Atmospheric temperature tides in the tropical upper troposphere and lower stratosphere

Atmospheric thermal tides are global-scale waves with periods that are harmonics of a solar day, mainly excited by diurnally varying diabatic heating in the troposphere and the stratosphere. Some recent studies suggested that the tidal temperature variations in the TTL might affect the appearance of cirrus clouds and, thus, the dehydration process. It should be noted, however, that the global pattern of diurnal temperature variations in the TTL still remains unclear. In this study, we aim at revealing the 3D structure of diurnal temperature variations around the TTL, including its seasonal variations, by using data from global reanalyses for the period of 2002-2006. It is found that the Sun synchronous tides have amplitudes of ~0.3 K (~0.5 K) at 100 hPa (70 hPa) in January. Superposed on these components, the non-Sun-synchronous tides are strong over the continent (South America, Africa); these may be excited by latent heat release associated with deep convections there. The total (i.e., Sun-synchronous plus non-Sun-synchronous) diurnal temperature amplitudes reach ~0.5 K (~1 K) at maxima at 100 hPa (70 hPa) in January. The seasonality and the impact on the dehydration will be discussed in the presentation

Validation of ozone data from the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES)

The Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) onboard the International Space Station provided global measurements of ozone profiles in the middle atmosphere from 12 October 2009 to 21 April 2010. We present validation studies of the SMILES version 2.1 ozone product based on coincidence statistics with satellite observations and outputs of chemistry and transport models (CTMs). Comparisons of the stratospheric ozone with correlative data show agreements that are generally within 10%. In the mesosphere, the agreement is also good and better than 30% even at a high altitude of 73km, and the SMILES measurements with their local time coverage also capture the diurnal variability very well. The recommended altitude range for scientific use is from 16 to 73km. We note that the SMILES ozone values for altitude above 26km are smaller than some of the correlative satellite datasets; conversely the SMILES values in the lower stratosphere tend to be larger than correlative data, particularly in the tropics, with less than 8% difference below similar to 24km. The larger values in the lower stratosphere are probably due to departure of retrieval results between two detection bands at altitudes below 28km; it is similar to 3% at 24km and is increasing rapidly down below

An Array of Ringing Global Free Modes Discovered in Tropical Surface Pressure Data

地球大気の共鳴振動を網羅的に検出 --大気は梵鐘のように「鳴り響いている」--. 京都大学プレスリリース. 2020-07-08.We used newly available ERA5 hourly global data to examine the variations of atmospheric circulation on global scales and high frequencies. The space–time spectrum of surface pressure displays a typical red background spectrum but also a striking number of isolated peaks. Some peaks represent astronomically forced tides, but we show that most peaks are manifestations of the ringing of randomly excited global-scale resonant modes, reminiscent of the tones in a spectrum of a vibrating musical instrument. A few such modes have been tentatively identified in earlier observational investigations, but we demonstrate the existence of a large array of normal mode oscillations with periods as short as 2 h. This is a powerful and uniquely detailed confirmation of the predictions of the theory of global oscillations that has its roots in the work of Laplace two centuries ago. The delineation of the properties of the modes provides valuable diagnostic information about the atmospheric circulation. Notably the amplitudes and widths of the normal mode spectral peaks contain information on the forcing mechanisms and energy dissipation for the modes, and the simulation of these properties for each of the many modes we have identified can serve as tests for global climate and weather prediction models

Diurnal Variations in Summertime Surface Wind upon Japanese Plains : Hodograph Rotation and Its Dynamics

This study investigates diurnal variations in surface wind in Japan during June-August of 1992-2006 using data from the Automated Meteorological Data Acquisition System (AMeDAS) and the Sapporo City Multisensor (MULTI). Harmonic analysis and hodograph analysis are employed to investigate the rotation direction and rotation rate of the wind vector at about 1000 stations. An analysis of six major plains in Japan reveals distinct clockwise and anticlockwise hodograph regions within each plain. The rotation direction is attributed to two lagged pressure-gradient forces of contrasting orientations: one between the land and sea, and another between the plain and adjacent mountains. An analysis of the linearized equations of motion reveals that rotation of the wind vector is mainly controlled by the balance between the pressure gradient force and the frictional force, with a small but non-negligible contribution by the Coriolis force, particularly near the coast. The observed rotation rates of the hodographs show a brief stagnation during the mid-afternoon and a longer stagnation during the nighttime. This irregular rotation rate is well explained by taking into account the semidiurnal component of the wind. The linearized equations of motion indicate that this semidiurnal component results from the semidiurnal component of the pressure gradient force, which is generated by non-sinusoidal solar heating over the course of a day

Diurnal Variations in Lower-Tropospheric Wind over Japan Part II: Analysis of Japan Meteorological Agency Mesoscale Analysis Data and Four Global Reanalysis Data Sets

Following on from the observation results obtained from Wind profiler Network and Data Acquisition System (WINDAS) data, as reported by Part I of this study, the dynamical processes responsible for the diurnal component in lower-tropospheric winds are examined using Japan Meteorological Agency (JMA) mesoscale analysis data (MANAL) and four global reanalysis data sets (JRA25/JCDAS, ERA-Interim, NCEP1, and NCEP2). Of these data sets, MANAL and JRA25 perform best in reproducing the WINDAS horizontal wind observations, including their diurnal and semidiurnal components. At 1-3 km height, Diurnal Eastward-moving Eddies (DEEs) with a phase speed of 10-15 m s^[-1] and diameter of ∼700 km move eastward over the Sea of Japan and over the Pacific throughout the year. The superposition of winds associated with DEEs over return currents controls the diurnal wind component over the main Japanese islands, generating diurnal amplitude maxima in spring and autumn at this height range. Analysis of global reanalysis data confirmed that the diurnal wind at 3-5 km in winter-spring is controlled mainly by medium-scale eastward-traveling waves with amplitude maxima around the tropopause. The diurnal wind at 3-5 km in summer-autumn is caused primarily by the diurnal tide with zonal wavenumbers of ≤10. For stations located on small islands south of the Japanese mainland, the diurnal wind is controlled mainly by the diurnal tide for the entire lower troposphere throughout the year

Diurnal Variations in Lower-Tropospheric Wind over Japan Part I: Observational Results using the Wind Profiler Network and Data Acquisition System (WINDAS)

This study investigates diurnal variations in lower-tropospheric wind over Japan during 2002-2008 using data from 31 stations of the Wind profiler Network and Data Acquisition System (WINDAS) and the Automated Meteorological Data Acquisition System (AMeDAS). The diurnal and semidiurnal components are extracted and analyzed to identify the dominant processes for each height range and for each season. Near the surface, the diurnal component is controlled by local wind systems (e.g., land-sea breezes) throughout the year. At 1-3 km, the diurnal component is primarily controlled by the return currents of local wind systems, with additional influence by other disturbances; the superposition of these two wind systems generates amplitude maxima in spring (∼0.5 m s^[-1]) and autumn (∼0.6 m s^[-1]). At 3-5 km, the diurnal wind in DJF-MAM is controlled by medium-scale eastward traveling waves, which generate the amplitude maximum (∼0.8 m s^[-1]) in winter-spring. In JJA-SON, the diurnal component is controlled by a large-scale wind system with an amplitude of ∼0.3 m s^[-1], probably related to the diurnal tide. At stations located on small islands located south of the Japanese mainland, the diurnal wind within the lower troposphere has different characteristics from those described above throughout the year. Throughout Japan, the semidiurnal wind component is controlled by the semidiurnal migrating tide above ∼1 km, and is influenced by local wind systems below ∼1 km. The amplitude of the semidiurnal tide below 5 km is largest in DJF (∼0.4 m s^[-1]) and smallest in JJA (∼0.2 m s^[-1])

Representation of solar tides in the stratosphere and lower mesosphere in state-of-the-art reanalyses and in satellite observations

Atmospheric solar tides in the stratosphere and the lower mesosphere are investigated using temperature data from five state-of-the-art reanalysis data sets (MERRA-2, MERRA, JRA-55, ERA-Interim, and CFSR) as well as TIMED SABER and Aura MLS satellite measurements. The main focus is on the period 2006–2012 during which the satellite observations are available for direct comparison with the reanalyses. Diurnal migrating tides, semidiurnal migrating tides, and nonmigrating tides are diagnosed. Overall the reanalyses agree reasonably well with each other and with the satellite observations for both migrating and nonmigrating components, including their vertical structure and the seasonality. However, the agreement among reanalyses is more pronounced in the lower stratosphere and relatively weaker in the upper stratosphere and mesosphere. A systematic difference between SABER and the reanalyses is found for diurnal migrating tides in the upper stratosphere and the lower mesosphere; specifically, the amplitude of trapped modes in reanalyses is significantly smaller than that in SABER, although such difference is less clear between MLS and the reanalyses. The interannual variability and the possibility of long-term changes in migrating tides are also examined using the reanalyses during 1980–2012. All the reanalyses agree in exhibiting a clear quasi-biennial oscillation (QBO) in the tides, but the most significant indications of long-term changes in the tides represented in the reanalyses are most plausibly explained by the evolution of the satellite observing systems during this period. The tides are also compared in the full reanalyses produced by the Japan Meteorological Agency (i.e., JRA-55) and in two parallel data sets from this agency: one (JRA-55C) that repeats the reanalysis procedure but without any satellite data assimilated and one (JRA-55AMIP) that is a free-running integration of the model constrained only by observed sea surface temperatures. Many aspects of the tides are closer in JRA-55C and JRA-55AMIP than these are to the full reanalysis JRA-55, demonstrating the importance of the assimilation of satellite data in representing the diurnal variability of the middle atmosphere. In contrast to the assimilated data sets, the free-running model has no QBO in equatorial stratospheric mean circulation and our results show that it displays no quasi-biennial variability in the tides

Three-dimensional structures of tropical nonmigrating tides in a high-vertical-resolution general circulation model

This paper investigates nonmigrating tides from the ground to the lower mesosphere using data from a high-resolution general circulation model (KANTO GCM), as well as observational data from the Sounding of the Atmosphere using Broadband Emission Radiometry instrument on board the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics satellite and from GPS radio occultation measurements obtained with the COSMIC/FORMOSAT-3 mission. We extract nonmigrating tides using a composite as a function of universal time in physical space, without performing a zonal wave number decomposition. The KANTO GCM clearly demonstrates that tropical nonmigrating tides are regarded as gravity waves excited by diabatic heating enhanced over two major continents, specifically Africa and South America. They propagate zonally, in a direction away from their sources; that is, west and eastward propagating waves are dominant on the western and eastern sides of the continents, respectively. These characteristics are observed in two satellite data sets as well, except that the amplitudes in the KANTO GCM are larger than those in the observations. Seasonal variations of nonmigrating tides are also investigated. It is suggested that filtering owing to the stratopause semiannual oscillation, as well as diabatic heating in the troposphere, is important for the seasonal variations of nonmigrating tides in the stratosphere and the lower mesosphere