[揽瓜阁精读] 309.Hurricane

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Since 1997, forecasters have used Global Positioning System dropwindsondes, a measuring device dropped from hurricane reconnaissance aircraft into the eyewall—the windiest part of the hurricane. The sonde system measures temperature, barometric pressure, water vapor, and wind data every 15 feet on its way down. This new method gave meteorologists an important glimpse into the true strength of these devastating storms. The analyses of the dropwindsonde data indicated that, on average, the maximum sustained surface-wind speed was about 90 percent of the wind speed measured at the 10,000-foot aircraft level flown as Andrew approached south Florida. In 1992 Andrew's wind speed was estimated at 75 to 80 percent of the aircraft observations. The research findings resulted in an increase in the estimated wind speeds of Hurricane Andrew from 145 mph to 165 mph.

One of the more difficult problems for operational tropical cyclone forecasters is the assessment of the cyclone's maximum sustained surface wind. Even when aircraft reconnaissance data are available, these are typically obtained from the 700 mb (10,000 ft) level; from these flight-level observations, the forecaster is left to estimate the surface winds. Based on comparisons of flight-level and buoy data, Powell and Black (1990) recommended that a ratio of 63%-73% be used to reduce reconnaissance flight-level wind observations. While operational practices at the National Hurricane Center (NHC) have varied over time, in recent years surface winds have typically been taken to be 80%-90% of the flight-level wind. In view of studies such as Powell and Black, use of these relatively high ratios has periodically resulted in criticism of NHC intensity estimates.

In 1997, the National Oceanic and Atmospheric Administration (NOAA) and Air Force Reserve Command (AFRC) hurricane reconnaissance aircraft began to deploy Global Positioning System (GPS)-based dropwindsondes (Hock and Franklin 1999) in the hurricane eyewall. These instruments provide for the first time, detailed, accurate profiles (15 ft vertical resolution, with 1-4 mph accuracy) of the inner core of a hurricane from flight level (typically 700 mb) down to the surface. More than 350 such profiles have been obtained through the 1999 hurricane season.

2. Data and Methodology

This study is based on a sample of 357 quality-controlled eyewall profiles from the following hurricanes: Guillermo and Erika in 1997; Bonnie, Danielle, Georges, Mitch, Lester, and Madeline in 1998; and Bret, Dennis, Floyd, Gert, Irene, Jose, Lenny, Dora and Eugene in 1999. A majority of these dropsonde releases were made from the 700 mb level. For sondes released from NOAA aircraft, airborne radar was used to determine whether a particular sonde was released in the eyewall; for AFRC sondes we relied on the comments of the operational air-crews, as well as examination of flight-level wind profiles.

The individual soundings have been used to construct a mean eyewall profile for the data set. Prior to the averaging, the wind at each level in the drop profile is normalized by the wind speed at 700 mb (10,000 ft).

3. Results

Figure 1 shows the mean eyewall wind speed profile, where the wind at each level has been normalized by the wind speed at 700 mb (taken from the dropsonde profile, if available, or from the aircraft 700 mb flight-level wind at the time of launch, if not). The strongest winds in the eyewall are found near 500 m (1600 ft) elevation; these are about 20% higher than the 700 mb wind, owing to the warm-core nature of the tropical cyclone. For comparison, the mean profile for non-eyewall sondes within 200 miles of the cyclone center is also shown. In the outer part of the vortex, the low-level wind maximum is found at a somewhat higher elevation and is not as pronounced as in the eyewall. The ratio of the surface to 700 mb wind (R700) is 0.78 in the outer vortex and 0.91 in the eyewall. Note that the former figure is not far from Powell and Black's (1990) estimate of 0.73. This is not surprising given that their sample was comprised almost exclusively of outer vortex observations.

While a reduction factor of about 0.9 may be appropriate in the mean, individual eyewall profiles illustrate how difficult it can be to estimate a hurricane's maximum surface winds from flight-level reconnaissance data. Figure 2 show an example from 1998's Hurricane Mitch. Over a period of several hours, the NOAA Hurricane Hunter aircraft could find flight-level winds no higher than 150 mph, yet this and several other dropsondes indicated much higher wind speeds near the surface. In this case, Mitch appeared to be weakening from the "top-down"; the circulation at flight-levels was decreasing but this trend had not yet begun at the surface. On the other hand, several storms (including Bonnie) have shown surface winds much lower than the flight-level wind.

4. Operational Recommendations

Based on these and similar analyses for other normalization altitudes, the following reduction factors are recommended for reducing flight-level winds in the inner core of a tropical cyclone to the surface (33 ft) level: for the 700 mb level, R = 0.90; for the 850 mb level (commonly flown in tropical storms), R = 0.80. For investigative flights at 1,000 ft, R = 0.85. As significant variations from these means have been noted in individual storms; these guidelines can be modified as conditions warrant. Storm-to-storm variability will primarily be influenced by wind speed, cyclone convective intensity, and sea-surface temperature.

The mean eyewall profile (Fig. 1) has implications for high-rise buildings and elevated terrain. Table 1 gives the wind at various altitudes as a percentage of the surface wind. Winds at the top of a 30-story building will average about 20 mph (one Saffir-Simpson category) higher than at the surface. This can be seen in an example from Hurricane Georges (Fig. 3). In this case, the surface winds are near the lower end of Category Three; yet at an altitude of 300 ft the winds are now in the middle of Category Four.

吱野

查不喜欢

讲的是台风测速的问题，中心速度和表面风速。
1、开头介绍了sonde system的应用：中心测速
2、话题转向：很难测表面的风速，举了几个案例，对于ratio的数有争议。
3、发展：1997年，运用GPS获取了很多数据
4、阐述了数据的来源；
- NOAA
- AFRC
5、研究结论：
（1）The ratio of the surface to 700 mb wind (R700) is 0.78 in the outer vortex and 0.91 in the eyewall.
（2）特例：Mitch ：surface winds much lower than the flight-level wind.
6、建议
（1）结论：大概得数值粗来了！同时会受到一系列因素的影响
（2）对于层高和地形的影响不同，不同的高度数值也不同。

calll

Simple story:
关于1997年开始的使用GPS来探测和计算飓风的历史数据和总结

1.        1997年, 预测者用GPS 来追踪及观测飓风. 用sonde 测量temperature….
2.        在GPS之前预测飓风的方式有一个很严重的问题是无法预测cyclone的表面风的持续性.
3.        1997年, 开始用NOAA和AFRC-- GPS drop wind sondes 在风眼 来测算精确的数据.  
4.        用357个数据来测算
5.        Results—通过data and methodology得出的results
6.        通过分析results, 总结了recommendations. 每一个等级的飓风的大概的尺寸.

xixio

309
生词：reconnaissance aircraft侦察机
-----介绍背景-----
Since 1997, used GPS measure hurricane---temperature, pressure…----provide important glimpse
细节补充: The maximum surface-wind speed was 90% (10000-foot level) , 1992 Andrew’s wind speed was 75-80%, the findings result in from 145mph to 165mph

One of the difficult problems for tropical forecasters: the assessment of the maximum surface wind---data are obtained from 10000ft level, but left to estimate the surface wind.
P and B recommend a ratio of 63%-73% be used to reduce flight-level observation. ==while in NHC, surface wind been taken to be 80-90%, which is too high in the view of P and B.

In 1997, NOAA and AFRC began to develop GPS---provide for more than 350 such profiles through 1999
----介绍本文研究的数据和方法-------
Based on a sample of 357 eyewall profiles from several hurricanes (a majority were made from 10000 level)
From NOAA---Airborne radar----determine whether a sonde was released in the eyewall
From AFRC----comment of air-crews and examination
Individual sounding---construct a mean
----提供研究结果------
Figure 1---mean
The strongest winds are found 1600ft---20% higher than the 1000ft wind----owing to warm-core nature in tropical area
Comparison---the mean of non-eyewall sondes
The ratio of the 1000ft wind is 0.78 in the outer and 0.91 in the eyewall---not far from P and B’s 0.73

While a reduction factor of about 0.9 (NHC) is appropriate in the mean
Figure 2---example from 1998’s hurricane Mitch
-----提供期望建议----
For 700mb level, R=0.9
For 850mb level, R=0.8
For investigative flight at 1000ft, R=0.85
最后是描述了一下他的数据结果

美女屠龙

P1
forecasters利用D设备来探测...数据
探测到的数据表明，地表的风力是万米高空风力的90%----1992年科学家认为是75-80%
（新设备的数据表明过去的观点是错误的）

P2
对forecaster来说，更大的困难是预估cyclone的最大地表风力
即使有数据（这些数据是在700mb观测的）

PP在1990提出：地表风力是高空风力的63-73%
而实操过程中，NHC一般认为地表风力是高空的80-90%
PP很质疑NHC的估计方式

P3：1997-1999，NOAA和AFRC开始利用D设备探测风力

yurifromcanada

P1-P3 : 背景，引出概念
1997年开始，天气预报开始使用gps dropwindsondes，这个设备可以深入the windiest part of the hurricane。
-这个系统测试温度等等因素，这个新的方法给了meteorologists机会去对这些风暴的真实强度一探究竟。对这些dropwindsonde data的分析发现，最大的持续的表面风速是blabla当Andrew approached south Florida。
-在1992年Andrew的风速已经达到75 to 80 percent of the aircraft observations。这个发现使得Hurricane Andrew的风速估值从145 mph涨到了165 mph。
P4-P5:  数据和方法
这个研究基于357个quality-controlled风眼样本。大部分dropsonde产生了700 mb level的风速。airborne radar用来决定是否特殊的NOAA aircraft sonde在风眼中被释放； AFRC sondes是通过 comments of the operational air-crews以及examination of flight-level wind profiles来决定的。
单个的soundings也被用来构造 mean eyewall的数据集档案。在平均之前，每个在drop file中的每个level的风都以700mb处的风速来标准化。
P6-P7 : 结果
-表格一：mean eyewall wind speed profile：
-每个level的风都被700mb的风标准化。
-最强的风是在500m左右，20% higher than 700mb，热带特征
-比较组：non-eyewall sondes within 200 miles of the cyclone center is also shown
-低level wind的最大值被在高一点的海拔被发现。0.78 in the outer vortex and 0.91 in the eyewall.
尽管reduction指数0.9能够支持in the mean，单一的eyewall的file体现出了从flight-level reconnaissance data中估计飓风surface winds的难度。
-表格二：1998's Hurricane Mitch为例
-the NOAA Hurricane Hunter aircraft：flight-level winds no higher than 150 mph-much higher wind speeds near the surface-Mitch appeared to be weakening from the "top-down"
一些其他风暴也表现出了surface winds much lower than the flight-level wind.
P8-P9 : 运作建议
-基于其他normalization altitudes和此实验的分析，以下reduction factors建议用来减少flight-level winds in the inner core of a tropical cyclone（一堆指数）。因为these means造成的显著的变化在individual storms中被发现，这些知道可以被修饰为条件保障。storms之间的变化也被各种因素所影响。
-The mean eyewall profile对于high-rise buildings and elevated terrain有指导作用。
-表格一——30层建筑的参考
-表格三——Hurricane Georges 的实例

Turv_vc

Hurricane:
2. 数据和方法：
Detail：这个研究基于357个质量监控过的风眼档案，后面都是龙卷风的名字。然后大部分这些dropsonde都是再700mb级别的所产生的。对于NOAA飞行器的Sondes，Airbone雷达被用来决定是否一个特定的sonde被风眼所释放；对于AFRC sondes我们依赖于可操作性的航天员工的评论和flight-level风档案的测试
态度：单体的soundings 被用作构建一个比较苛刻的风眼档案数据作为数据集。取平均前，在下行档案的每个级别的风都被标准化成风速在700mb中
3. 结果：
图片一展示了风眼墙的速度档案，被标准化成了风速在700mb。最强的风在风眼墙中式大搞在高度500m，因为热带风暴的暖核属性，这些最强风们高了20%对比于700mb的等。他们通过对比，比例等发现之前的比例数据和PB预测的0.73相差并不是很远。这也不惊讶的是因为他们的案例基本上是通过外部vortex观测所得到的。
然而一个0.9的减少的因素是合适的在于中位数的部分，单体的风眼墙档案展示了预测一个从飞行高度的reconnaissance数据中得到龙卷风的最大表面风是十分困难的。Figure2展示了1998的MItch龙卷风：超过了一段时间NOAA 的就找到一个飞行级别不超过150mph的风但是对比于其他的dropsondes去展示了更高的速度-这个Mitch就削弱了一个理论，证实飞行高度的环流正在减少，但这种趋势尚未在地面开始。另一方面，一些风暴(包括邦妮)显示地表风比飞行水平风低得多

Turv_vc

Bg: 预测者使用GPS去dropwindsondes，一个测量的飞行设备从飓风边缘扔到龙卷风眼的东西
Detail：这个Sonde 系统测量温度，大气压，水蒸气，有关风的数据。
态度： 这个新的方法给了什么学家一个重要的glimpse关于真正的这些龙卷风的力量
Detail: 这些数据的呈现表明了表面的最大可持续风是Andrew到达南佛罗里达州的速度90%
Detail：Andrew的速度是75-80% 飞行器所观察到的速度，最最这这个实验结果是Andrew 的实际速度从145-165mph

态度：更困难的问题是可操作性的热带风暴的预测速度是预测对他的表面风；
Detail：甚至当飞行器有着reconnaissance的数据他们保持着一个700mb的级别然后呢从一个飞行级别的观察来看，预测器只剩下去估测表面风了，更具对比FLIGHT-LIVEL 和BUOY数据，P和B 这两个科学家介绍了一种比例（63%-73%）去减少reconnaissance flight-LEVEL风的观察。然而另一个组织对这个比例随着时间更换，最近的这个比例变为80-90%针对于表面风的预测
态度： PB 的高比例导致了NHC这个组织的高强度预测

Detail：1997NOAA 和AFRC hurricane reconnaissance aircraft开始使用GPS Dropwindsondes
在风眼。这些设备提供了第一时间，细节，准确的档案在飓风的内核中心。超过了350这样的档案被收集

二三1

背景介绍：
直到1997年，GPS 还在使用——测量温度，气压....
新的方法——导致了测量值的增加——以前是75-80%，现在是90%

操作最大的困难是评估持续平面风的最大值。
在比较了飞行水平和浮标数据之后，P和B 推荐降低63-73d%的飞行高度风观测。
然后实际操作一直在变，在最近的几年，表面风已被认为是飞行水平风的80-90%
重新讲回GPS
GPS能够提供第一时间的，准确的数据-从飞行高度到表面。
介绍数据和研究方法
357数据来源：一系列的飓风....，
方法：大部分在700MB被测量，并且用雷达来测量sonde是否被放置在了eyewall。
结论：
图1：风眼风速的中值
1.最强的风大概在接近500m的位置；2.由于热带的温暖的自然气候，这比700风高了20%;
3.200米半径范围内的非风眼位置的中值也被展示出来
4.在V的外圈，低水平风的最大值在某些高度被发现并且和风眼的不一样。
5.700水平的风，表面radio 0.78，风眼的是0.91
6.发现这些数据和PB的相差不大。（这并不奇怪，因为他们的样本几乎完全由外部涡旋观测结果组成。）