Aircraft Observations of Tropical Cyclone Boundary Layer Turbulence over the South China Sea

Sparks, Nathan; Hon, K. K.; Chan, P. W.; Wang, Siyang; Chan, Johnny C. L.; Lee, T. C.; Toumi, Ralf

doi:10.1175/jas-d-19-0128.1

Cited by 21 publications

(15 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This result stresses the importance of the boundary layer in the intensification (especially the RI) of TCs, which has also been shown in previous studies [28,29]. Actually, to better understand the TC structure in the boundary layer, flight observations aimed at the TC boundary layer were conducted in the South China Sea since 2009, which comprised four eyewall penetrations [30]. To better use these observations to improve the RI forecast of a TC, some questions should be first addressed: (i) Does the uncertainty in the boundary layer influence the RI forecast uncertainty of a TC?…”

Section: Introductionsupporting

confidence: 79%

Forecast Uncertainty of Rapid Intensification of Typhoon Dujuan (201521) Induced by Uncertainty in the Boundary Layer

Qin

Duan

2020

Atmosphere

View full text Add to dashboard Cite

Using ensemble forecast experiments generated by the weather research and forecasting model, the forecast uncertainties of intensity and its rapid intensification (RI) induced by the uncertainty occurring in the boundary layer are investigated for Typhoon Dujuan (201521). The results show that the uncertainty in the boundary layer in the typhoon area, compared with that in other areas of the model domain, not only leads to a much larger forecast uncertainty of the typhoon intensity but also considerably perturbs the RI forecast uncertainty. Particularly, the uncertainty in the gale area in the boundary layer, compared with that in the inner-core and other areas, makes a much larger contribution to the forecast uncertainty of typhoon intensity, with the perturbations including moisture component being most strongly correlated with the occurrence of RI. Further analyses show that such perturbations increase the maximum tangential wind in the boundary layer and enhance the vorticity in the eyewall, which then facilitate the spin-up of the inner-core and induce the occurrence of RI. It is inferred that more observations, especially those associated with the moisture, should be preferentially assimilated in the gale area within the boundary layer of a tropical cyclone, which will help improve the forecast skill of the RI. These results also tell us that the boundary layer parameterization scheme should be further developed to improve the forecast skill of tropical cyclone intensity and its RI behavior.

show abstract

Section: Introductionsupporting

confidence: 79%

Forecast Uncertainty of Rapid Intensification of Typhoon Dujuan (201521) Induced by Uncertainty in the Boundary Layer

Qin

Duan

2020

Atmosphere

View full text Add to dashboard Cite

show abstract

“…The momentum budget estimates of Bell et al (2012) provide C D out to very high winds (10-m wind speeds above 70 m s 21 ), but the large inherent uncertainty in these approximations precludes any definitive conclusion about even the slope of C D versus wind speed beyond 40 m s 21 , let alone its precise value. The direct aircraft measurements of Sparks et al (2019) and Zhao et al (2020) made in Pacific typhoons suggest that the momentum flux changes with wind speed in a way consistent with a saturation of C D ; however, while extending out to 60 m s 21 , the measurements are again quite uncertain. Likewise, other direct measurements of boundary layer turbulence in tropical cyclones, namely, those of Zhang et al (2011a), are also uncertain and scarce in sample size.…”

Section: Introductionmentioning

confidence: 95%

Potential low bias in high-wind drag coefficient inferred from dropsonde data in hurricanes

Richter

Wainwright

Stern

et al. 2021

Journal of the Atmospheric Sciences

View full text Add to dashboard Cite

Understanding momentum exchange at the air-sea interface is important for accurate hurricane predictions and understanding fundamental storm dynamics. One method for estimating air-sea momentum transfer in high winds is the flux-profile method, which infers surface momentum fluxes and the corresponding drag coefficient from mean velocity profiles obtained from either dropsondes or meteorological towers, under the assumption that the boundary-layer wind profile at low altitudes exhibits a logarithmic profile with height. In this study, we use dropsonde data from reconnaissance aircraft, as well as “virtual sondes” from a turbulence-resolving simulation of an intense tropical cyclone, to critically analyze the diagnosis of drag coefficient CD at hurricane-force wind speeds. In particular, the “roll-off” of the drag coefficient, where CD decreases at 10-m wind speeds ¿ 35 m s−1, is called into question based on uncertainty due to relatively low sample size and a lack of robustness of the flux-profile at high winds. In addition, multiple factors appear to favor an underestimate of CD at hurricane-force winds relative to their true values, including uncertainty in the height of recorded dropsonde data, violation of Monin-Obukhov similarity theory near the eyewall, and the short vertical extent of the logarithmic layer. Due to these and other related sources of uncertainty, it is likely that a quantitative limit has been reached in inferring the specific values of u* and CD using the flux-profile method, while at the same time the potential for underestimation may cast doubt on the CD–U10 relationship inferred from this method at high winds.

show abstract

“…Furthermore, Chen and Li offered an investigation relevant to latent heat flux exchanges at the air-sea interface, which play important roles in the formation and development of tropical cyclones over the ocean [11]. Sparks and Hon presented an analysis of the first boundary layer flight observations on the ocean by the Hong Kong Observatory comprising four eyewall penetrations, which derived the vertical flux of momentum and vertical momentum diffusivity from observed turbulence parameters [12]. Based on generalizations of numerous measurements and calculations, Lukin found that the outer scale of turbulence in the surface layer of the atmosphere depends not only on the height above the underlying surface but also on the type of atmospheric stratification [13].…”

Section: Introductionmentioning

confidence: 99%

Atmospheric Optical Turbulence Characteristics over the Ocean Relevant to Astronomy and Atmospheric Physics

Shao

Weng

et al. 2021

Applied Sciences

View full text Add to dashboard Cite

Due to the space and time constraints of turbulence measurement equipment and the experiment scene, it is difficult to obtain the atmosphere refractive index structure constant over the ocean. In this paper, the characteristics of atmospheric optical turbulence in offshore and open ocean conditions are summarized by analyzing the meteorological data obtained from two ocean atmospheric optical parameter field experiments. Because of the influence of land undersurface, the turbulence strength in offshore conditions is roughly the same as that on land and presents different characteristics in open ocean. Compared with the offshore area, the turbulence strength over the open ocean near-surface decreases during the day and increases at night, and the diurnal variation characteristics weaken. The turbulence strength profiles over the offshore area show different characteristics at different times, where the turbulence strength in the morning is higher than that in the evening. By retrieving the meteorological factors affecting the turbulence, it is found that the temperature gradient and wind shear are in good agreement with turbulence strength in both offshore and open ocean areas. Furthermore, the integrated parameters for astronomy and optical telecommunication are derived from profiles over the offshore and open ocean areas. It is of great significance to research the turbulent characteristics of ocean atmosphere for optical transmission and astronomical observations.

show abstract

Aircraft Observations of Tropical Cyclone Boundary Layer Turbulence over the South China Sea

Cited by 21 publications

References 30 publications

Forecast Uncertainty of Rapid Intensification of Typhoon Dujuan (201521) Induced by Uncertainty in the Boundary Layer

Forecast Uncertainty of Rapid Intensification of Typhoon Dujuan (201521) Induced by Uncertainty in the Boundary Layer

Potential low bias in high-wind drag coefficient inferred from dropsonde data in hurricanes

Atmospheric Optical Turbulence Characteristics over the Ocean Relevant to Astronomy and Atmospheric Physics

Contact Info

Product

Resources

About