Daytime wave characteristics in the mesosphere lower thermosphere region: Results from the Balloon‐borne Investigations of Regional‐atmospheric Dynamics experiment

Abstract

Results obtained from a joint INDO-US experiment on the investigations of mesosphere/lower thermosphere wave dynamics using balloon-borne optical dayglow measurements in combination with ground-based optical, radio, and magnetometer data are presented. Ultraviolet OI 297.2 nm dayglow emissions that originate at~120 km were measured from low-magnetic latitudes from onboard a balloon on 8 March 2010. This paper describes the details of a new spectrograph that is capable of making high spectral resolution (0.2 nm at 297.2 nm) and large (80°) field of view ultraviolet dayglow emission measurements and presents the first results obtained from its operation onboard a high-altitude balloon. Waves of scale sizes ranging from 40 to 80 km in the zonal direction were observed in OI 297.2 nm emissions. Meridional scale sizes of similar waves were found to be 200 km as observed in the OI 557.7 nm emissions that originate from~100 km. Periodicities were also derived from the variations of equatorial electrojet strength and ionospheric height on that day. Common periodicities of waves (in optical, magnetic, and radio measurements) were in the range of 16 to 30 min, which result in intrinsic horizontal wave speeds in the range of 21 to 77 m s À1. It is argued that gravity waves of such scale sizes and speeds at these heights are capable of propagating well into the thermosphere because the background wind directions were favorable. These waves were potentially capable of forming the seeds for the generation of equatorial plasma irregularities which did occur on that night.

On Deriving Gravity Wave Characteristics in the Daytime Upper Atmosphere Using Radio Technique

“…Ground-based airglow emission measurements yield column integrated values; however, as they emanate from a finite thickness, they retain the information of fluctuations of smaller timescales as the reactants responsible for the airglow emissions do get affected by the passage of any wave-like fluctuations in the medium (e.g., Karan & Pallamraju, 2017, 2018Laskar et al, 2015;Pallamraju et al, 2010Pallamraju et al, , 2014Pallamraju et al, , 2016. Conventionally, established method for deriving GW periodicities, scale sizes, and propagation speeds has been through the analysis of temporal variation in optical airglow emission intensities.…”

“…While periodicities of planetary scale oscillations are of the order of several days and spread over lengths of several thousands of kilometers, the oscillations of diurnal scales of periodicities of 24 hr and its subharmonics (12, 8, and 6 hr) have scale lengths of several thousands of kilometers. GWs are known to be generated due to changes in orography (e.g., Alexander, 1996), convective activity (e.g., Singh & Pallamraju, 2016), presence of sharp longitudinal gradients, as in the case of solar terminator (e.g., Forbes et al, 2008), and wind shears (Pallamraju et al, 2014;Pramitha et al, 2015). Sometimes this forcing is intertwined with the planetary scale oscillations in the Earth's atmosphere.…”

First three dimensional wave characteristics in the daytime upper atmosphere derived from ground‐based multiwavelength oxygen dayglow emission measurements

“…During nighttime, both eastward/westward propagations have been noted in equatorial latitudes and southward propagation in middle latitudes [ Shiokawa et al , ]. It was seen in an earlier experiment that the periodicity of waves continues to remain the same from day to night at a given location [ Pallamraju et al , ]; however, for varying latitudes, it is envisaged that the daytime periodicities, phase speeds, scale sizes, and propagation directions would be different. Simultaneous, collocated day and night measurements in the future will provide greater insights into these aspects.…”

Effect of cyclone Nilofar on mesospheric wave dynamics as inferred from optical nightglow observations from Mount Abu, India

“…An in‐house built near‐infrared imaging spectrograph (NIRIS) has been used to carry out measurements of O 2 (0–1) and OH(6–2) band nightglow emission intensities which emanate at altitudes of 94 and 87 km, respectively. The details of NIRIS have been reported earlier [ Pallamraju et al , ], and the methodology adopted to derive mesospheric temperatures using rotational line intensity ratios of these band emissions from this instrument has been detailed in Singh and Pallamraju []. The accuracy of temperatures derived by NIRIS is ±3 K with a cadence of 5 min.…”