scholarly journals Separating the role of direct radiative heating and photolysis in modulating the atmospheric response to the 11-year solar cycle forcing

2018 ◽  
Author(s):  
Ewa M. Bednarz ◽  
Amanda C. Maycock ◽  
Peter Braesicke ◽  
Paul J. Telford ◽  
N. Luke Abraham ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Climate Model ◽  
Heating Temperature ◽  
Radiative Heating ◽  
Dynamical Response ◽  
Atmospheric Response ◽  
Active Season ◽  
Photolysis Rates ◽  
Induced Changes ◽  
The Tropics

Abstract. The atmospheric response to the 11-year solar cycle forcing is separated into the contributions from changes in direct radiative heating and photolysis rates using specially designed sensitivity simulations with the UM-UKCA chemistry-climate model. We find that contributions from changes in direct heating and photolysis rates are important for determining the shortwave heating, temperature and ozone responses to the solar cycle forcing. The combined effects of the processes are found to be largely additive in the tropics but non-additive in the high latitudes, in particular in the Southern Hemisphere (SH) during the dynamically active season. We find marked differences in the changes in magnitude and vertical structure of shortwave heating rates gradients across the SH in austral winter, thereby highlighting a potential sensitivity of the polar dynamical response to the altitude of the anomalous radiative tendencies. In addition, our results indicate that, in contrast to the original mechanism proposed in the literature, the solar-induced changes in the horizontal shortwave heating rate gradients not only in autumn/early winter, but throughout the dynamically active season are important for modulating the dynamical response. In spring, these gradients are strongly influenced by the shortwave heating anomalies at higher southern latitudes, which are closely linked to the concurrent changes in ozone. Our results suggest that solar-induced changes in ozone, both in the tropics/mid-latitudes and the polar regions, are important for modulating the SH dynamical response to the 11-year solar cycle. In addition, the markedly non-additive character of the SH polar vortex response simulated in austral spring highlights the need for consistent model implementation of the solar cycle forcing in both the radiative heating and photolysis schemes.

scholarly journals Separating the role of direct radiative heating and photolysis in modulating the atmospheric response to the amplitude of the 11-year solar cycle forcing

2019 ◽  
Vol 19 (15) ◽  
pp. 9833-9846
Author(s):  
Ewa M. Bednarz ◽  
Amanda C. Maycock ◽  
Peter Braesicke ◽  
Paul J. Telford ◽  
N. Luke Abraham ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Heating Temperature ◽  
Radiative Heating ◽  
Dynamical Response ◽  
Atmospheric Response ◽  
Active Season ◽  
Photolysis Rates ◽  
Induced Changes ◽  
The Tropics

Abstract. The atmospheric response to the 11-year solar cycle is separated into the contributions from changes in direct radiative heating and photolysis rates using specially designed sensitivity simulations with the UM-UKCA (Unified Model coupled to the United Kingdom Chemistry and Aerosol model) chemistry–climate model. We perform a number of idealised time-slice experiments under perpetual solar maximum (SMAX) and minimum conditions (SMIN), and we find that contributions from changes in direct heating and photolysis rates are both important for determining the stratospheric shortwave heating, temperature and ozone responses to the amplitude of the 11-year solar cycle. The combined effects of the processes are found to be largely additive in the tropics but nonadditive in the Southern Hemisphere (SH) high latitudes during the dynamically active season. Our results indicate that, in contrast to the original mechanism proposed in the literature, the solar-induced changes in the horizontal shortwave heating rate gradients not only in autumn/early winter but throughout the dynamically active season are important for modulating the dynamical response to changes in solar forcing. In spring, these gradients are strongly influenced by the shortwave heating anomalies at higher southern latitudes, which are closely linked to the concurrent changes in ozone. In addition, our simulations indicate differences in the winter SH dynamical responses between the experiments. We suggest a couple of potential drivers of the simulated differences, i.e. the role of enhanced zonally asymmetric ozone heating brought about by the increased solar-induced ozone levels under SMAX and/or sensitivity of the polar dynamical response to the altitude of the anomalous radiative tendencies. All in all, our results suggest that solar-induced changes in ozone, both in the tropics/mid-latitudes and the polar regions, are important for modulating the SH dynamical response to the 11-year solar cycle. In addition, the markedly nonadditive character of the SH polar vortex response simulated in austral spring highlights the need for consistent model implementation of the solar cycle forcing in both the radiative heating and photolysis schemes.

scholarly journals Simulating the atmospheric response to the 11-year solar cycle forcing with the UM-UKCA model: the role of detection method and natural variability

2018 ◽  
Author(s):  
Ewa M. Bednarz ◽  
Amanda C. Maycock ◽  
Paul J. Telford ◽  
Peter Braesicke ◽  
N. Luke Abraham ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Climate Model ◽  
Detection Method ◽  
Linear Regression Method ◽  
Data Sets ◽  
Atmospheric Response ◽  
Atmospheric Variability ◽  
Active Season ◽  
Atmospheric Forcings

Abstract. The 11-year solar cycle forcing is recognised as a potentially important atmospheric forcing; however, there remain uncertainties in characterising the effects of the solar variability on the atmosphere from observations and models. Here we present the first detailed assessment of the atmospheric response to the 11-year solar cycle in the UM-UKCA chemistry-climate model using an ensemble of integrations over the recent past. Comparison of the model simulations is made with observations and reanalysis. Importantly, in contrast to the majority of previous studies of the solar cycle impacts, we pay particular attention to the role of detection method by comparing the results diagnosed using both a composite and a multiple linear regression method. We show that stratospheric solar responses diagnosed using both techniques largely agree with each other within the associated uncertainties; however, the results show that apparently different signals can be identified by the methods in the troposphere and in the tropical lower stratosphere. Lastly, we focus on the role of internal atmospheric variability on the detection of the 11-year solar responses by comparing the results diagnosed from individual model ensemble members (as opposed to those diagnosed from the full ensemble). We show overall agreement between the ensemble members in the tropical and mid-latitude mid-stratosphere-to-lower-mesosphere, but larger apparent differences at NH high latitudes during the dynamically active season. Our results highlight the need for long data sets for confident detection of solar cycle impacts in the atmosphere, as well as for more research on possible interdependence of the solar cycle forcing with other atmospheric forcings and processes (e.g. QBO, ENSO… etc.).

scholarly journals Simulating the atmospheric response to the 11-year solar cycle forcing with the UM-UKCA model: the role of detection method and natural variability

2019 ◽  
Vol 19 (7) ◽  
pp. 5209-5233 ◽  
Author(s):  
Ewa M. Bednarz ◽  
Amanda C. Maycock ◽  
Paul J. Telford ◽  
Peter Braesicke ◽  
N. Luke Abraham ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Climate Model ◽  
Southern Oscillation ◽  
Critical Discussion ◽  
Atmospheric Response ◽  
Quasi Biennial Oscillation ◽  
Model Composite ◽  
Aerosol Model ◽  
Active Season

Abstract. The 11-year solar cycle forcing is recognised as an important atmospheric forcing; however, there remain uncertainties in characterising the effects of solar variability on the atmosphere from observations and models. Here we present the first detailed assessment of the atmospheric response to the 11-year solar cycle in the UM-UKCA (Unified Model coupled to the United Kingdom Chemistry and Aerosol model) chemistry–climate model (CCM) using a three-member ensemble over the recent past (1966–2010). Comparison of the model simulations is made with satellite observations and reanalysis datasets. The UM-UKCA model produces a statistically significant response to the 11-year solar cycle in stratospheric temperatures, ozone and zonal winds. However, there are also differences in magnitude, spatial structure and timing of the signals compared to observational and reanalysis estimates. This could be due to deficiencies in the model performance, and so we include a critical discussion of the model limitations, and/or uncertainties in the current observational estimates of the solar cycle signals. Importantly, in contrast to many previous studies of the solar cycle impacts, we pay particular attention to the role of the chosen analysis method in UM-UKCA by comparing the model composite and a multiple linear regression (MLR) results. We show that the stratospheric solar responses diagnosed using both techniques largely agree with each other within the associated uncertainties; however, the results show that apparently different signals can be identified by the methods in the troposphere and in the tropical lower stratosphere. Lastly, we examine how internal atmospheric variability affects the detection of the 11-year solar responses in the model by comparing the results diagnosed from the three individual ensemble members (as opposed to those diagnosed from the full ensemble). We show overall agreement between the responses diagnosed for the ensemble members in the tropical and mid-latitude mid-stratosphere to lower mesosphere but larger apparent differences at Northern Hemisphere (NH) high latitudes during the dynamically active season. Our UM-UKCA results suggest the need for long data sets for confident detection of solar cycle impacts in the atmosphere, as well as for more research on possible interdependence of the solar cycle forcing with other atmospheric forcings and processes (e.g. Quasi-Biennial Oscillation, QBO; El Niño–Southern Oscillation, ENSO).

scholarly journals Obliquity forcing of low-latitude climate

2015 ◽  
Vol 11 (1) ◽  
pp. 221-241 ◽  
Author(s):  
J. H. C. Bosmans ◽  
F. J. Hilgen ◽  
E. Tuenter ◽  
L. J. Lourens
Keyword(s):  
High Latitude ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Rotational Axis ◽  
Low Latitude ◽  
Low Latitudes ◽  
Paleoclimate Records ◽  
Induced Changes ◽  
The Tropics

Abstract. The influence of obliquity, the tilt of the Earth's rotational axis, on incoming solar radiation at low latitudes is small, yet many tropical and subtropical paleoclimate records reveal a clear obliquity signal. Several mechanisms have been proposed to explain this signal, such as the remote influence of high-latitude glacials, the remote effect of insolation changes at mid- to high latitudes independent of glacial cyclicity, shifts in the latitudinal extent of the tropics, and changes in latitudinal insolation gradients. Using a sophisticated coupled ocean–atmosphere global climate model, EC-Earth, without dynamical ice sheets, we performed two experiments of obliquity extremes. Our results show that obliquity-induced changes in tropical climate can occur without high-latitude ice sheet fluctuations. Furthermore, the tropical circulation changes are consistent with obliquity-induced changes in the cross-equatorial insolation gradient, implying that this gradient may be used to explain obliquity signals in low-latitude paleoclimate records instead of the classic 65° N summer insolation curve.

scholarly journals Obliquity forcing of low-latitude climate

2015 ◽  
Vol 11 (10) ◽  
pp. 1335-1346 ◽  
Author(s):  
J. H. C. Bosmans ◽  
F. J. Hilgen ◽  
E. Tuenter ◽  
L. J. Lourens
Keyword(s):  
High Latitude ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Rotational Axis ◽  
Tropical Circulation ◽  
Low Latitude ◽  
Low Latitudes ◽  
Induced Changes ◽  
The Tropics

Abstract. The influence of obliquity, the tilt of the Earth's rotational axis, on incoming solar radiation at low latitudes is small, yet many tropical and subtropical palaeoclimate records reveal a clear obliquity signal. Several mechanisms have been proposed to explain this signal, such as the remote influence of high-latitude glacials, the remote effect of insolation changes at mid- to high latitudes independent of glacial cyclicity, shifts in the latitudinal extent of the tropics, and changes in latitudinal insolation gradients. Using a sophisticated coupled ocean–atmosphere global climate model, EC-Earth, without dynamical ice sheets, we performed two idealized experiments of obliquity extremes. Our results show that obliquity-induced changes in tropical climate can occur without high-latitude ice sheet fluctuations. Furthermore, the tropical circulation changes are consistent with obliquity-induced changes in the cross-equatorial insolation gradient, suggesting that this gradient may be used to explain obliquity signals in low-latitude palaeoclimate records instead of the classical 65° N summer insolation curve.

scholarly journals The impact of volcanic aerosols on stratospheric ozone and the Northern Hemisphere polar vortex: separating radiative from chemical effects under different climate conditions

2015 ◽  
Vol 15 (10) ◽  
pp. 14275-14314 ◽  
Author(s):  
S. Muthers ◽  
F. Arfeuille ◽  
C. C. Raible ◽  
E. Rozanov
Keyword(s):  
Northern Hemisphere ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Volcanic Eruptions ◽  
Radiative Heating ◽  
Dynamical Response ◽  
Climate Conditions ◽  
Column Ozone ◽  
The Impact

Abstract. After strong volcanic eruptions stratospheric ozone changes are modulated by heterogeneous chemical reactions (HET) and dynamical perturbations related to the radiative heating in the lower stratosphere (RAD). Here, we assess the relative importance of both processes as well as the effect of the resulting ozone changes on the dynamics using ensemble simulations with the atmosphere–ocean–chemistry–climate model (AOCCM) SOCOL-MPIOM forced by eruptions with different strength. The simulations are performed under present day and preindustrial conditions to investigate changes in the response behaviour. The results show that the HET effect is only relevant under present day conditions and causes a pronounced global reduction of column ozone. These ozone changes further lead to a slight weakening of the Northern Hemisphere (NH) polar vortex during mid-winter. Independent from the climate state the RAD mechanism changes the column ozone pattern with negative anomalies in the tropics and positive anomalies in the mid-latitudes. The influence of the climate state on the RAD mechanism significantly differs in the polar latitudes, where an amplified ozone depletion during the winter months is simulated under present day conditions. This is in contrast to the preindustrial state showing a positive column ozone response also in the polar area. The dynamical response of the stratosphere is clearly dominated by the RAD mechanism showing an intensification of the NH polar vortex in winter. Still under present day conditions ozone changes due to the RAD mechanism slightly reduce the response of the polar vortex after the eruption.

scholarly journals Contrasting Impacts of Radiative Forcing in the Southern Ocean versus Southern Tropics on ITCZ Position and Energy Transport in One GFDL Climate Model

2018 ◽  
Vol 31 (14) ◽  
pp. 5609-5628 ◽  
Author(s):  
Baoqiang Xiang ◽  
Ming Zhao ◽  
Yi Ming ◽  
Weidong Yu ◽  
Sarah M. Kang
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Radiative Forcing ◽  
Climate Models ◽  
Energy Transport ◽  
Climate Model ◽  
Radiative Heating ◽  
Ocean Heat Uptake ◽  
Budget Analysis ◽  
The Tropics

Abstract Most current climate models suffer from pronounced cloud and radiation biases in the Southern Ocean (SO) and in the tropics. Using one GFDL climate model, this study investigates the migration of the intertropical convergence zone (ITCZ) with prescribed top-of-the-atmosphere (TOA) shortwave radiative heating in the SO (50°–80°S) versus the southern tropics (ST; 0°–20°S). Results demonstrate that the ITCZ position response to the ST forcing is twice as strong as the SO forcing, which is primarily driven by the contrasting sea surface temperature (SST) gradient over the tropics; however, the mechanism for the formation of the SST pattern remains elusive. Energy budget analysis reveals that the conventional energetic constraint framework is inadequate in explaining the ITCZ shift in these two perturbed experiments. For both cases, the anomalous Hadley circulation does not contribute to transport the imposed energy from the Southern Hemisphere to the Northern Hemisphere, given a positive mean gross moist stability in the equatorial region. Changes in the cross-equatorial atmospheric energy are primarily transported by atmospheric transient eddies when the anomalous ITCZ shift is most pronounced during December–May. The partitioning of energy transport between the atmosphere and ocean shows latitudinal dependence: the atmosphere and ocean play an overall equivalent role in transporting the imposed energy for the extratropical SO forcing, while for the ST forcing, the imposed energy is nearly completely transported by the atmosphere. This contrast originates from the different ocean heat uptake and also the different meridional scale of the anomalous ocean circulation.

scholarly journals Application and evaluation of McICA scheme with new radiation code in BCC_AGCM2.0.1

2013 ◽  
Vol 6 (3) ◽  
pp. 4933-4982 ◽  
Author(s):  
H. Zhang ◽  
X. Jing ◽  
J. Li
Keyword(s):  
Climate Model ◽  
Atmospheric Temperature ◽  
Horizontal Distribution ◽  
Radiative Heating ◽  
Specific Humidity ◽  
Storm Tracks ◽  
Heating Rates ◽  
Radiative Forcings ◽  
Horizontal Inhomogeneity ◽  
The Tropics

Abstract. This research incorporates the Monte Carlo Independent Column Approximation (McICA) scheme with the correlated k-distribution BCC-RAD radiation model into the climate model BCC_AGCM2.0.1 and examines the impacts on modeled climate through several simulations with variations in cloud structures. Results from experiments with consistent sub-grid cloud structures show that both clear-sky radiation fluxes and cloud radiative forcings (CRFs) calculated by the new scheme are mostly improved relative to those calculated from the original one. The modeled atmospheric temperature and specific humidity are also improved due to changes in the radiative heating rates. The vertical overlap of fractional clouds and horizontal distribution of cloud condensation are important for computing CRFs. The maximum changes in seasonal CRF using the general overlap assumption (GenO) with different decorrelation depths (Lcf) are larger than 10 and 20 Wm2 for longwave (LW) CRF and shortwave (SW) CRF, respectively, mostly located in the Tropics and mid-latitude storm tracks. Larger (smaller) Lcf in the Tropics (mid-latitude storm tracks) yield better cloud fraction and CRF compared with observations. The inclusion of an observation-based horizontal inhomogeneity of cloud condensation has a distinct impact on LW CRF and SW CRF, with global means of ∼1.2 Wm−2 and ∼3.7 Wm−2 at the top of atmosphere, respectively, making these much closer to observations. These results prove the reliability of the new model configuration to be used in BCC_AGCM2.0.1 for climate simulations, and also indicate that more detailed real-world information on cloud structures should be obtained to constrain cloud settings in McICA in the future.

scholarly journals The impacts of volcanic aerosol on stratospheric ozone and the Northern Hemisphere polar vortex: separating radiative-dynamical changes from direct effects due to enhanced aerosol heterogeneous chemistry

2015 ◽  
Vol 15 (20) ◽  
pp. 11461-11476 ◽  
Author(s):  
S. Muthers ◽  
F. Arfeuille ◽  
C. C. Raible ◽  
E. Rozanov
Keyword(s):  
Climate Model ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Volcanic Eruptions ◽  
Radiative Heating ◽  
Late Winter ◽  
Dynamical Response ◽  
Heterogeneous Chemistry ◽  
Series Of Experiments ◽  
Column Ozone

Abstract. After major volcanic eruptions the enhanced aerosol causes ozone changes due to greater heterogeneous chemistry on the particle surfaces (HET-AER) and from dynamical effects related to the radiative heating of the lower stratosphere (RAD-DYN). We carry out a series of experiments with an atmosphere–ocean–chemistry–climate model to assess how these two processes change stratospheric ozone and Northern Hemispheric (NH) polar vortex dynamics. Ensemble simulations are performed under present day and preindustrial conditions, and with aerosol forcings representative of different eruption strength, to investigate changes in the response behaviour. We show that the halogen component of the HET-AER effect dominates under present-day conditions with a global reduction of ozone (−21 DU for the strongest eruption) particularly at high latitudes, whereas the HET-AER effect increases stratospheric ozone due to N2O5 hydrolysis in a preindustrial atmosphere (maximum anomalies +4 DU). The halogen-induced ozone changes in the present-day atmosphere offset part of the strengthening of the NH polar vortex during mid-winter (reduction of up to −16 m s-1 in January) and slightly amplify the dynamical changes in the polar stratosphere in late winter (+11 m s-1 in March). The RAD-DYN mechanism leads to positive column ozone anomalies which are reduced in a present-day atmosphere by amplified polar ozone depletion (maximum anomalies +12 and +18 DU for present day and preindustrial, respectively). For preindustrial conditions, the ozone response is consequently dominated by RAD-DYN processes, while under present-day conditions, HET-AER effects dominate. The dynamical response of the stratosphere is dominated by the RAD-DYN mechanism showing an intensification of the NH polar vortex in winter (up to +10 m s-1 in January). Ozone changes due to the RAD-DYN mechanism slightly reduce the response of the polar vortex after the eruption under present-day conditions.

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