The Sub-Millimetre Radiometer (SMR) on board the Odin satellite provides almost 20 years of nitric oxide (NO) measurements in the mesosphere and lower thermosphere (MLT) at equatorial crossing local solar times (LSTs) of 6 AM and 6 PM. In this study, we use Odin/SMR observations to estimate how lower thermospheric NO mixing ratios at low latitudes are affected by solar nonmigrating tides. Most of the previous studies based on satellite data have focused on the signatures of diurnal tides in the MLT and above, while we concentrate here on nonmigrating semidiurnal tides. To study the contribution of these tides to NO mixing ratio variations, we average pairs of NO measurements along ascending and descending orbital tracks at 107 km altitude over latitudes between −40°and +40°. We consider monthly climatologies of these pair-averages and analyse residuals with respect to their zonal mean. In this way, it is possible to study the effect of nonmigrating even-numbered tidal components, albeit there is a non-tidal component arising largely from quasi-stationary planetary waves. Spectral wave amplitudes are extracted using a Fourier transform as function of (apparent) zonal wavenumber with a focus around −30°, −20°and 30°latitudes. From our analysis, it appears that the semidiurnal (apparent) zonal wavenumber 4 arising from the SW6 and SE2 tides is dominant close to the equator (e.g., at −20°), except during some boreal summer months (June, July, August). On the other hand, wave-1 plays a more prominent role at subtropical latitudes, especially in the southern hemisphere, where it surpasses wave-4 during 7 months (March and May-to-October) at −30°. There is little observational evidence to date documenting the presence of the semidiurnal nonmigrating tides in NO in the low-latitude MLT. Our results hence provide one of the first evidences of the climatological signature of these tides in NO, in an altitude range that remains poorly observed.

 Odin 卫星上的亚毫米辐射计 (SMR) 提供近 20 年上午 6 点和下午 6点当地太阳时 (LST) 穿过赤道的中间层和低层热层 (MLT) 的一氧化氮 (NO) 测量结果 。在这项研究中，我们使用 Odin/SMR 观测来估计低纬度地区较低的热层 NO 混合比如何受到太阳非迁移潮汐的影响。之前大多数基于卫星数据的研究都集中在MLT及以上的日潮特征上，而我们这里集中于非迁移的半日潮。为了研究这些潮汐对 NO 混合比变化的影响，我们对沿纬度 -40° 至 +40° 之间 107 公里高度的上升和下降轨道的 NO 测量值进行了平均。我们考虑这些对平均值的每月气候学，并分析其区域平均值的残差。通过这种方式，可以研究非迁移偶数潮汐分量的影响，尽管非潮汐分量主要来自准静止行星波。使用傅立叶变换提取光谱波振幅作为（视）带波数的函数，重点关注纬度 -30°、-20° 和 30° 周围。根据我们的分析，似乎由 SW6 和 SE2 潮汐产生的半日（视）纬向波数 4 在赤道附近（例如，-20°）占主导地位，除了一些北半球夏季月份（六月、七月、八月） 。另一方面，第1波在副热带纬度地区发挥着更为突出的作用，特别是在南半球，在-30°的7个月内（3月和5月至10月）超过了第4波。迄今为止，几乎没有观测证据证明低纬度 MLT 中 NO 中存在半日非迁移潮汐。因此，我们的结果提供了 NO 中这些潮汐气候特征的第一个证据，但其海拔范围仍然很少被观测到。