The effect of atmospheric nudging on the stratospheric residual circulation in chemistry–climate models

Abstract. We perform the first multi-model intercomparison of the impact of nudged meteorology on the stratospheric residual circulation using hindcast simulations from the Chemistry–Climate Model Initiative (CCMI). We examine simulations over the period 1980–2009 from seven models in which the meteorological fields are nudged towards a reanalysis dataset and compare these with their equivalent free-running simulations and the reanalyses themselves. We show that for the current implementations, nudging meteorology does not constrain the mean strength of the stratospheric residual circulation and that the inter-model spread is similar, or even larger, than in the free-running simulations. The nudged models generally show slightly stronger upwelling in the tropical lower stratosphere compared to the free-running versions and exhibit marked differences compared to the directly estimated residual circulation from the reanalysis dataset they are nudged towards. Downward control calculations applied to the nudged simulations reveal substantial differences between the climatological lower-stratospheric tropical upward mass flux (TUMF) computed from the modelled wave forcing and that calculated directly from the residual circulation. This explicitly shows that nudging decouples the wave forcing and the residual circulation so that the divergence of the angular momentum flux due to the mean motion is not balanced by eddy motions, as would typically be expected in the time mean. Overall, nudging meteorological fields leads to increased inter-model spread for most of the measures of the mean climatological stratospheric residual circulation assessed in this study. In contrast, the nudged simulations show a high degree of consistency in the inter-annual variability in the TUMF in the lower stratosphere, which is primarily related to the contribution to variability from the resolved wave forcing. The more consistent inter-annual variability in TUMF in the nudged models also compares more closely with the variability found in the reanalyses, particularly in boreal winter. We apply a multiple linear regression (MLR) model to separate the drivers of inter-annual and long-term variations in the simulated TUMF; this explains up to ∼75 % of the variance in TUMF in the nudged simulations. The MLR model reveals a statistically significant positive trend in TUMF for most models over the period 1980–2009. The TUMF trend magnitude is generally larger in the nudged models compared to their free-running counterparts, but the intermodel range of trends doubles from around a factor of 2 to a factor of 4 due to nudging. Furthermore, the nudged models generally do not match the TUMF trends in the reanalysis they are nudged towards for trends over different periods in the interval 1980–2009. Hence, we conclude that nudging does not strongly constrain long-term trends simulated by the chemistry–climate model (CCM) in the residual circulation. Our findings show that while nudged simulations may, by construction, produce accurate temperatures and realistic representations of fast horizontal transport, this is not typically the case for the slower zonal mean vertical transport in the stratosphere. Consequently, caution is required when using nudged simulations to interpret the behaviour of stratospheric tracers that are affected by the residual circulation.

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The effect of atmospheric nudging on the stratospheric residual circulation in chemistry-climate models

10.5194/acp-2019-260 ◽

2019 ◽

Author(s):

Andreas Chrysanthou ◽

Amanda C. Maycock ◽

Martyn P. Chipperfield ◽

Sandip Dhomse ◽

Hella Garny ◽

...

Keyword(s):

Model Comparison ◽

Lower Stratosphere ◽

Climate Model ◽

Positive Trend ◽

Residual Circulation ◽

Wave Forcing ◽

Free Running ◽

The Mean ◽

The Impact ◽

Mlr Model

Abstract. We perform the first multi-model comparison of the impact of nudged meteorology on the stratospheric residual circulation using hindcast simulations from the Chemistry Climate Model Initiative (CCMI). We examine simulations over the period 1980–2009 from 5 models in which the meteorological fields are nudged towards reanalysis data and compare with equivalent free-running simulations from 9 models. We show that nudging meteorology does not constrain the mean strength of the stratospheric residual circulation and that the inter-model spread is similar, or even larger, than in the free-running simulations. The nudged simulations also simulate stronger upwelling in the tropical lower stratosphere compared to the residual circulation estimated directly from the reanalyses they are nudged towards. Downward control calculations reveal substantial differences between the mean lower stratospheric tropical upward mass flux (TUMF) computed from the modeled wave forcing and that calculated directly from the residual circulation. Although the mean circulation is poorly constrained, the nudged simulations show a high degree of consistency in the interannual variability of the TUMF in the lower stratosphere, which is related to the contribution to variability from the resolved wave forcing. We apply a multiple linear regression (MLR) model to separate the drivers of interannual and long-term variations in the simulated TUMF. The MLR model explains up to ~ 75 % of the variance in TUMF in the nudged simulations and reveals a statistically significant positive trend for most models in TUMF over the period 1980–2009. Overall, nudging meteorological fields leads to increased inter-model spread for most of the measures of the mean climatological stratospheric residual circulation assessed in this study. Our findings show that while nudged simulations by construction produce accurate temperatures and realistic representations of fast horizontal transport, this is not necessarily the case for the slower zonal mean vertical transport. Consequently, caution is required when using nudged simulations to interpret long-lived stratospheric tracers that are controlled by the residual circulation.

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A Comprehensive Assessment of Tropical Stratospheric Upwelling in Specified Dynamics CESM1.2.2 (WACCM)

10.5194/gmd-2019-238 ◽

2019 ◽

Author(s):

Nicholas A. Davis ◽

Sean M. Davis ◽

Robert W. Portmann ◽

Eric Ray ◽

Karen H. Rosenlof ◽

...

Keyword(s):

Best Practices ◽

Climate Models ◽

Climate Model ◽

Meridional Circulation ◽

Trace Gas ◽

Mean Meridional Circulation ◽

Community Earth System Model ◽

Free Running ◽

The Mean ◽

Wave Momentum

Abstract. Specified dynamics (SD) schemes relax the circulation in climate models toward a reference meteorology to simulate historical variability. These simulations are widely used to isolate the dynamical contributions to variability and trends in trace gas species. However, it is not clear if trends in the stratospheric overturning circulation are properly reproduced by SD schemes. This study assesses numerous SD schemes and modeling choices in the Community Earth System Model (CESM) Whole Atmosphere Chemistry Climate Model (WACCM) to determine a set of best practices for reproducing interannual variability and trends in tropical stratospheric upwelling estimated by reanalyses. Nudging toward the reanalysis meteorology as is typically done in SD simulations expectedly changes the model’s mean upwelling compared to its free-running state, but does not accurately reproduce upwelling trends present in the underlying reanalysis. In contrast, nudging to anomalies from the climatological winds or from the zonal mean winds and temperatures preserves WACCM’s climatology and better reproduces trends in stratospheric upwelling. An SD scheme’s performance in simulating the acceleration of the shallow branch of the mean meridional circulation from 1980–2017 hinges on its ability to simulate the downward shift of subtropical lower stratospheric wave momentum forcing. Key to this is not nudging the zonal-mean temperature field. Gravity wave momentum forcing, which drives a substantial fraction of the upwelling in WACCM, cannot be constrained by nudging and presents an upper-limit on the performance of these schemes.

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A Method for Estimating the Evolution of Brewer-Dobson Circulation Upwelling

10.5194/egusphere-egu2020-8905 ◽

2020 ◽

Author(s):

Edward Charlesworth ◽

Felix Ploeger ◽

Mohamadu Diallo ◽

Thomas Birner ◽

Patrick Joeckel

Keyword(s):

Balance Equation ◽

Seasonal Cycle ◽

Inverse Method ◽

Lower Stratosphere ◽

Climate Model ◽

Vertical Mixing ◽

Model Data ◽

Absolute Value ◽

Multiple Datasets

<p>Both theory and climate model results suggest that the Brewer-Dobson circulation should strengthen in the stratosphere with increasing greenhouse gas concentrations. Directly measuring the circulation strength is not possible, so verification of this sensitivity has been limited to indirect inferences from observed tracer fields of long-lived species. These methods, however, are complex and accumulation of the data required for them is difficult. When limiting discussion to the tropical lower stratosphere, ozone concentrations have shown to be consistent with an accelerating circulation. These measurements are particularly useful because of the long timeseries available from multiple datasets, but they have only been used for indirect investigations of the circulation strength, up until now.</p><p>In this work, we invert the ozone balance equation to solve for upwelling. By limiting the investigation to 70 hPa in the southern tropics and estimating upwelling anomalies from the long-term mean (and not the absolute value of upwelling) most chemical terms and both horizontal and vertical mixing can be neglected, and calculation of the remaining terms is straight-forward. To verify the validity of the method, a calculation of upwelling is performed using climate model data, from which a comparison of actual upwelling and upwelling from the inverse method can be made. The seasonal cycle of upwelling anomalies is compared to upwelling anomalies from reanalyses and model results, and trends and variability are discussed.</p>

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Characterization of the long-term radiosonde temperature biases in the upper troposphere and lower stratosphere using COSMIC and Metop-A/GRAS data from 2006 to 2014

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-4493-2017 ◽

2017 ◽

Vol 17 (7) ◽

pp. 4493-4511 ◽

Cited By ~ 21

Author(s):

Shu-peng Ho ◽

Liang Peng ◽

Holger Vömel

Keyword(s):

Lower Stratosphere ◽

Temperature Measurements ◽

Climate Data ◽

Upper Troposphere ◽

Global Trend ◽

The Mean ◽

Temperature Climate

Abstract. Radiosonde observations (RAOBs) have provided the only long-term global in situ temperature measurements in the troposphere and lower stratosphere since 1958. In this study, we use consistently reprocessed Global Positioning System (GPS) radio occultation (RO) temperature data derived from the COSMIC and Metop-A/GRAS missions from 2006 to 2014 to characterize the inter-seasonal and interannual variability of temperature biases in the upper troposphere and lower stratosphere for different radiosonde sensor types. The results show that the temperature biases for different sensor types are mainly due to (i) uncorrected solar-zenith-angle-dependent errors and (ii) change of radiation correction. The mean radiosonde–RO global daytime temperature difference in the layer from 200 to 20 hPa for Vaisala RS92 is equal to 0.20 K. The corresponding difference is equal to −0.06 K for Sippican, 0.71 K for VIZ-B2, 0.66 K for Russian AVK-MRZ, and 0.18 K for Shanghai. The global daytime trend of differences for Vaisala RS92 and RO temperature at 50 hPa is equal to 0.07 K/5 yr. Although there still exist uncertainties for Vaisala RS92 temperature measurement over different geographical locations, the global trend of temperature differences between Vaisala RS92 and RO from June 2006 to April 2014 is within ±0.09 K/5 yr. Compared with Vaisala RS80, Vaisala RS90, and sondes from other manufacturers, the Vaisala RS92 seems to provide the most accurate RAOB temperature measurements, and these can potentially be used to construct long-term temperature climate data records (CDRs). Results from this study also demonstrate the feasibility of using RO data to correct RAOB temperature biases for different sensor types.

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Major oscillations in spontaneous home-cage activity with an infraradian periodicity in C57Bl/6 mice housed under constant conditions

10.1101/2020.09.09.290148 ◽

2020 ◽

Author(s):

K. Pernold ◽

E. Rullman ◽

B. Ulfhake

Keyword(s):

Spontaneous Activity ◽

Feeding Behaviour ◽

Home Cage ◽

Light Cycle ◽

Dark Light ◽

Cage Activity ◽

Free Running ◽

The Mean ◽

Home Cage Activity

AbstractUsing 14-20 months of cumulative 24/7 home-cage activity recorded with a non-intrusive technique and a data driven analytical approach, we here provide evidence for the existence of a circannual oscillation (1-2 SD of the mean, on average 65% higher during peak of highs than lows; P=7E-50) in spontaneous activity of male and female C57BL/6 mice held under constant barrier conditions (dark-light cycle 12/12 h (DL), temperature 21±1°C, humidity 40-60%). The periodicity of the season-like oscillation is in the range of 2-4 months (on average 97 days across cohorts of cages) and off-sets also responses to environmental stimuli but does not significantly alter the preference for activity during the dark hours of this nocturnal mouse strain (P=0.11 difference between highs and lows).The significance of this hitherto not recognized slow rhythmic alteration in spontaneous activity is further substantiated by its co-variation with the feeding behaviour of the mice. The absence of coordination within and between cohorts of cages or synchronization to the seasons of the year, suggests that the oscillation of in-cage activity and behavioural responses is generated by a free-running intrinsic oscillator devoid of synchronization with an out-of-cage environmental time-keeper. Since the variation over time has such a magnitude and correlate with the feeding behaviour it is likely that it will impact a range of long term experiments conducted on laboratory mice if left unrecognized.

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Introducing the Probabilistic Earth-System Model: Examining The Impact of Stochasticity in EC-Earth v3.2

10.5194/gmd-2018-337 ◽

2019 ◽

Author(s):

Kristian Strommen ◽

Hannah M. Christensen ◽

David MacLeod ◽

Stephan Juricke ◽

Tim N. Palmer

Keyword(s):

Climate Model ◽

Weather Forecasting ◽

Earth System Model ◽

System Model ◽

Earth System ◽

Beneficial Impact ◽

The Mean ◽

The Impact ◽

Mean State

Abstract. We introduce and study the impact of three stochastic schemes in the EC-Earth climate model, two atmospheric schemes and one stochastic land scheme. These form the basis for a probabilistic earth-system model in atmosphere-only mode. Stochastic parametrisations have become standard in several operational weather-forecasting models, in particular due to their beneficial impact on model spread. In recent years, stochastic schemes in the atmospheric component of a model have been shown to improve aspects important for the models long-term climate, such as ENSO, North Atlantic weather regimes and the Indian monsoon. Stochasticity in the land-component has been shown to improve variability of soil processes and improve the representation of heatwaves over Europe. However, the raw impact of such schemes on the model mean is less well studied, It is shown that the inclusion all three schemes notably change the model mean state. While many of the impacts are beneficial, some are too large in amplitude, leading to large changes in the model's energy budget. This implies that in order to keep the benefits of stochastic physics without shifting the mean state too far from observations, a full re-tuning of the model will typically be required.

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Understanding Recent Stratospheric Climate Change

Journal of Climate ◽

10.1175/2008jcli2482.1 ◽

2009 ◽

Vol 22 (8) ◽

pp. 1934-1943 ◽

Cited By ~ 59

Author(s):

David W. J. Thompson ◽

Susan Solomon

Keyword(s):

Climate Change ◽

Large Scale ◽

Lower Stratosphere ◽

Climate Model ◽

Longwave Radiation ◽

Volcanic Eruptions ◽

Stratospheric Temperature ◽

Ozone Trends ◽

Global Mean

Abstract The long-term, global-mean cooling of the lower stratosphere stems from two downward steps in temperature, both of which are coincident with the cessation of transient warming after the volcanic eruptions of El Chichón and Mount Pinatubo. Previous attribution studies reveal that the long-term cooling is linked to ozone trends, and modeling studies driven by a range of known forcings suggest that the steps reflect the superposition of the long-term cooling with transient variability in upwelling longwave radiation from the troposphere. However, the long-term cooling of the lower stratosphere is evident at all latitudes despite the fact that chemical ozone losses are thought to be greatest at middle and polar latitudes. Further, the ozone concentrations used in such studies are based on either 1) smooth mathematical functions fit to sparsely sampled observations that are unavailable during postvolcanic periods or 2) calculations by a coupled chemistry–climate model. Here the authors provide observational analyses that yield new insight into three key aspects of recent stratospheric climate change. First, evidence is provided that shows the unusual steplike behavior of global-mean stratospheric temperatures is dependent not only upon the trend but also on the temporal variability in global-mean ozone immediately following volcanic eruptions. Second, the authors argue that the warming/cooling pattern in global-mean temperatures following major volcanic eruptions is consistent with the competing radiative and chemical effects of volcanic eruptions on stratospheric temperature and ozone. Third, it is revealed that the contrasting latitudinal structures of recent stratospheric temperature and ozone trends are consistent with large-scale increases in the stratospheric overturning Brewer–Dobson circulation.

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Characterization of the Long-term Radiosonde Temperature Biases in the Lower Stratosphere using COSMIC and Metop-A/GRAS Data from 2006 to 2014

10.5194/acp-2016-801 ◽

2016 ◽

Author(s):

Shu-Peng Ho ◽

Liang Peng ◽

Holger Vömel

Keyword(s):

Global Positioning System ◽

Lower Stratosphere ◽

Temperature Measurements ◽

Global Trend ◽

Global Positioning ◽

The Mean ◽

Geographical Locations

Abstract. Radiosonde observations (RAOBs) have provided the only long-term global in situ temperature measurements in the troposphere and lower stratosphere since 1958. In this study, we use consistently reprocessed Global Positioning System (GPS) radio occultation (RO) temperature data derived from COSMIC and Metop-A/GRAS missions from 2006 to 2014 to characterize the inter-seasonal and inter-annual variability of temperature biases in the lower stratosphere for different sensor types. The results show that the RAOB temperature biases for different RAOB sensor types are mainly owing to i) uncorrected solar zenith angle dependent errors, and ii) change of radiation correction. The mean daytime temperature difference (ΔT) for Vaisala RS92 is equal to 0.18 K in Australia, 0.20 K in Germany, 0.10 K in Canada, 0.13 K in England, and 0.33 K in Brazil. The mean daytime ΔT is equal to −0.06 K for Sippican, 0.71 K for VIZ-B2, 0.66 K for AVK-MRZ, and 0.18 K for Shanghai. The daytime trend of anomalies for Vaisala RS92 and RO temperature at 50 hPa is equal to 0.00 K/5 yrs over United States, −0.02 K/5 yrs over Germany, 0.17 K/5 yrs over Australia, 0.23 K/5 yrs over Canada, 0.26 K/5 yrs over England, and 0.12 K/5 yrs over Brazil, respectively. Although there still exist uncertainties for Vaisala RS92 temperature measurements over different geographical locations, the global trend of temperature anomaly between Vaisala RS92 and RO from June 2006 to April 2014 is within +/−0.09 K/5 yrs globally. Comparing with Vaisala RS80, Vaisala RS90 and sondes from other manufacturers, the Vaisala RS92 seems to provide the best RAOB temperature measurements, which can potentially be used to construct long term temperature CDRs. Results from this study also demonstrate the feasibility to use RO data to correct RAOB temperature biases for different sensor types.

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Extratropical age of air trends and causative factors in climate projection simulations

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-7627-2019 ◽

2019 ◽

Vol 19 (11) ◽

pp. 7627-7647 ◽

Cited By ~ 3

Author(s):

Petr Šácha ◽

Roland Eichinger ◽

Hella Garny ◽

Petr Pišoft ◽

Simone Dietmüller ◽

...

Keyword(s):

Climate Change ◽

Climate Model ◽

Climate Projection ◽

Residual Circulation ◽

Wave Forcing ◽

Open Questions ◽

Transit Times ◽

Causative Factors ◽

Climate Model Simulations ◽

Changes Over Time

Abstract. Climate model simulations show an acceleration of the Brewer–Dobson circulation (BDC) in response to climate change. While the general mechanisms for the BDC strengthening are widely understood, there are still open questions concerning the influence of the details of the wave driving. Mean age of stratospheric air (AoA) is a useful transport diagnostic for assessing changes in the BDC. Analyzing AoA from a subset of Chemistry–Climate Model Initiative part 1 climate projection simulations, we find a remarkable agreement between most of the models in simulating the largest negative AoA trends in the extratropical lower to middle stratosphere of both hemispheres (approximately between 20 and 25 geopotential kilometers (gpkm) and 20–50∘ N and S). We show that the occurrence of AoA trend minima in those regions is directly related to the climatological AoA distribution, which is sensitive to an upward shift of the circulation in response to climate change. Also other factors like a reduction of aging by mixing (AbM) and residual circulation transit times (RCTTs) contribute to the AoA distribution changes by widening the AoA isolines. Furthermore, we analyze the time evolution of AbM and RCTT trends in the extratropics and examine the connection to possible drivers focusing on local residual circulation strength, net tropical upwelling and wave driving. However, after the correction for a vertical shift of pressure levels, we find only seasonally significant trends of residual circulation strength and zonal mean wave forcing (resolved and unresolved) without a clear relation between the trends of the analyzed quantities. This indicates that additional causative factors may influence the AoA, RCTT and AbM trends. In this study, we postulate that the shrinkage of the stratosphere has the potential to influence the RCTT and AbM trends and thereby cause additional AoA changes over time.

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