scholarly journals Sensitivity of Polar Amplification to Varying Insolation Conditions

2018 ◽  
Vol 31 (12) ◽  
pp. 4933-4947 ◽  
Author(s):  
Doyeon Kim ◽  
Sarah M. Kang ◽  
Yechul Shin ◽  
Nicole Feldl
Keyword(s):  
Energy Transport ◽  
Longwave Radiation ◽  
Atmospheric Model ◽  
Static Stability ◽  
Lapse Rate ◽  
Polar Surface ◽  
Surface Warming ◽  
Polar Amplification ◽  
Rate Feedback ◽  
Radiative Feedbacks

The mechanism of polar amplification in the absence of surface albedo feedback is investigated using an atmospheric model coupled to an aquaplanet slab ocean forced by a CO2 doubling. In particular, we examine the sensitivity of polar surface warming response under different insolation conditions from equinox (EQN) to annual mean (ANN) to seasonally varying (SEA). Varying insolation greatly affects the climatological static stability. The equinox condition, with the largest polar static stability, exhibits a bottom-heavy vertical profile of polar warming response that leads to the strongest polar amplification. In contrast, the polar warming response in ANN and SEA exhibits a maximum in the midtroposphere, which leads to only weak polar amplification. The midtropospheric warming maximum, which results from an increased poleward atmospheric energy transport in response to the tropics-to-pole energy imbalance, contributes to polar surface warming via downward clear-sky longwave radiation. However, it is cancelled by negative cloud radiative feedbacks locally. Furthermore, the polar lapse rate feedback, calculated from radiative kernels, is negative due to the midtropospheric warming maximum, and hence is not able to promote the polar surface warming. On the other hand, the polar lapse rate feedback in EQN is positive due to the bottom-heavy warming response, contributing to the strong polar surface warming. This contrast suggests that locally induced positive radiative feedbacks are necessary for strong polar amplification. Our results demonstrate how interactions among climate feedbacks determine the strength of polar amplification.

scholarly journals Sea ice and atmospheric circulation shape the high-latitude lapse rate feedback

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Nicole Feldl ◽  
Stephen Po-Chedley ◽  
Hansi K. A. Singh ◽  
Stephanie Hay ◽  
Paul J. Kushner
Keyword(s):  
Sea Ice ◽  
High Latitude ◽  
Energy Transport ◽  
Lower Troposphere ◽  
Longwave Radiation ◽  
Lapse Rate ◽  
Arctic Amplification ◽  
Albedo Feedback ◽  
Rate Feedback ◽  
Isentropic Surface

Abstract Arctic amplification of anthropogenic climate change is widely attributed to the sea-ice albedo feedback, with its attendant increase in absorbed solar radiation, and to the effect of the vertical structure of atmospheric warming on Earth’s outgoing longwave radiation. The latter lapse rate feedback is subject, at high latitudes, to a myriad of local and remote influences whose relative contributions remain unquantified. The distinct controls on the high-latitude lapse rate feedback are here partitioned into “upper” and “lower” contributions originating above and below a characteristic climatological isentropic surface that separates the high-latitude lower troposphere from the rest of the atmosphere. This decomposition clarifies how the positive high-latitude lapse rate feedback over polar oceans arises primarily as an atmospheric response to local sea ice loss and is reduced in subpolar latitudes by an increase in poleward atmospheric energy transport. The separation of the locally driven component of the high-latitude lapse rate feedback further reveals how it and the sea-ice albedo feedback together dominate Arctic amplification as a coupled mechanism operating across the seasonal cycle.

scholarly journals Decomposing the Drivers of Polar Amplification with a Single Column Model

2020 ◽  
pp. 1-33
Author(s):  
Matthew Henry ◽  
Timothy M. Merlis ◽  
Nicholas J. Lutsko ◽  
Brian E.J. Rose
Keyword(s):  
General Circulation ◽  
Energy Transport ◽  
Circulation Model ◽  
Lapse Rate ◽  
Arctic Amplification ◽  
Polar Surface ◽  
Surface Warming ◽  
Column Model ◽  
Single Column ◽  
Single Column Model

AbstractThe precise mechanisms driving Arctic amplification are still under debate. Previous attribution methods compute the vertically-uniform temperature change required to balance the top-of-atmosphere energy imbalance caused by each forcing and feedback, with any departures from vertically-uniform warming collected into the lapse-rate feedback. We propose an alternative attribution method using a single column model that accounts for the forcing-dependence of high latitude lapse-rate changes. We examine this method in an idealized General Circulation Model (GCM), finding that, even though the column-integrated carbon dioxide (CO2) forcing and water vapor feedback are stronger in the tropics, they contribute to polar-amplified surface warming as they produce bottom-heavy warming in high latitudes. A separation of atmospheric temperature changes into local and remote contributors shows that, in the absence of polar surface forcing (e.g., sea-ice retreat), changes in energy transport are primarily responsible for the polar amplified pattern of warming. The addition of surface forcing substantially increases polar surface warming and reduces the contribution of atmospheric dry static energy transport to the warming. This physically-based attribution method can be applied to comprehensive GCMs to provide a clearer view of the mechanisms behind Arctic amplification.

scholarly journals Understanding the Differences Between TOA and Surface Energy Budget Attributions of Surface Warming

2021 ◽  
Vol 9 ◽  
Author(s):  
Sergio A. Sejas ◽  
Xiaoming Hu ◽  
Ming Cai ◽  
Hanjie Fan
Keyword(s):  
Surface Energy ◽  
Energy Budget ◽  
Surface Energy Budget ◽  
Lapse Rate ◽  
Climate Feedback ◽  
Energy Budgets ◽  
Response Analysis ◽  
Surface Warming ◽  
Rate Feedback ◽  
Consistent Picture

Energy budget decompositions have widely been used to evaluate individual process contributions to surface warming. Conventionally, the top-of-atmosphere (TOA) energy budget has been used to carry out such attribution, while other studies use the surface energy budget instead. However, the two perspectives do not provide the same interpretation of process contributions to surface warming, particularly when executing a spatial analysis. These differences cloud our understanding and inhibit our ability to shrink the inter-model spread. Changes to the TOA energy budget are equivalent to the sum of the changes in the atmospheric and surface energy budgets. Therefore, we show that the major discrepancies between the surface and TOA perspectives are due to non-negligible changes in the atmospheric energy budget that differ from their counterparts at the surface. The TOA lapse-rate feedback is the manifestation of multiple processes that produce a vertically non-uniform warming response such that it accounts for the asymmetry between the changes in the atmospheric and surface energy budgets. Using the climate feedback-response analysis method, we are able to decompose the lapse-rate feedback into contributions by individual processes. Combining the process contributions that are hidden within the lapse-rate feedback with their respective direct impacts on the TOA energy budget allows for a very consistent picture of process contributions to surface warming and its inter-model spread as that given by the surface energy budget approach.

A multimodel investigation of atmospheric mechanisms for driving Arctic amplification in warmer climates

2021 ◽  
pp. 1-55
Author(s):  
Deepashree Dutta ◽  
Steven C. Sherwood ◽  
Katrin J. Meissner ◽  
Alex Sen Gupta ◽  
Daniel J. Lunt ◽  
...  
Keyword(s):  
Heat Transport ◽  
General Circulation ◽  
Energy Transport ◽  
Longwave Radiation ◽  
General Circulation Models ◽  
The Arctic ◽  
Arctic Warming ◽  
Surface Warming ◽  
Poleward Heat Transport ◽  
Warm Climates

AbstractWhen simulating past warm climates, such as the early Cretaceous and Paleogene periods, general circulation models (GCMs) underestimate the magnitude of warming in the Arctic. Additionally, model intercomparisons show a large spread in the magnitude of Arctic warming for these warmer-than-modern climates. Several mechanisms have been proposed to explain these disagreements, including the unrealistic representation of polar clouds or underestimated poleward heat transport in the models. This study provides an intercomparison of Arctic cloud and atmospheric heat transport (AHT) responses to strong imposed polar-amplified surface ocean warming across four atmosphere-only GCMs. All models simulate an increase in high clouds throughout the year; the resulting reduction in longwave radiation loss to space acts to support the imposed Arctic warming. The response of low and mid-level clouds varies considerably across the models, with models responding differently to surface warming and sea ice removal. The AHT is consistently weaker in the imposed warming experiments due to a large reduction in dry static energy transport that offsets a smaller increase in latent heat transport, thereby opposing the imposed surface warming. Our idealised polar amplification experiments require very large increases in implied ocean heat transport (OHT) to maintain steady state. Increased CO2 or tropical temperatures that likely characterised past warm climates, reduces the need for such large OHT increases.

scholarly journals Dependence of Climate Response on Meridional Structure of External Thermal Forcing

2014 ◽  
Vol 27 (14) ◽  
pp. 5593-5600 ◽  
Author(s):  
Sarah M. Kang ◽  
Shang-Ping Xie
Keyword(s):  
Mixed Layer ◽  
Atmospheric Stability ◽  
Atmospheric Model ◽  
Thermal Forcing ◽  
Surface Warming ◽  
Mixed Layer Ocean ◽  
Radiative Feedbacks ◽  
The Tropics ◽  
The Given ◽  
Global Surface

Abstract This study shows that the magnitude of global surface warming greatly depends on the meridional distribution of surface thermal forcing. An atmospheric model coupled to an aquaplanet slab mixed layer ocean is perturbed by prescribing heating to the ocean mixed layer. The heating is distributed uniformly globally or confined to narrow tropical or polar bands, and the amplitude is adjusted to ensure that the global mean remains the same for all cases. Since the tropical temperature is close to a moist adiabat, the prescribed heating leads to a maximized warming near the tropopause, whereas the polar warming is trapped near the surface because of strong atmospheric stability. Hence, the surface warming is more effectively damped by radiation in the tropics than in the polar region. As a result, the global surface temperature increase is weak (strong) when the given amount of heating is confined to the tropical (polar) band. The degree of this contrast is shown to depend on water vapor– and cloud–radiative feedbacks that alter the effective strength of prescribed thermal forcing.

Local atmospheric response to the Kuroshio large meander path in summer and its remote influence on the climate of Japan

2021 ◽  
pp. 1-56
Author(s):  
Shusaku Sugimoto ◽  
Bo Qiu ◽  
Niklas Schneider
Keyword(s):  
Water Vapor ◽  
Vertical Mixing ◽  
Longwave Radiation ◽  
Atmospheric Model ◽  
Large Meander ◽  
Near Surface ◽  
Surface Warming ◽  
Downward Longwave Radiation ◽  
Kanto District ◽  
The Kuroshio

AbstractThe Kanto district, Japan, including Tokyo, has 40 million inhabitants and its summer climate is characterized by high temperature and humidity. The Kuroshio that flows off the southern coast of Kanto district has taken a large meander (LM) path since the summer of 2017 for the first time since the 2004–2005 event. Recently-developed satellite observations detected marked coastal warming off the Kanto-Tokai district during the LM path period. By conducting regional atmospheric model experiments, it is found that summertime coastal warming increases water vapor in the low-level atmosphere through enhanced evaporation from the ocean and influences near-surface winds via the vertical mixing effect over the warming area. These two changes induce an increase in water vapor in Kanto district, leading to an increase in downward longwave radiation at the surface and then surface warming through a local greenhouse effect. Resultantly the summer in Kanto district becomes increasingly hot and humid in LM years, with double the number of discomfort days compared with non-LM years. Our simulations and supplementary observational studies reveal the significant impacts of the LM-induced coastal warming on the summertime climate in Japan, which can exceed previously identified atmospheric teleconnections and climate patterns. Our results could improve weather and seasonal climate forecasts in this region.

Surface warming patterns dominate the uncertainty in global water vapor plus lapse rate feedback

2020 ◽  
Vol 39 (3) ◽  
pp. 81-89 ◽  
Author(s):  
Jingchun Zhang ◽  
Jian Ma ◽  
Jing Che ◽  
Zhenqiang Zhou ◽  
Guoping Gao
Keyword(s):  
Water Vapor ◽  
Lapse Rate ◽  
Surface Warming ◽  
Rate Feedback ◽  
Global Water

scholarly journals Contrasting Local and Remote Impacts of Surface Heating on Polar Warming and Amplification

2018 ◽  
Vol 31 (8) ◽  
pp. 3155-3166 ◽  
Author(s):  
Kiwoong Park ◽  
Sarah M. Kang ◽  
Doyeon Kim ◽  
Malte F. Stuecker ◽  
Fei-Fei Jin
Keyword(s):  
Local Heating ◽  
Static Stability ◽  
Polar Surface ◽  
Surface Warming ◽  
Tropical Forcing ◽  
Poleward Heat Transport ◽  
Warming Pattern ◽  
Ocean Layer ◽  
The Individual ◽  
Global Mean

Abstract The polar region has been one of the fastest warming places on Earth in response to greenhouse gas (GHG) forcing. Two distinct processes contribute to the observed warming signal: (i) local warming in direct response to the GHG forcing and (ii) the effect of enhanced poleward heat transport from low latitudes. A series of aquaplanet experiments, which excludes the surface albedo feedback, is conducted to quantify the relative contributions of these two physical processes to the polar warming magnitude and degree of amplification relative to the global mean. The globe is divided into zonal bands with equal area in eight experiments. For each of these, an external heating is prescribed beneath the slab ocean layer in the respective forcing bands. The summation of the individual temperature responses to each local heating in these experiments is very similar to the response to a globally uniform heating. This allows the authors to decompose the polar warming and amplification signal into the effects of local and remote heating. Local polar heating that induces surface-trapped warming due to the large tropospheric static stability in this region accounts for about half of the polar surface warming. Cloud radiative effects act to enhance this local contribution. In contrast, remote nonpolar heating induces a robust polar warming pattern that features a midtropospheric peak, regardless of the meridional location of the forcing. Among all remote forcing experiments, the deep tropical forcing case contributes most to the polar-amplified surface warming pattern relative to the global mean, while the high-latitude forcing cases contribute most to enhancing the polar surface warming magnitude.

scholarly journals Polar Amplification in CCSM4: Contributions from the Lapse Rate and Surface Albedo Feedbacks

2014 ◽  
Vol 27 (12) ◽  
pp. 4433-4450 ◽  
Author(s):  
Rune G. Graversen ◽  
Peter L. Langen ◽  
Thorsten Mauritsen
Keyword(s):  
Radiative Forcing ◽  
Surface Albedo ◽  
Temperature Response ◽  
Global Scale ◽  
Lapse Rate ◽  
The Arctic ◽  
High Latitudes ◽  
Climate System Model ◽  
Polar Amplification ◽  
Rate Feedback

Abstract A vertically nonuniform warming of the troposphere yields a lapse rate feedback by altering the infrared irradiance to space relative to that of a vertically uniform tropospheric warming. The lapse rate feedback is negative at low latitudes, as a result of moist convective processes, and positive at high latitudes, due to stable stratification conditions that effectively trap warming near the surface. It is shown that this feedback pattern leads to polar amplification of the temperature response induced by a radiative forcing. The results are obtained by suppressing the lapse rate feedback in the Community Climate System Model, version 4 (CCSM4). The lapse rate feedback accounts for 15% of the Arctic amplification and 20% of the amplification in the Antarctic region. The fraction of the amplification that can be attributed to the surface albedo feedback, associated with melting of snow and ice, is 40% in the Arctic and 65% in Antarctica. It is further found that the surface albedo and lapse rate feedbacks interact considerably at high latitudes to the extent that they cannot be considered independent feedback mechanisms at the global scale.

scholarly journals Intermodel Spread in the Pattern Effect and Its Contribution to Climate Sensitivity in CMIP5 and CMIP6 Models

2020 ◽  
Vol 33 (18) ◽  
pp. 7755-7775 ◽  
Author(s):  
Yue Dong ◽  
Kyle C. Armour ◽  
Mark D. Zelinka ◽  
Cristian Proistosescu ◽  
David S. Battisti ◽  
...  
Keyword(s):  
Time Scales ◽  
Climate Sensitivity ◽  
Atmospheric Model ◽  
Warm Pool ◽  
Cmip5 Models ◽  
Fast Time ◽  
Pattern Effect ◽  
Surface Warming ◽  
Early Portion ◽  
Radiative Feedbacks

AbstractRadiative feedbacks depend on the spatial patterns of sea surface temperature (SST) and thus can change over time as SST patterns evolve—the so-called pattern effect. This study investigates intermodel differences in the magnitude of the pattern effect and how these differences contribute to the spread in effective equilibrium climate sensitivity (ECS) within CMIP5 and CMIP6 models. Effective ECS in CMIP5 estimated from 150-yr-long abrupt4×CO2 simulations is on average 10% higher than that estimated from the early portion (first 50 years) of those simulations, which serves as an analog for historical warming; this difference is reduced to 7% on average in CMIP6. The (negative) net radiative feedback weakens over the course of the abrupt4×CO2 simulations in the vast majority of CMIP5 and CMIP6 models, but this weakening is less dramatic on average in CMIP6. For both ensembles, the total variance in the effective ECS is found to be dominated by the spread in radiative response on fast time scales, rather than the spread in feedback changes. Using Green’s functions derived from two AGCMs shows that the spread in feedbacks on fast time scales may be primarily due to differences in atmospheric model physics, whereas the spread in feedback evolution is primarily governed by differences in SST patterns. Intermodel spread in feedback evolution is well explained by differences in the relative warming in the west Pacific warm-pool regions for the CMIP5 models, but this relation fails to explain differences across the CMIP6 models, suggesting that a stronger sensitivity of extratropical clouds to surface warming may also contribute to feedback changes in CMIP6.

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