Short-Term Variability of Non-Migrating Diurnal Tides in the Stratosphere from CMAM30, ERA-Interim, and FORMOSAT-3/COSMIC  
[PERSON]  
1 Indian Institute of Information Technology Kalyani, Kalyani 741235, India 1  
[PERSON]  
1 Corresponded: 1 [EMAIL_ADDRESS] Indian Institute of Information Technology Kalyani, Kalyani 741235, India 1  
Footnote 1: email: {dos202  
Tidal variability in temperature and wind fields helps us to understand the dynamics of the atmosphere, including long-term and short-term variabilities in the atmosphere. The average global variability of migrating and non-migrating tides in the middle atmosphere has been established by investigations of various ground-based measurements [7; 8; 9; 10] and satellite datasets [3; 11; 12; 13; 14; 15; 16; 17], models [18; 19], and reanalysis datasets [13; 20]. Short-term tidal variability in the middle atmosphere is still not understood due to a lack of sufficient data from satellite and ground-based measurements. The diurnal oscillation has been observed with an amplitude of 1 to 1.5 m/s over Indonesia using radiosonde measurements of winds below 25 km [21]. Such studies based on a single location are mostly focused on the troposphere region. However, the migrating and non-migrating components cannot be resolved without simultaneous measurements over different longitudes. Even if such types of measurements are possible in a given latitude circle, all latitudes cannot be covered due to the land-sea distribution of the globe. On the other hand, satellites take global measurements (asynoptic) and are capable of resolving the migrating and non-migrating tides [22; 23; 24]. DW1 is found to exhibit a strong semi-annual variation with maxima during the equinox and minima during the solstice, as observed in Upper Atmosphere Research Satellite (UARS) measurements over low latitudes in the 50-120 km region [25]. Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) satellite data have provided many insights into the tidal variability. The sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on-board the TIMED satellite can cover all 24 h local times over a given location in \(\sim\)60 days due to the yaw of the satellite [26; 27]. Hence, \(\sim\)60 days of data are combined to extract tidal characteristics, thereby providing the average variability of the tidal field in that duration. [PERSON] et al. [13] showed that tidal amplitudes increase with altitude (up to 4 K in the lower mesosphere in SABER data) and also have a peak of 3.5 K at 1 hPa. [PERSON] et al. [28] observed that the DW1 amplitudes maximised over the equator in the mesosphere region from 2002 to 2007, with amplitudes reaching up to 19 K at 90 km. In the stratosphere, the amplitudes increased towards mid-latitudes, reaching 4 to 5 K at the stratopause. The migrating diurnal tide shows distinctive features of the first symmetric propagating mode above 70 km height. They are related to the main maximum at the equator and secondary maximum near 35\({}^{\circ}\) latitude with a 180\({}^{\circ}\) phase shift. A trapped diurnal component is observed in the height range of 40 to 60 km [28]. The climatology of the diurnal tide was investigated using extended-CMAM data from 1979 to 2010 in the stratosphere and Mesosphere and Lower Thermosphere (MLT) region and compared with that obtained from SABER data [18]. During the Northern Hemisphere summer, DW1 has the largest amplitude below 65 km, but DE3 becomes the strongest in the MLT region. Semi-annual variation is observed at 95 km and annual variation is observed at 45 km in the SABER data. Spectral analysis of inter-annual variability shows a strong peak at 25 to 26 months in ext-CMAM and SABER data, which indicates the modulation of DW1 and DE3 tides by stratospheric Quasi Biennial-Oscillation (QBO) [18; 29]. Although the average tidal variability is obtained in these studies, the background variations are found to alias into the diurnal migrating tide, DW1, thereby overestimating the amplitudes [13].