scholarly journals Inclusion of mountain wave-induced cooling for the formation of PSCs over the Antarctic Peninsula in a chemistry–climate model

2014 ◽  
Vol 14 (12) ◽  
pp. 18277-18314 ◽  
Author(s):  
A. Orr ◽  
J. S. Hosking ◽  
L. Hoffmann ◽  
J. Keeble ◽  
S. M. Dean ◽  
...  

Abstract. An important source of polar stratospheric clouds (PSCs), which play a crucial role in controlling polar stratospheric ozone depletion, is from the temperature fluctuations induced by mountain waves. However, this formation mechanism is usually missing in chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate the representation of stratospheric mountain wave-induced temperature fluctuations by the UK Met Office Unified Model (UM) at high and low spatial resolution against Atmospheric Infrared Sounder satellite observations for three case studies over the Antarctic Peninsula. At a high horizontal resolution (4 km) the mesoscale configuration of the UM correctly simulates the magnitude, timing, and location of the measured temperature fluctuations. By comparison, at a low horizontal resolution (2.5° × 3.75°) the climate configuration fails to resolve such disturbances. However, it is demonstrated that the temperature fluctuations computed by a mountain wave parameterisation scheme inserted into the climate configuration (which computes the temperature fluctuations due to unresolved mountain waves) are in excellent agreement with the mesoscale configuration responses. The parameterisation was subsequently used to compute the local mountain wave-induced cooling phases in the chemistry–climate configuration of the UM. This increased stratospheric cooling was passed to the PSC scheme of the chemistry–climate model, and caused a 30–50% increase in PSC surface area density over the Antarctic Peninsula compared to a 30 year control simulation.

2015 ◽  
Vol 15 (2) ◽  
pp. 1071-1086 ◽  
Author(s):  
A. Orr ◽  
J. S. Hosking ◽  
L. Hoffmann ◽  
J. Keeble ◽  
S. M. Dean ◽  
...  

Abstract. An important source of polar stratospheric clouds (PSCs), which play a crucial role in controlling polar stratospheric ozone depletion, is from the temperature fluctuations induced by mountain waves. However, this formation mechanism is usually missing in chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate the representation of stratospheric mountain-wave-induced temperature fluctuations by the UK Met Office Unified Model (UM) at climate scale and mesoscale against Atmospheric Infrared Sounder satellite observations for three case studies over the Antarctic Peninsula. At a high horizontal resolution (4 km) the regional mesoscale configuration of the UM correctly simulates the magnitude, timing, and location of the measured temperature fluctuations. By comparison, at a low horizontal resolution (2.5° × 3.75°) the global climate configuration fails to resolve such disturbances. However, it is demonstrated that the temperature fluctuations computed by a mountain wave parameterisation scheme inserted into the climate configuration (which computes the temperature fluctuations due to unresolved mountain waves) are in relatively good agreement with the mesoscale configuration responses for two of the three case studies. The parameterisation was used to include the simulation of mountain-wave-induced PSCs in the global chemistry–climate configuration of the UM. A subsequent sensitivity study demonstrated that regional PSCs increased by up to 50% during July over the Antarctic Peninsula following the inclusion of the local mountain-wave-induced cooling phase.


2020 ◽  
Author(s):  
Andrew Orr ◽  
Scott Hosking ◽  
Aymeric Delon ◽  
Tracy Moffat-Griffin ◽  
Lars Hoffman ◽  
...  

<p>An important source of polar stratospheric clouds (PSCs), which play a crucial role in controlling polar stratospheric ozone depletion, is from the temperature fluctuations induced by mountain waves, enabling stratospheric temperatures to fall below the threshold value for PSC formation in the cold phases of these waves even if the synoptic-scale temperatures are too high. However, this formation mechanism is usually missing in chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate the representation of parameterised stratospheric mountain-wave-induced temperature fluctuations over the Antarctic Peninsula from a 30-year run of the global chemistry-climate configuration of the UM-UKCA model against climatologies of Atmospheric Infrared Sounder (AIRS) radiance measurements and high-resolution radiosonde temperature soundings from Rothera. The results demonstrate that the local mountain wave-induced cooling phases computed by the scheme are in relatively good agreement with both sets of observations. For example, the scheme is able to capture the observed probability distribution of the temperature fluctuations, particularly the cold tails of the distribution that are critical for exceeding the temperature threshold for PSC formation. Further analysis shows that the increased stratospheric cooling induced by the scheme results in a large increase in total PSC ‘pseudo-volume’ of the area over the Antarctic Peninsula where the model temperature exceeds the temperature threshold of formation of PSCs.</p>


2020 ◽  
Vol 20 (21) ◽  
pp. 12483-12497
Author(s):  
Andrew Orr ◽  
J. Scott Hosking ◽  
Aymeric Delon ◽  
Lars Hoffmann ◽  
Reinhold Spang ◽  
...  

Abstract. An important source of polar stratospheric clouds (PSCs), which play a crucial role in controlling polar stratospheric ozone depletion, is the temperature fluctuations induced by mountain waves. These enable stratospheric temperatures to fall below the threshold value for PSC formation in regions of negative temperature perturbations or cooling phases induced by the waves even if the synoptic-scale temperatures are too high. However, this formation mechanism is usually missing in global chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate in detail the episodic and localised wintertime stratospheric cooling events produced over the Antarctic Peninsula by a parameterisation of mountain-wave-induced temperature fluctuations inserted into a 30-year run of the global chemistry–climate configuration of the UM-UKCA (Unified Model – United Kingdom Chemistry and Aerosol) model. Comparison of the probability distribution of the parameterised cooling phases with those derived from climatologies of satellite-derived AIRS brightness temperature measurements and high-resolution radiosonde temperature soundings from Rothera Research Station on the Antarctic Peninsula shows that they broadly agree with the AIRS observations and agree well with the radiosonde observations, particularly in both cases for the “cold tails” of the distributions. It is further shown that adding the parameterised cooling phase to the resolved and synoptic-scale temperatures in the UM-UKCA model results in a considerable increase in the number of instances when minimum temperatures fall below the formation temperature for PSCs made from ice water during late austral autumn and early austral winter and early austral spring, and without the additional cooling phase the temperature rarely falls below the ice frost point temperature above the Antarctic Peninsula in the model. Similarly, it was found that the formation potential for PSCs made from ice water was many times larger if the additional cooling is included. For PSCs made from nitric acid trihydrate (NAT) particles it was only during October that the additional cooling is required for temperatures to fall below the NAT formation temperature threshold (despite more NAT PSCs occurring during other months). The additional cooling phases also resulted in an increase in the surface area density of NAT particles throughout the winter and early spring, which is important for chlorine activation. The parameterisation scheme was finally shown to make substantial differences to the distribution of total column ozone during October, resulting from a shift in the position of the polar vortex.


2021 ◽  
Vol 21 (12) ◽  
pp. 9515-9543
Author(s):  
Michael Weimer ◽  
Jennifer Buchmüller ◽  
Lars Hoffmann ◽  
Ole Kirner ◽  
Beiping Luo ◽  
...  

Abstract. Polar stratospheric clouds (PSCs) are a driver for ozone depletion in the lower polar stratosphere. They provide surface for heterogeneous reactions activating chlorine and bromine reservoir species during the polar night. The large-scale effects of PSCs are represented by means of parameterisations in current global chemistry–climate models, but one process is still a challenge: the representation of PSCs formed locally in conjunction with unresolved mountain waves. In this study, we investigate direct simulations of PSCs formed by mountain waves with the ICOsahedral Nonhydrostatic modelling framework (ICON) with its extension for Aerosols and Reactive Trace gases (ART) including local grid refinements (nesting) with two-way interaction. Here, the nesting is set up around the Antarctic Peninsula, which is a well-known hot spot for the generation of mountain waves in the Southern Hemisphere. We compare our model results with satellite measurements of PSCs from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and gravity wave observations of the Atmospheric Infrared Sounder (AIRS). For a mountain wave event from 19 to 29 July 2008 we find similar structures of PSCs as well as a fairly realistic development of the mountain wave between the satellite data and the ICON-ART simulations in the Antarctic Peninsula nest. We compare a global simulation without nesting with the nested configuration to show the benefits of adding the nesting. Although the mountain waves cannot be resolved explicitly at the global resolution used (about 160 km), their effect from the nested regions (about 80 and 40 km) on the global domain is represented. Thus, we show in this study that the ICON-ART model has the potential to bridge the gap between directly resolved mountain-wave-induced PSCs and their representation and effect on chemistry at coarse global resolutions.


2020 ◽  
Author(s):  
Michael Weimer ◽  
Jennifer Buchmüller ◽  
Lars Hoffmann ◽  
Ole Kirner ◽  
Beiping Luo ◽  
...  

Abstract. Polar stratospheric clouds (PSCs) are a driver for ozone depletion in the lower polar stratosphere. They provide surfaces for heterogeneous reactions activating chlorine and bromine reservoir species during the polar night. PSCs are represented in current global chemistry-climate models, but one process is still a challenge: the representation of PSCs formed locally in conjunction with unresolved mountain waves. In this study, we present simulations with the ICOsahedral Nonhydrostatic modelling framework (ICON) with its extension for Aerosols and Reactive Trace gases (ART) that include local grid refinements (nesting) with two-way interaction. Here, the nesting is set up around the Antarctic Peninsula which is a well-known hot spot for the generation of mountain waves in the southern hemisphere. We compare our model results with satellite measurements from the Cloud-Aerosol LIdar with Orthogonal Polarisation (CALIOP) and the Atmospheric InfraRed Sounder (AIRS). We study a mountain wave event that took place from 19 to 29 July 2008 and find similar structures of PSCs as well as a fairly realistic development of the mountain wave in the Antarctic Peninsula nest. We compare a global simulation without nesting with the nested configuration to show the benefit. Although the mountain waves cannot be resolved adequately in the used global resolution (about 160 km), their effect from the nested regions (about 80 and 40 km) on the global domain is represented. Thus, we show in this study that by using the two-way nesting technique the gap between directly resolved mountain-wave induced PSCs and their representation and effect on chemistry in coarse global resolutions can be bridged by the ICON-ART model.


2020 ◽  
Author(s):  
Michael Weimer ◽  
Jennifer Schröter ◽  
Lars Hoffmann ◽  
Oliver Kirner ◽  
Roland Ruhnke ◽  
...  

<p>Polar Stratospheric Clouds (PSCs) play a key role in explaining ozone depletion on large<br>scales as well as on regional scales. Mountain waves can be formed in the lee of a mountain<br>in a stably stratified atmosphere. They can propagate upwards into the stratosphere and<br>induce temperature changes in the order of 10 to 15 K. Thus, large PSCs localised around the<br>mountain ridge can be formed, leading to increased chlorine activation and subsequently to<br>a larger ozone depletion. It was estimated that 30 % of the southern hemispheric PSCs can<br>be explained by mountain waves. However, for the direct simulation of mountain-wave<br>induced PSCs, the mountains have to be represented adequately in global chemistry climate<br>models which was a challenge in the past due to too low horizontal resolution.</p><p><br>The ICOsahedral Nonhydrostatic (ICON) modelling framework with its extension for Aerosols<br>and Reactive Trace gases (ART) includes a PSC scheme coupled to the atmospheric chemistry<br>in the model. The PSC scheme calculates the formation of all three PSC types independently<br>resulting in the calculation of the heterogeneous reaction rates of chlorine and bromine<br>species on the surface of PSCs. ICON-ART provides the possibility of local grid refinement<br>with two-way interaction. With this, the grid around a mountain can be refined so that<br>mountain waves can be directly simulated in this region with a feedback to the coarser<br>global resolution.</p><p><br>In this study, we show the formation of mountain-wave induced PSCs with ICON-ART for the<br>example of a mountain wave event in July 2008 around the Antarctic Peninsula. It is<br>evaluated with satellite measurements of AIRS and CALIOP and its impact on chlorine and<br>bromine activation as well as on the ozone depletion in the southern hemisphere are<br>analysed. We demonstrate that the effect of mountain-wave induced PSCs can be<br>represented in the coarser global grid by using local grid refinement with two-way<br>interaction. Thus, this study bridges the gap between directly simulated mountain-wave<br>induced PSCs and their representation in a global simulation.</p>


2020 ◽  
Author(s):  
Andrew Orr ◽  
J. Scott Hosking ◽  
Aymeric Delon ◽  
Lars Hoffmann ◽  
Reinhold Spang ◽  
...  

Abstract. An important source of polar stratospheric clouds (PSCs), which play a crucial role in controlling polar stratospheric ozone depletion, is from the temperature fluctuations induced by mountain waves. These enable stratospheric temperatures to fall below the threshold value for PSC formation in regions of negative temperature perturbations or cooling-phases induced by the waves even if the synoptic-scale temperatures are too high. However, this formation mechanism is usually missing in global chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. Here, we investigate in detail the episodic and localised wintertime stratospheric cooling events produced over the Antarctic Peninsula by a parameterisation of mountain-wave-induced temperature fluctuations inserted into a 30-year run of the global chemistry-climate configuration of the UM-UKCA (Unified Model – United Kingdom Chemistry and Aerosol) model. Comparison of the probability distribution of the parameterised cooling-phases with those derived from climatologies of satellite-derived AIRS brightness temperature measurements and high-resolution radiosonde temperature soundings from Rothera Research Station on the Antarctic Peninsula shows that they broadly agree with the AIRS-observations and agree well with the radiosonde-observations, particularly in both cases for the “cold tails” of the distributions. It is further shown that adding the parameterised cooling-phase to the resolved/synoptic-scale temperatures in the UM-UKCA model results in a considerable increase in the number of instances when minimum temperatures fall below the formation temperature for PSCs made from ice water during late austral autumn/early austral winter and early austral spring, and without the additional cooling-phase the ice frost point is rarely exceeded above the Antarctic Peninsula in the model. Similarly, it was found that the formation potential for PSCs made from ice water was many times larger if the additional cooling is included. For PSCs made from NAT particles it was only during October that the additional cooling is required for the NAT temperature threshold to be exceeded (despite more NAT PSCs occurring during other months). The additional cooling-phases also resulted in an increase in the surface area density of NAT particles throughout the winter and early spring, which is important for chlorine activation. The parameterisation scheme was finally shown to make substantial differences to the distribution of total column ozone during October, resulting from a shift in the position of the polar vortex.


2016 ◽  
Vol 10 (1) ◽  
pp. 271-285 ◽  
Author(s):  
J. M. van Wessem ◽  
S. R. M. Ligtenberg ◽  
C. H. Reijmer ◽  
W. J. van de Berg ◽  
M. R. van den Broeke ◽  
...  

Abstract. This study presents a high-resolution (∼  5.5 km) estimate of surface mass balance (SMB) over the period 1979–2014 for the Antarctic Peninsula (AP), generated by the regional atmospheric climate model RACMO2.3 and a firn densification model (FDM). RACMO2.3 is used to force the FDM, which calculates processes in the snowpack, such as meltwater percolation, refreezing and runoff. We evaluate model output with 132 in situ SMB observations and discharge rates from six glacier drainage basins, and find that the model realistically simulates the strong spatial variability in precipitation, but that significant biases remain as a result of the highly complex topography of the AP. It is also clear that the observations significantly underrepresent the high-accumulation regimes, complicating a full model evaluation. The SMB map reveals large accumulation gradients, with precipitation values above 3000 mm we yr−1 in the western AP (WAP) and below 500 mm we yr−1 in the eastern AP (EAP), not resolved by coarser data sets such as ERA-Interim. The average AP ice-sheet-integrated SMB, including ice shelves (an area of 4.1  ×  105 km2), is estimated at 351 Gt yr−1 with an interannual variability of 58 Gt yr−1, which is dominated by precipitation (PR) (365 ± 57 Gt yr−1). The WAP (2.4  ×  105 km2) SMB (276 ± 47 Gt yr−1), where PR is large (276 ± 47 Gt yr−1), dominates over the EAP (1.7  ×  105 km2) SMB (75 ± 11 Gt yr−1) and PR (84 ± 11 Gt yr−1). Total sublimation is 11 ± 2 Gt yr−1 and meltwater runoff into the ocean is 4 ± 4 Gt yr−1. There are no significant trends in any of the modelled AP SMB components, except for snowmelt that shows a significant decrease over the last 36 years (−0.36 Gt yr−2).


2005 ◽  
Vol 5 (3) ◽  
pp. 739-753 ◽  
Author(s):  
S. H. Svendsen ◽  
N. Larsen ◽  
B. Knudsen ◽  
S. D. Eckermann ◽  
E. V. Browell

Abstract. A scheme for introducing mountain wave-induced temperature pertubations in a microphysical PSC model has been developed. A data set of temperature fluctuations attributable to mountain waves as computed by the Mountain Wave Forecast Model (MWFM-2) has been used for the study. The PSC model has variable microphysics, enabling different nucleation mechanisms for nitric acid trihydrate, NAT, to be employed. In particular, the difference between the formation of NAT and ice particles in a scenario where NAT formation is not dependent on preexisting ice particles, allowing NAT to form at temperatures above the ice frost point, Tice, and a scenario, where NAT nucleation is dependent on preexisting ice particles, is examined. The performance of the microphysical model in the different microphysical scenarios and a number of temperature scenarios with and without the influence of mountain waves is tested through comparisons with lidar measurements of PSCs made from the NASA DC-8 on 23 and 25 January during the SOLVE/THESEO 2000 campaign in the 1999-2000 winter and the effect of mountain waves on local PSC production is evaluated in the different microphysical scenarios. Mountain waves are seen to have a pronounced effect on the amount of ice particles formed in the simulations. Quantitative comparisons of the amount of solids seen in the observations and the amount of solids produced in the simulations show the best correspondence when NAT formation is allowed to take place at temperatures above Tice. Mountain wave-induced temperature fluctuations are introduced in vortex-covering model runs, extending the full 1999-2000 winter season, and the effect of mountain waves on large-scale PSC production is estimated in the different microphysical scenarios. It is seen that regardless of the choice of microphysics ice particles only form as a consequence of mountain waves whereas NAT particles form readily as a consequence of the synoptic conditions alone if NAT nucleation above Tice is included in the simulations. Regardless of the choice of microphysics, the inclusion of mountain waves increases the amount of NAT particles by as much as 10%. For a given temperature scenario the choice of NAT nucleation mechanism may alter the amount of NAT substantially; three-fold increases are easily found when switching from the scenario which requires pre-existing ice particles in order for NAT to form to the scenario where NAT forms independently of ice.


2004 ◽  
Vol 4 (4) ◽  
pp. 4581-4609 ◽  
Author(s):  
S. H. Svendsen ◽  
N. Larsen ◽  
B. Knudsen ◽  
S. D. Eckermann ◽  
E. V. Browell

Abstract. A scheme for introducing mountain wave-induced temperature pertubations in a microphysical PSC model has been developed. A data set of temperature fluctuations attributable to mountain waves as computed by the Mountain Wave Forecast Model (MWFM-2) has been used for the study. The PSC model has variable microphysics, enabling different nucleation mechanisms for nitric acid trihydrate, NAT, to be employed. In particular, the difference between the formation of NAT and ice particles in a scenario where NAT formation is not dependent on preexisting ice particles, allowing NAT to form at temperatures above the ice frost point, Tice, and a scenario, where NAT nucleation is dependent on preexisting ice particles, is examined. The performance of the microphysical model in the different microphysical scenarios and a number of temperature scenarios with and without the influence of mountain waves is tested through comparisons with lidar measurements of PSCs made from the NASA DC-8 on 23 and 25 January during the SOLVE/THESEO 2000 campaign in the 1999–2000 winter and the effect of mountain waves on local PSC production is evaluated in the different microphysical scenarios. Mountain wave-induced temperature fluctuations are introduced in vortex-covering model runs, extending the full 1999–2000 winter season, and the effect of mountain waves on large-scale PSC production is estimated in the different microphysical scenarios.


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