In this article,we address both recent advances and open questions in some mathematical and computational issues in geophysical fluid dynamics(GFD)and climate dynamics.The main focus is on 1)the primitive equations(PEs)models and their related mathematical and computational issues,2)climate variability,predictability and successive bifurcation,and 3)a new dynamical systems theory and its applications to GFD and climate dynamics.
The lightning-induced-damages in the mid-latitude regions are usually caused during severe thunder-storms. But the discharge parameters of natural lightning are difficult to be measured. Five lightning flashes have been artificially triggered with the rocket-wire technique during the passage of two severe thunderstorms. The discharge current and close electric field of return stroke in artificially triggered lightning have been obtained in microsecond time resolution by using current measuring systems and electric field change sensors. The results show that the five triggered lightning flashes include 1 to 10 return strokes, and the average return stroke current is 11.9 kA with a maximum of 21.0 kA and a mini-mum of 6.6 kA, similar to the subsequent return strokes in natural lightning. The half peak width of the current waveform is 39 μs, which is much larger than the usual result. The peak current of stroke Ip (kA) and the neutralized charge Q(C) has a relationship of Ip = 18.5Q0.65. The radiation field of return stroke is 5.9 kV·m-1 and 0.39 kV·m-1 at 60 m and 550 m, respectively. The radiation field decreases as r -1.119 with increase of horizontal distance r from the discharge channel. Based on the well-accepted transmission line model, the speed of return stroke is estimated to be about 1.4×108 m·s-1, with a variation range of (1.1―1.6)×108 m·s-1. Because of the similarities of the triggered lightning and natural lightning, the results in this article can be used in the protection design of natural lightning.
QIE XiuShu ZHANG QiLin ZHOU YunJun FENG GuiLi ZHANG TingLong YANG Jing KONG XiangZhen XIAO QingFu WU ShuJun
Red sprites, different from lightning flashes occurring in the troposphere, are large and brief dis-charges which appear in the altitude range from about 40 to 90 km above large thunderstorms and are usually caused by cloud-to-ground lightning discharges (CGs). A total of 17 sprites over two thunder-storms were first observed during the summer of 2007. One of the sprites occurred on July 28 above a thunderstorm in Guan County and the center of the storm was about 272 km from the observation site. The other sprites were recorded at the late night of August 1 and in the early morning of August 2, and the storm center was about 315 km away. All of the observed sprites occurred in cluster, and their appearances were very different, including 'columniform sprites', 'columniform sprites' with angel-like wings, 'carrot sprites', 'dancing sprites', etc. The duration of the sprites varied from a minimum of 40 ms to a maximum of 160 ms with a geometric mean (GM) of 61 ms. The time delay between parental positive cloud-to-ground lightning flashes (+CGs) and the associated sprites varied from 3.4 to 11.8 ms with a GM of 7.1 ms. The ratio of the number of +CGs to the total number of CGs during the time period with sprites was 7 times larger than that when no sprites occurred. Sprites did not appear fre-quently at the time when the convective activity is strong but when the thunderstorm starts to become weak.
YANG JingQIE XiuShuZHANG GuangShuZHAO YangZHANG Tong
By using the cloud-to-ground (CG) lightning location data from the lightning detection network of He- nan Province, surface Doppler radar data and standard orbit data of PR, TMI and LIS on TRMM satellite, the spatial and temporal characteristics of CG lightning flashes in 10 severe hailstorms are analyzed. The results show that the percentage of +CG lightning in these hailstorms is high with an average value of 45.5%. There is a distinct increase in CG flash rate during the rapid development stage of hailstorms. The hailstone falling corresponds to an active positive flash period, and the increase of +CG flash rate is generally accompanied with a decrease of –CG flash rate. The flash rate declines rapidly during the dissipating stage of hailstorms. The precipitation structure and lightning activity in two typical hail- storms are studied in detail. It is found that strong convective cells with reflectivity greater than 30dBZ mainly are situated in the front region of hailstorms, whereas the trailing stratiform region is in the rear part of the hailstorms. The maximum heights of echo top are higher than 14 km. Convective rain con- tributes much more rainfall to the total than stratiform rain, and the convective rain takes about 85% and 97% of the total in the two cases, respectively. Total lightning in the hailstorms is very active with the flash rate up to 183 fl/min and 55 fl/min, respectively. The results also indicate that most lightning flashes occurred in the echo region greater than 30 dBZ and its immediate periphery. The probability of lightning occurrence is 20 times higher in the convective region than in the stratiform region. The result suggests that the lightning information is helpful to the identification of convective rain region. The linear relationship between flash rate and ice water content is disclosed primarily.
FENG GuiLi1,2, QIE XiuShu3,1, YUAN Tie1 & NIU ShuZhen4 1 Laboratory of Lightning and Thunderstorm, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China
