scholarly journals Impact of the Anomalous Latent Heat Flux Over the Kuroshio Extension on Western North American Rainfall in Spring: Interannual Variation and Mechanism

2021 ◽  
Vol 8 ◽  
Author(s):  
Jingchao Long ◽  
Chunlei Liu ◽  
Zifeng Liu ◽  
Jianjun Xu
Keyword(s):  
Heat Flux ◽  
North America ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Cyclonic Circulation ◽  
Western Canada ◽  
Jet Stream ◽  
The Impact ◽  
The Kuroshio ◽  
Anomalous Cyclonic Circulation

The Kuroshio and its extension (KE) significantly influences regional climate through meridional heat transport from the tropical ocean. In this study, the observational and reanalysis datasets are used to investigate the impact of the latent heat flux (LHF) over the KE region on downstream rainfall and the underlying mechanism. The result shows a “seesaw” structure in rainfall anomaly, dominating the Western Canada and the southwestern North America with a correlation coefficient of 0.77 between the two modes. In strong LHF years, strengthened LHF favors to enhance precipitation in the Western Canada and reduce that in the southwestern North America. This is primarily associated with an anomalous cyclonic circulation over the KE region, which enhances southwesterly precipitation and latent heating in the middle troposphere. The heating excites an anomalous cyclonic circulation to its west and an anticyclonic circulation to its east, helping to reinforce the existing anomalous cyclonic circulation in turn and form a positive feedback. The conditions associated with La Niña events favor to above processes. To the upper troposphere, the deepened anomalous cyclonic circulation due to enhanced eddy activities and atmospheric baroclinic instability over the KE strengthens subtropical westerly jet stream and thereby extends eastward on the 200 hPa level. Correspondingly, an elongated zonally lower level cyclonic circulation anomaly across the North Pacific leads to a moisture convergence in the Western Canada, which is mainly resulted from the anomalous positive vorticity advection over the left side of the exit region of the jet stream. The opposite circumstance occurs in weak LHF years, presenting an opposed anomalous circulation and rainfall pattern.

Land–Atmosphere Interaction in Tropical Africa

2020 ◽  
Author(s):  
Cathy Hohenegger
Keyword(s):  
Heat Flux ◽  
Soil Moisture ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Surface State ◽  
Land Surface ◽  
Large Scale ◽  
Moisture Distribution ◽  
Sahel Region ◽  
The Impact

Even though many features of the vegetation and of the soil moisture distribution over Africa reflect its climatic zones, the land surface has the potential to feed back on the atmosphere and on the climate of Africa. The land surface and the atmosphere communicate via the surface energy budget. A particularly important control of the land surface, besides its control on albedo, is on the partitioning between sensible and latent heat flux. In a soil moisture-limited regime, for instance, an increase in soil moisture leads to an increase in latent heat flux at the expanse of the sensible heat flux. The result is a cooling and a moistening of the planetary boundary layer. On the one hand, this thermodynamically affects the atmosphere by altering the stability and the moisture content of the vertical column. Depending on the initial atmospheric profile, convection may be enhanced or suppressed. On the other hand, a confined perturbation of the surface state also has a dynamical imprint on the atmospheric flow by generating horizontal gradients in temperature and pressure. Such gradients spin up shallow circulations that affect the development of convection. Whereas the importance of such circulations for the triggering of convection over the Sahel region is well accepted and well understood, the effect of such circulations on precipitation amounts as well as on mature convective systems remains unclear. Likewise, the magnitude of the impact of large-scale perturbations of the land surface state on the large-scale circulation of the atmosphere, such as the West African monsoon, has long been debated. One key issue is that such interactions have been mainly investigated in general circulation models where the key involved processes have to rely on uncertain parameterizations, making a definite assessment difficult.

Land-atmosphere coupling during compound extreme heat and drought events in the LUCAS experiment: a new coupling metric for climate extremes

2021 ◽  
Author(s):  
Rita M. Cardoso ◽  
Daniela D. C. A. Lima ◽  
Pedro M. M. Soares ◽  
Diana Rechid ◽  
Marcus Breil ◽  
...  
Keyword(s):  
Land Use ◽  
Heat Flux ◽  
Soil Moisture ◽  
Land Cover ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Heat Waves ◽  
Extreme Heat ◽  
Positive Temperature ◽  
The Impact

<p>Land-atmosphere energy and water exchanges are fundamentally linked to soil-moisture. The distribution of the planets’ biomes hinges on the surface-atmosphere coupling since soil moisture and temperature feedbacks have a strong influence on plant transpiration and photosynthesis. Land use/land cover changes (LUC) modify locally land surface properties that control the land-atmosphere mass, energy, and momentum exchanges. The impact of these changes depends on the scale and nature of land cover modifications and is very difficult to quantify. However, large inconsistencies in the LUC impacts are observed between models, highlighting the need for common LUC across a large ensemble of models. The Flagship Pilot Study LUCAS (Land Use & Climate Across Scales) provides a coordinated effort to study LUC using an ensemble of regional climate models (RCMs). In the first phase of the project 3 experiments were performed for continental Europe: EVAL (current climate); GRASS (trees replaced by grassland) and FOREST (grasses and shrubs replaced by trees).  An analysis of the energy and moisture balance for the three experiments is performed, focusing on the relationship between the fluxes partitioning, heat waves and droughts. To better asses the link between extreme temperatures and soil moisture or evapotranspiration, a new coupling metric for short time scales is proposed, the Latent Heat Flux-Temperature Coupling Magnitude (LETCM). This new metric is computed for a specific period, considering the positive temperature extremes and the negative latent heat flux extremes. Areas with positive magnitude values imply higher temperature anomaly, due to a negative latent heat flux anomaly. This new metric only considers periods of strong coupling, with positive signals in areas of high temperatures and evaporative stress, allowing for the detection of events that are extreme for energy and water cycle. Concurrently, a new decile based normalised drought index is used to examine the concurrent heat extremes and droughts. The analysis focuses on the three experiments revealing that the number, amplitude and spatial distribution of compound extreme heat and drought is highly model dependant. The impact of afforestation or deforestation is not consistent across models.</p><p><strong>Acknowledgements</strong></p><p> The authors wish to acknowledge project LEADING (PTDC/CTA-MET/28914/2017) and FCT - project UIDB/50019/2020 - Instituto Dom Luiz.</p>

scholarly journals Evolving Land–Atmosphere Interactions over North America from CMIP5 Simulations

2013 ◽  
Vol 26 (19) ◽  
pp. 7313-7327 ◽  
Author(s):  
Paul A. Dirmeyer ◽  
Yan Jin ◽  
Bohar Singh ◽  
Xiaoqin Yan
Keyword(s):  
Heat Flux ◽  
North America ◽  
Boundary Layers ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Forced Response ◽  
Surface Fluxes ◽  
Future Climate Change ◽  
Cloud Base ◽  
Climate Change Scenarios

Abstract Long-term changes in land–atmosphere interactions during spring and summer are examined over North America. A suite of models from phase 5 of the Coupled Model Intercomparison Project simulating preindustrial, historical, and severe future climate change scenarios are examined for changes in soil moisture, surface fluxes, atmospheric boundary layer characteristics, and metrics of land–atmosphere coupling. Simulations of changes from preindustrial to modern conditions show warming brings stronger surface fluxes at high latitudes, while subtropical regions of North America respond with drier conditions. There is a clear anthropogenic aerosol response in midlatitudes that reduces surface radiation and heat fluxes, leading to shallower boundary layers and lower cloud base. Over the Great Plains, the signal does not reflect a purely radiatively forced response, showing evidence that the expansion of agriculture may have offset the aerosol impacts on the surface energy and water cycle. Future changes show soils are projected to dry across North America, even though precipitation increases north of a line that retreats poleward from spring to summer. Latent heat flux also has a north–south dipole of change, increasing north and decreasing south of a line that also moves northward with the changing season. Metrics of land–atmosphere feedback increase over most of the continent but are strongest where latent heat flux increases in the same location and season where precipitation decreases. Combined with broadly elevated cloud bases and deeper boundary layers, land–atmosphere interactions are projected to become more important in the future with possible consequences for seasonal climate prediction.

Horizontal heat impacts of a bare facade on air temperature in an adjacent green plot within pedestrian heights in Beijing

2019 ◽  
pp. 1420326X1989267
Author(s):  
Hongxuan Zhou ◽  
Guan Wang ◽  
Dan Hu ◽  
Jing Sun
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Air Temperature ◽  
Sensible Heat Flux ◽  
Atmospheric Environment ◽  
Dominant Factor ◽  
Sensible Heat ◽  
Significance Level ◽  
The Impact

This study focuses on the horizontal heat impact of facades on the surrounding atmospheric environment at pedestrian heights. The results show that (1) the horizontal heat impact of a facade on the surrounding atmosphere was relatively uniform due to the homogeneous energy flux near the facade; (2) the significance of horizontal heat impacts gradually weakened with height, and the average significance was 48.74% in the spring and 47.81% in the summer; (3) energy factors, such as net radiation, soil heat flux, sensible heat flux, latent heat flux, and ground radiation, influenced the significance of the air temperature difference between the two observation sites where the investigation was conducted; one site was near the facade (distance = 0.30 m), the other one was far from the wall (distance = 10 m), and no dominant factor was found; and (4) the sensible heat flux was higher at the site near the facade than at the site far from the facade at the 0.05 significance level in the summer, which could be attributed to the strong horizontal heat impact from the facade. In contrast, the impact of the facade on the latent heat flux was not significant at the 0.05 significance level in the summer.

The Impact of Vertical Measurement Depth on the Information Content of Soil Moisture for Latent Heat Flux Estimation

2016 ◽  
Vol 17 (9) ◽  
pp. 2419-2430 ◽  
Author(s):  
Jianxiu Qiu ◽  
Wade T. Crow ◽  
Grey S. Nearing
Keyword(s):  
Heat Flux ◽  
Time Series ◽  
Soil Moisture ◽  
Information Content ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Heat Flux Estimation ◽  
Vertical Support ◽  
Flux Estimation ◽  
The Impact

Abstract This study aims to identify the impact of vertical support on the information content of soil moisture (SM) for latent heat flux estimation. This objective is achieved via calculation of the mutual information (MI) content between multiple soil moisture variables (with different vertical supports) and current/future evaporative fraction (EF) using ground-based soil moisture and latent/sensible heat flux observations acquired from the AmeriFlux network within the contiguous United States. Through the intercomparison of MI results from different SM–EF pairs, the general value (for latent heat flux estimation) of superficial soil moisture observations , vertically integrated soil moisture observations , and vertically extrapolated soil moisture time series [soil wetness index (SWI) from a simple low-pass transformation of ] are examined. Results suggest that, contrary to expectations, 2-day averages of and have comparable mutual information with regards to EF. That is, there is no clear evidence that the information content for flux estimation is enhanced via deepening the vertical support of superficial soil moisture observations. In addition, the utility of SWI in monitoring and forecasting EF is partially dependent on the adopted parameterization of time-scale parameter T in the exponential filter. Similar results are obtained when analyses are conducted at the monthly time scale, only with larger error bars. The contrast between the results of this paper and past work focusing on utilizing soil moisture to predict vegetation condition demonstrates that the particular application should be considered when characterizing the information content of soil moisture time series measurements.

scholarly journals MODIS-Based Estimation of Terrestrial Latent Heat Flux over North America Using Three Machine Learning Algorithms

2017 ◽  
Vol 9 (12) ◽  
pp. 1326 ◽  
Author(s):  
Xuanyu Wang ◽  
Yunjun Yao ◽  
Shaohua Zhao ◽  
Kun Jia ◽  
Xiaotong Zhang ◽  
...  
Keyword(s):  
Machine Learning ◽  
Heat Flux ◽  
North America ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Learning Algorithms ◽  
Machine Learning Algorithms

scholarly journals Influence of concurrence of extreme drought and heat events on carbon and energy fluxes in dominant ecosystems in the Pacific Northwest region

2018 ◽  
Author(s):  
Hyojung Kwon ◽  
Whitney Creason ◽  
Beverly E. Law ◽  
Christopher J. Still ◽  
Chad Hanson
Keyword(s):  
Heat Flux ◽  
Pacific Northwest ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Ponderosa Pine ◽  
Douglas Fir ◽  
Energy Fluxes ◽  
Extreme Climate ◽  
Climate Stress ◽  
The Impact

Abstract. The impacts of drought intensities and vapor pressure deficits (VPD) beyond historic norms in Pacific Northwest (PNW), USA, are critical in understanding the potential future function and resilience of ecosystems in the region. While ecosystems in this region are adapted to seasonal droughts, June 2015 temperatures were the highest recorded in the region and strongly coupled with relatively low soil moisture. June is usually the best month for growth in the PNW. Here, we examined the impact of the June 2015 climate extremes on carbon and energy fluxes at sagebrush in the high desert, young and mature ponderosa pine in the semi-arid Great Basin, and Douglas-fir in the mesic Coast Range ecoregion compared to an average climate year (2014). We assessed if the ecosystems recover from extreme climate stress within the growing season. The monthly anomalies in temperature and VPD were 3 standard deviations, and precipitation was 1 standard deviation, outside the 30-year mean at all sites. In sagebrush, the carry-over effect of precipitation (i.e., intensive precipitation prior to the drought and heat) mitigated the immediate impact of extreme climate stress, leading to 25–40 % increase in net ecosystem production (NEP) and gross primary production (GPP), with little change in ecosystem respiration (RE) and 65 % increase in latent heat flux, compared to the June 2014. The drought and heat lowered NEP by 35–65 % and GPP by 15–33 % in ponderosa pine and Douglas-fir. A greater increase in latent heat flux was observed in Douglas-fir (110 %) than in ponderosa pine (

scholarly journals Impact of Deforestation on Land–Atmosphere Coupling Strength and Climate in Southeast Asia

2020 ◽  
Vol 12 (15) ◽  
pp. 6140
Author(s):  
Merja H. Tölle
Keyword(s):  
Heat Flux ◽  
Land Cover ◽  
Southeast Asia ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Coupling Strength ◽  
El Niño ◽  
El Nino ◽  
La Nina ◽  
The Impact

Southeast Asia (SEA) is a deforestation hotspot. A thorough understanding of the accompanying biogeophysical consequences is crucial for sustainable future development of the region’s ecosystem functions and society. In this study, data from ERA-Interim driven simulations conducted with the state-of-the-art regional climate model COSMO-CLM (CCLM; version 4.8.17) at 14 km horizontal resolution are analyzed over SEA for the period from 1990 to 2004, and during El Niño–Southern Oscillation (ENSO) events for November to March. A simulation with large-scale deforested land cover is compared to a simulation with no land cover change. In order to attribute the differences due to deforestation to feedback mechanisms, the coupling strength concept is applied based on Pearson correlation coefficients. The correlations were calculated based on 10-day means between the latent heat flux and maximum temperature, the latent and sensible heat flux, and the latent heat flux and planetary boundary layer height. The results show that the coupling strength between land and atmosphere increased for all correlations due to deforestation. This implies a strong impact of the land on the atmosphere after deforestation. Differences in environmental conditions due to deforestation are most effective during La Niña years. The strength of La Nina events on the region is reduced as the impact of deforestation on the atmosphere with drier and warmer conditions superimpose this effect. The correlation strength also intensified and shifted towards stronger coupling during El Niño events for both Control and Grass simulations. However, El Niño years have the potential to become even warmer and drier than during usual conditions without deforestation. This could favor an increase in the formation of tropical cyclones. Whether deforestation will lead to a permanent transition to agricultural production increases in this region cannot be concluded. Rather, the impact of deforestation will be an additional threat besides global warming in the next decades due to the increase in the occurrence of multiple extreme events. This may change the type and severity of upcoming impacts and the vulnerability and sustainability of our society.

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