Climatology and seasonal variation of the thermospheric tides and their response to solar activities over Arecibo

https://doi.org/10.1016/j.jastp.2021.105592Get rights and content

Highlights

  • A long-term observational study on the thermospheric tides is presented over Arecibo for the first time.

  • Climatology and seasonal variation of the thermospheric tides are revealed.

  • The thermospheric diurnal tide responds most strongly to solar activity among the three tidal components.

Abstract

A long-term statistical analysis of thermospheric tides in an altitude range from 150 to 400 km is presented. The analysis is based on a dataset with 31 multi-day experiments conducted from an incoherent scatter radar at Arecibo Observatory between 1984 and 2015. This is the first time that the climatological mean and seasonal variations of the thermospheric tides and their response to solar activities are reported using an extensive dataset. The climatological mean amplitude of diurnal tide (DT) is dominant while the amplitudes of the semidiurnal tide (SDT) and terdiurnal tide (TDT) are comparable. Below 250 km, the SDT and TDT phases show downward propagation with vertical wavelengths of 300 and 240 km, respectively. Above 250 km, the DT is the most prominent component except in autumn while the SDT dominates below 250 km except in winter. Above 250 km, the DT is the strongest in winter and its amplitude varies around 28 m/s. Below 250 km, the SDT is prominent in autumn and fluctuates around 35 m/s. The TDT is the most important in winter compared to the other three seasons and its amplitude is slightly less than 20 m/s. The DT and SDT amplitudes show the opposite response to solar activity. Above 250 km, the former increases with increasing solar activity while the latter is the opposite. The enhanced DT amplitude and its phase structure under the high solar activity indicates that the in-situ EUV radiation plays a major role in generating the thermospheric DT over Arecibo.

Introduction

Atmospheric solar tides are global-scale oscillations and they are mainly generated by the solar radiation (Chapman and Lindzen, 1970). The periods of the solar tides are related to a solar day, which are 24, 12, 8, and 6 h. The diurnal tide (DT) and semidiurnal tide (SDT) usually have strong horizontal amplitudes and are frequently observed by various instruments (e.g., Forbes, 1995). Comparing to numerous studies on the DT and SDT, the terdiurnal tide (TDT) and quarter-diurnal tide have received less attention due to their relatively small amplitudes and short durations (e.g., Gong and Zhou, 2011; Gong et al., 2018). Owing to their significant impacts on the transportation of atmospheric energy, atmospheric tides have been studied extensively in numerous publications (e.g., Zhou et al., 1997; Huang et al., 2006, 2007; Forbes et al., 2008, 2011; Hagan et al., 1999; Hagan and Forbes, 2002; Oberheide et al., 2007, 2011; Gong et al., 2013; Dhadly et al., 2018; Liu et al., 2019).

Chapman and Lindzen (1970) solved the zonal structure of atmospheric tides and provided a review of the tidal theory. Using numerical models, Forbes (1982a, 1982b) investigated the vertical structure of diurnal and semidiurnal tides in an altitude range from 100 to 400 km. Hagan et al. (1995) established the Global Scale Fluctuation Model (GSWM) that allows users to define important atmospheric parameters such as background wind field, tidal driving force, and dissipation terms. The basic generation mechanisms and characteristics of the migrating solar tides in the mesosphere and lower thermosphere (MLT) region are introduced by Forbes (1995). Hagan et al. (1999) revised the GSWM to predict the migrating solar tide in the troposphere, stratosphere, mesosphere, and lower thermosphere. Hagan and Roble (2001) suggested that non-migrating tides could be excited by nonlinear interaction between migrating tides and planetary waves based on the data obtained from the thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM). Using the GSWM, Hagan and Forbes (2002) reported that in the troposphere, non-migrating tides are mainly excited by latent heat release. Based on the self-established numerical tidal model, Huang et al. (2006, 2007) studied the nonlinear interactions on the migrating diurnal and semidiurnal tides.

Aside from numerical studies, extensive observation analyses on atmospheric tides have been reported using ground-based and satellite measurements like meteor radars (e.g., Huang et al., 2013; Yu et al., 2013; Davis et al., 2013), MF radars (e.g., Zhao et al., 2012; Singh and Gurubaran, 2017), Lidars (e.g., Lübken et al., 2011; Fong et al., 2014; Kopp et al., 2015; Baumgarten et al., 2018) and satellites (e.g., Oberheide and Forbes, 2008; Oberheide et al., 2011; Jin et al., 2012; Pancheva et al., 2012; Sakazaki et al., 2012; Moudden and Forbes, 2013; Singh et al., 2018; Liu et al., 2019). The data taken from the Doppler interferometer on board the TIMED satellite allows Oberheide et al. (2007) to report the climatology of nonmigrating semidiurnal tides. Using multi-year observations obtained from meteor radars, Pokhotelov et al. (2018) reported the seasonal variability of atmospheric tides. Liu et al. (2019) presented the vertical structures of the diurnal, semidiurnal, and terdiurnal tides using 15 years’ data collected from the Syowa MF radar (69°S, 39°E).

Due to the limitation of detecting instruments, observational studies of atmospheric tides in the altitude range from 120 to 400 km are limited (Oberheide et al., 2011). However, investigating the characteristics of the atmospheric tides in that altitude range is important in understanding the ionosphere-thermosphere system. Above 120 km, incoherent scatter radar (ISR) is an effective instrument to obtain the altitude and time dependence of wind at that altitude range. Using ISR measurements at Millstone Hill (42°N) and St. Santin (45°N), Salah et al. (1975) observed a strong SDT in the altitude range from 100 to 130 km, which is likely excited in the lower atmosphere. Goncharenko and Salah (1998) reported the seasonal and climatological variability of the SDT in the altitude range from 90 to 140 km based on data collected from the Millstone Hill ISR between 1987 and 1997. Using the Arecibo ISR, Harper (1981), Zhou et al. (1997), Gong and Zhou (2011), and Gong et al. (2013, 2018) presented the vertical structure of the atmospheric tides in the thermosphere. Although the Arecibo ISR has been used to study the tidal characteristics in the thermosphere, a statistic and systematic analysis with a long-term dataset is still lacking.

In this study, the climatological mean and seasonal variation of the DT, SDT, and TDT in the thermosphere and their response to solar activities are investigated using the Arecibo ISR experiments conducted between 1984 and 2015. The dataset used in this study and the processing method is described in section 2. The climatological mean and seasonal variation of the thermospheric tides are given in sections 3 Climatological characteristics, 4 Seasonal variations, respectively. The response of the thermospheric tides to the solar activities are presented in section 5. Conclusions are summarized in section 6.

Section snippets

Data analysis

A dataset with 31 multi-day experiments conducted between 1984 and 2015 using the ISR at the Arecibo Observatory, Puerto Rico (18.3N, 66.7W) is applied in this study. The dates of the dataset and the corresponding geophysical conditions are listed in Table 1. The dataset covers a total of 140 days of measurements and reflects a large variety of geophysical conditions including periods of low, moderate, and high solar activities and different seasons. In this study, we define March, April, and

Climatological characteristics

In order to investigate the climatological characteristics of tidal waves in the thermosphere, all the results of the tidal amplitudes and phases are averaged together. The averaged results of the DT (red), SDT (blue), and TDT (orange) are shown in Fig. 3. To describe the variability of the climatological mean tidal amplitudes and phases, the standard deviation of the results is computed and presented as error bars in Fig. 3. The ratio of the standard deviations to the climatological mean tidal

Seasonal variations

The vertical variations of DT (left), SDT (middle), and TDT (right) amplitudes (red) and phases (blue) in spring (first row), summer (second row), autumn (third row), and winter (fourth row) are shown in Fig. 4. The error bars represent the standard deviations. As shown in the first row of Fig. 4, in spring, the amplitudes of the DT is about 15 m/s, which is ~3 m/s larger than the SDT and TDT amplitudes above 250 km. Below 250 km, the SDT is generally larger than the DT and TDT. However, the DT

Tidal response to solar activities

The amplitudes and phases of the diurnal (red curve) and semidiurnal (blue curve) components under low (first panel), moderate (middle panel), and high (bottom panel) solar activities in the thermosphere are obtained and presented in Fig. 5. Since the thermospheric terdiurnal tide has a limited response to different solar activities, the results of the TDT are not presented in this paper. As shown in Fig. 5, the DT amplitude increases with increasing solar activity except for the amplitude

Summary and conclusions

The dataset used in this study consists of 31 multi-day experiments conducted by the Arecibo incoherent scatter radar between 1984 and 2015. The vertical structures of the thermospheric diurnal, semidiurnal, and terdiurnal tides in each experiment are derived. To our knowledge, this is the first time that a long-term statistical analysis of the atmospheric tides in the altitude range from 150 to 400 km has been reported. The climatological mean and seasonal variation of tidal components and

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The Arecibo Observatory is operated by the University of Central Florida under a cooperative agreement with the National Science Foundation. The Arecibo data used here can be obtained from the Madrigal Database at the Arecibo Observatory through http://www.naic.edu/madrigal/index.html/. The F10.7 indexes were downloaded from the SPDF OMNIWeb database (https://omniweb.gsfc.nasa.gov/form/dx1.html). The study is supported by the National Natural Science Foundation of China (through grants 41574142

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