‘brightband’ in article
11/2’11
Radar
characteristics of continental, coastal, and maritime convection observed
during AMMA/NAMMA
Quarterly Journal of the Royal Meteorological Society
Volume 137, Issue 658, July 2011
Part A, Pages: 1241–1256, Nick Guy, Steven A. Rutledge and Robert Cifelli
Article first published online : 8
JUN 2011, DOI: 10.1002/qj.839
o
Abstract
l Keywords:mesoscale convective system;African easterly wave;West African monsoon;convective and stratiform precipitation;regional precipitation
l Abstract
l Ground-based radar observations at three distinct geographical locations in West Africa along a common latitudinal band (Niamey, Niger (continental)【アフリカ大陸の西部、南にギニア湾】, Kawsara, Senegal (coastal), and Praia, Republic of Cape Verde (maritime)) are analyzed to determine convective system characteristics in each domain during a 29-day period in 2006. Ancillary datasets provided by the African Monsoon Multidisciplinary Analyses (AMMA) and NASA-AMMA (NAMMA) field campaigns are also used to place the radar observations in context. Results show that the total precipitation is dominated by propagating mesoscale convective systems. Convective characteristics vary according to environmental properties, such as vertical shear, CAPE, and the degree of synoptic forcing. Data are bifurcated【二つに分ける】 based on the presence or absence of African easterly waves. In general, African easterly waves appear to enhance mesoscale convective system strength characteristics (e.g. total precipitation and vertical reflectivity profiles) at the inland and maritime sites. The wave regime also resulted in an increased population of the largest observed mesoscale convective systems observed near the coast, which led to an increase in stratiform precipitation. Despite this increase, differentiation of convective strength characteristics was less obvious between wave and no-wave regimes at the coast. Owing to the propagating nature of these advecting mesoscale convective systems, interaction with the regional thermodynamic and dynamic environment appears to result in more variability than enhancements due to the wave regime, independent of location. Copyright © 2011 Royal Meteorological Society
l レーダを同一緯度上において対流雲の観測を行った。対象は2006年の29日間。アフリカの海岸を対象として対流雲の伝搬【海上から陸上への移動】に伴い、降水がどのように変化するかを調べた。降水はメソ対流系によるものがほとんどであった。データはアフリカの東波があるかないかで2分した。この東波は一般にメソの対流系を強める。波は海岸付近で対流系を多く発生させ、層状性の降水を増やしている【？海上から来た雲が変質するのか？】。ただし、降水が増加しているが、東波のあるなしで対流性の降水強度の違いは、明確でない。これは、メソ対流系の伝搬する特性によるもので、場所によらない波の特性による強化よりも変動が大きいためと思われる。11/2’11
Quarterly Journal of the Royal Meteorological Society
Volume 129, Issue 587, January 2003
Part A, Pages: 83–95, Marion P. Mittermaier and
Anthony J. Illingworth
Article first published online : 29
DEC 2006, DOI: 10.1256/qj.02.19
o
Abstract
l Abstract
l
In the current operational Met Office scheme for deriving
rainfall rates from radar, the height of the enhanced radar return associated
with melting snow, the bright band, is determined using the height of the 
isotherm obtained from
the Met Office Unified Meso-scale Model (UM) forecast. 【融解層高度を予測するシステムがあるのだろう】In this paper the potential errors of using model forecast heights as
input to the bright-band correction scheme are investigated. The UM and
European Centre for Medium-Range Weather Forecasts (ECMWF) model forecasts of
wet-bulb isotherm heights (WBZ)
are compared with the height of the ‘step’ increase in
reflectivity in the vertical profiles recorded by the vertically pointing 94
GHz Galileo cloud radar at Chilbolton.
High-frequency radars do not measure an enhanced ‘bright
band’ at the melting layer, rather a sudden increase of
reflectivity as the ice particles become coated in water.【雪の層は減衰で見えなくなっているそこでのギャップを融解層判断に利用】 This sudden step can be used to locate accurately the height of the
WBZ.
l
Results show that the UM predicts the WBZ height with a
root-mean-square error of 147 m and a bias of 15 m. This is within the
worst-case tolerance of 200 m of the operational bright-band correction scheme.
Factors that may influence the accuracy are the presence of deep isothermal
layers【深い等温層の存在】
and timing errors concerning the passage of fronts, but these are found not to
be serious. An investigation into the deterioration of the UM 36-hour forecast
shows that half the error is introduced at the initialization time,
highlighting the fact that further improvements can be achieved through a
better definition of the initial state of the atmosphere. The ECMWF forecast is
for a longer lead time【初期値が良くなれば予測精度が上がると期待できるだろう】, but
comparison for the same lead-time errors as the UM shows that the performance
of the two models is comparable.【しかし、メソモデルの結果はどちらも同じくらいであった】
l
An alternative approach is to derive the bright-band
height from volumetric radar scans at different elevations. 【体積探査で融解層を見つける方法もある；一般論】This study suggests that, at least in the UK, operational model
predictions of the freezing-level height are within the specified 200 m error【今回の研究からUKの予報では融解層高度の誤差は200m以内に収めることができる】, but that the use of volumetric scans, even under idealized
conditions, cannot achieve this accuracy.【体積単は200mの誤差には収まらないだろう】11/9’11
深い等温層があるときや前線の通過を間違えて予測したときに、融解層の判断誤差が大きい。ただし、それほど深刻ではない。
Using
mesoscale model winds for correcting wind-drift errors in radar estimates of
surface rainfall
Quarterly Journal of the Royal Meteorological Society
Volume 130, Issue 601, July 2004
Part B, Pages: 2105–2123, Marion P. Mittermaier,
Robin J. Hogan and Anthony J. Illingworth
Article first published online : 29
DEC 2006, DOI: 10.1256/qj.03.156
o
Abstract
Keywords:Fall streak;Radar vertical profile of reflectivity;Shear
Abstract
For operational
radars at middle and high latitudes, even the lowest beam of a scan sequence may
be above the melting layer for a considerable proportion of the total range.
This means that surface rainfall estimates are inferred from measurements made
in the snow and ice… Snow and ice are more susceptible to wind drift than rain
because of the low fall speed of around 1 m/s. Sampling these wind-induced
fall-streak patterns results in a displacement of the radar-rainfall field when
compared to ground measurements. To date wind-drift corrections have only been
attempted in the rain, but corrections of around 2 km are generally smaller
than the resolution of the grid on which the rainfall field is reported.
Observational evidence from this study shows fall streaks in the snow can lead
to displacements of the order of 10–20 km—a significant effect, especially in
colder climates and seasons.
レーダで観測している降水粒子の移流効果を調べた。雨は２㎞程度しか移動しないので誤差は小さいが雪は10－20㎞移動するので移流効果は大きい。
In this paper a
method for calculating and applying a wind-drift correction between the top of
the fall streak【降水粒子のできているトップ？】 and the bright-band height is presented. The
forecast wind profile from the meso scale version of the UK Met Office Unified
Model is used to calculate the vertical shear of the horizontal wind. We assume
the shear and the fall speed in the layer are constant. Results show that the
method is able to reproduce observed displacements from high-resolution radar
data in the range–height plane. Assessing the
effect of applying the method in plan view shows an improvement in the placement of rainfall
at the ground, reflected by an increase in the calculated skill scores. The
displacement can be corrected to within 20%. This also shows that whereas
wind-drift corrections in the rain have been found to be insignificant,
corrections in the snow are not. Applying a wind-drift correction also appears
to reduce the variability of vertical profiles of reflectivity (VPR) when they
are extracted along a fall-streak path, and lead to a smaller reflectivity
lapse rate locally. This would suggest that at least part of the reported
variability in VPRs is due to wind effects.
本文献では流跡線のトップとブライトバンドまでの降水粒子の移流効果を計算する手法を提案する。風の場はUKのメソモデルを使う。シアと落下速度は一定。結果はRHI画面で表示可能。平面分布はスキルスコアで評価して落下個所の表示が改善した。ずれ補正は20％以内。雨の移流補正は重要でないとわかったが、雪では重要でないことはない。移流補正を使うと、落下流跡線に沿って強度プロファイルを作成するときの誤差が小さくなる。局所的には【流跡線の中では？】減率が小さくなる。このことからVPRの変動のわずかの部分が風の影響であると言える。
人工降雨にかかる文献を追加
2003-2004の一冬を評価。
RAMSで山岳地系の降雨を30事例評価。モデルは降水量を過大に評価する場合があり、南西風の時が顕著であった。これは実際にはそれほど対流が強くないにもかかわらず、モデルが強めの対流を予測するためである。原因について議論する。
11/8’11,11/11'11修正
⇒保留
融解層関連の文献を整理
OPERAの評価報告書（２期、12/12/2006）から7章；ブライトバンドの同定
ブライトバンド同定の目的
・QPEに対して非常に大きなエラーとなる
・対流性の雲については同定が難しい
・偏波を用いた研究ではS帯（Zrnicら1993）、C帯で(BaldiniとGorgucci2006)がある。
・融解層ではZh、ZDRが増加【後出の仰角に対する記述から90°でなく高仰角を用いる観測を想定】、ρhvが減少する。また、融解中の大粒子があると後方散乱の影響が大きくφdpを小さくするかもしれない【おそらくわかっていない】。LDRを図ることができれば融解層で増加を示す【ZDRと同じ】。これらの変化量は多岐にわたる。Brandes&Ikeda(2004)は長期観測と現地集中観測の結果からZは8dB、LDRは9dBの増加、ρhvは0.92まで減少とモデル化した。後でフランスのTrappesレーダの結果を示すが集中的(concentric)な様子が示される。
【本題】フランスのTrappesを用いて20事例選んだ。2004年12月から2006年3月まで。ここでは仰角9度を鉛直に読み替えた【？retrieval】11/16’11
SN比が、10デシより低いデータを捨て、ZDRはバイアス補正、少なくとも1/4のデータ(=180)【ということは、720セクタ？多い】が有効なレンジについて平均をとったプロファイルを気候値として図7.1に示す。314個ある。原点はρhvが最小値を示すところ。ZhとZDRは地上の値で規格化している。
図7.1：Z、ρhv、ZDR,φdp【Zは個数が寄与するのですぐに抜けると値が小さくなる。このため、Zのピークはρhvよりやや高くなる。また、φdpはBB高度の前方で小さく、後方で大きくなる】11/18’11
Tabary 2006 が基本（ERAD2006出世さんのJMC引用）Weather and forecast2007にあり。←ERAD2010を参照すべき。
11/22’11