Propagation of ENSO temperature signals into the middle atmosphere: A comparison of two general circulation models and ERA-40 reanalysis data

Abstract. Seasonal variability of surface air temperature and baroclinicity from the ECMWF ERA-Interim (ERAI) reanalysis and six coupled atmosphere-ocean general circulation models (AOGCMs) participating in the Coupled Model Intercomparison Project phase 3 and 5 (CMIP3 and CMIP5) are examined. In particular, the annual and semiannual cycles of hemispherically averaged fields are studied using spectral analysis. The aim is to assess the ability of coupled general circulation models to properly reproduce the observed amplitude and phase of these cycles, and investigate the relationship between surface temperature and baroclinicity (coherency and relative phase) in such frequency bands. The overall results of power spectra agree in displaying a statistically significant peak at the annual frequency in the zonally averaged fields of both hemispheres. The semiannual peak, instead, shows less power and in the NH seems to have a more regional character, as is observed in the North Pacific Ocean region. Results of bivariate analysis for such a region and Southern Hemisphere midlatitudes show some discrepancies between ERAI and model data, as well as among models, especially for the semiannual frequency. Specifically: (i) the coherency at the annual and semiannual frequency observed in the reanalysis data is well represented by models in both hemispheres; (ii) at the annual frequency, estimates of the relative phase between surface temperature and baroclinicity are bounded between about &pm;15° around an average value of 220° (i.e., approximately 1 month phase shift), while at the semiannual frequency model phases show a wider dispersion in both hemispheres with larger errors in the estimates, denoting increased uncertainty and some disagreement among models. The most recent CMIP climate models (CMIP5) show several improvements when compared with CMIP3 but a degree of discrepancy still persists though masked by the large errors characterizing the semiannual frequency. These findings contribute to better characterize the cyclic response of current global atmosphere-ocean models to the external (solar) forcing that is of interest for seasonal forecasts.

Download Full-text

Forecast skill of autumn snow for European winter climate during the 20th century: A multi member seasonal prediction experiment

10.5194/egusphere-egu21-2586 ◽

2021 ◽

Author(s):

Martin Wegmann ◽

Yvan Orsolini ◽

Antje Weisheimer ◽

Bart van den Hurk ◽

Gerrit Lohmann

Keyword(s):

Snow Cover ◽

General Circulation ◽

Initial Conditions ◽

Internal Variability ◽

Seasonal Prediction ◽

General Circulation Models ◽

Reanalysis Data ◽

Winter Climate ◽

European Continent ◽

Near Surface

As the leading climate mode to explain wintertime climate variability over Europe, the North Atlantic Oscillation (NAO) has been extensively studied over the last decades. Recently, studies highlighted the state of the Northern Hemispheric cryosphere as possible predictor for the wintertime NAO (Cohen et al. 2014). Although several studies could find seasonal prediction skill in reanalysis data (Orsolini et al. 2016, Duville et al. 2017,Han & Sun 2018), experiments with ocean-atmosphere general circulation models (AOGCMs) still show conflicting results (Furtado et al. 2015, Handorf et al. 2015, Francis 2017, Gastineau et al. 2017).&#160;Here we use two kinds ECMWF seasonal prediction ensembles starting with November initial conditions taken from the long-term reanalysis ERA-20C and forecasting the following three winter months. Besides the 110-year ensemble of 50 members representing internal variability of the atmosphere, we investigate a second ensemble of 20 members where initial conditions are split between low and high snow cover years for the Northern Hemisphere. We compare two recently used Eurasian snow cover indices for their skill in predicting winter climate for the European continent. Analyzing the two forecast experiments, we found that prediction runs starting with high snow index values in November result in significantly more negative NAO states in the following winter (DJF), which in turn modulates near surface temperatures. We track the atmospheric anomalies triggered by the high snow index through the tropo- and stratosphere as well as for the individual winter months to provide a physical explanation for the formation of this particular climate state.&#160;

Download Full-text

Net effect of the QBO in a chemistry climate model

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-6505-2008 ◽

2008 ◽

Vol 8 (21) ◽

pp. 6505-6525 ◽

Cited By ~ 11

Author(s):

H. J. Punge ◽

M. A. Giorgetta

Keyword(s):

General Circulation ◽

Climate Models ◽

Climate Model ◽

Middle Atmosphere ◽

Meridional Circulation ◽

Vortex Formation ◽

General Circulation Models ◽

Quasi Biennial Oscillation ◽

The Mean ◽

The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the level of maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall seasons in both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affect mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

Download Full-text

Annual and semiannual cycles of midlatitude near-surface temperature and tropospheric baroclinicity: reanalysis data and AOGCM simulations

Earth System Dynamics ◽

10.5194/esd-8-295-2017 ◽

2017 ◽

Vol 8 (2) ◽

pp. 295-312 ◽

Cited By ~ 2

Author(s):

Valerio Lembo ◽

Isabella Bordi ◽

Antonio Speranza

Keyword(s):

Surface Temperature ◽

General Circulation ◽

Relative Phase ◽

North Pacific Ocean ◽

General Circulation Models ◽

Reanalysis Data ◽

Seasonal Forecasts ◽

Frequency Model ◽

Near Surface ◽

Annual Frequency

Abstract. Seasonal variability in near-surface air temperature and baroclinicity from the ECMWF ERA-Interim (ERAI) reanalysis and six coupled atmosphere–ocean general circulation models (AOGCMs) participating in the Coupled Model Intercomparison Project phase 3 and 5 (CMIP3 and CMIP5) are examined. In particular, the annual and semiannual cycles of hemispherically averaged fields are studied using spectral analysis. The aim is to assess the ability of coupled general circulation models to properly reproduce the observed amplitude and phase of these cycles, and investigate the relationship between near-surface temperature and baroclinicity (coherency and relative phase) in such frequency bands. The overall results of power spectra agree in displaying a statistically significant peak at the annual frequency in the zonally averaged fields of both hemispheres. The semiannual peak, instead, shows less power and in the NH seems to have a more regional character, as is observed in the North Pacific Ocean region. Results of bivariate analysis for such a region and Southern Hemisphere midlatitudes show some discrepancies between ERAI and model data, as well as among models, especially for the semiannual frequency. Specifically, (i) the coherency at the annual and semiannual frequency observed in the reanalysis data is well represented by models in both hemispheres, and (ii) at the annual frequency, estimates of the relative phase between near-surface temperature and baroclinicity are bounded between about ±15° around an average value of 220° (i.e., approximately 1-month phase shift), while at the semiannual frequency model phases show a wider dispersion in both hemispheres with larger errors in the estimates, denoting increased uncertainty and some disagreement among models. The most recent CMIP climate models (CMIP5) show several improvements when compared with CMIP3, but a degree of discrepancy still persists though masked by the large errors characterizing the semiannual frequency. These findings contribute to better characterizing the cyclic response of current global atmosphere–ocean models to the external (solar) forcing that is of interest for seasonal forecasts.

Download Full-text

South Pacific Subtropical High from the late Holocene to the end of the 21st century: insights from climate proxies and general circulation models

10.5194/cp-2019-69 ◽

2019 ◽

Author(s):

Valentina Flores-Aqueveque ◽

Maisa Rojas ◽

Catalina Aguirre ◽

Paola A. Arias ◽

Charles González

Keyword(s):

General Circulation ◽

South Pacific ◽

General Circulation Models ◽

Reanalysis Data ◽

Hadley Cell ◽

Subtropical High ◽

South American ◽

The South ◽

Paleoclimate Records ◽

South American Climate

Abstract. The South Pacific Subtropical High (SPSH) is a predominant feature of South American climate. The variability of this high-pressure center induces changes in the intensity of coastal alongshore winds and precipitation, among others, over southwestern South America. In recent decades, a strengthening and expansion of the SPSH have been observed and attributed to the current global warming. These changes have led an intensification of the southerly winds along the coast of northern to central Chile, and a decrease in precipitation from central to southern Chile. Motivated by improving our understanding about the regional impacts of climate change in this part of the Southern Hemisphere, we analyze SPSH changes during the two most extreme climate events of the last millennium: the Little Ice Age (LIA) and the Current Warm Period (CWP: 1970–2000), based on paleoclimate records and CMIP5/PMIP3 model simulations. In order to assess the level of agreement of general circulation models, we also compare them with ERA-Interim reanalysis data for the 1979–2009 period as a complementary analysis. Finally, with the aim of evaluating future SPSH behaviour, we include 21th century projections under a RCP8.5 scenario in our analyses. Our results indicate that during the relative warm (cold) period, the SPSH expands (contracts). Together with this change, alongshore winds intensify (weaken) south (north) of ~ 35º S; also, Southern Westerly Winds become stronger (weaker) and shift southward (northward). Model results generally underestimate reanalysis data. These changes are in good agreement with paleoclimate records, which suggest that these variations could be related to tropical climate dynamics but also to extratropical phenomena. However, although models adequately represent most of the South American climate changes, they fail in representing the Intertropical Convergence Zone - Hadley Cell system dynamics. Climate model projections indicate that changes recently observed will continue during next decades, highlighting the need to establish effective mitigation and adaptation strategies against their environmental and socio-economic impacts.

Download Full-text

Net effect of the QBO in a chemistry climate model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-12115-2008 ◽

2008 ◽

Vol 8 (3) ◽

pp. 12115-12162 ◽

Cited By ~ 1

Author(s):

H. J. Punge ◽

M. A. Giorgetta

Keyword(s):

General Circulation ◽

Climate Models ◽

Climate Model ◽

Middle Atmosphere ◽

Meridional Circulation ◽

Vortex Formation ◽

General Circulation Models ◽

Quasi Biennial Oscillation ◽

The Mean ◽

The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall on both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affecting mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

Download Full-text

Temporal variability of tidal and gravity waves during a record long 10 day continuous lidar sounding

10.5194/acp-2017-537 ◽

2017 ◽

Author(s):

Kathrin Baumgarten ◽

Michael Gerding ◽

Gerd Baumgarten ◽

Franz-Josef Lübken

Keyword(s):

Gravity Waves ◽

General Circulation ◽

Middle Atmosphere ◽

Wave Interaction ◽

Weather Conditions ◽

General Circulation Models ◽

Driving Mechanism ◽

Lidar Measurement ◽

Large Variability ◽

Tidal Waves

Abstract. Gravity waves (GW) as well as solar tides are a key driving mechanism for the circulation in the Earth's atmosphere. The propagation of gravity waves is strongly infected by tidal waves as they modulate the mean background wind field and vice versa, which is not yet fully understood and not implemented in many circulation models. The daylight capable Rayleigh-Mie-Raman (RMR) lidar at Kühlungsborn (54° N, 12&deg E) typically provides temperature data to investigate both wave phenomena during one full day or several consecutive days in the middle atmosphere between 30 and 75 km altitude. Outstanding weather conditions in May 2016 allowed for an unprecedented 10-day continuous lidar measurement which shows a large variability of gravity waves and tides on time scales of days. Using a 1-dimensional spectral filtering technique, gravity and tidal waves are separated according to their specific periods or vertical wavelengths, and their temporal evolution is studied. During the measurement a strong 24 h-wave occurs only between 40 and 60 km and vanishes after a few days. The disappearance is related to an enhancement of gravity waves with periods of 4–8 h. Wind data provided by ECMWF are used to analyze the meteorological situation at our site. The local wind structure changes during the observation period, which leads to different propagation conditions for gravity waves in the last days of the measurement and therefore a strong GW activity. The analysis indicates a further change in wave-wave interaction resulting in a minimum of the 24 h tide. The observed variability of tides and gravity waves on timescales of a few days clearly demonstrates the importance of continuous measurements with high temporal and spatial resolution to detect interaction phenomena, which can help to improve parametrization schemes of GW in general circulation models.

Download Full-text

Temporal variability of tidal and gravity waves during a record long 10-day continuous lidar sounding

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-371-2018 ◽

2018 ◽

Vol 18 (1) ◽

pp. 371-384 ◽

Cited By ~ 16

Author(s):

Kathrin Baumgarten ◽

Michael Gerding ◽

Gerd Baumgarten ◽

Franz-Josef Lübken

Keyword(s):

Gravity Waves ◽

General Circulation ◽

Middle Atmosphere ◽

Weather Conditions ◽

General Circulation Models ◽

Driving Mechanism ◽

Lidar Measurement ◽

Large Variability ◽

Tidal Waves ◽

Measurement Period

Abstract. Gravity waves (GWs) as well as solar tides are a key driving mechanism for the circulation in the Earth's atmosphere. The propagation of gravity waves is strongly affected by tidal waves as they modulate the mean background wind field and vice versa, which is not yet fully understood and not adequately implemented in many circulation models. The daylight-capable Rayleigh–Mie–Raman (RMR) lidar at Kühlungsborn (54∘ N, 12∘ E) typically provides temperature data to investigate both wave phenomena during one full day or several consecutive days in the middle atmosphere between 30 and 75 km altitude. Outstanding weather conditions in May 2016 allowed for an unprecedented 10-day continuous lidar measurement, which shows a large variability of gravity waves and tides on timescales of days. Using a one-dimensional spectral filtering technique, gravity and tidal waves are separated according to their specific periods or vertical wavelengths, and their temporal evolution is studied. During the measurement period a strong 24 h wave occurs only between 40 and 60 km and vanishes after a few days. The disappearance is related to an enhancement of gravity waves with periods of 4–8 h. Wind data provided by ECMWF are used to analyze the meteorological situation at our site. The local wind structure changes during the observation period, which leads to different propagation conditions for gravity waves in the last days of the measurement period and therefore a strong GW activity. The analysis indicates a further change in wave–wave interaction resulting in a minimum of the 24 h tide. The observed variability of tides and gravity waves on timescales of a few days clearly demonstrates the importance of continuous measurements with high temporal and spatial resolution to detect interaction phenomena, which can help to improve parametrization schemes of GWs in general circulation models.

Download Full-text

Sensitivity of lake ice regimes to climate change in the Nordic region

The Cryosphere ◽

10.5194/tc-8-1589-2014 ◽

2014 ◽

Vol 8 (4) ◽

pp. 1589-1605 ◽

Cited By ~ 15

Author(s):

S. Gebre ◽

T. Boissy ◽

K. Alfredsen

Keyword(s):

General Circulation ◽

Climate Model ◽

General Circulation Models ◽

Reanalysis Data ◽

Ice Thickness ◽

Annual Maximum ◽

Climate Scenarios ◽

Lake Ice ◽

Data Set ◽

Nordic Region

Abstract. A one-dimensional process-based multi-year lake ice model, MyLake, was used to simulate lake ice phenology and annual maximum lake ice thickness for the Nordic region comprising Fennoscandia and the Baltic countries. The model was first tested and validated using observational meteorological forcing on a candidate lake (Lake Atnsjøen) and using downscaled ERA-40 reanalysis data set. To simulate ice conditions for the contemporary period of 1961–2000, the model was driven by gridded meteorological forcings from ERA-40 global reanalysis data downscaled to a 25 km resolution using the Rossby Centre Regional Climate Model (RCA). The model was then forced with two future climate scenarios from the RCA driven by two different general circulation models (GCMs) based on the Special Report on Emissions Scenarios (SRES) A1B. The two climate scenarios correspond to two future time periods namely the 2050s (2041–2070) and the 2080s (2071–2100). To take into account the influence of lake morphometry, simulations were carried out for four different hypothetical lake depths (5 m, 10 m, 20 m, 40 m) placed at each of the 3708 grid cells. Based on a comparison of the mean predictions in the future 30-year periods with the control (1961–1990) period, ice cover durations in the region will be shortened by 1 to 11 weeks in 2041–2070, and 3 to 14 weeks in 2071–2100. Annual maximum lake ice thickness, on the other hand, will be reduced by a margin of up to 60 cm by 2041–2070 and up to 70 cm by 2071–2100. The simulated changes in lake ice characteristics revealed that the changes are less dependent on lake depths though there are slight differences. The results of this study provide a regional perspective of anticipated changes in lake ice regimes due to climate warming across the study area by the middle and end of this century.

Download Full-text

Explicitly Stochastic Parameterization of Nonorographic Gravity Wave Drag

Journal of the Atmospheric Sciences ◽

10.1175/2011jas3684.1 ◽

2011 ◽

Vol 68 (8) ◽

pp. 1749-1765 ◽

Cited By ~ 37

Author(s):

Stephen D. Eckermann

Keyword(s):

Gravity Wave ◽

General Circulation ◽

Middle Atmosphere ◽

General Circulation Models ◽

Wave Drag ◽

Single Wave ◽

Order Of Magnitude ◽

Simple Conversion ◽

Wave Induced ◽

Stochastic Analog

Abstract A straightforward methodology is presented for converting the deterministic multiwave parameterizations of nonorographic gravity wave drag, currently used in general circulation models (GCMs), to stochastic analogs that use fewer waves (in the example herein, a single wave) within each grid box. Deterministic discretizations of source-level momentum flux spectra using a fixed spectrum of many waves with predefined phase speeds are replaced by sampling these source spectra stochastically using waves with randomly assigned phase speeds. Using simple conversion formulas, it is shown that time-mean wave-induced drag, diffusion, and heating-rate profiles identical to those from the deterministic scheme are produced by the stochastic analog. Furthermore, in these examples the need for bulk intermittency factors of small value is largely obviated through the explicit incorporation of stochastic intermittency into the scheme. When implemented in a GCM, the single-wave stochastic analog of an existing deterministic scheme reproduces almost identical time-mean middle-atmosphere climate and drag as its deterministic antecedent but with an order of magnitude reduction in computational expense. The stochastically parameterized drag is also accompanied by inherent variability about the time-mean profile that forces the smallest space–time scales of the GCM. Studies of mean GCM kinetic energy spectra show that this additional stochastic forcing does not lead to excessive increases in dynamical variability at these smallest GCM scales. The results show that the expensive deterministic schemes currently used in GCMs are easily modified and replaced by cheap stochastic analogs without any obvious deleterious impacts on GCM climate or variability, while offering potential advantages of computational savings, reduction of systematic climate biases, and greater and more realistic ensemble spread.

Download Full-text