The Lifecycle and Physical Drivers of Heatwaves in a Hierarchy of Model Simulations  

2021 ◽  
Author(s):  
Bernat Jiménez-Esteve ◽  
Daniela I.V. Domeisen
Keyword(s):  
Surface Temperature ◽  
Extreme Temperature ◽  
Model Complexity ◽  
Extreme Weather Events ◽  
Horizontal Wind ◽  
Physical Processes ◽  
Near Surface ◽  
Temperature Anomalies ◽  
Model Configuration ◽  
Diabatic Processes

<p>Heatwaves are extreme weather events characterized by extreme near-surface temperature anomalies that persist for several days, which lead to catastrophic impacts on natural ecosystems, agriculture, human health, and economies. Different physical processes can contribute to the increase in temperature associated with heatwaves. Previous studies have shown that adiabatic compression due to subsidence and local land-atmosphere coupling are important drivers of summer heatwaves. However, less is known about the respective roles of these processes for heat extremes occurring in different seasons and latitudes.</p><p>By analyzing the different terms of the temperature tendency equation, we quantify the relative importance of horizontal wind advection, adiabatic, and diabatic processes (including radiation and surface fluxes) during the lifecycle of realistic and idealized heatwaves. We identify heatwaves both in reanalysis and in simulations using the ICOsahedral Nonhydrostatic (ICON) climate model. These simulations range from a simple zonally symmetric temperature relaxation and dry dynamics to a simulation using full physics, with coupled land and sea surface temperature forcing. This step-wise inclusion of physical processes and increasing model complexity allows us to identify the key drivers of extreme warm events and the characteristics of these across the different model complexities. In the simplest model configuration, i.e. only dry dynamics and no surface coupling, extreme temperature events are generally shorter but produce more intense temperature anomalies in the midlatitudes, where the horizontal temperature gradient is strongest. These idealized heatwaves are almost entirely driven by a very strong advection of warm air from more equatorward locations and are linked to local amplification of Rossby wave packets and atmospheric blocking. In contrast, in the complex model configuration as well as in reanalysis, summer heatwaves over land areas are mainly driven by adiabatic and diabatic processes, while advection is of secondary importance. On the other hand, extreme warm periods during winter are mainly driven by advection both in the model and reanalysis. Identifying the most relevant processes driving heatwaves can potentially benefit the prediction and representation of extreme events in operational weather and climate forecasts.</p>

scholarly journals A Pilot Climate Sensitivity Study Using the CEN Coupled Adjoint Model (CESAM)

2018 ◽  
Vol 31 (5) ◽  
pp. 2031-2056 ◽  
Author(s):  
D. Stammer ◽  
A. Köhl ◽  
A. Vlasenko ◽  
I. Matei ◽  
F. Lunkeit ◽  
...  
Keyword(s):  
Sea Ice ◽  
Surface Temperature ◽  
Climate Sensitivity ◽  
North Atlantic ◽  
Sensitivity Study ◽  
Northern Europe ◽  
Surface Salinity ◽  
Near Surface ◽  
Temperature Anomalies ◽  
Northern European

A pilot coupled climate sensitivity study is presented based on the newly developed adjoint coupled climate model, Centrum für Erdsystemforschung und Nachhaltigkeit (CEN) Earth System Assimilation Model (CESAM). To this end the components of the coupled forward model are summarized, and the generation of the adjoint code out of the model forward code through the application of the Transformation of Algorithms in FORTRAN (TAF) adjoint compiler is discussed. It is shown that simulations of the intermediate-complexity CESAM are comparable in quality to CMIP-type coupled climate models, justifying the usage of the model to compute adjoint sensitivities of the northern Europe near-surface temperature to anomalies in surface temperature, sea surface salinity, and sea ice over the North Atlantic and the Arctic on time scales of up to one month. Results confirm that on a time scale of up to a few days surface temperatures over northern Europe are influenced by Atlantic temperature anomalies just upstream of the target location. With increasingly longer time lapse, however, it is the influence of SSTs over the central and western North Atlantic on the overlying atmosphere and the associated changes in storm-track pattern that dominate the evolution of the surface European temperature. Influences of surface salinity and sea ice on the northern European temperature appear to have similar sensitivity mechanisms, invoked indirectly through their influence on near-surface temperature anomalies. The adjoint study thus confirms that the SST’s impact on the atmospheric dynamics, notably storm tracks, is the primary cause for the influence of northern European temperature changes.

scholarly journals SPECTRAL CHARACTERISTICS OF TUNDRA AND FOREST TUNDRA LANDSCAPES DURING THE YEARS OF SUMMER TEMPERATURE ANOMALIES

2020 ◽  
Vol 4 ◽  
pp. 88-103
Author(s):  
T.B. Titkova ◽  
◽  
A.N. Zolotokrylin ◽  
V.V. Vinogradov ◽  
◽  
...  
Keyword(s):  
Surface Temperature ◽  
Regulatory Mechanism ◽  
Spectral Characteristics ◽  
Extreme Temperature ◽  
Regulatory Mechanisms ◽  
Spectral Parameters ◽  
Vegetation Diversity ◽  
Forest Tundra ◽  
Temperature Anomalies ◽  
Novaya Zemlya

The warming at high latitudes, remaining in recent years, has a direct impact on arctic and subarctic landscapes. Possible changes of this landscapes under the climate warming are closely related with regulatory mechanisms for the underlying surface temperature. The circumstances of forming radiation and evapotranspirational regulatory mechanisms for the surface temperature were explored for tundra (from arctic to southern) and forest tundra landscapes of Novaya Zemlya and Western Siberia. The MODIS data of surface spectral characteristics were used, and more specifically albedo (Al) and surface temperature (Ts) for July 2000-2019. The work shows that the radiation regulatory mechanism of the surface temperature is dominated in glacial and polar desert landscapes of Arctic and Subarctic with a predominance of stony and rubble types of surfaces with lichens. At the same time, radiative surface temperature control mechanism in mountain and arctic tundra of Novaya Zemlya almost does not depend on weather anomalies and so far has a little implication for the temperature trend. In the mainland and forest tundra, the evapotranspirational regulatory mechanism for the surface temperature starts to prevail. This is supported by the increasing of monthly average air temperatures to 15-16°С, which is beneficial to the vegetation diversity. In subzones of the southern and forest tundra, the connection of albedo and surface temperature depends on altitudes, slope exposure and especially on extreme temperature anomalies. In basins, or hydromorphic complexes, in cold years against the backdrop of wetlands the regulatory mechanism for the surface temperature prevails, and in warm years the humidity decreasing leads to the highest vegetation development and the connection type can turn into the evapotranspirational one. On the high grounds the return process is observed, which is also connected with the changes in humidification conditions. In forest tundra, where the air temperature rises and the canopy height increases, the evapotranspirational mechanism of spectral parameters Al–Ts connections is weakening. As a result, in southern and forest tundra two balanced steady states of the connection types of surface spectral characteristics can exist in relation to lighting conditions and temperature anomalies.

Determining the range for CMIP climate projections for Europe using a sub-selected model ensemble based on key model performance indicators and key regional physical processes.

2020 ◽  
Author(s):  
Tamzin Palmer ◽  
Carol Mc Sweeney ◽  
Ben Booth
Keyword(s):  
Surface Temperature ◽  
Performance Indicators ◽  
Model Performance ◽  
Cmip5 Models ◽  
Climate Projections ◽  
Physical Processes ◽  
Near Surface ◽  
European Area ◽  
The Uk ◽  
The Impact

<p>An alternative approach to constraining climate projections based on a probabilistic approach with observational constraints, is to select a subset of models from the ensemble based on their ability to represent key physical processes, along with some indicators of model performance. The method that is presented here is based on the assumption that if a model is unable to reproduce the key factors important for determining the regional climate, the projections from this model are not considered reliable. The projection range for CMIP5 for the three EUCP European regions is assessed using two different subsampled model ensembles.</p><p>The first sub-sampling method presented uses the approach of Mc Sweeney et al. (2015), which assessed the models based on their performance for the UK climate. Each model in the CMIP5 ensemble (where data is available), is firstly assessed against these key performance indicators and poor performers eliminated from the selection. Several models also share large portions of code and therefore have similar errors and projections, Sanderson et al 2015a and 2015b quantifies these similarities. This analysis was used identify ‘near-neighbours’ and further reduce the selection. The applicability of a sub-selection of models based on their performance for the UK climate is assessed for the wider European area and found to reduce the projected range for the Northern European Area (NEU), for precipitation and near surface temperature considerably. The impact on the projected ranges for the Central European Area (CEU) and the Mediterranean (MED) was not as large, suggesting that a different set of physical processes are of primary importance for these regions.</p><p>To further investigate the effect of subsampling based on physical processes, a subset of CMIP5 models identified by the approach of Vogel et al. (2018) has been applied for the EUCP European areas. Vogel et al. (2018) looked at the ability of the CMIP5 models to reproduce the correlation between the hottest day of the year and precipitation within the same range as that found in the observations. This approach is designed to subsample the ensemble based on the ability of the model to represent soil moisture feedback processes with the atmosphere. It is thought that these processes are likely to be increasingly important for determining the projected climate in the CEU and MED regions.  </p><p>Finally, the projection range for the CMIP6 ensemble in the EUCP regions for precipitation and the near surface temperature will be presented and compared with those for CMIP5.</p>

scholarly journals A Dynamical Perspective on Atmospheric Temperature Variability and Its Response to Climate Change

2019 ◽  
Vol 32 (6) ◽  
pp. 1707-1724 ◽  
Author(s):  
Talia Tamarin-Brodsky ◽  
Kevin Hodges ◽  
Brian J. Hoskins ◽  
Theodore G. Shepherd
Keyword(s):  
Temperature Distribution ◽  
Spatial Structure ◽  
Surface Temperature ◽  
Southern Hemisphere ◽  
Atmospheric Temperature ◽  
Storm Tracks ◽  
Near Surface ◽  
Temperature Anomalies ◽  
Poleward Shift ◽  
Meridional Advection

Abstract The atmospheric temperature distribution is typically described by its mean and variance, while higher-order moments, such as skewness, have received less attention. Skewness is a measure of the asymmetry between the positive and negative tails of the distribution, which has implications for extremes. It was recently shown that near-surface temperature in the Southern Hemisphere is positively skewed on the poleward side of the storm tracks and negatively skewed on the equatorward side. Here we take a dynamical approach to further study what controls the spatial structure of the near-surface temperature distribution in this region. We employ a tracking algorithm to study the formation, intensity, and movement of warm and cold temperature anomalies. We show that warm anomalies are generated on the equatorward side of the storm tracks and propagate poleward, while cold anomalies are generated on the poleward side and propagate equatorward. We further show that while the perturbation growth is mainly achieved through linear meridional advection, it is the nonlinear meridional advection that is responsible for the meridional movement of the temperature anomalies and therefore to the differential skewness. The projected poleward shift and increase of the temperature variance maximum in the Southern Hemisphere under global warming is shown to be composed of a poleward shift and increase in the maximum intensity of both warm and cold anomalies, and a decrease in their meridional displacements. An analytic expression is derived for the nonlinear meridional temperature tendency, which captures the spatial structure of the skewness and its projected changes.

scholarly journals Impact of Soil Moisture–Atmosphere Interactions on Surface Temperature Distribution

2014 ◽  
Vol 27 (21) ◽  
pp. 7976-7993 ◽  
Author(s):  
Alexis Berg ◽  
Benjamin R. Lintner ◽  
Kirsten L. Findell ◽  
Sergey Malyshev ◽  
Paul C. Loikith ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Temperature Distribution ◽  
Surface Temperature ◽  
Extreme Temperature ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Near Surface ◽  
Soil Moisture Dynamics ◽  
Available Energy ◽  
Mean And Variance ◽  
Moisture Dynamics

Abstract Understanding how different physical processes can shape the probability distribution function (PDF) of surface temperature, in particular the tails of the distribution, is essential for the attribution and projection of future extreme temperature events. In this study, the contribution of soil moisture–atmosphere interactions to surface temperature PDFs is investigated. Soil moisture represents a key variable in the coupling of the land and atmosphere, since it controls the partitioning of available energy between sensible and latent heat flux at the surface. Consequently, soil moisture variability driven by the atmosphere may feed back onto the near-surface climate—in particular, temperature. In this study, two simulations of the current-generation Geophysical Fluid Dynamics Laboratory (GFDL) Earth System Model, with and without interactive soil moisture, are analyzed in order to assess how soil moisture dynamics impact the simulated climate. Comparison of these simulations shows that soil moisture dynamics enhance both temperature mean and variance over regional “hotspots” of land–atmosphere coupling. Moreover, higher-order distribution moments, such as skewness and kurtosis, are also significantly impacted, suggesting an asymmetric impact on the positive and negative extremes of the temperature PDF. Such changes are interpreted in the context of altered distributions of the surface turbulent and radiative fluxes. That the moments of the temperature distribution may respond differentially to soil moisture dynamics underscores the importance of analyzing moments beyond the mean and variance to characterize fully the interplay of soil moisture and near-surface temperature. In addition, it is shown that soil moisture dynamics impacts daily temperature variability at different time scales over different regions in the model.

A Simple Technique for Creating Regional Composites of Sea Surface Temperature from MODIS for Use in Operational Mesoscale NWP

2010 ◽  
Vol 49 (11) ◽  
pp. 2267-2284 ◽  
Author(s):  
Jason C. Knievel ◽  
Daran L. Rife ◽  
Joseph A. Grim ◽  
Andrea N. Hahmann ◽  
Joshua P. Hacker ◽  
...  
Keyword(s):  
High Resolution ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Real Time ◽  
Simple Technique ◽  
Weather Prediction ◽  
Sea Breeze ◽  
Sea Surface ◽  
Horizontal Wind ◽  
Near Surface

Abstract This paper describes a simple technique for creating regional, high-resolution, daytime and nighttime composites of sea surface temperature (SST) for use in operational numerical weather prediction (NWP). The composites are based on observations from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Aqua and Terra. The data used typically are available nearly in real time, are applicable anywhere on the globe, and are capable of roughly representing the diurnal cycle in SST. The composites’ resolution is much higher than that of many other standard SST products used for operational NWP, including the low- and high-resolution Real-Time Global (RTG) analyses. The difference in resolution is key because several studies have shown that highly resolved SSTs are important for driving the air–sea interactions that shape patterns of static stability, vertical and horizontal wind shear, and divergence in the planetary boundary layer. The MODIS-based composites are compared to in situ observations from buoys and other platforms operated by the National Data Buoy Center (NDBC) off the coasts of New England, the mid-Atlantic, and Florida. Mean differences, mean absolute differences, and root-mean-square differences between the composites and the NDBC observations are all within tenths of a degree of those calculated between RTG analyses and the NDBC observations. This is true whether or not one accounts for the mean offset between the skin temperatures of the MODIS dataset and the bulk temperatures of the NDBC observations and RTG analyses. Near the coast, the MODIS-based composites tend to agree more with NDBC observations than do the RTG analyses. The opposite is true away from the coast. All of these differences in point-wise comparisons among the SST datasets are small compared to the ±1.0°C accuracy of the NDBC SST sensors. Because skin-temperature variations from land to water so strongly affect the development and life cycle of the sea breeze, this phenomenon was chosen for demonstrating the use of the MODIS-based composite in an NWP model. A simulated sea breeze in the vicinity of New York City and Long Island shows a small, net, but far from universal improvement when MODIS-based composites are used in place of RTG analyses. The timing of the sea breeze’s arrival is more accurate at some stations, and the near-surface temperature, wind, and humidity within the breeze are more realistic.

scholarly journals An Analysis of the Potential for Extreme Temperature Change Based on Observations and Model Simulations

2007 ◽  
Vol 20 (8) ◽  
pp. 1539-1554 ◽  
Author(s):  
Barry H. Lynn ◽  
Richard Healy ◽  
Leonard M. Druyan
Keyword(s):  
United States ◽  
Surface Temperature ◽  
Temperature Change ◽  
Extreme Temperature ◽  
Sea Surface ◽  
Eastern Pacific ◽  
Moist Convection ◽  
Eastern United States ◽  
Maximum Surface ◽  
Temperature Anomalies

Abstract The study analyzes observational climate data for June–August 1977–2004 and simulations of current and future climate scenarios from a nested GCM/regional climate model system to assess the potential for extreme temperature change over the eastern United States. Observational evidence indicates that anomalously warm summers in the eastern United States coincide with anomalously cool eastern Pacific sea surface temperatures, conditions that are conducive to geopotential ridging over the east, less frequent precipitation, and lower accumulated rainfall. The study also found that days following nighttime rain are warmer on average than daytime rain events, emphasizing the importance of the timing of precipitation on the radiation balance. Precipitation frequency and eastern Pacific sea surface temperature anomalies together account for 57% of the 28-yr variance in maximum surface temperature anomalies. Simulation results show the sensitivity of maximum surface air temperature to the moist convection parameterization that is employed, since different schemes produce different diurnal cycles and frequencies of precipitation. The study suggests that, in order to accurately project scenarios of extreme temperature change, models need to realistically simulate changes in the surface energy balance caused by the interannual variation of these precipitation characteristics. The mesoscale model that was realistic in this respect predicted much warmer mean and maximum surface air temperatures for five future summers than the parallel GCM driving simulation.

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