Primary Versus Secondary Gravity Wave Responses at F‐Region Heights Generated by a Convective Source
Primary Versus Secondary Gravity Wave Responses at F‐Region Heights Generated by a Convective Source
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DOI：
10.1029/2021ja029947
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发表时间：
2021-12
期刊：
影响因子：
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通讯作者：
C. Heale;P. Inchin;J. Snively
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作者：
C. Heale;P. Inchin;J. Snively
采用二维非线性可压缩模型模拟了声重力波（AGW，即包括声波和重力波的频谱）对雷暴飑线型源的响应。我们研究了热层中的初级和次级中性AGW响应，这些响应与可以耦合到F区电离层等离子体的波一致，并表现为行进电离层扰动（TIDs）。我们发现，在海拔z = 240 km处，主波的波长和相速分别在170 ~ 270 km和180 ~ 320 m/s之间。产生的二次波的波长范围为~ 100 ~ 600 km，相速度为300 ~ 630 m/s。虽然在波谱中存在重叠，但我们发现次级波（即由初级波非线性变换或次级/随后产生的波）通常比初级波具有更快的相位。我们还评估了在F区高度观测到的具有快速相速（超过从中间层到热层传播的理论上限）的波必须是二次波的概念，例如，在低层热层中由波破裂在原位产生的波，而不是直接从其源传播一次波。我们发现，相速大于这个上限的主波可以穿过低层/中层大气的深层部分，并在热层中以传播波的形式出现。因此，将TID /GWs相速度与该上限进行比较并不是确定观测到的TID是来自主AGW还是次AGW的可靠方法。
A 2D nonlinear, compressible model is used to simulate the acoustic‐gravity wave (AGW, i.e., encompassing the spectrum of acoustic and gravity waves) response to a thunderstorm squall‐line type source. We investigate the primary and secondary neutral AGW response in the thermosphere, consistent with waves that can couple to the F‐region ionospheric plasma, and manifest as Traveling Ionospheric Disturbances (TIDs). We find that primary waves at z = 240 km altitude have wavelengths and phase speeds in the range 170–270 km, and 180–320 m/s, respectively. The secondary waves generated have wavelengths ranging from ∼100 to 600 km, and phase speeds from 300 to 630 m/s. While there is overlap in the wave spectra, we find that the secondary waves (i.e., those that have been nonlinearly transformed or generated secondarily/subsequently from the primary wave) generally have faster phases than the primary waves. We also assess the notion that waves with fast phase speeds (that exceed proposed theoretical upper limits on passing from the mesosphere to thermosphere) observed at F‐region heights must be secondary waves, for example, those generated in situ by wave breaking in the lower thermosphere, rather than directly propagating primary waves from their sources. We find that primary waves with phase speeds greater than this proposed upper limit can tunnel through a deep portion of the lower/middle atmosphere and emerge as propagating waves in the thermosphere. Therefore, comparing a TID's/GWs phase speed with this upper limit is not a robust method of identifying whether an observed TID originates from a primary versus secondary AGW.