Prevalent lightning sferics at 600 megahertz near Jupiter's poles
Prevalent lightning sferics at 600 megahertz near Jupiter's poles
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DOI：
10.1038/s41586-018-0156-5
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发表时间：
2018-06-07
期刊：
影响因子：
64.8
通讯作者：
Connerney, John
中科院分区：
文献类型：
--
作者：
Brown, Shannon;Janssen, Michael;Connerney, John
所有来访的航天器通过夜间光学成像和哨声(闪电产生的无线电波)信号探测到木星上的闪电(1-6)。木星闪电被认为是通过凝结的液态水和水-冰颗粒之间的电荷分离过程在对流水云的混合相(液体-冰)区域产生的，类似于地面(云对云)闪电(7-9)。与地面闪电不同的是，地面闪电在射电频谱上发射的频率高达千兆赫(10，11)，而木星上的闪电只在千赫兹频率下被探测到，尽管人们在寻找兆赫范围内的信号(12)。强烈的电离层衰减或比地球上慢得多的闪电放电被认为是这种差异的可能解释(13，14)。在这里，我们报道了朱诺号航天器上的微波辐射计(15)在600兆赫处观测到的木星闪电脉冲(宽带电磁脉冲)。这些探测表明，木星闪电与地球闪电并不像之前认为的那样截然不同。在朱诺的前八个轨道中，我们从一极到另一极探测到377个闪电。我们发现闪电在极地地区很普遍，赤道附近没有闪电，最频繁的是北半球，北纬40度以上。由于闪电的分布是湿对流活动的代表，湿对流活动被认为是从行星内部向外输送能量的重要来源(16，17)，因此，向两极对流的增加可能表明向外的内部热通量优先向极(9，16，18)加权。湿对流的分布对于了解木星的组成、大气环流和能量输送具有重要意义。
Lightning has been detected on Jupiter by all visiting spacecraft through night-side optical imaging and whistler (lightning-generated radio waves) signatures(1-6). Jovian lightning is thought to be generated in the mixed-phase (liquid-ice) region of convective water clouds through a charge-separation process between condensed liquid water and water-ice particles, similar to that of terrestrial (cloud-to-cloud) lightning(7-9). Unlike terrestrial lightning, which emits broadly over the radio spectrum up to gigahertz frequencies(10,11),lightning on Jupiter has been detected only at kilohertz frequencies, despite a search for signals in the megahertz range(12). Strong ionospheric attenuation or a lightning discharge much slower than that on Earth have been suggested as possible explanations for this discrepancy(13,14). Here we report observations of Jovian lightning sferics (broadband electromagnetic impulses) at 600 megahertz from the Microwave Radiometer(15) onboard the Juno spacecraft. These detections imply that Jovian lightning discharges are not distinct from terrestrial lightning, as previously thought. In the first eight orbits of Juno, we detected 377 lightning sferics from pole to pole. We found lightning to be prevalent in the polar regions, absent near the equator, and most frequent in the northern hemisphere, at latitudes higher than 40 degrees north. Because the distribution of lightning is a proxy for moist convective activity, which is thought to be an important source of outward energy transport from the interior of the planet(16,17,) increased convection towards the poles could indicate an outward internal heat flux that is preferentially weighted towards the poles(9,16,18). The distribution of moist convection is important for understanding the composition, general circulation and energy transport on Jupiter.