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121.
地基微波辐射计对咸宁一次冰雹天气过程的监测分析 总被引:7,自引:2,他引:5
利用咸宁MP-3000A地基微波辐射计探测资料对2010年4月12日发生在咸宁的一次冰雹天气过程进行了监测分析。结果表明:(1)在这次冰雹天气过程中,冰雹云中上升气流非常强盛,引起云底高度剧烈波动,同时将底层空气的感热和潜热向上输送导致等温线上抬,并伴随贝吉隆增长和过冷水滴与冰晶消耗等过程,由于这些宏观和微观过程使得整层水汽与液态水含量连续出现下降和上升过程,产生了多峰结构;(2)在4.2—8km高度过冷层的冰雹云中,08时40分—13时的固、液、气混合相态变化非常复杂,过冷水滴与冰粒子消耗过程、贝吉隆过程和过冷水滴与冰晶增长过程交替出现,产生了相对湿度在6km以下低于80%的区域,且液态水含量在4.2—8km高度处出现0.7—1.8g/m3的大值区,从而形成了冰雹生长过程中交替干、湿增长生长环境,非常有利于冰雹粒子群快速累积以及分层增长;(3)利用微波辐射计资料计算分析了MKI、KI、TT和HI四个不稳定指数,这些指数对强对流天气有很好的指示作用,并对强对流天气有一定的临近预警潜力,若选取KI≥38作为该地区强对流天气预警指标,可以提前45min预警第1次降雹强对流天气,且分别提前20、40和42min预警第2、3、4个对流单体影响该地区。 相似文献
122.
Retrieval of Liquid Water Path Inside Nonprecipitating Clouds Using TMI Measurements 总被引:1,自引:0,他引:1
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Quantitative estimates of liquid water path (LWP) in clouds using satellite measurements are critical to understanding of cloud properties and the assessment of global climate change. In this paper, the relationship between microwave brightness temperature (TB) and LWP in the nonprecipitating clouds is studied by using satellite microwave measurements from the TRMM Microwave Imager (TMI) onboard the Tropical Rainfall Measuring Mission (TRMM), together with a radiative transfer model for microwave radiance calculations. Radiative transfer modeling shows that the sensitivity is higher at both 37.0- and 85.5-GHz horizontal polarization channels for the LWP retrievals. Also, the differences between the retrieved values responding to TBs of various channels and the theoretical values are displayed by the model. Based upon above simulations, with taking into account the factor of resolution and retrieval bias for a single,channel, a nonprecipitating cloud LWP in the summer subtropical marine environment retrieval algorithm is formulated by the combination of the two TMI horizontal polarization channels, 37.0 and 85.5 GHz. Moreover,by using TMI measurements (1Bll), this algorithm is applied to retrieving respectively LWPs for clear sky, nonprecipitating clouds, and typhoon precipitating clouds. In the clear sky case, the LWP cl~anges from -1 to 1 g m-2, and its mean value is about 10^-5 g m^-2. It indicates that, using this combination retrieval algorithm, there are no obvious systemic deviations when the LWP is low enough. The LWP values varying from 0 to 1000 g m^-2 in nonprecipitating clouds are reasonable, and its distribution pattern is very similar to the detected results in the visible channel of Visible and Infrared Scanner (VIRS) on the TRMM. In typhoon precipitating clouds, there is much more proportion of high LWP in the mature phase than the early stage. When surface rainfall rate is lower than 5 mm h^-1, the LWP increases with increasing rainfall rate. 相似文献
123.
The large active region AR NOAA 5200 from October 1988 is used to investigate the concept of the “halo,” a magnetosphere-like
structure above the active region. This structure is studied by using radio spectral polarization observations with high spatial
resolution obtained mainly with the radio telescope RATAN-600. In the case of AR 5200 the halo emission accounted for >50%
of the total AR emission. The results of the analysis of the observational data and of the model calculations allow us to
reach the following conclusions: (1) The halo is a large, nonstructured, source of emission with a size of the total AR, with
the emission centered at the dividing (neutral) line of polarities of the bipolar sunspot group. (2) The emission spectrum
allows us to distinguish two components: a thermal part and a nonthermal part. The presence of two components implies that
there are two populations of particles with different energy levels in the emission region. The phenomenon of inversion of
the polarized halo radio emission could be explained by the influence of propagation conditions inside the source. The term
“self-inversion” is introduced. The maximum in the halo density flux spectrum at wavelengths of 5 –10 cm may be explained
by scattering resulting from the strong suppression of the emissivity of nonthermal electrons at these and longer wavelengths. 相似文献
124.
This work provides an overview of various methods for estimating snow cover and properties in high mountains using remote sensing techniques involving microwaves. Satellite-based remote sensing with its characteristics such as synoptic view, repetitive coverage and uniformity over large areas has great potential for identifying the temporal snow cover. Many sensors have been used in the past with various algorithms and accuracies for this purpose. These methods have been improving with the use of Synthetic Aperture Radar sensors, working in different microwave frequencies, polarisation and acquisition modes. The limitations, advantages and drawbacks are illustrated while error sources and strategies on how to ease their impacts are also reviewed. An extensive list of references, with an emphasis on studies since 1990s, allows the reader to delve into specific topics. 相似文献
125.
126.
Ground Penetrating Radar (GPR) airborne systems are gaining an increasing attention as effective monitoring tools capable of underground investigation of wide areas. With respect to this frame, the paper deals with a reconstruction approach specifically designed to image buried targets from airborne gathered scattered field data. The role of the measurement configuration is investigated in order to address the practical problem of how multi-monostatic and multi-frequency data should be gathered, in terms of synthetic aperture length and frequency range, and how the available data affect the achievable reconstruction capabilities. Such an analysis allows us to evaluate the performance of the reconstruction approach in terms of transversal and depth resolution limits. Finally, an experimental validation of the approach is performed by processing real data. 相似文献
127.
参加了Flares22和Max'91国际联合观测之后,我们处理了三个频率(1.42,2.84,3.67GHz)和四个频率(1.42,2.00,2.84,4.00GHz)或(1.42,2.13,2.84,4.26GHz)快速采样射电望远镜的观测资料。结果除了发现射电爆发源的局部区域中存在有射电辐射的第四种基本分量而外,还在微波爆发快速精细结构中发现了三种基本时间单元。其量级分别是:0.1秒>τ1≥1毫秒;1秒>τ2≥0.1秒;100秒>τ3≥1秒。尽管出现在各自基本时间单元内的FFS事件的形态及特性各自不同,但是,叠加在射电爆发背景之上的特性,构成了它们的共同属性。三种基本时间单元的确认,对于研究微波快速活动的精细时间结构,划分FFS事件的种类找到了根据。三种基本时间单元的研究,对于深入探讨产生FFS源的ECM理论,也具有重要的科学价值。 相似文献
128.
129.
Akira Shibata 《Journal of Oceanography》2006,62(3):321-330
Ocean microwave emissions changed by the ocean wind at 6 GHz were investigated by combining data of the Advanced Microwave
Scanning Radiometer (AMSR) and SeaWinds, both aboard the Advanced Earth Observation Satellite-II (ADEOS-II). This study was
undertaken to improve the accuracy of the sea surface temperature (SST) retrieved from the AMSR 6 GHz data. Two quantities,
6V*(H*), were defined by the brightness temperature of the AMSR at 6 GHz with two polarizations (V-pol and H-pol), adjusted
for atmospheric effects and with a calm ocean surface emission removed. These quantities represent a microwave emission change
due to the ocean wind at 6 GHz. 6V* does not change in a region where 6H* is less than around 4 K (referred to as z0). Both
6V* and 6H* increase above z0. The 6V* to 6H* ratio, sp, varies with the relative wind directions. Furthermore, the sp values
vary with the SST, between the northern and southern hemisphere, and seasonally. By specifying appropriate values for z0 and
sp, the SST error between AMSR and buoy measurement became flat against 6H*, which is related to the ocean wind. Two extreme
cases were observed: the Arabian Sea in summer and the Northwestern Atlantic Ocean in winter. The air-sea temperature difference
in the former case was largely positive, while it was largely negative in the latter. The 6V* and 6H* relations differed from
global conditions in both cases, which resulted in incorrect SSTs in both areas when global coefficients were applied. 相似文献
130.
简要介绍了微波通信技术,根据微波传播特性与光的传播特性相似的原理,提出了利用测量中有关觇标高计算公式进行微波天线高度计算的方法,推导出确定微波通道保护参数的公式,并结合实践给出应用示例。 相似文献