scholarly journals Impacts of Atmospheric Reanalysis Uncertainty on Atlantic Overturning Estimates at 25°N

2018 ◽  
Vol 31 (21) ◽  
pp. 8719-8744 ◽  
Author(s):  
Helen R. Pillar ◽  
Helen L. Johnson ◽  
David P. Marshall ◽  
Patrick Heimbach ◽  
So Takao
Keyword(s):  
Climate Model ◽  
Surface Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Labrador Sea ◽  
Surface Heat Fluxes ◽  
Ensemble Mean ◽  
Meridional Overturning ◽  
The Impact ◽  
Average Uncertainty

Atmospheric reanalyses are commonly used to force numerical ocean models, but despite large discrepancies reported between different products, the impact of reanalysis uncertainty on the simulated ocean state is rarely assessed. In this study, the impact of uncertainty in surface fluxes of buoyancy and momentum on the modeled Atlantic meridional overturning at 25°N is quantified for the period January 1994–December 2011. By using an ocean-only climate model and its adjoint, the space and time origins of overturning uncertainty resulting from air–sea flux uncertainty are fully explored. Uncertainty in overturning induced by prior air–sea flux uncertainty can exceed 4 Sv (where 1 Sv ≡ 106 m3 s−1) within 15 yr, at times exceeding the amplitude of the ensemble-mean overturning anomaly. A key result is that, on average, uncertainty in the overturning at 25°N is dominated by uncertainty in the zonal wind at lags of up to 6.5 yr and by uncertainty in surface heat fluxes thereafter, with winter heat flux uncertainty over the Labrador Sea appearing to play a critically important role.

scholarly journals Diagnosing Natural Variability of North Atlantic Water Masses in HadCM3

2005 ◽  
Vol 18 (12) ◽  
pp. 1925-1941 ◽  
Author(s):  
Keith Haines ◽  
Chris Old
Keyword(s):  
Mixed Layer ◽  
General Circulation ◽  
Circulation Model ◽  
Surface Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Mode Water ◽  
Surface Heat Fluxes ◽  
Mode Waters ◽  
Winter Mixed Layer

Abstract A study of thermally driven water mass transformations over 100 yr in the ocean component of the Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) is presented. The processes of surface-forced transformations, subduction and mixing, both above and below the winter mixed layer base, are quantified. Subtropical Mode Waters are formed by surface heat fluxes and subducted at more or less the same rate. However, Labrador Seawater and Nordic Seawater classes (the other main subduction classes) are primarily formed by mixing within the mixed layer with very little formation directly from surface heat fluxes. The Subpolar Mode Water classes are dominated by net obduction of water back into the mixed layer from below. Subtropical Mode Water (18°C) variability shows a cycle of formation by surface fluxes, subduction ∼2 yr later, followed by mixing with warmer waters below the winter mixed layer base during the next 3 yr, and finally obduction back into the mixed layer at 21°C, ∼5 yr after the original formation. Surface transformation of Subpolar Mode Waters, ∼12°C, are led by surface transformations of warmer waters by up to 5 yr as water is transferred from the subtropical gyre. They are also led by obduction variability from below the mixed layer, by ∼2 yr. The variability of obduction in Subpolar Mode Waters also appears to be preceded, by 3–5 yr, by variability in subduction of Labrador Sea Waters at ∼6°C. This supports a mechanism in which southward-propagating Labrador seawater anomalies below the subpolar gyre can influence the upper water circulation and obduction into the mixed layer.

The Role of WISHE in the Rapid Intensification of Tropical Cyclones

2020 ◽  
Vol 77 (9) ◽  
pp. 3139-3160
Author(s):  
Chieh-Jen Cheng ◽  
Chun-Chieh Wu
Keyword(s):  
Tropical Cyclones ◽  
Potential Temperature ◽  
Surface Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Rapid Intensification ◽  
Surface Heat Fluxes ◽  
Peak Intensity ◽  
Before And After

Abstract This study examines the role of surface heat fluxes, particularly in relation to the wind-induced surface heat exchange (WISHE) mechanism, in the rapid intensification (RI) of tropical cyclones (TCs). Sensitivity experiments with capped surface fluxes and thus reduced WISHE exhibit delayed RI and weaker peak intensity, while WISHE could affect the evolutions of TCs both before and after the onset of RI. Before RI, more WISHE leads to faster increase of equivalent potential temperature in the lower levels, resulting in more active and stronger convection. In addition, TCs in experiments with more WISHE reach a certain strength earlier, before the onset of RI. During the RI period, more surface heat fluxes could provide convective instability in the lower levels, and cause a consequent development in the convective activity. More efficient intensification in a TC is found with higher surface heat fluxes and larger inertial stability, leading to a stronger peak intensity, more significant and deeper warm core in TC center, and the axisymmetrization of convection in the higher levels. In both stages, different levels of WISHE alter the thermodynamic environment and convective-scale processes. In all, this study supports the crucial role of WISHE in affecting TC intensification rate for TCs with RI.

The Impact of Outer-Core Surface Heat Fluxes on the Convective Activities and Rapid Intensification of Tropical Cyclones

2020 ◽  
Vol 77 (11) ◽  
pp. 3907-3927
Author(s):  
Chin-Hsuan Peng ◽  
Chun-Chieh Wu
Keyword(s):  
Inner Core ◽  
Surface Wind ◽  
Outer Core ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Intensity Change ◽  
Rapid Intensification ◽  
Core Surface ◽  
Surface Heat Fluxes ◽  
The Impact

AbstractThe rapid intensification (RI) of Typhoon Soudelor (2015) is simulated using a full-physics model. To investigate how the outer-core surface heat fluxes affect tropical cyclone (TC) structure and RI processes, a series of numerical experiments are performed by suppressing surface heat fluxes between various radii. It is found that a TC would become quite weaker when the surface heat fluxes are suppressed outside the radius of 60 or 90 km [the radius of maximum surface wind in the control experiment (CTRL) at the onset of RI is roughly 60 km]. However, interestingly, the TC would experience stronger RI when the surface heat fluxes are suppressed outside the radius of 150 km. For those sensitivity experiments with capped surface heat fluxes, the members with greater intensification rate show stronger inner-core mid- to upper-level updrafts and higher heating efficiency prior to the RI periods. Although the outer-core surface heat fluxes in these members are suppressed, the inner-core winds become stronger, extracting more ocean energy from the inner core. Greater outer-core low-level stability in these members results in aggregation of deep convection and subsequent generation and concentration of potential vorticity inside the inner core, thus confining the strongest winds therein. The abovementioned findings are also supported by partial-correlation analyses, which reveal the positive correlation between the inner-core convection and subsequent 6-h intensity change, and the competition between the inner-core and outer-core convections (i.e., eyewall and outer rainbands).

scholarly journals Estimating surface fluxes over middle and upper streams of the Heihe River Basin with ASTER imagery

2009 ◽  
Vol 6 (3) ◽  
pp. 4619-4635 ◽  
Author(s):  
W. Ma ◽  
Y. Ma ◽  
Z. Hu ◽  
B. Su ◽  
J. Wang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Land Surface ◽  
Sensible Heat Flux ◽  
Surface Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Heihe River ◽  
Surface Heat Fluxes ◽  
Aster Data ◽  
Land Surface Heat Fluxes

Abstract. Surface fluxes are important boundary conditions for climatological modeling and the Asian monsoon system. Recent availability of high-resolution, multi-band imagery from the ASTER (Advanced Space-borne Thermal Emission and Reflection Radiometer) sensor has enabled us to estimate surface fluxes to bridge the gap between local scale flux measurements using micrometeorological instruments and regional scale land-atmosphere exchanges of water and heat fluxes that are fundamental for the understanding of the water cycle in the Asian monsoon system. A Surface Energy Balance System (SEBS) method based on ASTER data and field observations has been proposed and tested for deriving net radiation flux (Rn), soil heat flux (G0), sensible heat flux (H) and latent heat flux (λ E) over heterogeneous land surface in this paper. As a case study, the methodology was applied to the experimental area of the WATER (Watershed Allied Telemetry Experimental Research), located at the mid-to-upstream sections of the Heihe River, northwest China. The ASTER data of 3 May and 4 June in 2008 was used in this paper for the case of mid-to-upstream sections of the Heihe River Basin. To validate the proposed methodology, the ground-measured land surface heat fluxes (net radiation flux (Rn), soil heat flux (G0), sensible heat flux (H) and latent heat flux (λ E)) were compared to the ASTER derived values. The results show that the derived surface variables and land surface heat fluxes in different months over the study area are in good accordance with the land surface status. It is therefore concluded that the proposed methodology is successful for the retrieval of land surface heat fluxes using the ASTER data and filed observation over the study area.

The Role of Low-Level Flow Direction on Tropical Cyclone Intensity Changes in a Moderate-Sheared Environment

2021 ◽  
Author(s):  
Tsung-Yung Lee ◽  
Chun-Chieh Wu ◽  
Rosimar Rios-Berrios
Keyword(s):  
Inner Core ◽  
Deep Layer ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Background Flow ◽  
Surface Heat Fluxes ◽  
Low Level ◽  
Flow Profiles ◽  
Group Experiences ◽  
The Impact

AbstractThe impact of low-level flow (LLF) direction on the intensification of intense tropical cyclones under moderate deep-layer shear is investigated based on idealized numerical experiments. The background flow profiles are constructed by varying the LLF direction with the same moderate deep-layer shear. When the maximum surface wind speed of the simulation without background flow reaches 70 knots, the background flow profiles are imposed. After a weakening period in the first 12 h, the members with upshear-left-pointing LLF (fast-intensifying group) intensify faster between 12–24 h than those members (slow-intensifying group) with downshear-right-pointing LLF. The fast-intensifying group experiences earlier development of inner-core structures after 12 h, such as potential vorticity below the mid-troposphere, upper-level warm core, eyewall axisymmmetrization, and moist entropy gradient, while the inner-core features of the slow-intensifying group remain relatively weak and asymmetric. The FI group experiences smaller tilt increase and stronger mid-level PV ring development. The upshear-left convection during 6–12 h is responsible for the earlier development of the inner core by reducing ventilation, providing axisymmetric heating and benefiting the eyewall development. The LLF of the fast-intensifying group enhances surface heat fluxes in the downshear side, resulting in higher energy supply to the upshear-left convection from the boundary layer. In all, this study provides new insights on the impact of LLF direction on intense storms under moderate shear by modulating the surface heat fluxes and eyewall convection.

THE IMPACT OF SURFACE HEAT FLUXES ON THE SIMULATION OF THE BRAZIL CURRENT

2014 ◽  
Vol 31 (2) ◽  
Author(s):  
Vladimir Santos da Costa ◽  
Afonso De Moraes Paiva
Keyword(s):  
Thermal Structure ◽  
Ocean Model ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Ocean Modeling ◽  
Surface Heat Fluxes ◽  
Brazil Current ◽  
Regional Ocean Model ◽  
The Impact ◽  
No Fluxes

The impact of different formulations of surface heat fluxes (no fluxes, climatological fluxes, restoring of SST towards climatology, climatological fluxes plus SST restoring, and model-computed fluxes via bulk formulas) on the modeling of the Brazil Current off southeast Brazil is investigated in numerical simulations performed with the Regional Ocean Model (ROMS). While mechanical forcing may be dominant in this region, it is shown that correct upper ocean currents and thermal structure can only be obtained when heat fluxes are implemented, even in regions of strong horizontal advection, and that some kind of feedback of the ocean state upon the fluxes is also necessary. This results are of particular importance for ocean modeling developed having operational oceanography in view.

scholarly journals Precipitation Sensitivity to Surface Heat Fluxes over North America in Reanalysis and Model Data

2013 ◽  
Vol 14 (3) ◽  
pp. 722-743 ◽  
Author(s):  
Alexis Berg ◽  
Kirsten Findell ◽  
Benjamin R. Lintner ◽  
Pierre Gentine ◽  
Christopher Kerr
Keyword(s):  
North America ◽  
Rainfall Variability ◽  
Surface Flux ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Eastern United States ◽  
Convective Rainfall ◽  
Surface Heat Fluxes ◽  
Functional Relationships ◽  
The Impact

Abstract A new methodology for assessing the impact of surface heat fluxes on precipitation is applied to data from the North American Regional Reanalysis (NARR) and to output from the Geophysical Fluid Dynamics Laboratory’s Atmospheric Model 2.1 (AM2.1). The method assesses the sensitivity of afternoon convective rainfall frequency and intensity to the late-morning partitioning of latent and sensible heating, quantified in terms of evaporative fraction (EF). Over North America, both NARR and AM2.1 indicate sensitivity of convective rainfall triggering to EF but no appreciable influence of EF on convective rainfall amounts. Functional relationships between the triggering feedback strength (TFS) metric and mean EF demonstrate the occurrence of stronger coupling for mean EF in the range of 0.6 to 0.8. To leading order, AM2.1 exhibits spatial distributions and seasonality of the EF impact on triggering resembling those seen in NARR: rainfall probability increases with higher EF over the eastern United States and Mexico and peaks in Northern Hemisphere summer. Over those regions, the impact of EF variability on afternoon rainfall triggering in summer can explain up to 50% of seasonal rainfall variability. However, the AM2.1 metrics also exhibit some features not present in NARR, for example, strong coupling extending northwestward from the central Great Plains into Canada. Sources of disagreement may include model hydroclimatic biases that affect the mean patterns and variability of surface flux partitioning, with EF variability typically much lower in NARR. Finally, the authors also discuss the consistency of their results with other assessments of land–precipitation coupling obtained from different methodologies.

scholarly journals Estimating surface fluxes over the north Tibetan Plateau area with ASTER imagery

2009 ◽  
Vol 13 (1) ◽  
pp. 57-67 ◽  
Author(s):  
Weiqiang Ma ◽  
Yaoming Ma ◽  
Maoshan Li ◽  
Zeyong Hu ◽  
Lei Zhong ◽  
...  
Keyword(s):  
Heat Flux ◽  
Tibetan Plateau ◽  
Land Surface ◽  
Sensible Heat Flux ◽  
Surface Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Surface Heat Fluxes ◽  
Aster Data ◽  
Land Surface Heat Fluxes

Abstract. Surface fluxes are important boundary conditions for climatological modeling and Asian monsoon system. The recent availability of high-resolution, multi-band imagery from the ASTER (Advanced Space-borne Thermal Emission and Reflection radiometer) sensor has enabled us to estimate surface fluxes to bridge the gap between local scale flux measurements using micrometeorological instruments and regional scale land-atmosphere exchanges of water and heat fluxes that are fundamental for the understanding of the water cycle in the Asian monsoon system. A parameterization method based on ASTER data and field observations has been proposed and tested for deriving surface albedo, surface temperature, Normalized Difference Vegetation Index (NDVI), Modified Soil Adjusted Vegetation Index (MSAVI), vegetation coverage, Leaf Area Index (LAI), net radiation flux, soil heat flux, sensible heat flux and latent heat flux over heterogeneous land surface in this paper. As a case study, the methodology was applied to the experimental area of the Coordinated Enhanced Observing Period (CEOP) Asia-Australia Monsoon Project (CAMP) on the Tibetan Plateau (CAMP/Tibet), located at the north Tibetan Plateau. The ASTER data of 24 July 2001, 29 November 2001 and 12 March 2002 was used in this paper for the case of summer, winter and spring. To validate the proposed methodology, the ground-measured surface variables (surface albedo and surface temperature) and land surface heat fluxes (net radiation flux, soil heat flux, sensible heat flux and latent heat flux) were compared to the ASTER derived values. The results show that the derived surface variables and land surface heat fluxes in three different months over the study area are in good accordance with the land surface status. Also, the estimated land surface variables and land surface heat fluxes are in good accordance with ground measurements, and all their absolute percentage difference (APD) is less than 10% in the validation sites. It is therefore concluded that the proposed methodology is successful for the retrieval of land surface variables and land surface heat fluxes using the ASTER data and filed observation over the study area.

Thermal Characteristics of Urban Surface Materials

2012 ◽  
Vol 629 ◽  
pp. 443-447
Author(s):  
G. Galli ◽  
A. Vallati
Keyword(s):  
Climate Model ◽  
Thermal Characteristics ◽  
Heat Fluxes ◽  
Surface Heat Fluxes ◽  
Urban Structures ◽  
Green Areas ◽  
Surface Materials ◽  
Soil Temperatures ◽  
Urban Square ◽  
The Impact

This paper studies the influence of different urban coverings (green areas or dry cover) on the urban microclimate. Different urban structures in a small area show different microclimatic behavior, depending on the thermophysical properties of the surface materials, in particular on the presence and extent of green areas. The research has been developed in downtown Rome in the summer period. In order to evaluate the impact of different urban envelopes, a typical urban square has been considered and analyzed systematically with the microscale climate model ENVI-met. A number of simulations has been performed with various kinds of surface covers and of vegetation and their effect on the air and soil temperatures and on the surface heat fluxes has been determined.

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