scholarly journals CO at 40–80 km above Kiruna observed by the ground-based microwave radiometer KIMRA and simulated by the whole atmosphere community climate model

2012 ◽  
Vol 12 (1) ◽  
pp. 559-587 ◽  
Author(s):  
C. G. Hoffmann ◽  
D. E. Kinnison ◽  
R. R. Garcia ◽  
M. Palm ◽  
J. Notholt ◽  
...  
Keyword(s):  
Time Series ◽  
Gravity Wave ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Microwave Radiometer ◽  
The Arctic ◽  
Mutual Correlation ◽  
Community Climate Model ◽  
Middle Atmosphere Dynamics ◽  
Community Climate

Abstract. This study compares CO in the Arctic stratosphere and mesosphere measured by ground-based microwave radiometry with simulations made with the Whole Atmosphere Community Climate Model driven with specified dynamical fields (SD-WACCM4) for the Arctic winters 2008/2009 and 2009/2010. CO is a tracer for polar winter middle atmosphere dynamics, hence the representation of polar dynamics in the model is examined indirectly. Measurements were taken with the Kiruna Microwave Radiometer (KIMRA). The instrument, which is located in Kiruna, Northern Sweden (67.8° N, 20.4° E), provides CO profiles between 40 and 80 km altitude. The present comparison, which is one of the first between SD-WACCM4 and measurements, is performed on the smallest space and time scales currently simulated by the model; the global model is evaluated daily at the particular model grid-point closest to Kiruna. As a guide to what can generally be expected from such a comparison, the same analysis is repeated for observations of CO from the Microwave Limb Sounder (MLS), a microwave radiometer onboard NASA's Aura satellite, which has global coverage. First, time-mean profiles of CO are compared, revealing that the profile shape of KIMRA deviates from SD-WACCM4 and MLS, especially in the upper mesosphere. SD-WACCM4 and MLS are mostly consistent throughout the range of altitude considered; however, SD-WACCM4 shows slightly lower values above 60 km and this discrepancy increases with altitude. Second, the time evolution is compared for the complete time series, as well as for the slowly and rapidly evolving parts alone. Overall, the agreement among the datasets is very good and the model is almost as consistent with the measurements as the measurements are with each other. Mutual correlation coefficients of the slowly varying part of the CO time series are ≥0.9 over a wide altitude range. This demonstrates that the polar winter middle atmosphere dynamics is very well represented in SD-WACCM4 and that the relaxation to analyzed meteorological fields below 50 km constrains the behavior of the simulation sufficiently, even at higher altitudes, such that the simulation above 50 km is close to the measurements. However, above 50 km, the model-measurement correlation for the rapidly varying part of the CO time series is lower (0.3) than the measurement-measurement correlation (0.6). This is attributed to the fact that the gravity wave parametrization in WACCM is based on a generic gravity wave spectrum and cannot be expected to capture the instantaneous behavior of the actual gravity wave field present in the atmosphere.

scholarly journals CO at 40–80 km above Kiruna observed by the ground-based microwave radiometer KIMRA and simulated by the Whole Atmosphere Community Climate Model

2012 ◽  
Vol 12 (7) ◽  
pp. 3261-3271 ◽  
Author(s):  
C. G. Hoffmann ◽  
D. E. Kinnison ◽  
R. R. Garcia ◽  
M. Palm ◽  
J. Notholt ◽  
...  
Keyword(s):  
Time Series ◽  
Gravity Wave ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Microwave Radiometer ◽  
The Arctic ◽  
Mutual Correlation ◽  
Community Climate Model ◽  
Middle Atmosphere Dynamics ◽  
Community Climate

Abstract. This study compares CO in the Arctic stratosphere and mesosphere measured by ground-based microwave radiometry with simulations made with the Whole Atmosphere Community Climate Model driven with specified dynamical fields (SD-WACCM4) for the Arctic winters 2008/2009 and 2009/2010. CO is a tracer for polar winter middle atmosphere dynamics, hence the representation of polar dynamics in the model is examined indirectly. Measurements were taken with the KIruna Microwave RAdiometer (KIMRA). The instrument, which is located in Kiruna, Northern Sweden (67.8° N, 20.4° E), provides CO profiles between 40 and 80 km altitude. The present comparison, which is one of the first between SD-WACCM4 and measurements, is performed on the smallest space and time scales currently simulated by the model; the global model is evaluated daily at the particular model grid-point closest to Kiruna. As a guide to what can generally be expected from such a comparison, the same analysis is repeated for observations of CO from the Microwave Limb Sounder (MLS), a microwave radiometer onboard NASA's Aura satellite, which has global coverage. First, time-mean profiles of CO are compared, revealing that the profile shape of KIMRA deviates from SD-WACCM4 and MLS, especially in the upper mesosphere. SD-WACCM4 and MLS are mostly consistent throughout the range of altitude considered; however, SD-WACCM4 shows slightly lower values in the upper mesosphere. Second, the time evolution is compared for the complete time series, as well as for the slowly and rapidly evolving parts alone. Overall, the agreement among the datasets is very good and the model is almost as consistent with the measurements as the measurements are with each other. Mutual correlation coefficients of the slowly varying part of the CO time series are ≥0.9 over a wide altitude range. This demonstrates that the polar winter middle atmosphere dynamics is very well represented in SD-WACCM4 and that the relaxation to analyzed meteorological fields below 50 km constrains the behavior of the simulation sufficiently, even at higher altitudes, such that the simulation above 50 km is close to the measurements. However, above 50 km, the model-measurement correlation for the rapidly varying part of the CO time series is lower (0.3) than the measurement-measurement correlation (0.6). This is attributed to the fact that the gravity wave parametrization in WACCM is based on a generic gravity wave spectrum and cannot be expected to capture the instantaneous behavior of the actual gravity wave field present in the atmosphere.

scholarly journals The Response of the Southern Hemisphere Middle Atmosphere to the Madden–Julian Oscillation during Austral Winter Using the Specified-Dynamics Whole Atmosphere Community Climate Model

2017 ◽  
Vol 30 (20) ◽  
pp. 8317-8333 ◽  
Author(s):  
Chengyun Yang ◽  
Tao Li ◽  
Anne K. Smith ◽  
Xiankang Dou
Keyword(s):  
Southern Hemisphere ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Phase 1 ◽  
High Latitudes ◽  
Madden Julian Oscillation ◽  
Community Climate Model ◽  
Dominant Component ◽  
Wave Trains ◽  
Community Climate

Abstract Using the specified-dynamics (SD) Whole Atmosphere Community Climate Model (SD-WACCM), the effects of the Madden–Julian oscillation (MJO) on the midwinter stratosphere and mesosphere in the Southern Hemisphere (SH) are investigated. The most significant responses of the SH polar cap temperature to the MJO are found about 30 days after MJO phase 1 (P1) and about 10 days after MJO phase 5 (P5) in both the ERA-Interim data and the SD-WACCM simulation. The 200- and 500-hPa geopotential height anomalies in the SH reveal that wave trains emanate from the Indian and Pacific Oceans when the MJO convection is enhanced in the eastern Indian Ocean and the western Pacific. As a result, the upward propagation and dissipation of planetary waves (PWs) in the middle and high latitudes of the SH stratosphere is significantly enhanced, the Brewer–Dobson (BD) circulation in the SH stratosphere strengthens, and temperatures in the SH polar stratosphere increase. Wavenumber 1 in the stratosphere is the dominant component of the PW perturbation induced by the MJO convection. In the SH mesosphere, the MJO leads to enhancement of the dissipation and breaking of gravity waves (GWs) propagating as a result of wind-filtering change in the SH extratropics and causes anomalous downwelling in the middle and high latitudes of the mesosphere. The circulation thus changes significantly, resulting in anomalous cooling in the mesosphere in response to MJO P1 and P5 at lags of 10 and 30 days, respectively.

scholarly journals Large-scale gravity wave perturbations in the mesopause region above Northern Hemisphere midlatitudes during autumnal equinox: a joint study by the USU Na lidar and Whole Atmosphere Community Climate Model

2017 ◽  
Vol 35 (2) ◽  
pp. 181-188 ◽  
Author(s):  
Xuguang Cai ◽  
Tao Yuan ◽  
Han-Li Liu
Keyword(s):  
Gravity Wave ◽  
Large Scale ◽  
Climate Model ◽  
Temperature Measurements ◽  
State University ◽  
Mesopause Region ◽  
Community Climate Model ◽  
Lidar Measurements ◽  
Autumnal Equinox ◽  
Community Climate

Abstract. To investigate gravity wave (GW) perturbations in the midlatitude mesopause region during boreal equinox, 433 h of continuous Na lidar full diurnal cycle temperature measurements in September between 2011 and 2015 are utilized to derive the monthly profiles of GW-induced temperature variance, T′2, and the potential energy density (PED). Operating at Utah State University (42° N, 112° W), these lidar measurements reveal severe GW dissipation near 90 km, where both parameters drop to their minima (∼ 20 K2 and ∼ 50 m2 s−2, respectively). The study also shows that GWs with periods of 3–5 h dominate the midlatitude mesopause region during the summer–winter transition. To derive the precise temperature perturbations a new tide removal algorithm suitable for all ground-based observations is developed to de-trend the lidar temperature measurements and to isolate GW-induced perturbations. It removes the tidal perturbations completely and provides the most accurate GW perturbations for the ground-based observations. This algorithm is validated by comparing the true GW perturbations in the latest mesoscale-resolving Whole Atmosphere Community Climate Model (WACCM) with those derived from the WACCM local outputs by applying this newly developed tidal removal algorithm.

scholarly journals Transport of mesospheric H<sub>2</sub>O during and after the stratospheric sudden warming of January 2010: observation and simulation

2011 ◽  
Vol 11 (12) ◽  
pp. 32811-32846
Author(s):  
C. Straub ◽  
B. Tschanz ◽  
K. Hocke ◽  
N. Kämpfer ◽  
A. K. Smith
Keyword(s):  
Water Vapor ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Microwave Radiometer ◽  
The Arctic ◽  
Strong Increase ◽  
Time Interval ◽  
Backward Trajectory ◽  
Stratospheric Sudden Warming ◽  
Vapor Distribution

Abstract. The transportable ground based microwave radiometer MIAWARA-C monitored the upper stratospheric and lower mesospheric (USLM) water vapor distribution over Sodankylä, Finland (67.4° N, 26.6° N) from January to June 2010. At the end of January, approximately 2 weeks after MIAWARA-C's start of operation in Finland, a stratospheric sudden warming (SSW) disturbed the circulation of the middle atmosphere. Shortly after the onset of the SSW water vapor in the USLM rapidly increased from approximately 5.5 to 7 ppmv in the end of January. Backward trajectory calculations show that this strong increase is due to the break down of the polar vortex and meridional advection of subtropical air to the arctic USLM region. In addition, mesospheric upwelling in the course of the SSW led to an increase in observed water vapor between 0.1 and 0.03 hPa. After the SSW MIAWARA-C observed a decrease in mesospheric water vapor volume mixing ratio (VMR) due to the subsidence of H2O poor air masses in the polar region. Backward trajectory analysis and the zonal mean water vapor distribution from the Microwave Limb Sounder on the Aura satellite (Aura/MLS) indicate the occurrence of two regimes of circulation from 50° N to the north pole: 1) regime of enhanced meridional mixing throughout February and 2) regime of an eastward circulation in the USLM region reestablished between early March and equinox. The polar descent rate determined from MIAWARA-C's 5.2 ppmv isopleth is 350 m d−1 in the pressure range 0.6 to 0.06 hPa between mid February and early March. For the same time interval the descent rate was determined using trajectories calculated from the Transformed Eulerian Mean (TEM) wind fields simulated by means of the Whole Atmosphere Community Climate Model (WACCM). The values found using these different methods are in good agreement.

Modification of the Gravity Wave Parameterization in the Whole Atmosphere Community Climate Model: Motivation and Results

2017 ◽  
Vol 74 (1) ◽  
pp. 275-291 ◽  
Author(s):  
Rolando R. Garcia ◽  
Anne K. Smith ◽  
Douglas E. Kinnison ◽  
Álvaro de la Cámara ◽  
Damian J. Murphy
Keyword(s):  
Gravity Wave ◽  
Southern Hemisphere ◽  
Gravity Waves ◽  
Climate Model ◽  
Lower Thermosphere ◽  
Careful Examination ◽  
Control Analysis ◽  
Community Climate Model ◽  
The Impact ◽  
Community Climate

Abstract The current standard version of the Whole Atmosphere Community Climate Model (WACCM) simulates Southern Hemisphere winter and spring temperatures that are too cold compared with observations. This “cold-pole bias” leads to unrealistically low ozone column amounts in Antarctic spring. Here, the cold-pole problem is addressed by introducing additional mechanical forcing of the circulation via parameterized gravity waves. Insofar as observational guidance is ambiguous regarding the gravity waves that might be important in the Southern Hemisphere stratosphere, the impact of increasing the forcing by orographic gravity waves was investigated. This reduces the strength of the Antarctic polar vortex in WACCM, bringing it into closer agreement with observations, and accelerates the Brewer–Dobson circulation in the polar stratosphere, which warms the polar cap and improves substantially the simulation of Antarctic temperature. These improvements are achieved without degrading the performance of the model in the Northern Hemisphere stratosphere or in the mesosphere and lower thermosphere of either hemisphere. It is shown, finally, that other approaches that enhance gravity wave forcing can also reduce the cold-pole bias such that careful examination of observational evidence and model performance will be required to establish which gravity wave sources are dominant in the real atmosphere. This is especially important because a “downward control” analysis of these results suggests that the improvement of the cold-pole bias itself is not very sensitive to the details of how gravity wave drag is altered.

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