Horizontal structure of the electric field in the stratiform region of an Oklahoma mesoscale convective system
Horizontal structure of the electric field in the stratiform region of an Oklahoma mesoscale convective system
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DOI：
10.1029/2001jd001140
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发表时间：
2003-04
影响因子：
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通讯作者：
Q. Mo;A. Detwiler;J. Hallett;R. Black
中科院分区：
文献类型：
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作者：
Q. Mo;A. Detwiler;J. Hallett;R. Black
[1]这项分析结合了两架在两层水平飞行的研究飞机观测到的垂直电场分量Ez，以及由五个气球所作的热力参数和Ez的垂直探测，以产生1991年6月2日下午晚些时候在俄克拉荷马州中部发展起来的中尺度对流系统(MCS)后面的拖尾层状云区中空间电荷分布的准三维视图。当MCS向东移动时，气球每隔一小时从两个相距80公里的南北线站点连续发射，在MCS后面的准稳定拖尾层状区内产生了两个EZ结构的东西向时间-高度截面。气球测量与垂直堆叠的五个向后和向下倾斜的交替极性的水平电荷层是一致的，从底部开始，负电荷层低于0°C水平，正电层靠近0°C水平。这种结构持续了两个多小时。在气球发射期间，两架飞机沿着南北线来回飞行，穿过气球发射场。飞机测量表明，恒定高度的垂直电场沿南北方向变化。从机载仪器系统得到的Ez峰值与气球在4.5和5.8 KmAGL高度上的测量结果基本一致。飞机在0°C以上4.5公里处观测到峰值为>；50kVm−1的Ez极快速反转，证实了气球在那里观测到的薄的集中正电荷层，并表明该电荷层至少在南北方向上在4.5公里高度以上和以下起伏。从微观上讲，这一层包含了大团聚体和低云液水浓度的小块。在5.8公里高度，EZ的极性始终为正，但其大小在0~25kVm−1之间变化。两个高度的飞机观测EZ在水平尺度上的变化都在∼10公里或更大的水平尺度上，这表明利用一维无限层高斯定律近似得到的电荷密度应用于EZ气球探测是有效的。这些观测表明，电荷层在风暴相对意义上向后平流时可以持续数小时，这可能是由于持续的就地电荷分离，和/或由于低迁移率低终端速度冰水流星上附着的电荷的弱分散、缓慢复合和缓慢沉降。
[1] This analysis combines vertical electric field components Ez observed by two research aircraft flying horizontally at two levels, with vertical soundings of thermodynamic parameters and Ez made by five balloons, to produce a quasi-three-dimensional view of the space charge distribution in the trailing stratiform cloud region behind a mesoscale convective system (MCS) that developed in central Oklahoma late in the afternoon of 2 June 1991. The balloons were launched serially at one-hour intervals from two sites separated by 80 km along a north-south line as the MCS moved eastward, yielding two east-west time-height cross-sections of the Ez structure within the quasi-steady state trailing stratiform region behind the MCS. The balloon measurements are consistent with a vertical stack of five rearward- and downward-sloping horizontal sheets of charge of alternating polarity, beginning at the bottom with a negative charge layer below the 0°C level and a positive layer near the 0°C level. This structure persisted for more than 2 hours. The two aircraft flew back and forth along a north-south line through the balloon launch sites during the balloon launch period. Aircraft measurements demonstrated that the vertical electric field (Ez) at constant altitude varied in the north-south direction. The peak magnitudes of Ez deduced from the airborne instrument systems agreed with the magnitudes deduced from the balloon measurements at the aircraft altitudes of 4.5 km and 5.8 km AGL. Rapid reversals in polarity of Ez with peak magnitude >50 kV m−1 observed by the aircraft at 4.5 km, just above the 0°C level, confirms the thin concentrated positive charge layer observed there by balloons and suggests that this charge layer is undulating above and below 4.5 km altitude, at least in the north-south direction. Microphysically, this layer contained large aggregates and pockets of low cloud liquid water concentration. At the 5.8 km level, the polarity of Ez was always positive but the magnitude varied from zero to 25 kV m−1. Aircraft-observed Ez at both altitudes varied on horizontal scales of ∼10 km or greater at both levels, suggesting that the charge density derived using the one-dimensional infinite-layer Gauss's law approximation applied to the balloon soundings of Ez is valid in this study. These observations show that layers of charge can persist for hours as they advect rearward in a storm-relative sense, possibly due to continuing in situ charge separation, and/or due to weak dispersion, slow recombination and slow settling of charge attached to low mobility low terminal velocity ice hydrometeors.