Horizontal structure of convergent wind shear associated with sporadic E layers over East Asia

At present,the main detection instruments for observing sporadic E(Es)layers are ground-based radars,dense networks of ground-based global navigation satellite system(GNSS)receivers,and GNSS radio occultation,but they cannot capture the whole picture of the horizontal structure of Es layers.This study employs the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension model(WACCM-X 2.1)to derive the horizontal structure of the ion convergence region(HSICR)to explore the shapes of the large-scale Es layers over East Asia for the period from June 1 to August 31,2008.The simulation produced the various shapes of the HSICRs elongated in the northwest-southeast,northeast-southwest,or composed of individual small patches.The close connection between Es layer critical frequency(foEs)and vertical ion convergence indicates that the HSICR is a good candidate for revealing and explaining the horizontal structure of the large-scale Es layers.

Influence of Wind Turbine Structural Parameters on Wind Shear and Tower Shadow Effect

To overcome the problems of natural decreases in power quality,and to eliminate wind speed fluctuation due to wind shear and tower shadow effect arising from wind turbine structural parameters,an improved prediction model accounting for the dual effect of wind shear and tower shadow is,in this paper,built.Compared to the conventional prediction model,the proposed model contains a new constraint condition,which makes the disturbance term caused by the tower shadow effect always negative so that the prediction result is closer to the actual situation.Furthermore,wind turbine structural parameters such as hub height,rotor diameter,the diameter of the tower top,and rotor overhang on wind shear and tower shadow effect are also explored in detail.The results show that the wind shear effect became weaker with the increase in hub height.The hub height is independent of the tower shadow effect.The rotor diameter is positively correlated with the wind shear and tower shadow effect.The tower shadow effect is positively correlated with the diameter of the tower top and negatively correlated with the rotor overhang.

EFFECTS OF VERTICAL WIND SHEAR ON INTENSITY AND STRUCTURE OF TROPICAL CYCLONE

In this study,the effect of vertical wind shear(VWS)on the intensification of tropical cyclone(TC)is investigated via the numerical simulations.Results indicate that weak shear tends to facilitate the development of TC while strong shear appears to inhibit the intensification of TC.As the VWS is imposed on the TC,the vortex of the cyclone tends to tilt vertically and significantly in the upper troposphere.Consequently,the upward motion is considerably enhanced in the downshear side of the storm center and correspondingly,the low-to mid-level potential temperature decreases under the effect of adiabatic cooling,which leads to the increase of the low-to mid-level static instability and relative humidity and then facilitates the burst of convection.In the case of weak shear,the vertical tilting of the vortex is weak and the increase of ascent,static instability and relative humidity occur in the area close to the TC center.Therefore,active convection happens in the TC center region and facilitates the enhancement of vorticity in the inner core region and then the intensification of TC.In contrast,due to strong VWS,the increase of the ascent,static instability and relative humidity induced by the vertical tilting mainly appear in the outer region of TC in the case with stronger shear,and the convection in the inner-core area of TC is rather weak and convective activity mainly happens in the outer-region of the TC.Therefore,the development of a warm core is inhibited and then the intensification of TC is delayed.Different from previous numerical results obtained by imposing VWS suddenly to a strong TC,the simulation performed in this work shows that,even when the VWS is as strong as 12 m s-1,the tropical storm can still experience rapid intensification and finally develop into a strong tropical cyclone after a relatively long period of adjustment.It is found that the convection plays an important role in the adjusting period.On one hand,the convection leads to the horizontal convergence of the low-level vorticity flux and therefore leads to the enhancement of the low-level vorticity in the inner-core area of the cyclone.On the other hand,the active ascent accompanying the convection tends to transport the low-level vorticity to the middle levels.The enhanced vorticity in the lower to middle troposphere strengths the interaction between the low-and mid-level cyclonical circulation and the upper-level circulation deviated from the storm center under the effect of VWS.As a result,the vertical tilting of the vortex is considerably decreased,and then the cyclone starts to develop rapidly.

EFFECTS OF VERTICAL WIND SHEAR ON TROPICAL CYCLONE INTENSITY CHANGE

The effects of vertical wind shear on tropical cyclone(TC) intensity change are examined based on the TC data from the China Meteorological Administration and the NCEP reanalysis daily data from 2001 to 2006.First,the influence of wind shear between different vertical levels and averages in different horizontal areas are compared.The results indicate that the effect of wind shear between 200 and 850 hPa averaged within a 200-800 km annulus on TC intensity change is larger than any other calculated vertical wind shear.High-latitude and intense TCs tend to be less sensitive to the effects of VWS than low-latitude and weak TCs.TCs experience time lags between the imposition of the shear and the weakening in TC intensity.A vertical shear of 8-9 m/s(9-10 m/s) would weaken TC intensity within 60 h(48 h).A vertical shear greater than 10 m/s would weaken TC intensity within 6 h.Finally,a statistical TC intensity prediction scheme is developed by using partial least squares regression,which produces skillful intensity forecasts when potential predictors include factors related to the vertical wind shear.Analysis of the standardized regression coefficients further confirms the obtained statistical results.

Directional Filtering Due to Mesospheric Wind Shear on the Propagation of Acoustic-gravity Waves

Gravity waves with periods close to the Brunt-V(a|¨)is(a|¨)l(a|¨) period of the upper troposphere are often observed at mesopause altitudes as short period,quasi-monochromatic waves.The assumption that these short period waves originate in the troposphere may be problematic because their upward propagation to the mesosphere and lower thermosphere region could be significantly impeded due to an extended region of strong evanescence above the stratopause.To reconcile this apparent paradox,an alternative explanation is proposed in this paper.The inclusion of mean winds and their vertical shears is sufficient to allow certain short period waves to remain internal above the stratopause and to propagate efficiently to higher altitudes.A time-dependent numerical model is used to demonstrate the feasibility of this and to determine the circumstances under which the mesospheric wind shears play a role in the removal and directional filtering of short period gravity waves. Finally this paper concludes that the combination of the height-dependent mean winds and the mean temperature structure probably explains the existence of short period,quasi-monochromatic structures observed in airglow images of mesopause region.

WIND SHEAR IDENTIFICATION WITH THE RETRIEVED WIND OF DOPPLER WEATHER RADAR

Wind shear reflects that the wind field is not uniform, which is one of the primary factors which make the retrieval of the wind field difficult. Based on volume velocity process(VVP) wind field retrieval technique, the intensity of wind shear is identified in this paper. After analyzing the traditional techniques that rely on the difference of radial velocity to identify wind shear, a fixed difference among radial velocities that may cause false identification in a uniform wind field was found. Because of the non-uniformity in wind shear areas, the difference of retrieved results between surrounding analysis volumes can be used as a measurement to show how strong the wind shear is. According to the analysis of a severe convective weather process that occurred in Guangzhou, it can be found that the areas of wind shear appeared with the strength significantly larger than in other regions and the magnitude generally larger than4.5 m/(s·km). Besides, by comparing the variation of wind shear strength during the convection, it can be found that new cells will be more likely to generate when the strength is above 3.0 m/(s·km). Therefore, the analysis of strong wind shear's movement and development is helpful to forecasting severe convections.

Effects of Vertical Wind Shear on Intensity and Rainfall Asymmetries of Strong Tropical Storm Bilis (2006)

The effects of environmental vertical wind shear(VWS)on the intensity and rainfall asymmetries in Tropical Storm(TS)Bilis(2006)have been analyzed based on TRMM/TMI-estimated surface rainfall data,QuikSCAT wind fields,850-and 200-hPa winds of the NCEP-NCAR reanalysis,precipitation data at 5-min intervals from automatic weather stations over China's Mainland,and the best track data of TS Bilis(2006). The results show that the simultaneous and 6-hour-lagged correlation coeffcients between VWS and storm intensity(the minimum central sea level pressure)are 0.59145 and 0.57438(P<0.01),respectively.The averaged VWS was found to be about 11 m s-1 and thus suppressed the intensification of Bilis(2006). Distribution of precipitation in Bilis(2006)was highly asymmetric.The azimuthally-averaged rainfall rate in the partial eyewall,however,was smaller than that in a major outer rainband.As the storm intensified,the major rainband showed an unusual outward propagation.The VWS had a great impact on the asymmetric distribution of precipitation.Consistent with previous modeling studies,heavy rainfall generally occurred downshear to downshear-left of the VWS vector both near and outside the eyewall,showing a strong wavenumber-one asymmetry,which was amplified as the VWS increased.

Characteristics for wind energy and wind turbines by considering vertical wind shear

The probability distributions of wind speeds and the availability of wind turbines were investigated by considering the vertical wind shear. Based on the wind speed data at the standard height observed at a wind farm, the power-law process was used to simulate the wind speeds at a hub height of 60 m. The Weibull and Rayleigh distributions were chosen to express the wind speeds at two different heights. The parameters in the model were estimated via the least square(LS) method and the maximum likelihood estimation(MLE) method, respectively. An adjusted MLE approach was also presented for parameter estimation. The main indices of wind energy characteristics were calculated based on observational wind speed data. A case study based on the data of Hexi area, Gansu Province of China was given. The results show that MLE method generally outperforms LS method for parameter estimation, and Weibull distribution is more appropriate to describe the wind speed at the hub height.

Efects of Vertical Wind Shear, Radiation and Ice Microphysics on Precipitation Efciency during a Torrential Rainfall Event in China

The efects of vertical wind shear,radiation and ice microphysics on precipitation efciency(PE)were investigated through analysis of modeling data of a torrential rainfall event over Jinan,China during July2007.Vertical wind shear afected PE by changing the kinetic energy conversion between the mean and perturbation circulations.Cloud–radiation interaction impacted upon PE,but the relationship related to cloud radiative efects on PE was not statistically significant.The reduction in deposition processes associated with the removal of ice microphysics suppressed efciency.The relationships related to efects of vertical wind shear,radiation and ice clouds on PEs defined in cloud and surface rainfall budgets were more statistically significant than that defined in the rain microphysical budget.

Effects of Vertical Wind Shear on the Pre-Summer Heavy Rainfall Budget:A Cloud-Resolving Modeling Study

This study investigates the effects of vertical wind shear on the torrential rainfall response to the large-scale forcing using a rainfall separation analysis of a pair of two-dimensional cloud-resolving model sensitivity experiments for a pre-summer heavy rainfall event over southern China from 3-8 June 2008 coupled with National Centers for Environmental Prediction(NCEP)/Global Data Assimilation System(GDAS) data.The rainfall partitioning analysis based on the surface rainfall budget indicates that the exclusion of vertical wind shear decreases the contribution to total rainfall from the largest contributor,which is the rainfall associated with local atmospheric drying,water vapor divergence,and hydrometeor loss/convergence,through the reduction of the rainfall area and reduced rainfall during the rainfall event.The removal of vertical wind shear increases the contribution to total rainfall from the rainfall associated with local atmospheric drying,water vapor convergence,and hydrometeor loss/convergence through the expansion of the rainfall area and enhanced rainfall.The elimination of vertical wind shear enhances heavy rainfall and expands its area,whereas it reduces moderate rainfall and its area.

Revisiting the response of western North Pacific tropical cyclone intensity change to vertical wind shear in different directions

不同方向垂直风切变对热带气旋强度变化的影响存在明显差异,但对热带气旋无维强度变化的影响却差异较小.研究发现不同方向垂直风切变对无维强度变化的影响的细微差异与热带气旋周围的高层西风槽,倒槽,低层季风槽等天气系统配置有关.这一结果表明,在研究不同方向切变对热带气旋强度变化的影响时,除了下垫面热力作用外,还应考虑与切变相关的天气尺度系统的热,动力作用.

Low-Level Wind Shear Characteristics and Lidar-Based Alerting at Lanzhou Zhongchuan International Airport,China

Lanzhou Zhongchuan International Airport[International Civil Aviation Organization(ICAO)code ZLLL]is located in a wind shear prone area in China,where most low-level wind shear events occur in dry weather conditions.We analyzed temporal distribution and synoptic circulation background for 18 dry wind shear events reported by pilots at ZLLL by using the NCEP final(FNL)operational global analysis data,and then proposed a lidar-based regional divergence algorithm(RDA)to determine wind shear intensity and location.Low-level wind shear at ZLLL usually occurs in the afternoon and evening in dry conditions.Most wind shear events occur in an unstable atmosphere over ZLLL,with changes in wind speed or direction generally found at 700 hPa and 10-m height.Based on synoptic circulations at 700 hPa,wind shear events could be classified as strong northerly,convergence,southerly,and weak wind types.The proposed RDA successfully identified low-level wind shear except one southerly case,achieving94%alerting rate compared with 82%for the operational system at ZLLL and 88%for the ramp detection algorithm(widely used in some operational alert systems)based on the same dataset.The RDA-unidentified southerly case occurred in a near neutral atmosphere,and wind speed change could not be captured by the Doppler lidar.

A Lagrangian Trajectory Analysis of Azimuthally Asymmetric Equivalent Potential Temperature in the Outer Core of Sheared Tropical Cyclones

In this study,the characteristics of azimuthally asymmetric equivalent potential temperature(θ_(e))distributions in the outer core of tropical cyclones(TCs)encountering weak and strong vertical wind shear are examined using a Lagrangian trajectory method.Evaporatively forced downdrafts in the outer rainbands can transport low-entropy air downward,resulting in the lowestθ_(e)in the downshear-left boundary layer.Quantitative estimations ofθ_(e)recovery indicate that air parcels,especially those originating from the downshear-left outer core,can gradually revive from a low entropy state through surface enthalpy fluxes as the parcels move cyclonically.As a result,the maximumθ_(e)is observed in the downshear-right quadrant of a highly sheared TC.The trajectory analyses also indicate that parcels that move upward in the outer rainbands and those that travel through the inner core due to shear make a dominant contribution to the midlevel enhancement ofθ_(e)in the downshear-left outer core.In particular,the former plays a leading role in suchθ_(e)enhancements,while the latter plays a secondary role.As a result,moist potential stability occurs in the middle-to-lower troposphere in the downshear-left outer core.

A Statistical Analysis on the Effect of Vertical Wind Shear on Tropical Cyclone Development

用为 1992-2002 的时期的美国和 NCEP/NCARreanalysis 数据的从联合台风警告的西方的 NorthPacific 数据的最好的轨道和紧张集中的热带气旋(TC )(JTWC ) ， TC 紧张上的风的垂直切变的效果被检验。样品被限制到向西或在 5 ° N and20 ° N 之间的向西北的移动 TC 以便最小化热力学的效果。在 TC 紧张变化上的 200 和 500 hPa 之间的风的垂直切变的效果比在 500 之间的 shear 和 850hPa 的大，这被发现，当类似时到在 200 和 850 hPa 之间的 shear 的。风的垂直切变可以有阀值价值，它趋于到 TC 加强的减少。当 TC 的加强的率变弱，一般水准砍增加。大砍有禁止 TC 开发的明显的趋势。Theaverage 能发展成台风(热带气旋或热带风暴) 的 TC 砍是 below7 m s^(-1)( 在 8 m s~ 上面(-1)) 。

Observation of Wind Shear during Evening Transition and an Estimation of Submicron Aerosol Concentrations in Beijing Using a Doppler Wind Lidar

The wind speed and direction measured over six months by a Doppler wind lidar(Windcube-8)were compared with wind cup anemometers mounted on the 325-m Beijing meteorological tower(BMT).Five mountain–plain wind cases characterized by wind direction shear were selected based on the high-frequency(1.1 s)wind profile of the Windcube-8 and analyzed with 1-h mesoscale surface weather charts.Also analyzed was the relationship between insitu PM_1(aerodynamic diameter≤1μm)concentrations measured at 260 m on BMT and the carrier-to-noise ratio(CNR)of the co-located Windcube-8.The results showed that the 10-min averaged wind speed and direction were highly correlated(R=0.96–0.99)at three matched levels(80,140,and 200 m).The evening transition duration was1–3 h,with an average wind speed of 1 m s^(–1) at 80 m above the ground.In addition,there was a zero horizontalwind-speed zone along the wind direction shear line,and in one case,the wind speed was characterized by a Kelvin–Helmholtz gravity wave.The variability of the PM_1 concentrations was captured by the CNR of the Windcube-8 in a fair weather period without the long-range transport of dust.

Insight into the Role of Lower-Layer Vertical Wind Shear in Tropical Cyclone Intensification over the Western North Pacific

Vertical wind shear fundamentally influences changes in tropical cyclone (TC) intensity. The effects of vertical wind shear on tropical cyclogenesis and evolution in the western North Pacific basin are not well understood. We present a new statistical study of all named TCs in this region during the period 2000-2006 using a second-generation partial least squares (PLS) regression technique. The results show that the lower-layer (between 850 hPa and 10 m above the sea surface) wind shear is more important than the commonly analyzed deep-layer shear (between 200 and 850 hPa) for changes in TC intensity during the TC intensification period. This relationship is particularly strong for westerly low-level shear. Downdrafts induced by the lower-layer shear bring low θ e air into the boundary layer from above, significantly reducing values of θ e in the TC inflow layer and weakening the TC. Large values of deep-layer shear over the ocean to the east of the Philippine Islands inhibit TC formation, while large values of lower-layer shear over the central and western North Pacific inhibit TC intensification. The critical value of deep-layer shear for TC formation is approximately 10 ms-1 , and the critical value of lower-layer shear for TC intensification is approximately ±1.5 ms-1 .

Lightning Activity and Its Relationship with Typhoon Intensity and Vertical Wind Shear for Super Typhoon Haiyan (1330)

Super Typhoon Haiyan(1330), which occurred in 2013, is the most powerful typhoon during landfall in the meteorological record. In this study, the temporal and spatial distributions of lightning activity of Haiyan were analyzed by using the lightning data from the World Wide Lightning Location Network,typhoon intensity and position data from the China Meteorological Administration, and horizontal wind data from the ECMWF. Three distinct regions were identified in the spatial distribution of daily average lightning density, with the maxima in the inner core and the minima in the inner rainband. The lightning density in the intensifying stage of Haiyan was greater than that in its weakening stage. During the time when the typhoon intensity measured with maximum sustained wind speed was between 32.7 and 41.4 m s-1, the storm had the largest lightning density in the inner core, compared with other intensity stages.In contrast to earlier typhoon studies, the eyewall lightning burst out three times. The first two eyewall lightning outbreaks occurred during the period of rapid intensification and before the maximum intensity of the storm, suggesting that the eyewall lightning activity could be used to identify the change in tropical cyclone intensity. The flashes frequently occurred in the inner core, and in the outer rainbands with the black body temperature below 220 K. Combined with the ECMWF wind data, the influences of vertical wind shear(VWS) on the azimuthal distribution of flashes were also analyzed, showing that strong VWS produced downshear left asymmetry of lightning activity in the inner core and downshear right asymmetry in the rainbands.

Shearing Wind Helicity and Thermal Wind Helicity

在Ⅴ和ω分别地是速度和涡度向量的地方， Helicity 被定义为 H = Ⅴ·ω。许多工作指出了那越大他合法地是，天气系统的生活周期是越多 longer。然而，直接关系他合法地对天气系统的进化不够清楚。在这篇论文，这个概念他合法地作为砍被概括风他合法地(SWH ) 。动态地，平均 SWH 是，这被发现直接与天气系统的平均气旋的旋转的增加有关。身体上，事实上， SWH 在涡度方程是扭转学期和分叉学期的和，这也被指出。热风(TWH ) 作为 SWH 的衍生物，因为它连接温度地和垂直的风，他也合法地这里被讨论地。这二数量可能为诊断一个天气系统是有效的。这篇论文在圆柱的坐标使用这二数量学习飓风安德鲁的发展验证他们的实际使用。通过分析飓风， TWH 能很好描述象潜伏的热的强壮的传送对流和版本那样的飓风的特征，这被发现。SWH 是为为诊断飓风的发展诊断天气系统，而且一个有效天气系统的不仅好数量。