SOME ASPECTS OF WIND STRUCTURE OF BAY CYCLONE OF MAY 1990

Abstract The GPS dropsonde allows observations at unprecedentedly high horizontal and vertical resolution, and of very high accuracy, within the tropical cyclone boundary layer. These data are used to document the boundary layer wind field of the core of Hurricane Georges (1998) when it was close to its maximum intensity. The spatial variability of the boundary layer wind structure is found to agree very well with the theoretical predictions in the works of Kepert and Wang. In particular, the ratio of the near-surface wind speed to that above the boundary layer is found to increase inward toward the radius of maximum winds and to be larger to the left of the track than to the right, while the low-level wind maximum is both more marked and at lower altitude on the left of the storm track than on the right. However, the expected supergradient flow in the upper boundary layer is not found, with the winds being diagnosed as close to gradient balance. The tropical cyclone boundary layer model of Kepert and Wang is used to simulate the boundary layer flow in Hurricane Georges. The simulated wind profiles are in good agreement with the observations, and the asymmetries are well captured. In addition, it is found that the modeled flow in the upper boundary layer at the eyewall is barely supergradient, in contrast to previously studied cases. It is argued that this lack of supergradient flow is a consequence of the particular radial structure in Georges, which had a comparatively slow decrease of wind speed with radius outside the eyewall. This radial profile leads to a relatively weak gradient of inertial stability near the eyewall and a strong gradient at larger radii, and hence the tropical cyclone boundary layer dynamics described by Kepert and Wang can produce only marginally supergradient flow near the radius of maximum winds. The lack of supergradient flow, diagnosed from the observational analysis, is thus attributed to the large-scale structure of this particular storm. A companion paper presents a similar analysis for Hurricane Mitch (1998), with contrasting results.

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Empirical inner boundary conditions and rotation rates for solar wind models

10.5194/egusphere-egu21-782 ◽

2021 ◽

Author(s):

Huw Morgan

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Boundary Conditions ◽

Coronal Magnetic Field ◽

Height Range ◽

Rotation Rates ◽

Wind Structure ◽

Solar Wind Structure ◽

Coronal Electron ◽

Made In

<p>To date, the inner boundary conditions for solar wind models are either directly or indirectly based on magnetic field extrapolation models of the photosphere. Furthermore, between the photosphere and Earth, there are no other direct empirical constraints on models. New breakthroughs in coronal rotation tomography, applied to coronagraph observations, allow maps of the coronal electron density to be made in the heliocentric height range 4-12 solar radii (Rs). We show that these maps (i) give a new empirical boundary condition for solar wind structure at a height where the coronal magnetic field has become radial, thus avoiding the need to model the complex inner coronal magnetic field, and (ii) give accurate rotation rates for the corona, of crucial importance to the accuracy of solar wind models and forecasts.</p>

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Extended optical spectroscopic monitoring of wind structure in HD 152408

Astronomy and Astrophysics ◽

10.1051/0004-6361:20000532 ◽

2001 ◽

Vol 367 (3) ◽

pp. 891-909 ◽

Cited By ~ 12

Author(s):

R. K. Prinja ◽

O. Stahl ◽

A. Kaufer ◽

S. R. Colley ◽

P. A. Crowther ◽

...

Keyword(s):

Spectroscopic Monitoring ◽

Wind Structure

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Solar cycle changes of large-scale solar wind structure

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309992912 ◽

2009 ◽

Vol 5 (S264) ◽

pp. 356-358 ◽

Cited By ~ 3

Author(s):

P. K. Manoharan

Keyword(s):

Solar Wind ◽

Solar Cycle ◽

Large Scale ◽

Interplanetary Space ◽

The Sun ◽

Wind Structure ◽

Level Of Activity ◽

Solar Wind Structure ◽

Current Minimum ◽

Inner Heliosphere

AbstractIn this paper, I present the results on large-scale evolution of density turbulence of solar wind in the inner heliosphere during 1985–2009. At a given distance from the Sun, the density turbulence is maximum around the maximum phase of the solar cycle and it reduces to ~70%, near the minimum phase. However, in the current minimum of solar activity, the level of turbulence has gradually decreased, starting from the year 2005, to the present level of ~30%. These results suggest that the source of solar wind changes globally, with the important implication that the supply of mass and energy from the Sun to the interplanetary space has significantly reduced in the present low level of activity.

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Tropospheric eddy feedback to different stratospheric conditions in idealised baroclinic life cycles

Weather and Climate Dynamics ◽

10.5194/wcd-2-111-2021 ◽

2021 ◽

Vol 2 (1) ◽

pp. 111-128

Author(s):

Philip Rupp ◽

Thomas Birner

Keyword(s):

Lower Stratosphere ◽

Polar Vortex ◽

Surface Friction ◽

Life Cycles ◽

Synoptic Scale ◽

Final State ◽

Northern Annular Mode ◽

Wind Structure ◽

Basic Set ◽

Set Up

Abstract. A pronounced signature of stratosphere–troposphere coupling is a robust negative anomaly in the surface northern annular mode (NAM) following sudden stratospheric warming (SSW) events, consistent with an equatorward shift in the tropospheric jet. It has previously been pointed out that tropospheric synoptic-scale eddy feedbacks, mainly induced by anomalies in the lowermost extratropical stratosphere, play an important role in creating this surface NAM signal. Here, we use the basic set-up of idealised baroclinic life cycles to investigate the influence of stratospheric conditions on the behaviour of tropospheric synoptic-scale eddies. Particular attention is given to the enhancement of the tropospheric eddy response by surface friction and the sensitivity to wind anomalies in the lower stratosphere. We find systems that include a tropospheric jet only (modelling post-SSW conditions) to be characterised by an equatorward shift in the tropospheric jet in the final state of the life cycle, relative to systems that include a representation of the polar vortex (mimicking more undisturbed stratospheric wintertime conditions), consistent with the observed NAM response after SSWs. The corresponding relative surface NAM signal is increased if the system includes surface friction, presumably due to a direct coupling of the eddy field at tropopause level to the surface winds. We further show that the jet shift signal observed in our experiments is mainly caused by changes in the zonal wind structure of the lowermost stratosphere, while changes in the wind structure of the middle and upper stratosphere have almost no influence.

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Analysis of wind structure over water waves using a flow visualization method.

Papers in Meteorology and Geophysics ◽

10.2467/mripapers.32.99 ◽

1981 ◽

Vol 32 (2) ◽

pp. 99-108 ◽

Cited By ~ 4

Author(s):

Tatsuo Konishi

Keyword(s):

Flow Visualization ◽

Water Waves ◽

Visualization Method ◽

Wind Structure

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Modeling the wind structure of AG Peg by fitting of C IV and N V resonance doublets

Astronomy and Astrophysics ◽

10.1051/0004-6361:20034086 ◽

2004 ◽

Vol 422 (3) ◽

pp. 987-999 ◽

Cited By ~ 15

Author(s):

M. Eriksson ◽

S. Johansson ◽

G. M. Wahlgren

Keyword(s):

Wind Structure

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The Benguela Upwelling System: Quantifying the Sensitivity to Resolution and Coastal Wind Representation in a Global Climate Model*

Journal of Climate ◽

10.1175/jcli-d-15-0192.1 ◽

2015 ◽

Vol 28 (23) ◽

pp. 9409-9432 ◽

Cited By ~ 69

Author(s):

R. Justin Small ◽

Enrique Curchitser ◽

Katherine Hedstrom ◽

Brian Kauffman ◽

William G. Large

Keyword(s):

Wind Stress ◽

Climate Model ◽

Coastal Upwelling ◽

Ocean Model ◽

Wind Stress Curl ◽

Upwelling System ◽

Wind Structure ◽

Eastern Boundary ◽

Benguela Upwelling ◽

Atmosphere Model

Abstract Of all the major coastal upwelling systems in the world’s oceans, the Benguela, located off southwest Africa, is the one that climate models find hardest to simulate well. This paper investigates the sensitivity of upwelling processes, and of sea surface temperature (SST), in this region to resolution of the climate model and to the offshore wind structure. The Community Climate System Model (version 4) is used here, together with the Regional Ocean Modeling System. The main result is that a realistic wind stress curl at the eastern boundary, and a high-resolution ocean model, are required to well simulate the Benguela upwelling system. When the wind stress curl is too broad (as with a 1° atmosphere model or coarser), a Sverdrup balance prevails at the eastern boundary, implying southward ocean transport extending as far as 30°S and warm advection. Higher atmosphere resolution, up to 0.5°, does bring the atmospheric jet closer to the coast, but there can be too strong a wind stress curl. The most realistic representation of the upwelling system is found by adjusting the 0.5° atmosphere model wind structure near the coast toward observations, while using an eddy-resolving ocean model. A similar adjustment applied to a 1° ocean model did not show such improvement. Finally, the remote equatorial Atlantic response to restoring SST in a broad region offshore of Benguela is substantial; however, there is not a large response to correcting SST in the narrow coastal upwelling zone alone.

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Statistical Tropical Cyclone Wind Radii Prediction Using Climatology and Persistence

Weather and Forecasting ◽

10.1175/waf1026.1 ◽

2007 ◽

Vol 22 (4) ◽

pp. 781-791 ◽

Cited By ~ 84

Author(s):

John A. Knaff ◽

Charles R. Sampson ◽

Mark DeMaria ◽

Timothy P. Marchok ◽

James M. Gross ◽

...

Keyword(s):

Tropical Cyclone ◽

Department Of Defense ◽

Parametric Model ◽

Forecast Method ◽

Operational Model ◽

Wind Structure ◽

East Pacific ◽

Operational Forecasts ◽

National Hurricane Center ◽

Joint Typhoon Warning Center

Abstract An operational model used to predict tropical cyclone wind structure in terms of significant wind radii (i.e., 34-, 50-, and 64-kt wind radii, where 1 kt = 0.52 m s−1) at the National Oceanic and Atmospheric Administration/National Hurricane Center (NHC) and the Department of Defense/Joint Typhoon Warning Center (JTWC) is described. The statistical-parametric model employs aspects of climatology and persistence to forecast tropical cyclone wind radii through 5 days. Separate versions of the model are created for the Atlantic, east Pacific, and western North Pacific by statistically fitting a modified Rankine vortex, which is generalized to allow wavenumber-1 asymmetries, to observed values of tropical cyclone wind radii as reported by NHC and JTWC. Descriptions of the developmental data and methods used to formulate the model are given. A 2-yr verification and comparison with operational forecasts and an independently developed wind radii forecast method that also employs climatology and persistence suggests that the statistical-parametric model does a good job of forecasting wind radii. The statistical-parametric model also provides reliable operational forecasts that serve as a baseline for evaluating the skill of operational forecasts and other wind radii forecast methods in these tropical cyclone basins.

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