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首页> 外文期刊>Journal of Geophysical Research, A. Space Physics: JGR >Causes of low thermospheric density during the 2007-2009 solar minimum
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Causes of low thermospheric density during the 2007-2009 solar minimum

机译：2007-2009年太阳最低值期间热圈密度低的原因

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摘要

Satellite drag data indicate that the thermosphere was lower in density, and therefore cooler, during the protracted solar minimum period of 2007-2009 than at any other time in the past 47 years. Measurements indicate that solar EUV irradiance was also lower than during the previous solar minimum. However, secular change due to increasing levels of CO2 and other greenhouse gases, which cool the upper atmosphere, also plays a role in thermospheric climate, and changes in geomagnetic activity could also contribute to the lower density. Recent work used solar EUV measurements from the Solar EUV Monitor (SEM) on the Solar and Heliospheric Observatory, and the NCAR ThermosphereIonosphere-Electrodynamics General Circulation Model, finding good agreement between the density changes from 1996 to 2008 and the changes in solar EUV. Since there is some uncertainty in the long-term calibration of SEM measurements, here we perform model calculations using the MgII core-to-wing ratio as a solar EUV proxy index. We also quantify the contributions of increased CO_2 and decreased geomagnetic activity to the changes. In these simulations, CO_2 and geomagnetic activity play small but significant roles, and the primary cause of the low temperatures and densities remains the unusually low levels of solar EUV irradiance.
机译：卫星阻力数据表明，在旷日持久的2007年至2009年期间，热圈的密度较低，因此温度较低，这比过去47年中的任何其他时间都要高。测量表明，太阳EUV辐照度也低于之前的最低太阳照度。但是，由于CO2和其他温室气体水平升高引起的长期变化会冷却高层大气，在高温层气候中也起作用，地磁活动的变化也可能导致密度降低。最近的工作使用了太阳和日球天文台的太阳EUV监测器（SEM）的太阳EUV测量值，以及NCAR热球电离层-电动力学通用环流模型，发现1996年至2008年的密度变化与太阳EUV的变化之间有很好的一致性。由于SEM测量的长期校准存在一些不确定性，因此在这里我们使用MgII核翼比作为太阳EUV代理指标进行模型计算。我们还量化了增加CO_2和减少地磁活动对变化的贡献。在这些模拟中，CO_2和地磁活动起着很小但重要的作用，而低温和高密度的主要原因仍然是太阳EUV辐照度异常低。

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