Spray-Mediated Enthalpy Flux to the Atmosphere and Salt Flux to the Ocean in High Winds

2010 ◽  
Vol 40 (3) ◽  
pp. 608-619 ◽  
Author(s):  
Edgar L. Andreas
Keyword(s):  
Large Scale ◽  
Pure Water ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Salt Flux ◽  
Freshwater Flux ◽  
Near Surface ◽  
Storm Intensity ◽  
Spray Droplets ◽  
High Winds

Abstract Forecasts for the intensity and intensity changes of tropical cyclones have not improved as much as track forecasts. In high winds, two routes exist by which air and sea exchange heat and momentum: by spray-mediated processes and by interfacial transfer right at the air–sea interface, the only exchange route currently parameterized in most storm models. This manuscript quantifies two processes mediated by sea spray that could affect predictions of storm intensity when included in coupled ocean–atmosphere models. Because newly formed spray droplets cool rapidly to an equilibrium temperature that is lower than the air temperature, they cool the ocean when they reenter it, clearly transferring enthalpy from sea to air. These reentrant droplets proliferate in storm winds and are predicted to transfer enthalpy at a rate comparable to interfacial processes when the near-surface wind speed reaches 30 m s−1. Because reentrant spray droplets give up pure water to the atmosphere during their brief lifetime, they return to the sea saltier than the surface ocean water and thus also constitute an effective salt flux to the ocean (also related to a freshwater flux and a buoyancy flux). That is, reentrant spray droplets add enthalpy to the atmosphere to power storms and destabilize the ocean by increasing the salinity at the surface. Both processes can affect storm intensity. This manuscript demonstrates the magnitudes of the spray enthalpy and salt fluxes by combining a sophisticated microphysical model and data from the study of Humidity Exchange over the Sea (HEXOS) and the Fronts and Atlantic Storm-Tracks Experiment (FASTEX). It goes on to develop a fast algorithm for predicting these two fluxes in large-scale models.

Assessing reasons for skilful predictions of winter windstorms over the Atlantic/European region

2020 ◽  
Author(s):  
Lisa Degenhardt ◽  
Gregor Leckebusch ◽  
Adam Scaife
Keyword(s):  
Large Scale ◽  
Surface Wind ◽  
Forecast Model ◽  
Surface Wind Speed ◽  
Seasonal Forecast ◽  
Forecast Skill ◽  
Seasonal Forecasts ◽  
Financial Industry ◽  
Near Surface ◽  
Skill Scores

<p>Severe Atlantic winter storms are affecting densely populated regions of Europe (e.g. UK, France, Germany, etc.). Consequently, different parts of the society, financial industry (e.g., insurance) and last but not least the general public are interested in skilful forecasts for the upcoming storm season (usually December to March). To allow for a best possible use of steadily improved seasonal forecasts, the understanding which factors contribute to realise forecast skill is essential and will allow for an assessment whether to expect a forecast to be skilful or not.</p><p>This study analyses the predictability of the seasonal forecast model of the UK MetOffice, the GloSea5. Windstorm events are identified and tracked following Leckebusch et al. (2008) via the exceedance of the 98<sup>th</sup> percentile of the near surface wind speed.</p><p>Seasonal predictability of windstorm frequency in comparison to observations (based e.g., on ERA5 reanalysis) are calculated and different statistical methods (skill scores) are compared.</p><p>Large scale patterns (e.g., NAO, AO, EAWR, etc.) and dynamical factors (e.g., Eady Growth Rate) are analysed and their predictability is assessed in comparison to storm frequency forecast skill. This will lead to an idea how the forecast skill of windstorms is depending on the forecast skill of forcing factors conditional to the phase of large-scale variability modes. Thus, we deduce information, which factors are most important to generate seasonal forecast skill for severe extra-tropical windstorms.</p><p>The results can be used to get a better understanding of the resulting skill for the upcoming windstorm season.</p>

scholarly journals Centennial-scale variability of terrestrial near-surface wind speed over China from reanalysis

2021 ◽  
pp. 1-52
Author(s):  
Cheng Shen ◽  
Jinlin Zha ◽  
Jian Wu ◽  
Deming Zhao
Keyword(s):  
Wind Speed ◽  
Large Scale ◽  
Stepwise Regression ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Near Surface ◽  
Wind Speeds ◽  
Ocean Atmosphere ◽  
Forward Stepwise ◽  
Strong Winds

AbstractInvestigations of variations and causes of near-surface wind speed (NWS) further understanding of the atmospheric changes and improve the ability of climate analysis and projections. NWS varies on multiple temporal scales; however, the centennial-scale variability in NWS and associated causes over China remains unknown. In this study, we employ the European Centre for Medium-Range Weather Forecasts (ECMWF) twentieth century reanalysis (ERA-20C) to study the centennial-scale changes in NWS from 1900–2010. Meanwhile, a forward stepwise regression algorithm is used to reveal the relationships between NWS and large-scale ocean-atmosphere circulations. The results show three unique periods in annual mean NWS over China from 1900–2010. The annual mean NWS displayed a decreasing trend of -0.87% decade-1 and -11.75% decade-1 from 1900–1925 and 1957–2010, respectively, which were caused by the decreases in the days with strong winds, with trends of -6.64 and -4.66 days decade-1, respectively. The annual mean NWS showed an upward trend of 55.47% decade-1 from 1926–1956, which was caused by increases in the days with moderate (0.43 days decade-1) and strong winds (23.55 days decade-1). The reconstructed wind speeds based on forward stepwise regression algorithm matched well with the original wind speeds; therefore, the decadal changes in NWS over China at centennial-scale were mainly induced by large-scale ocean-atmosphere circulations, with the total explanation power of 66%. The strongest explanation power was found in winter (74%), and the weakest explanation power was found in summer (46%).

scholarly journals A Statistical Analysis on the Dependence of Tropical Cyclone Intensification Rate on the Storm Intensity and Size in the North Atlantic

2015 ◽  
Vol 30 (3) ◽  
pp. 692-701 ◽  
Author(s):  
Jing Xu ◽  
Yuqing Wang
Keyword(s):  
Tropical Cyclone ◽  
North Atlantic ◽  
Turning Point ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Outer Core ◽  
Near Surface ◽  
Storm Intensity ◽  
The North ◽  
Intensity Prediction

Abstract The dependence of tropical cyclone (TC) intensification rate IR on storm intensity and size was statistically analyzed for North Atlantic TCs during 1988–2012. The results show that IR is positively (negatively) correlated with storm intensity (the maximum sustained near-surface wind speed Vmax) when Vmax is below (above) 70–80 knots (kt; 1 kt = 0.51 m s−1), and negatively correlated with storm size in terms of the radius of maximum wind (RMW), the average radius of gale-force wind (AR34), and the outer-core wind skirt parameter DR34 (=AR34 − RMW). The turning point for Vmax of 70–80 kt is explained as a balance between the potential intensification and the maximum potential intensity (MPI). The highest IR occurs for Vmax = 80 kt, RMW ≤ 40 km, and AR34 = DR34 = 150 km. The high frequency of occurrence of intensifying TCs occurs for Vmax ≤ 80 kt and RMW between 20 and 60 km, AR34 ≤ 200 km, and DR34 ≤ 150 km. Rapid intensification (RI) often occurs in a relatively narrow parameter space in storm intensity and both inner- and outer-core sizes. In addition, a theoretical basis for the intensity dependency has also been provided based on a previously constructed simplified dynamical system for TC intensity prediction.

scholarly journals Tornado-scale vortices in the tropical cyclone boundary layer: numerical simulation with the WRF–LES framework

2019 ◽  
Vol 19 (4) ◽  
pp. 2477-2487 ◽  
Author(s):  
Liguang Wu ◽  
Qingyuan Liu ◽  
Yubin Li
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Large Scale ◽  
Surface Wind ◽  
Wrf Model ◽  
Surface Wind Speed ◽  
Horizontal Scale ◽  
Lower Altitude ◽  
Near Surface ◽  
Research Aircraft

Abstract. A tornado-scale vortex in the tropical cyclone (TC) boundary layer (TCBL) has been observed in intense hurricanes and the associated intense turbulence poses a severe threat to the manned research aircraft when it penetrates hurricane eyewalls at a lower altitude. In this study, a numerical experiment in which a TC evolves in a large-scale background over the western North Pacific is conducted using the Advanced Weather Research and Forecast (WRF) model by incorporating the large-eddy simulation (LES) technique. The simulated tornado-scale vortex shows features similar to those revealed with limited observational data, including the updraft–downdraft couplet, the sudden jump of wind speeds, the location along the inner edge of the eyewall, and the small horizontal scale. It is suggested that the WRF–LES framework can successfully simulate the tornado-scale vortex with grids at a resolution of 37 m that cover the TC eye and eyewall. The simulated tornado-scale vortex is a cyclonic circulation with a small horizontal scale of ∼1 km in the TCBL. It is accompanied by strong updrafts (more than 15 m s−1) and large vertical components of relative vorticity (larger than 0.2 s−1). The tornado-scale vortex favorably occurs at the inner edge of the enhanced eyewall convection or rainband within the saturated, high-θe layer, mostly below an altitude of 2 km. In nearly all the simulated tornado-scale vortices, the narrow intense updraft is coupled with the relatively broad downdraft, constituting one or two updraft–downdraft couplets, as observed by the research aircraft. The presence of the tornado-scale vortex also leads to significant gradients in the near-surface wind speed and wind gusts.

scholarly journals Tornado-Scale Vortices in the Tropical Cyclone Boundary Layer: Numerical Simulation with WRF-LES Framework

2018 ◽  
Author(s):  
Liguang Wu ◽  
Qingyuan Liu ◽  
Yubing Li
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Large Scale ◽  
Surface Wind ◽  
Wrf Model ◽  
Surface Wind Speed ◽  
Horizontal Scale ◽  
Lower Altitude ◽  
Near Surface ◽  
Research Aircraft

Abstract. The tornado-scale vortex in the tropical cyclone (TC) boundary layer (TCBL) has been observed in intense hurricanes and the associated intense turbulence poses a severe threat to the manned research aircraft when it penetrates hurricane eyewalls at a lower altitude. In this study, a numerical experiment in which a TC evolves in a large-scale background over the western North Pacific is conducted using the Advanced Weather Research and Forecast (WRF) model by incorporating the large eddy simulation (LES) technique. The simulated tornado-scale vortex shows the similar features as revealed with the limited observational data, including the updraft/downdraft couplet, the sudden jump of wind speeds, the favorable location, and the horizontal scale. It is suggested that the WRF-LES framework can successfully simulate the tornado-scale vortex with the grids at the resolution of 37 m that cover the TC eye and eyewall. The simulated tornado-scale vortex is a cyclonic circulation with a small horizontal scale of ~ 1 km in the TCBL. It is accompanied by strong updrafts (more than 15 m s−1) and large vertical components of relative vorticity (larger than 0.2 s−1). The tornado-scale vortex favorably occurs at the inner edge of the enhanced eyewall convection or rainband within the saturated, high-θe layer, mostly below the altitude of 2 km. Nearly in all the simulated tornado-scale vortices, the narrow intense updraft is coupled with the relatively broad downdraft, constituting one or two updraft/downdraft couplets or horizontal rolling vortices, as observed by the research aircraft. The presence of the tornado-scale vortex also leads to significant gradients in the near surface wind speed and wind gusts.

scholarly journals Homogenization and Assessment of Observed Near-Surface Wind Speed Trends across Sweden, 1956–2013

2016 ◽  
Vol 29 (20) ◽  
pp. 7397-7415 ◽  
Author(s):  
Lorenzo Minola ◽  
Cesar Azorin-Molina ◽  
Deliang Chen
Keyword(s):  
Wind Speed ◽  
Large Scale ◽  
Surface Wind ◽  
Geostrophic Wind ◽  
Surface Wind Speed ◽  
Downward Trend ◽  
Near Surface ◽  
Speed Increase ◽  
Nao Index ◽  
Positive Tendency

Abstract Multidecadal variability of observed near-surface wind speed from 24 stations across Sweden has been analyzed for 1956–2013, with a focus on 1979–2008 (incorporating an additional 9 stations) for comparison with previous studies. Wind speed data have been subjected to a robust data processing protocol, consisting of quality control, reconstruction, and homogenization, by using geostrophic wind speed series as reference. The homogenized dataset displays a significant (at p < 0.05) downward trend for 1956–2013 (−0.06 m s−1 decade−1) and an even larger decreasing trend for 1979–2008 (−0.14 m s−1 decade−1). However, differences have been observed seasonally, with significant decreasing values in spring, summer, and autumn and a small downward trend in winter for 1956–2013. Most interestingly, a nonsignificant wind speed increase has been detected in winter for 1979–2008, which contrasts with the marked “stilling” reported for this season in much of midlatitude regions. The decreasing rate in wind speed is larger for coastal stations and in the southern part of Sweden. Decreasing trends were found at 91.7% of the stations during summer, whereas 58.3% of the stations displayed decreasing trends in winter. On the contrary, increasing trends occurred in 41.7% of the stations for winter and in only 8.3% for summer. The possible impact of the North Atlantic Oscillation (NAO) index has also been investigated, showing evidence that the small increasing trend in winter for 1979–2008 is hypothetically associated with the positive tendency of the NAO index during the last decades. These results reveal the influence of large-scale atmospheric circulation on wind speed variability across Sweden.

Recurrence Characteristics Analysis of Near-Surface Wind Speed Signal with Different Sampling Frequencies

2014 ◽  
Vol 599-601 ◽  
pp. 1605-1609 ◽  
Author(s):  
Ming Zeng ◽  
Zhan Xie Wu ◽  
Qing Hao Meng ◽  
Jing Hai Li ◽  
Shu Gen Ma
Keyword(s):  
Wind Speed ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Recurrence Plot ◽  
Sampling Frequency ◽  
Near Surface ◽  
Gas Leakage ◽  
Time Period ◽  
Characteristics Analysis ◽  
Quantification Analysis

The wind is the main factor to influence the propagation of gas in the atmosphere. Therefore, the wind signal obtained by anemometer will provide us valuable clues for searching gas leakage sources. In this paper, the Recurrence Plot (RP) and Recurrence Quantification Analysis (RQA) are applied to analyze the influence of recurrence characteristics of the wind speed time series under the condition of the same place, the same time period and with the sampling frequency of 1hz, 2hz, 4.2hz, 5hz, 8.3hz, 12.5hz and 16.7hz respectively. Research results show that when the sampling frequency is higher than 5hz, the trends of recurrence nature of different groups are basically unchanged. However, when the sampling frequency is set below 5hz, the original trend of recurrence nature is destroyed, because the recurrence characteristic curves obtained using different sampling frequencies appear cross or overlapping phenomena. The above results indicate that the anemometer will not be able to fully capture the detailed information in wind field when its sampling frequency is lower than 5hz. The recurrence characteristics analysis of the wind speed signals provides an important basis for the optimal selection of anemometer.

Ocean Salinity changes in the global ocean under global warming conditions Part 1: Mechanisms in a strong warming scenario

2021 ◽  
pp. 1-56
Author(s):  
Anju Sathyanarayanan ◽  
Armin Köhl ◽  
Detlef Stammer
Keyword(s):  
Large Scale ◽  
Water Cycle ◽  
Spatial Scales ◽  
Sea Surface Salinity ◽  
Global Ocean ◽  
Dynamical Response ◽  
Freshwater Flux ◽  
Near Surface ◽  
Salinity Changes ◽  
Circulation Changes

AbstractWe investigate mechanisms underlying salinity changes projected to occur under strong representative concentration pathway (RCP) 8.5 forcing conditions. The study is based on output of the Max Planck Institute Earth System Model Mixed Resolution (MPI-ESM-MR) run with an ocean resolution of 0.4°. In comparison to the present-day oceanic conditions, sea surface salinity (SSS) increases towards the end of the 21st century in the tropical and the subtropical Atlantic. In contrast, a basin-wide surface freshening can be observed in the Pacific and Indian Oceans. The RCP8.5 scenario of the MPI-ESM-MR with a global surface warming of ~2.3°C marks a water cycle amplification of 19 %, which is equivalent to ~8%°C−1 and thus close to the water cycle amplification predicted according to the Clausius–Clapeyron (CC) relationship (~7%°C−1). Large scale global SSS changes are driven by adjustments of surface freshwater fluxes. On smaller spatial scales, it is predominantly advection related to circulation changes that affects near-surface SSS. With respect to subsurface salinity, it is changes in surface freshwater flux that drive their changes over the upper 500 m of the subtropical Pacific and Indian oceans by forcing changes in water mass formation (spice signal). In the subtropical Atlantic Ocean, in contrast, the dynamical response associated with wind stress, circulation changes and associated heaving of isopycnals is equally important in driving subsurface salinity changes over the upper 1000 m.

scholarly journals Fifty-Seven-Year California Reanalysis Downscaling at 10 km (CaRD10). Part I: System Detail and Validation with Observations

2007 ◽  
Vol 20 (22) ◽  
pp. 5553-5571 ◽  
Author(s):  
Masao Kanamitsu ◽  
Hideki Kanamaru
Keyword(s):  
Time Scales ◽  
Large Scale ◽  
Global Analysis ◽  
Regional Climate ◽  
Regional Scale ◽  
Surface Wind ◽  
Lateral Boundary ◽  
Climate Change Research ◽  
Near Surface ◽  
Precipitation Analysis

Abstract For the purpose of producing datasets for regional-scale climate change research and application, the NCEP–NCAR reanalysis for the period 1948–2005 was dynamically downscaled to hourly, 10-km resolution over California using the Regional Spectral Model. This is Part I of a two-part paper, describing the details of the downscaling system and comparing the downscaled analysis [California Reanalysis Downscaling at 10 km (CaRD10)] against observation and global analysis. An extensive validation of the downscaled analysis was performed using station observations, Higgins gridded precipitation analysis, and Precipitation-Elevation Regression on Independent Slopes Model (PRISM) precipitation analysis. In general, the CaRD10 near-surface wind and temperature fit better to regional-scale station observations than the NCEP–NCAR reanalysis used to force the regional model, supporting the premise that the regional downscaling is a viable method to attain regional detail from large-scale analysis. This advantage of CaRD10 was found on all time scales, ranging from hourly to decadal scales (i.e., from diurnal variation to multidecadal trend). Dynamically downscaled analysis provides ways to study various regional climate phenomena of different time scales because all produced variables are dynamically, physically, and hydrologically consistent. However, the CaRD10 is not free from problems. It suffers from positive bias in precipitation for heavy precipitation events. The CaRD10 is inaccurate near the lateral boundary where regional detail is damped by the lateral boundary relaxation. It is important to understand these limitations before the downscaled analysis is used for research.

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