss the peak variability tends to be south of the ITCZ, and there is a smaller contrast between tropical and extratropical variability. These differences in variability occur because the distribution of transit times from northern midlatitudes is very broad and tracers with more rapid loss are more sensitive to changes in fast transit times than the mean age tracer. These simulations suggest that the seasonal–interannual variability in the southern extratropics of trace gases with predominantly NH midlatitude sources may differ depending on the gases' chemical lifetimes.

scholarly journals Trends in the polar sea ice coverage under climate change scenario

MAUSAM ◽  
2021 ◽  
Vol 62 (4) ◽  
pp. 609-616
Author(s):  
AMITA PRABHU ◽  
P.N. MAHAJAN ◽  
R.M. KHALADKAR
Keyword(s):  
Sea Ice ◽  
Interannual Variability ◽  
Arctic Region ◽  
The Arctic ◽  
Change Scenario ◽  
Polar Regions ◽  
Sea Ice Extent ◽  
Ice Coverage ◽  
Satellite Microwave ◽  
The Antarctic

The development in the satellite microwave technology during the past three decades has offered an opportunity to the scientific community to access the sea ice data over the polar regions, which was otherwise inaccessible for continuous monitoring by any other means. The present study focuses on the trends in the Sea Ice Extent (SIE) over different sectors of the Arctic and the Antarctic regions and the interannual variability in their extremes. In general, the data over the period (1979-2007) reveal marked interannual variability in the sea ice cover with an increasing and the decreasing trend over the Antarctic and the Arctic region respectively. Over the southern hemisphere, only the Bellingshausen and Amundsen Seas sector shows an exceptional decreasing trend. However, in the northern hemisphere, all the sectors show a decreasing trend, with the Kara and Barents Seas sector being the most prominent one. Although, the decreasing trend of the SIE over the Arctic could be attributed to the global warming, an intriguing question still remains as to why the other polar region shows a different behaviour.

scholarly journals Spatial and Temporal Variability of Interhemispheric Transport Times

2017 ◽  
Author(s):  
Xiaokang Wu ◽  
Huang Yang ◽  
Darryn W. Waugh ◽  
Clara Orbe ◽  
Simone Tilmes ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Transit Time ◽  
Mean Transit Time ◽  
Spatial And Temporal Variability ◽  
Fast Time ◽  
Seasonal And Interannual Variability ◽  
The Mean ◽  
Convergence Zones ◽  
The Tropics ◽  
Interhemispheric Transport

Abstract. The seasonal and interannual variability of transport times from the northern mid-latitude surface into the southern hemisphere is examined using simulations of three idealized age tracers: A ideal age tracer that yields the mean transit time from northern mid-latitudes and two tracers with uniform 50-day and 5-day decay. For all tracers the largest seasonal and interannual variability occurs near the surface within the tropics, and is generally closely coupled to movement of the intertropical convergence zones (ITCZ). There are, however, notable differences in variability between different tracers. The largest seasonal and interannual variability in the mean age is generally confined to latitudes spanning the ITCZ, with very weak variability in the southern extratropics. In contrast, for tracers subject to spatially uniform exponential loss the peak variability tends to be south of the ITCZ, and there is a smaller contrast between tropical and extratropical variability. These differences in variability occur because the distribution of transit time from northern mid-latitudes is very broad and tracers with more rapid loss are more sensitive to changes in fast time scales than the mean age tracer. These simulations suggest that the seasonal/interannual variability in the southern extratropics of trace gases, with predominantly NH mid-latitude sources, may differ depending on the gases' chemical lifetimes.

scholarly journals Recent changes in pan-Antarctic region surface snowmelt detected by AMSR-E and AMSR2

2020 ◽  
Vol 14 (11) ◽  
pp. 3811-3827
Author(s):  
Lei Zheng ◽  
Chunxia Zhou ◽  
Tingjun Zhang ◽  
Qi Liang ◽  
Kang Wang
Keyword(s):  
Sea Ice ◽  
Remote Sensing Data ◽  
Microwave Remote Sensing ◽  
Open Water ◽  
Southern Annular Mode ◽  
Temporal Variations ◽  
Polar Regions ◽  
Antarctic Region ◽  
Marginal Sea ◽  
The Antarctic

Abstract. Surface snowmelt in the pan-Antarctic region, including the Antarctic ice sheet (AIS) and sea ice, is crucial to the mass and energy balance in polar regions and can serve as an indicator of climate change. In this study, we investigate the spatial and temporal variations in surface snowmelt over the entire pan-Antarctic region from 2002 to 2017 by using passive microwave remote sensing data. The stable orbits and appropriate acquisition times of the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) and the Advanced Microwave Scanning Radiometer 2 (AMSR2) enable us to take full advantage of daily brightness temperature (Tb) variations to detect surface snowmelt. The difference between AMSR-E/2 ascending and descending 36.5 GHz Tb values in vertical polarization (DAV36) was utilized to map the pan-Antarctic region snowmelt, as this method is unaffected by snow metamorphism. We evaluated the DAV36 algorithm against ground-based measurements and further improved the method over the marginal sea ice zone by excluding the effect of open water. Snowmelt detected by AMSR-E/2 data was more extensive and persistent than that detected by the Special Sensor Microwave/Imager (SSM/I) data. Continuous melt onset (CMO) ranged from August in the marginal sea ice zone to January in the Antarctic inland, and the early transient melt events occurred several days to more than 2 months earlier. The pan-Antarctic region CMO was significantly correlated (R=0.54, p<0.05) with the summer Southern Annular Mode (SAM). The decreased AIS melt extent was very likely linked (R=-0.82, p<0.01) with the enhanced summer SAM.

scholarly journals How much snow falls on the Antarctic ice sheet?

2014 ◽  
Vol 8 (1) ◽  
pp. 1279-1304 ◽  
Author(s):  
C. Palerme ◽  
J. E. Kay ◽  
C. Genthon ◽  
T. L'Ecuyer ◽  
N. B. Wood ◽  
...  
Keyword(s):  
Climate Models ◽  
Ice Sheet ◽  
Satellite Observation ◽  
Polar Regions ◽  
Antarctic Ice Sheet ◽  
Precipitation Characteristics ◽  
Model Independent ◽  
The Mean ◽  
Antarctic Precipitation ◽  
The Antarctic

Abstract. Climate models predict Antarctic precipitation to increase during the 21st century, but their present day Antarctic precipitation differs. A fully model-independent climatology of the Antarctic precipitation characteristics, such as snowfall rates and frequency, is needed to assess the models, but was not available so far. Satellite observation of precipitation by active spaceborne sensors has been possible in the polar regions since the launch of CloudSat in 2006. Here we use CloudSat products to build the first multi-year model-independent climatology of Antarctic precipitation. The mean snowfall rate from August 2006 to April 2011 is 171 mm yr−1 over the Antarctic ice sheet north of 82° S. The ECMWF ERA Interim dataset agrees well with the new satellite climatology.

scholarly journals An investigation of seasonal temperature trends in the Antarctic using CHAMP GPS radio occultation data

2011 ◽  
Vol 4 (1) ◽  
pp. 511-525
Author(s):  
K. Zhang ◽  
E. Fu ◽  
D. Silcock ◽  
Y. Kuleshov
Keyword(s):  
Radio Occultation ◽  
Space Mission ◽  
Radiosonde Data ◽  
Polar Regions ◽  
Temperature Profiles ◽  
Seasonal Temperature ◽  
Antarctic Region ◽  
Gps Radio Occultation ◽  
Temperature Trends ◽  
The Antarctic

Abstract. GPS radio occultation (RO) has been recognized as an alternative atmospheric upper air observation technique due to its distinct features and technological merits. This technique is best used for meteorological studies in remote and/or difficult-to-access areas such as the Polar Regions. The CHAllenging Minisatellite Payload (CHAMP) space mission has provided about eight years of high quality global coverage atmospheric profiles. This study first evaluates the accuracy of CHAMP RO retrieved temperature profiles in the Antarctic region by using radiosonde data. Different collocation criteria have been applied. The overall results show a good agreement between the two data sets. Utilizing seven completed years of CHAMP temperature profiles, the study then investigates seasonal temperature trends at 100 hPa and 500 hPa pressure levels in the Antarctic region. Detailed temperature variations in both spatial and temporal domains are revealed and their implications for climate change are discussed.

scholarly journals On the Role of the Atmospheric Energy Transport in 2 × CO2–Induced Polar Amplification in CESM1

2019 ◽  
Vol 32 (13) ◽  
pp. 3941-3956 ◽  
Author(s):  
Rune G. Graversen ◽  
Peter L. Langen
Keyword(s):  
Global Warming ◽  
Southern Hemisphere ◽  
Energy Transport ◽  
The Arctic ◽  
Polar Regions ◽  
Antarctic Region ◽  
Atmospheric Energy ◽  
Atmospheric Energy Transport ◽  
The Antarctic ◽  
Co2 Forcing

AbstractA doubling of the atmospheric CO2 content leads to global warming that is amplified in the polar regions. The CO2 forcing also leads to a change of the atmospheric energy transport. This transport change affects the local warming induced by the CO2 forcing. Using the Community Earth System Model (CESM), the direct response to the transport change is investigated. Divergences of the transport change associated with a CO2 doubling are implemented as a forcing in the 1 × CO2 preindustrial control climate. This forcing is zero in the global mean. In response to a CO2 increase in CESM, the northward atmospheric energy transport decreases at the Arctic boundary. However, the transport change still leads to a warming of the Arctic. This is due to a shift between dry static and latent transport components, so that although the dry static transport decreases, the latent transport increases at the Arctic boundary, which is consistent with other model studies. Because of a greenhouse effect associated with the latent transport, the cooling caused by a change of the dry static component is more than compensated for by the warming induced by the change of the latent transport. Similar results are found for the Antarctic region, but the transport change is larger in the Southern Hemisphere than in its northern counterpart. As a consequence, the Antarctic region warms to the extent that this warming leads to global warming that is likely enhanced by the surface albedo feedback associated with considerable ice retreat in the Southern Hemisphere.

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