scholarly journals Soil Moisture–Atmosphere Interactions during the 2003 European Summer Heat Wave

2007 ◽  
Vol 20 (20) ◽  
pp. 5081-5099 ◽  
Author(s):  
E. M. Fischer ◽  
S. I. Seneviratne ◽  
P. L. Vidale ◽  
D. Lüthi ◽  
C. Schär
Keyword(s):  
Soil Moisture ◽  
Heat Wave ◽  
Regional Climate ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Net Radiation ◽  
Temperature Anomalies ◽  
Continental Scale ◽  
Summer Heat

Abstract The role of land surface–related processes and feedbacks during the record-breaking 2003 European summer heat wave is explored with a regional climate model. All simulations are driven by lateral boundary conditions and sea surface temperatures from the ECMWF operational analysis and 40-yr ECMWF Re-Analysis (ERA-40), thereby prescribing the large-scale circulation. In particular, the contribution of soil moisture anomalies and their interactions with the atmosphere through latent and sensible heat fluxes is investigated. Sensitivity experiments are performed by perturbing spring soil moisture in order to determine its influence on the formation of the heat wave. A multiyear regional climate simulation for 1970–2000 using a fixed model setup is used as the reference period. A large precipitation deficit together with early vegetation green-up and strong positive radiative anomalies in the months preceding the extreme summer event contributed to an early and rapid loss of soil moisture, which exceeded the multiyear average by far. The exceptionally high temperature anomalies, most pronounced in June and August 2003, were initiated by persistent anticyclonic circulation anomalies that enabled a dominance of the local heat balance. In this experiment the hottest phase in early August is realistically simulated despite the absence of an anomaly in total surface net radiation. This indicates an important role of the partitioning of net radiation in latent and sensible heat fluxes, which is to a large extent controlled by soil moisture. The lack of soil moisture strongly reduced latent cooling and thereby amplified the surface temperature anomalies. The evaluation of the experiments with perturbed spring soil moisture shows that this quantity is an important parameter for the evolution of European heat waves. Simulations indicate that without soil moisture anomalies the summer heat anomalies could have been reduced by around 40% in some regions. Moreover, drought conditions are revealed to influence the tropospheric circulation by producing a surface heat low and enhanced ridging in the midtroposphere. This suggests a positive feedback mechanism between soil moisture, continental-scale circulation, and temperature.

The Role of Northern Lakes in a Regional Energy Balance

2005 ◽  
Vol 6 (3) ◽  
pp. 291-305 ◽  
Author(s):  
Wayne R. Rouse ◽  
Claire J. Oswald ◽  
Jacqueline Binyamin ◽  
Christopher Spence ◽  
William M. Schertzer ◽  
...  
Keyword(s):  
Surface Energy ◽  
Heat Storage ◽  
Regional Climate ◽  
Heat Fluxes ◽  
Net Radiation ◽  
Large Lakes ◽  
Regional Energy ◽  
Energy Balances ◽  
Lake Size

Abstract There are many lakes of widely varying morphometry in northern latitudes. For this study region, in the central Mackenzie River valley of western Canada, lakes make up 37% of the landscape. The nonlake components of the landscape are divided into uplands (55%) and wetlands (8%). With such abundance, lakes are important features that can influence the regional climate. This paper examines the role of lakes in the regional surface energy and water balance and evaluates the links to the frequency–size distribution of lakes. The primary purpose is to examine how the surface energy balance may influence regional climate and weather. Lakes are characterized by both the magnitude and temporal behavior of their surface energy balances during the ice-free period. The impacts of combinations of various-size lakes and land–lake distributions on regional energy balances and evaporation cycles are presented. Net radiation is substantially greater over all water-dominated surfaces compared with uplands. The seasonal heat storage increases with lake size. Medium and large lakes are slow to warm in summer. Their large cumulative heat storage, near summer’s end, fuels large convective heat fluxes in fall and early winter. The evaporation season for upland, wetland, and small, medium, and large lakes lasts for 19, 21, 22, 24, and 30 weeks, respectively. The regional effects of combinations of surface types are derived. The region is initially treated as comprising uplands only. The influences of wetland, small, medium, and large lakes are added sequentially, to build up to the energy budget of the actual landscape. The addition of lakes increases the regional net radiation, the maximum regional subsurface heat storage, and evaporation substantially. Evaporation decreases slightly in the first half of the season but experiences a large enhancement in the second half. The sensible heat flux is reduced substantially in the first half of the season, but changes little in the second half. For energy budget modeling the representation of lake size is important. Net radiation is fairly independent of size. An equal area of medium and large lakes, compared with small lakes, yields substantially larger latent heat fluxes and lesser sensible heat fluxes. Lake size also creates large differences in regional flux magnitudes, especially in the spring and fall periods.

scholarly journals Capability of the variogram to quantify the spatial patterns of surface fluxes and soil moisture simulated by land surface models

2021 ◽  
Vol 45 (2) ◽  
pp. 279-293
Author(s):  
S Garrigues ◽  
A Verhoef ◽  
E Blyth ◽  
A Wright ◽  
B Balan-Sarojini ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Spatial Variability ◽  
Spatial Patterns ◽  
Land Surface ◽  
Heat Fluxes ◽  
Surface Model ◽  
Sensible Heat ◽  
Net Radiation ◽  
Land Surface Models ◽  
Surface Models

Up to now, relatively little effort has been dedicated to the quantitative assessment of the differences in spatial patterns of model outputs. In this paper, we employed a variogram-based methodology to quantify the differences in the spatial patterns of root-zone soil moisture, net radiation, and latent and sensible heat fluxes simulated by three land surface models (SURFEX/ISBA, JULES and CHTESSEL) over three European geographic domains – namely, UK, France and Spain. The model output spatial patterns were quantified through two metrics derived from the variogram: i) the variogram sill, which quantifies the degree of spatial variability of the data; and ii) the variogram integral range, which represents the spatial length scale of the data. The higher seasonal variation of the spatial variability of sensible and latent heat fluxes over France and Spain, compared to the UK, is related to a more frequent occurrence of a soil-moisture-limited evapotranspiration regime during summer dry spells in the south of France and Spain. The small differences in spatial variability of net radiation between models indicate that the spatial patterns of net radiation are mostly driven by the climate forcing data set. However, the models exhibit larger differences in latent and sensible heat flux spatial variabilities, which are related to their differences in i) soil and vegetation ancillary datasets and ii) physical process representation. The highest discrepancies in spatial patterns between models are observed for soil moisture, which is mainly related to the type of soil hydraulic function implemented in the models. This work demonstrates the capability of the variogram to enhance our understanding of the spatiotemporal structure of the uncertainties in land surface model outputs. Therefore, we strongly encourage the implementation of the variogram metrics in model intercomparison exercises.

scholarly journals Midwinter melts in the Canadian prairies: energy balance and hydrological effects

2019 ◽  
Vol 23 (4) ◽  
pp. 1867-1883 ◽  
Author(s):  
Igor Pavlovskii ◽  
Masaki Hayashi ◽  
Daniel Itenfisu
Keyword(s):  
Surface Runoff ◽  
Hydrological Cycle ◽  
Remote Sensing Data ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Net Radiation ◽  
Present Climate ◽  
Canadian Prairies ◽  
Energy Inputs ◽  
Hydrological Effects

Abstract. Snowpack accumulation and depletion are important elements of the hydrological cycle in the Canadian prairies. The surface runoff generated during snowmelt is transformed into streamflow or fills numerous depressions driving the focussed recharge of groundwater in this dry setting. The snowpack in the prairies can undergo several cycles of accumulation and depletion in a winter. The timing of the melt affects the mechanisms of snowpack depletion and their hydrological implications. The effects of midwinter melts were investigated at four instrumented sites in the Canadian prairies. Unlike net radiation-driven snowmelt during spring melt, turbulent sensible heat fluxes were the dominant source of energy inputs for midwinter melt occurring in the period with low solar radiation inputs. Midwinter melt events affect several aspects of hydrological cycle with lower runoff ratios than subsequent spring melt events, due to their role in the timing of the focussed recharge. Remote sensing data have shown that midwinter melt events regularly occur under the present climate throughout the Canadian prairies, indicating applicability of the study findings throughout the region.

The Tropical Transition of the October 1996 Medicane in the Western Mediterranean Sea: A Warm Seclusion Event

2017 ◽  
Vol 145 (7) ◽  
pp. 2575-2595 ◽  
Author(s):  
Edoardo Mazza ◽  
Uwe Ulbrich ◽  
Rupert Klein
Keyword(s):  
Wind Shear ◽  
Climate Model ◽  
Regional Climate ◽  
Vertical Wind Shear ◽  
Lower Troposphere ◽  
Western Mediterranean ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Western Mediterranean Sea ◽  
Warm Core

The processes leading to the tropical transition of the October 1996 medicane in the western Mediterranean are investigated on the basis of a 50-member ensemble of regional climate model (RCM) simulations. By comparing the composites of transitioning and nontransitioning cyclones it is shown that standard extratropical dynamics are responsible for the cyclogenesis and that the transition results from a warm seclusion process. As the initial thermal asymmetries and vertical tilt of the cyclones are reduced, a warm core forms in the lower troposphere. It is demonstrated that in the transitioning cyclones, the upper-tropospheric warm core is also a result of the seclusion process. Conversely, the warm core remains confined below 600 hPa in the nontransitioning systems. In the baroclinic stage, the transitioning cyclones are characterized by larger vertical wind shear and intensification rates. The resulting stronger low-level circulation in turn is responsible for significantly larger latent and sensible heat fluxes throughout the seclusion process.

scholarly journals Disentangling the response of forest and grassland energy exchange to heatwaves under idealized land–atmosphere coupling

2014 ◽  
Vol 11 (4) ◽  
pp. 5969-5995
Author(s):  
C. C. van Heerwaarden ◽  
A. J. Teuling
Keyword(s):  
Heat Wave ◽  
Heat Waves ◽  
Dynamic Properties ◽  
Sensible Heat Flux ◽  
Early Morning ◽  
Stomatal Resistance ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Area Index ◽  
Wave Conditions

Abstract. This study investigates the difference in land–atmosphere interactions between grassland and forest during typical heat wave conditions in order to understand the controversial results of Teuling et al. (2010) (T10, hereafter), who have found the systematic occurrence of higher sensible heat fluxes over forest than over grassland during heat wave conditions. With a simple, but accurate coupled land–atmosphere model, we are able to reproduce the findings of T10 for both normal summer and heat wave conditions, and to carefully explore the sensitivity of the coupled land–atmosphere system to changes in incoming radiation and early-morning temperature. Our results emphasize the importance of fast processes during the onset of heat waves, since we are able to explain the results of T10 without having to take into account changes in soil moisture. In order to disentangle the contribution of differences in several static and dynamic properties between forest and grassland, we have performed an experiment in which new land use types are created that are equal to grassland, but with one of its properties replaced by that of forest. From these, we conclude that the closure of stomata in the presence of dry air is by far the most important process in creating the different behavior of grassland and forest during the onset of a heat wave. However, we conclude that for a full explanation of the results of T10 also the other properties (albedo, roughness and the ratio of minimum stomatal resistance to leaf-area index) play an important, but indirect role; their influences mainly consist of strengthening the feedback that leads to the closure of the stomata by providing more energy that can be converted into sensible heat. The model experiment also confirms that, in line with the larger sensible heat flux, higher atmospheric temperatures occur over forest.

scholarly journals Summer Heat and Ice Balances on Hodges Glacier, South Georgia, Falkland Islands Dependencies

1982 ◽  
Vol 28 (99) ◽  
pp. 221-238 ◽  
Author(s):  
I. G. G. Hogg ◽  
J. G. Paren ◽  
R. J. Timmis
Keyword(s):  
Latent Heat ◽  
Heat Balance ◽  
Significant Contribution ◽  
Heat Fluxes ◽  
Falkland Islands ◽  
Mountain Range ◽  
Ablation Zone ◽  
Net Radiation ◽  
Summer Heat ◽  
The Heat Balance

AbstractThe heat and ice balances of a temperate sub-Antarctic cirque glacier were measured through the 1973–74 melt season at an altitude midway between the climatic firn limit and the snout. The melt calculated from mean daily measurements at a single level of net radiation, wind-speed, temperature, and humidity agreed with that observed at nearby budget stakes. In the central ablation zone, radiation provided (54 ± 6)% and sensible fluxes (46 ± 6)% of the heat income through the summer, which was exceptionally warm and sunny. Latent-heat fluxes made no significant contribution to the heat balance. The calculation by Smith (1960) that the radiative, sensible, and latent heat fluxes contribute about equally to ablation in this zone has not been substantiated by measurement. The measured partition of the glacier’s heat balance suggested that maritime influences on its regime are mitigated by its position in the lee of a major mountain range.

scholarly journals Water tracks intensify surface energy and mass exchange in the Antarctic McMurdo Dry Valleys

2019 ◽  
Vol 13 (8) ◽  
pp. 2203-2219 ◽  
Author(s):  
Tobias Linhardt ◽  
Joseph S. Levy ◽  
Christoph K. Thomas
Keyword(s):  
Climate Change ◽  
Energy Balance ◽  
Surface Energy ◽  
Surface Energy Balance ◽  
Heat Fluxes ◽  
Dry Valleys ◽  
Sensible Heat ◽  
Net Radiation ◽  
Taylor Valley ◽  
The Antarctic

Abstract. The hydrologic cycle in the Antarctic McMurdo Dry Valleys (MDV) is mainly controlled by surface energy balance. Water tracks are channel-shaped high-moisture zones in the active layer of permafrost soils and are important solute and water pathways in the MDV. We evaluated the hypothesis that water tracks alter the surface energy balance in this dry, cold, and ice-sheet-free environment during summer warming and may therefore be an increasingly important hydrologic feature in the MDV in the face of landscape response to climate change. The surface energy balance was measured for one water track and two off-track reference locations in Taylor Valley over 26 d of the Antarctic summer of 2012–2013. Turbulent atmospheric fluxes of sensible heat and evaporation were observed using the eddy-covariance method in combination with flux footprint modeling, which was the first application of this technique in the MDV. Soil heat fluxes were analyzed by measuring the heat storage change in the thawed layer and approximating soil heat flux at ice table depth by surface energy balance residuals. For both water track and reference locations over 50 % of net radiation was transferred to sensible heat exchange, about 30 % to melting of the seasonally thawed layer, and the remainder to evaporation. The net energy flux in the thawed layer was zero. For the water track location, evaporation was increased by a factor of 3.0 relative to the reference locations, ground heat fluxes by 1.4, and net radiation by 1.1, while sensible heat fluxes were reduced down to 0.7. Expecting a positive snow and ground ice melt response to climate change in the MDV, we entertained a realistic climate change response scenario in which a doubling of the land cover fraction of water tracks increases the evaporation from soil surfaces in lower Taylor Valley in summer by 6 % to 0.36 mm d−1. Possible climate change pathways leading to this change in landscape are discussed. Considering our results, an expansion of water track area would make new soil habitats accessible, alter soil habitat suitability, and possibly increase biological activity in the MDV. In summary, we show that the surface energy balance of water tracks distinctly differs from that of the dominant dry soils in polar deserts. With an expected increase in area covered by water tracks, our findings have implications for hydrology and soil ecosystems across terrestrial Antarctica.

scholarly journals Northern Eurasian Heat Waves and Droughts

2014 ◽  
Vol 27 (9) ◽  
pp. 3169-3207 ◽  
Author(s):  
Siegfried D. Schubert ◽  
Hailan Wang ◽  
Randal D. Koster ◽  
Max J. Suarez ◽  
Pavel Ya. Groisman
Keyword(s):  
Soil Moisture ◽  
Heat Wave ◽  
Extreme Events ◽  
Decadal Variability ◽  
Heat Waves ◽  
Precipitation Variability ◽  
Northern Eurasia ◽  
Temperature And Precipitation ◽  
Warming World

Abstract This article reviews the understanding of the characteristics and causes of northern Eurasian summertime heat waves and droughts. Additional insights into the nature of temperature and precipitation variability in Eurasia on monthly to decadal time scales and into the causes and predictability of the most extreme events are gained from the latest generation of reanalyses and from supplemental simulations with the NASA Goddard Earth Observing System model, version 5 (GEOS-5). Key new results are 1) the identification of the important role of summertime stationary Rossby waves in the development of the leading patterns of monthly Eurasian surface temperature and precipitation variability (including the development of extreme events such as the 2010 Russian heat wave); 2) an assessment of the mean temperature and precipitation changes that have occurred over northern Eurasia in the last three decades and their connections to decadal variability and global trends in SST; and 3) the quantification (via a case study) of the predictability of the most extreme simulated heat wave/drought events, with some focus on the role of soil moisture in the development and maintenance of such events. A literature survey indicates a general consensus that the future holds an enhanced probability of heat waves across northern Eurasia, while there is less agreement regarding future drought, reflecting a greater uncertainty in soil moisture and precipitation projections. Substantial uncertainties remain in the understanding of heat waves and drought, including the nature of the interactions between the short-term atmospheric variability associated with such extremes and the longer-term variability and trends associated with soil moisture feedbacks, SST anomalies, and an overall warming world.

scholarly journals The Role of Latent and Sensible Heat Fluxes in an Explosive Cyclogenesis over the South American East Coast

2011 ◽  
Vol 89 (6) ◽  
pp. 637-663 ◽  
Author(s):  
Everson DAL PIVA ◽  
Manoel Alonso GAN ◽  
Marley Cavalcante de Lima MOSCATI
Keyword(s):  
East Coast ◽  
Heat Fluxes ◽  
South American ◽  
Sensible Heat ◽  
The South ◽  
American East Coast

scholarly journals Severe summer heat waves over Georgia: trends, patterns and driving forces

2015 ◽  
Vol 6 (2) ◽  
pp. 2273-2322 ◽  
Author(s):  
I. Keggenhoff ◽  
M. Elizbarashvili ◽  
L. King
Keyword(s):  
Soil Moisture ◽  
Heat Wave ◽  
Driving Forces ◽  
Heat Waves ◽  
Longwave Radiation ◽  
Meridional Wind ◽  
Surface Heating ◽  
Ural Mountains ◽  
Summer Heat ◽  
Excess Heat Factor

Abstract. During the last 50 years Georgia experienced a rising number of severe summer heat waves causing increasing heat-health impacts. In this study, the 10 most severe heat waves between 1961 and 2010 and recent changes in heat wave characteristics have been detected from 22 homogenized temperature minimum and maximum series using the Excess Heat Factor (EHF). A composite and Canonical Correlation Analysis (CCA) have been performed to study summer heat wave patterns and their relationships to the selected predictors: mean Sea Level Pressure (SLP), Geopotential Height at 500 mb (Z500), Sea Surface Temperature (SST), Zonal (u-wind500) and Meridional Wind at 500 mb (v-wind500), Vertical Velocity at 500 mb (O500), Outgoing Longwave Radiation (OLR), Relative Humidity (RH500), Precipitation (RR) and Soil Moisture (SM). Most severe heat events during the last 50 years are identified in 2007, 2006 and 1998. Largest significant trend magnitudes for the number, intensity and duration of low and high-impact heat waves have been found during the last 30 years. Significant changes in the heat wave predictors reveal that all relevant surface and atmospheric patterns contributing to heat waves have been intensified between 1961 and 2010. Composite anomalies and CCA patterns provide evidence of a large anticyclonic blocking pattern over the southern Ural Mountains, which attracts warm air masses from the Southwest, enhances subsidence and surface heating, shifts the African Intertropical Convergence Zone (ITCZ) northwards, and causes a northward shift of the subtropical jet. Moreover, pronounced precipitation and soil moisture deficiency throughout Georgia contribute to the heat wave formation and persistence over Georgia. Due to different large- to mesoscale circulation patterns and the local terrain, heat wave effects over Eastern Georgia are dominated by subsidence and surface heating, while convective rainfall and cooling are observed in the West.

Sign in / Sign up

Export Citation Format

Share Document