近日，美国国家航空航天局戈达德太空飞行中心的Glyn A. Collinson及其研究团队取得一项新进展。经过不懈努力，他们对地球的双极静电场及其在离子逃逸到太空中的作用进行研究。相关研究成果已于2024年8月28日在国际权威学术期刊《自然》上发表。

本文报道了在距离行星250km至768km范围内，存在一个+0.55±0.09V的电势降，这是由电离层电子向外压力单独产生的行星静电场（E_∥^⊕=1.09±0.17μVm^-1）所导致的。研究人员通过实验证明，地球的双极场控制着极区电离层的结构，使标高增加了271%。

研究人员推断，这会使进入磁层的冷O⁺离子供应量增加超过3800%，而其他机制，如波粒相互作用，可进一步加热并加速这些离子，使其达到逃逸速度。地球的静电场本身足够强，可以驱动极风，并可能是构成磁层大部分区域的冷H⁺离子群体的来源。

据悉，最近发现，源自电离层的冷等离子体对地球磁层的影响远超预期。已提出多种相互竞争的机制来解释离子逃逸到太空的原因，包括波粒相互作用产生的加热和加速作用，以及电离层与太空之间存在的全局静电场（称为双极场或极化场）。磁层中受热O⁺离子的观测结果与波粒相互作用共振一致。相比之下，对从极区电离层流出的冷超声速H⁺（称为极风）的观测结果表明，存在静电场。

附：英文原文

Title: Earth’s ambipolar electrostatic field and its role in ion escape to space

Author: Collinson, Glyn A., Glocer, Alex, Pfaff, Robert, Barjatya, Aroh, Conway, Rachel, Breneman, Aaron, Clemmons, James, Eparvier, Francis, Michell, Robert, Mitchell, David, Imber, Suzie, Akbari, Hassanali, Davis, Lance, Kavanagh, Andrew, Robertson, Ellen, Swanson, Diana, Xu, Shaosui, Miller, Jacob, Cameron, Timothy, Chornay, Dennis, Uribe, Paulo, Nguyen, Long, Clayton, Robert, Graves, Nathan, Debchoudhury, Shantanab, Valentine, Henry, Ghalib, Ahmed

Issue&Volume: 2024-08-28

Abstract: Cold plasma of ionospheric origin has recently been found to be a much larger contributor to the magnetosphere of Earth than expected. Numerous competing mechanisms have been postulated to drive ion escape to space, including heating and acceleration by wave–particle interactions and a global electrostatic field between the ionosphere and space (called the ambipolar or polarization field). Observations of heated O⁺ ions in the magnetosphere are consistent with resonant wave–particle interactions. By contrast, observations of cold supersonic H⁺ flowing out of the polar ionosphere (called the polar wind) suggest the presence of an electrostatic field. Here we report the existence of a +0.55±0.09V electric potential drop between 250km and 768km from a planetary electrostatic field (E_∥^⊕=1.09±0.17μVm^-1) generated exclusively by the outward pressure of ionospheric electrons. We experimentally demonstrate that the ambipolar field of Earth controls the structure of the polar ionosphere, boosting the scale height by 271%. We infer that this increases the supply of cold O⁺ ions to the magnetosphere by more than 3,800%, in which other mechanisms such as wave–particle interactions can heat and further accelerate them to escape velocity. The electrostatic field of Earth is strong enough by itself to drive the polar wind and is probably the origin of the cold H⁺ ion population1 that dominates much of the magnetosphere.

DOI: 10.1038/s41586-024-07480-3

Source: https://www.nature.com/articles/s41586-024-07480-3