Evolving Land–Atmosphere Interactions over North America from CMIP5 Simulations

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.

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Evaluation of Two Land Surface Schemes Used in Terrains of Increasing Aridity in West Africa

Journal of Hydrometeorology ◽

10.1175/2007jhm797.1 ◽

2008 ◽

Vol 9 (2) ◽

pp. 173-193 ◽

Cited By ~ 11

Author(s):

D. Schüttemeyer ◽

A. F. Moene ◽

A. A. M. Holtslag ◽

H. A. R. de Bruin

Keyword(s):

Heat Flux ◽

West Africa ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Sensible Heat Flux ◽

Surface Fluxes ◽

Semiarid Region ◽

Canopy Conductance ◽

Net Radiation

Abstract In this study different parameterizations for land surface models currently employed in meteorological models at ECMWF [Tiled ECMWF Surface Scheme for Exchange Processes over Land (TESSEL)] and NCEP (Noah) are evaluated for a semiarid region in Ghana, West Africa. Both schemes utilize the Jarvis–Stewart approach to calculate canopy conductance as the critical variable for partitioning the available energy into sensible and latent heat flux. Additionally, an approach within Noah is tested to calculate canopy conductance based on plant physiology (A-gs method), where the photosynthetic assimilation is coupled to the leaf stomatal conductance. All parameterizations were run offline for a seasonal cycle in 2002/03 using observations as forcings at two test sites. The two locations are in the humid tropical southern region and in the drier northern region. For the purpose of forcing and evaluation, a new set of data has been utilized to include surface fluxes obtained by scintillometry. The measurements include the rapid wet-to-dry transition after the wet season at both sites. As a general trend, it has been found that during the wet period of a season net radiation is described well by all parameterizations. During the drying process the errors in modeled net radiation increased at both sites. The models perform poorly in simulating soil heat fluxes with larger errors for TESSEL for both sites. The evolution in time for sensible heat flux and latent heat flux was tackled in different ways by the utilized parameterizations and sites with enhanced model performance for the more southern site. Soil moisture in the upper soil layers is modeled with small errors for the different parameterizations. Key adjustments for reducing net radiation during the dry period of a season are discussed. In particular, the ratio of roughness length of momentum and heat was found to be an important parameter, but will require seasonal adjustments.

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Wind Speed, Surface Flux, and Convection Coupling from CYGNSS Data

10.5194/egusphere-egu21-12855 ◽

2021 ◽

Author(s):

Eric Maloney ◽

Hien Bui ◽

Emily Riley Dellaripa ◽

Bohar Singh

Keyword(s):

Heat Flux ◽

Wind Speed ◽

Latent Heat ◽

Latent Heat Flux ◽

Surface Wind ◽

Surface Flux ◽

Surface Wind Speed ◽

Surface Fluxes ◽

Heat Fluxes ◽

Boreal Summer

<p>This study analyzes wind speed and surface latent heat flux anomalies from the Cyclone Global Navigation Satellite System (CYGNSS), aiming to understand the physical mechanisms regulating intraseasonal convection, particularly associated with the Madden-Julian oscillation (MJO). The importance of wind-driven surface flux variability for supporting east Pacific diurnal convective disturbances during boreal summer is also examined. An advantage of CYGNSS compared to other space-based datasets is that its surface wind speed retrievals have reduced attenuation by precipitation, thus providing improved information about the importance of wind-induced surface fluxes for the maintenance of convection. Consistent with previous studies from buoys, CYGNSS shows that enhanced MJO precipitation is associated with enhanced wind speeds, and that associated surface heat fluxes anomalies have a magnitude about 7%-12% of precipitation anomalies. Thus, latent heat flux anomalies are an important maintenance mechanism for MJO convection through the column moist static energy budget. A composite analysis during boreal summer over the eastern north Pacific also supports the idea that wind-induced surface flux is important for MJO maintenance there. We also show the surface fluxes help moisten the atmosphere in advance of diurnal convective disturbances that propagate offshore from the Colombian Coast during boreal summer, helping to sustain such convection. &#160;</p>

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Precipitation Characteristics of Trade Wind Clouds during RICO Derived from Radar, Satellite, and Aircraft Measurements

Journal of Applied Meteorology and Climatology ◽

10.1175/2008jamc1946.1 ◽

2009 ◽

Vol 48 (3) ◽

pp. 464-483 ◽

Cited By ~ 60

Author(s):

Eric R. Snodgrass ◽

Larry Di Girolamo ◽

Robert M. Rauber

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Latent Heat Flux ◽

Rainfall Rate ◽

Cloud Base ◽

Trade Wind ◽

Cold Pool ◽

Aircraft Measurements ◽

Early Afternoon ◽

Precipitation Characteristics

Abstract Precipitation characteristics of trade wind clouds over the Atlantic Ocean near Barbuda are derived from radar and aircraft data and are compared with satellite-observed cloud fields collected during the Rain in Cumulus over the Ocean (RICO) field campaign. S-band reflectivity measurements Z were converted to rainfall rates R using a Z–R relationship derived from aircraft measurements. Daily rainfall rates varied from 0 to 22 mm day−1. The area-averaged rainfall rate for the 62-day period was 2.37 mm day−1. If corrected for evaporation below cloud base, this value is reduced to 2.23 mm day−1, which translates to a latent heat flux to the atmosphere of 63 W m−2. When compared with the wintertime ocean-surface latent heat flux from this region, the average return of water to the ocean through precipitation processes within the trade wind layer during RICO was 31%–39%. A weak diurnal cycle was observed in the area-averaged rainfall rate. The magnitude of the rainfall and the frequency of its occurrence had a maximum in the predawn hours and a minimum in the midmorning to early afternoon on 64% of the days. Radar data were collocated with data from the Multiangle Imaging Spectroradiometer (MISR) to develop relationships between cloud-top height, cloud fraction, 866-nm bidirectional reflectance factor (BRF), and radar-derived precipitation. The collocation took place at the overpass time of ∼1045 local time. These relationships revealed that between 5.5% and 10.5% of the cloudy area had rainfall rates that were > 0.1 mm h−1, and between 1.5% and 3.5% of the cloudy area had rainfall rates that were >1 mm h−1. Cloud-top heights between ∼3 and 4 km and BRFs between 0.4 and 1.0 contributed ∼50% of the total rainfall. For cloudy pixels having detectable rain, average rainfall rates increased from ∼1 to 4 mm h−1 as cloud-top heights increased from ∼1 to 4 km. Rainfall rates were closely tied to the type of mesoscale organization, with much of the rainfall originating from shallow (<5 km) cumulus clusters shaped as arcs associated with cold-pool outflows.

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

Frontiers in Earth Science ◽

10.3389/feart.2020.609619 ◽

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.

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

Remote Sensing ◽

10.3390/rs9121326 ◽

2017 ◽

Vol 9 (12) ◽

pp. 1326 ◽

Cited By ~ 8

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

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Coupled and decoupled stratocumulus-topped boundary layers: turbulence properties

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-10965-2021 ◽

2021 ◽

Vol 21 (14) ◽

pp. 10965-10991

Author(s):

Jakub L. Nowak ◽

Holger Siebert ◽

Kai-Erik Szodry ◽

Szymon P. Malinowski

Keyword(s):

Heat Flux ◽

Boundary Layers ◽

Latent Heat ◽

Latent Heat Flux ◽

Power Spectra ◽

Structure Functions ◽

Inertial Range ◽

Heat Fluxes ◽

Observation System ◽

Entire Depth

Abstract. We compare turbulence properties in coupled and decoupled marine stratocumulus-topped boundary layers (STBLs) using high-resolution in situ measurements performed by the helicopter-borne Airborne Cloud Turbulence Observation System (ACTOS) platform in the region of the eastern North Atlantic. The thermodynamically well-mixed coupled STBL was characterized by a comparable latent heat flux at the surface and in the cloud-top region, and substantially smaller sensible heat flux in the entire depth. Turbulence kinetic energy (TKE) was efficiently generated by buoyancy in the cloud and at the surface, and dissipated with comparable rate across the entire depth. Structure functions and power spectra of velocity fluctuations in the inertial range were reasonably consistent with the predictions of Kolmogorov theory. The turbulence was close to isotropic. In the decoupled STBL, decoupling was most obvious in humidity profiles. Heat fluxes and buoyant TKE production at the surface were similar to the coupled case. Around the transition level, latent heat flux decreased to zero and TKE was consumed by weak stability. In the cloud-top region, heat fluxes almost vanished and buoyancy production was significantly smaller than for the coupled case. The TKE dissipation rate inside the decoupled STBL varied between its sublayers. Structure functions and power spectra in the inertial range deviated from Kolmogorov scaling. This was more pronounced in the cloud and subcloud layer in comparison to the surface mixed layer. The turbulence was more anisotropic than in the coupled STBL, with horizontal fluctuations dominating. The degree of anisotropy was largest in the cloud and subcloud layer of the decoupled STBL. Integral length scales, of the order of 100 m in both cases, indicate turbulent eddies smaller than the depth of the coupled STBL or of the sublayers of the decoupled STBL. We hypothesize that turbulence produced in the cloud or close to the surface is redistributed across the entire coupled STBL but rather only inside the sublayers where it was generated in the case of the decoupled STBL. Scattered cumulus convection, developed below the stratocumulus base, may play a role in transport between those sublayers.

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Intraseasonal Latent Heat Flux Based on Satellite Observations

Journal of Climate ◽

10.1175/2009jcli2901.1 ◽

2009 ◽

Vol 22 (17) ◽

pp. 4539-4556 ◽

Cited By ~ 35

Author(s):

Semyon A. Grodsky ◽

Abderrahim Bentamy ◽

James A. Carton ◽

Rachel T. Pinker

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Latent Heat Flux ◽

Mixed Layer ◽

Heat Budget ◽

Mixed Layer Depth ◽

Intraseasonal Variability ◽

Surface Fluxes ◽

Tropical Region ◽

Surprising Result

Abstract Weekly average satellite-based estimates of latent heat flux (LHTFL) are used to characterize spatial patterns and temporal variability in the intraseasonal band (periods shorter than 3 months). As expected, the major portion of intraseasonal variability of LHTFL is due to winds, but spatial variability of humidity and SST are also important. The strongest intraseasonal variability of LHTFL is observed at the midlatitudes. It weakens toward the equator, reflecting weak variance of intraseasonal winds at low latitudes. It also decreases at high latitudes, reflecting the effect of decreased SST and the related decrease of time-mean humidity difference between heights z = 10 m and z = 0 m. Within the midlatitude belts the intraseasonal variability of LHTFL is locally stronger (up to 50 W m−2) in regions of major SST fronts (like the Gulf Stream and Agulhas). Here it is forced by passing storms and is locally amplified by unstable air over warm SSTs. Although weaker in amplitude (but still significant), intraseasonal variability of LHTFL is observed in the tropical Indian and Pacific Oceans due to wind and humidity perturbations produced by the Madden–Julian oscillations. In this tropical region intraseasonal LHTFL and incoming solar radiation vary out of phase so that evaporation increases just below the convective clusters. Over much of the interior ocean where the surface heat flux dominates the ocean mixed layer heat budget, intraseasonal SST cools in response to anomalously strong upward intraseasonal LHTFL. This response varies geographically, in part because of geographic variations of mixed layer depth and the resulting variations in thermal inertia. In contrast, in the eastern tropical Pacific and Atlantic cold tongue regions intraseasonal SST and LHTFL are positively correlated. This surprising result occurs because in these equatorial upwelling areas SST is controlled by advection rather than by surface fluxes. Here LHTFL responds to rather than drives SST.

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Influence of a New Turbulence Regime on the Global Air–Sea Heat Fluxes

Journal of Climate ◽

10.1175/2008jcli2279.1 ◽

2008 ◽

Vol 21 (22) ◽

pp. 5925-5941 ◽

Cited By ~ 7

Author(s):

Erik Sahlée ◽

Ann-Sofi Smedman ◽

Anna Rutgersson ◽

Ulf Högström

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Latent Heat Flux ◽

Sensible Heat Flux ◽

Sensitivity Study ◽

Surface Fluxes ◽

Heat Fluxes ◽

Turbulence Structure ◽

Sensible Heat ◽

Monsoon Period

Abstract Recent research has found that boundary layer turbulence changes its organization as the stratification approaches neutral from the unstable side. When the thermal forcing weakens in combination with wind speed above approximately 10 m s−1, detached eddies are formed in the upper part of the surface layer. These eddies effectively transport drier and colder air from aloft to the surface as they move downward, thereby enhancing the surface fluxes of sensible and latent heat. This effect has been observed over both land and sea; that is, it is not dependent on the nature of the underlying surface. Here the authors perform a sensitivity study of how this reorganization of the turbulence structure influences the global air–sea heat fluxes. Using modified bulk formulations incorporating this effect, the magnitude of the enhancement in a climatic sense was estimated by the use of 40-yr ECMWF Re-Analysis (ERA-40) data in the bulk formulas. It is found that for the 1979–2001 period, the global increase of the latent and sensible heat fluxes over the ice-free oceans is 3.6 and 1.2 W m−2, respectively. These numbers suggest that this effect is of some significance. The results also indicate that the regional and seasonal variability may be large. The largest annual increases are found over the southern oceans between 30° and 60°S where the sensible heat flux increases by 2.3 W m−2 and the latent heat flux by 6.5 W m−2. Ocean areas close to the equator experience almost no increase, whereas the latent heat flux from the Arabian Sea during the monsoon period is enhanced by 11.5 W m−2.

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