scholarly journals High-Resolution Satellite Surface Latent Heat Fluxes in North Atlantic Hurricanes

2011 ◽  
Vol 139 (9) ◽  
pp. 2735-2747 ◽  
Author(s):  
Jiping Liu ◽  
Judith A. Curry ◽  
Carol Anne Clayson ◽  
Mark A. Bourassa
Keyword(s):  
High Resolution ◽  
Latent Heat ◽  
North Atlantic ◽  
Weather Prediction ◽  
Surface Flux ◽  
Ocean Surface ◽  
Ocean Waves ◽  
Heat Fluxes ◽  
Atlantic Hurricanes ◽  
Better Than

This study presents a new high-resolution satellite-derived ocean surface flux product, XSeaFlux, which is evaluated for its potential use in hurricane studies. The XSeaFlux employs new satellite datasets using improved retrieval methods, and uses a new bulk flux algorithm formulated for high wind conditions. The XSeaFlux latent heat flux (LHF) performs much better than the existing numerical weather prediction reanalysis and satellite-derived flux products in a comparison with measurements from the Coupled Boundary Layer Air–Sea Transfer (CBLAST) field experiment. Also, the XSeaFlux shows well-organized LHF structure and large LHF values in response to hurricane conditions relative to the other flux products. The XSeaFlux dataset is used to interpret details of the ocean surface LHF for selected North Atlantic hurricanes. Analysis of the XSeaFlux dataset suggests that ocean waves, sea spray, and cold wake have substantial impacts on LHF associated with the hurricanes.

scholarly journals Averaging-Related Biases in Monthly Latent Heat Fluxes

2012 ◽  
Vol 29 (7) ◽  
pp. 974-986 ◽  
Author(s):  
Paul J. Hughes ◽  
Mark A. Bourassa ◽  
Jeremy J. Rolph ◽  
Shawn R. Smith
Keyword(s):  
Latent Heat ◽  
Classical Method ◽  
Surface Flux ◽  
Heat Fluxes ◽  
Western Boundary ◽  
State University ◽  
Boundary Current ◽  
Surface Energy Fluxes ◽  
Temporal Averaging ◽  
The Impact

Abstract Seasonal-to-multidecadal applications that require ocean surface energy fluxes often require accuracies of surface turbulent fluxes to be 5 W m−2 or better. While there is little doubt that uncertainties in the flux algorithms and input data can cause considerable errors, the impact of temporal averaging has been more controversial. The biases resulting from using monthly averaged winds, temperatures, and humidities in the bulk aerodynamic formula (i.e., the so-called classical method) to estimate the monthly mean latent heat fluxes are shown to be substantial and spatially varying in a manner that is consistent with most prior work. These averaging-related biases are linked to nonnegligible submonthly covariances between the wind, temperature, and humidity. To provide additional insight into the averaging-related bias, the methodology behind the third-generation Florida State University monthly mean surface flux product (FSU3) is detailed to highlight additional sources of errors in gridded datasets. The FSU3 latent heat fluxes suffer from this averaging-related bias, which can be as large as 90 W m−2 in western boundary current regions during winter and can exceed 40 W m−2 in synoptically active portions of the tropics. The regional impacts of these biases on the mixed layer temperature tendency are shown to demonstrate that the error resulting from applying the classical method is physically substantial.

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

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.  </p>

scholarly journals A Bulk Turbulent Air–Sea Flux Algorithm for High-Wind, Spray Conditions

2008 ◽  
Vol 38 (7) ◽  
pp. 1581-1596 ◽  
Author(s):  
Edgar L. Andreas ◽  
P. Ola G. Persson ◽  
Jeffrey E. Hare
Keyword(s):  
Latent Heat ◽  
Large Scale ◽  
Surface Flux ◽  
Heat Fluxes ◽  
High Wind ◽  
Molecular Processes ◽  
Tropical Ocean ◽  
Wind Speeds ◽  
The Mean ◽  
High Winds

Abstract Sensible and latent heat can cross the air–sea interface by two routes: as interfacial fluxes controlled by molecular processes right at the interface, and as spray fluxes from the surface of sea spray droplets. Once the 10-m wind speed over the ocean reaches approximately 11–13 m s−1, the spray sensible and latent heat fluxes become significant fractions (i.e., 10% or greater) of the corresponding interfacial fluxes. The analysis here establishes that result by combining the Tropical Ocean-Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (COARE) version 2.6 bulk interfacial flux algorithm with a microphysical spray model to partition measured heat fluxes from two good high-wind datasets into spray and interfacial flux contributions. The measurements come from the Humidity Exchange over the Sea (HEXOS) experiment and the Fronts and Atlantic Storm-Tracks Experiment (FASTEX); wind speeds in these two datasets span 5 to 20 m s−1. After the measured heat fluxes are separated into spray and interfacial contributions, the spray fluxes are used to develop a fast spray flux algorithm to combine with the COARE version 2.6 interfacial flux algorithm in a unified turbulent surface flux algorithm for use in large-scale and ocean storm models. A sensitivity analysis of the spray and interfacial components of this unified flux algorithm demonstrates how the two component fluxes scale differently with the mean meteorological variables and why they must therefore be parameterized separately in models intended to treat air–sea fluxes in high winds.

scholarly journals Assessing the Benefits of Convection-Permitting Models by Neighborhood Verification: Examples from MAP D-PHASE

2010 ◽  
Vol 138 (9) ◽  
pp. 3418-3433 ◽  
Author(s):  
Tanja Weusthoff ◽  
Felix Ament ◽  
Marco Arpagaus ◽  
Mathias W. Rotach
Keyword(s):  
High Resolution ◽  
Spatial Scales ◽  
Weather Prediction ◽  
Grid Point ◽  
Skill Score ◽  
Verification Methods ◽  
Driving Model ◽  
High Resolution Models ◽  
Precipitation Events ◽  
Better Than

Abstract High-resolution numerical weather prediction (NWP) models produce more detailed precipitation structures but the real benefit is probably the more realistic statistics gained with the higher resolution and not the information on the specific grid point. By evaluating three model pairs, each consisting of a high-resolution NWP system resolving convection explicitly and its low-resolution-driving model with parameterized convection, on different spatial scales and for different thresholds, this paper addresses the question of whether high-resolution models really perform better than their driving lower-resolution counterparts. The model pairs are evaluated by means of two fuzzy verification methods—upscaling (UP) and fractions skill score (FSS)—for the 6 months of the D-PHASE Operations Period and in a highly complex terrain. Observations are provided by the Swiss radar composite and the evaluation is restricted to the area covered by the Swiss radar stations. The high-resolution models outperform or equal the performance of their respective lower-resolution driving models. The differences between the models are significant and robust against small changes in the verification settings. An evaluation based on individual months shows that high-resolution models give better results, particularly with regard to convective, more localized precipitation events.

scholarly journals Improved Nowcasts by Blending Extrapolation and Model Forecasts

2015 ◽  
Vol 30 (5) ◽  
pp. 1201-1217 ◽  
Author(s):  
Yunsung Hwang ◽  
Adam J. Clark ◽  
Valliappa Lakshmanan ◽  
Steven E. Koch
Keyword(s):  
Image Processing ◽  
High Resolution ◽  
Numerical Weather Prediction ◽  
Weather Prediction ◽  
Processing Method ◽  
Lead Times ◽  
New Approach ◽  
Simple Extrapolation ◽  
Model Initialization ◽  
Better Than

Abstract Planning and managing commercial airplane routes to avoid thunderstorms requires very skillful and frequently updated 0–8-h forecasts of convection. The National Oceanic and Atmospheric Administration’s High-Resolution Rapid Refresh (HRRR) model is well suited for this purpose, being initialized hourly and providing explicit forecasts of convection out to 15 h. However, because of difficulties with depicting convection at the time of model initialization and shortly thereafter (i.e., during model spinup), relatively simple extrapolation techniques, on average, perform better than the HRRR at 0–2-h lead times. Thus, recently developed nowcasting techniques blend extrapolation-based forecasts with numerical weather prediction (NWP)-based forecasts, heavily weighting the extrapolation forecasts at 0–2-h lead times and transitioning emphasis to the NWP-based forecasts at the later lead times. In this study, a new approach to applying different weights to blend extrapolation and model forecasts based on intensities and forecast times is applied and tested. An image-processing method of morphing between extrapolation and model forecasts to create nowcasts is described and the skill is compared to extrapolation forecasts and forecasts from the HRRR. The new approach is called salient cross dissolve (Sal CD), which is compared to a commonly used method called linear cross dissolve (Lin CD). Examinations of forecasts and observations of the maximum altitude of echo-top heights ≥18 dBZ and measurement of forecast skill using neighborhood-based methods shows that Sal CD significantly improves upon Lin CD, as well as the HRRR at 2–5-h lead times.

Air–Sea Fluxes over the Gulf Stream Region: Atmospheric Controls and Trends

2010 ◽  
Vol 23 (10) ◽  
pp. 2651-2670 ◽  
Author(s):  
Jeffrey Shaman ◽  
R. M. Samelson ◽  
Eric Skyllingstad
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
North Atlantic ◽  
Gulf Stream ◽  
Heat Fluxes ◽  
High Flux ◽  
Mode Water ◽  
The North ◽  
Storm Frequency ◽  
The North Atlantic

Abstract The intraseasonal variability of turbulent surface heat fluxes over the Gulf Stream extension and subtropical mode water regions of the North Atlantic, and long-term trends in these fluxes, are explored using NCEP–NCAR reanalysis. Wintertime sensible and latent heat fluxes from these surface waters are characterized by episodic high flux events due to cold air outbreaks from North America. Up to 60% of the November–March (NDJFM) total sensible heat flux and 45% of latent heat flux occurs on these high flux days. On average 41% (34%) of the total NDJFM sensible (latent) heat flux takes place during just 17% (20%) of the days. Over the last 60 years, seasonal NDJFM sensible and latent heat fluxes over the Climate Variability and Predictability (CLIVAR) Mode Water Dynamic Experiment (CLIMODE) region have increased owing to an increased number of high flux event days. The increased storm frequency has altered average wintertime temperature conditions in the region, producing colder surface air conditions over the North American eastern seaboard and Labrador Sea and warmer temperatures over the Sargasso Sea. These temperature changes have increased low-level vertical wind shear and baroclinicity along the North Atlantic storm track over the last 60 years and may further favor the trend of increasing storm frequency over the Gulf Stream extension and adjacent region.

scholarly journals Improved ocean wind forcing products

2020 ◽  
Author(s):  
Rianne Giesen ◽  
Ana Trindade ◽  
Marcos Portabella ◽  
Ad Stoffelen
Keyword(s):  
High Resolution ◽  
Weather Prediction ◽  
Surface Wind ◽  
Ocean Surface ◽  
Ocean Model ◽  
Wind Forcing ◽  
Small Scale ◽  
Wind Fields ◽  
Ocean Surface Wind ◽  
Ocean Wind

<p>The ocean surface wind plays an essential role in the exchange of heat, gases and momentum at the atmosphere-ocean interface. It is therefore crucial to accurately represent this wind forcing in physical ocean model simulations. Scatterometers provide high-resolution ocean surface wind observations, but have limited spatial and temporal coverage. On the other hand, numerical weather prediction (NWP) model wind fields have better coverage in time and space, but do not resolve the small-scale variability in the air-sea fluxes. In addition, Belmonte Rivas and Stoffelen (2019) documented substantial systematic error in global NWP fields on both small and large scales, using scatterometer observations as a reference.</p><p>Trindade et al. (2019) combined the strong points of scatterometer observations and atmospheric model wind fields into ERA*, a new ocean wind forcing product. ERA* uses temporally-averaged differences between geolocated scatterometer wind data and European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis fields to correct for persistent local NWP wind vector biases. Verified against independent observations, ERA* reduced the variance of differences by 20% with respect to the uncorrected NWP fields. As ERA* has a high potential for improving ocean model forcing in the CMEMS Model Forecasting Centre (MFC) products, it is a candidate for a future CMEMS Level 4 (L4) wind product. We present the ongoing work to further improve the ERA* product and invite potential users to discuss their L4 product requirements.</p><p>References:</p><p>Belmonte Rivas, M. and A. Stoffelen (2019): <em>Characterizing ERA-Interim and ERA5 surface wind biases using ASCAT</em>, Ocean Sci., 15, 831–852, doi: 10.5194/os-15-831-2019.</p><p>Trindade, A., M. Portabella, A. Stoffelen, W. Lin and A. Verhoef (2019), <em>ERAstar: A High-Resolution Ocean Forcing Product</em>, IEEE Trans. Geosci. Remote Sens., 1-11, doi: 10.1109/TGRS.2019.2946019.</p>

scholarly journals Contributions from California Coastal-Zone Surface Fluxes to Heavy Coastal Precipitation: A CALJET Case Study during the Strong El Niño of 1998

2005 ◽  
Vol 133 (5) ◽  
pp. 1175-1198 ◽  
Author(s):  
P. Ola G. Persson ◽  
P. J. Neiman ◽  
B. Walter ◽  
J-W. Bao ◽  
F. M. Ralph
Keyword(s):  
Boundary Layer ◽  
Latent Heat ◽  
El Niño ◽  
Model Simulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Surface Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sst Anomalies

Abstract Analysis of the case of 3 February 1998, using an extensive observational system in the California Bight during an El Niño winter, has revealed that surface sensible and latent heat fluxes within 150 km of the shore contributed substantially to the destabilization of air that subsequently produced strong convection and flooding along the coast. Aircraft, dropsonde, and satellite observations gathered offshore documented the sea surface temperatures (SSTs), surface fluxes, stratification, and frontal structures. These were used to extrapolate the effects of the fluxes on the warm-sector, boundary layer air ahead of a secondary cold front as this air moved toward the coast. The extrapolated structure was then validated in detail with nearshore aircraft, wind profiler, sounding, and buoy observations of the frontal convection along the coast, and the trajectory transformations were confirmed with a model simulation. The results show that the surface fluxes increased CAPE by about 26% such that the nearshore boundary layer values of 491 J kg−1 were near the upper end of those observed for cool-season California thunderstorms. The increased CAPE due to upward sensible and latent heat fluxes was a result of the anomalously warm coastal SSTs (+1°–3°C) typical of strong El Niño events. Applications of the extrapolation method using a surface flux parameterization scheme and different SSTs suggested that convective destabilization due to nearshore surface fluxes may only occur during El Niño years when positive coastal SST anomalies are present. The fluxes may have no effect or a stabilizing effect during non–El Niño years, characterized by zero or negative coastal SST anomalies. In short, during strong El Niños, it appears that the associated coastal SST anomalies serve to further intensify the already anomalously strong storms in southern California, thus contributing to the increased flooding. This modulating effect by El Niño–Southern Oscillation (ENSO) of a mesoscale process has not been considered before in attempts at assessing the impacts of ENSO on U.S. west coast precipitation.

scholarly journals The Impact of Satellite Winds and Latent Heat Fluxes in a Numerical Simulation of the Tropical Pacific Ocean

2006 ◽  
Vol 19 (22) ◽  
pp. 5889-5902 ◽  
Author(s):  
Ludos-Herve Ayina ◽  
Abderrahim Bentamy ◽  
Alberto M. Mestas-Nuñez ◽  
Gurvan Madec
Keyword(s):  
Pacific Ocean ◽  
Latent Heat ◽  
Weather Prediction ◽  
Turbulent Fluxes ◽  
Tropical Pacific ◽  
Heat Fluxes ◽  
Tropical Pacific Ocean ◽  
Equatorial Pacific Ocean ◽  
The Impact ◽  
The Tropical Pacific

Abstract Several oceanic operational programs use remotely sensed fluxes to complement atmospheric operational analyses from major national weather prediction centers. The main goal of this study is to evaluate the ability of the ocean model (ORCA) to correctly simulate the dynamic of the tropical Pacific Ocean in 1996–98 when forced by the satellite turbulent fluxes (wind stress and latent heat fluxes). The results are compared with the oceanic response resulting from forcing the model with the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis. Three sensitivity simulations forced with satellite and atmospheric analysis fields are performed. The control experiment is forced with the ECMWF fluxes. The solutions of these simulations are compared with data from the Tropical Atmosphere–Ocean (TAO) buoys and from sea surface temperatures analysis by Reynolds and Smith in the equatorial Pacific Ocean. The analysis results indicate that the model reproduces well the major spatial and temporal oceanic structures including the main characteristics of the 1997–98 El Niño. More specifically, the comparisons with buoys indicate that the experiment forced by the winds and the satellite latent heat fluxes is closer to the observations. They provide weak rms difference and strong correlations along the whole 500-m depth column. Furthermore, the correlations with the SST analysis vary between 75% and 95% compared to 65% and 77% for the experiment forced by ECMWF fluxes. The currents in the first 350 m also show a strong sensitivity to satellite turbulent fluxes.

Impacts of Air–Sea Flux Parameterizations on the Intensity and Structure of Tropical Cyclones

2013 ◽  
Vol 141 (7) ◽  
pp. 2308-2324 ◽  
Author(s):  
Benjamin W. Green ◽  
Fuqing Zhang
Keyword(s):  
Wind Speed ◽  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Latent Heat ◽  
Weather Prediction ◽  
Surface Flux ◽  
Surface Fluxes ◽  
Sensible Heat ◽  
Near Surface ◽  
Flux Parameterization

Abstract Fluxes of momentum and moist enthalpy across the air–sea interface are believed to be one of the most important factors in determining tropical cyclone intensity. Because these surface fluxes cannot be directly resolved by numerical weather prediction models, their impacts on tropical cyclones must be accounted for through subgrid-scale parameterizations. There are several air–sea surface flux parameterization schemes available in the Weather Research and Forecasting (WRF) Model; these schemes differ from one another in their formulations of the wind speed–dependent exchange coefficients of momentum, sensible heat, and moisture (latent heat). The effects of surface fluxes on the intensity and structure of tropical cyclones are examined through convection-permitting WRF simulations of Hurricane Katrina (2005). It is found that the intensity (and, to a lesser extent, structure) of the simulated storms is sensitive to the choice of surface flux parameterization scheme. In agreement with recent studies, the drag coefficient CD is found to affect the pressure–wind relationship (between minimum sea level pressure and maximum 10-m wind speed) and to change the radius of maximum near-surface winds of the tropical cyclone. Fluxes of sensible and latent heat (i.e., moist enthalpy) affect intensity but do not significantly change the pressure–wind relationship. Additionally, when low-level winds are strong, the contribution of dissipative heating to calculations of sensible heat flux is not negligible. Expanding the sensitivity tests to several dozen cases from the 2008 to 2011 Atlantic hurricane seasons demonstrates the robustness of these findings.

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