Observations of short-period waves with an all-sky camera in the infrared airglow above Yakutsk

The parameters of internal gravity waves detected based on the variations in the hydroxyl molecule emission are statistically analyzed. The wave structures were registered with an all-sky infrared camera at Maimaga optical station (? = 63° N, λ = 129.5° E). The data obtained in the winter period of 1998–2002 are analyzed. In total, 162 waves, the majority of which propagated westward, were recorded. The wavelengths vary from 15.4 to 100 km (the average value is ～31 km); the observed horizontal phase velocities change from 19 to 166 m/s (the average value is ～60 m/s), and the estimated periods are 9–90 min (the average value is ～11 min). The statistical characteristics of the waves do not differ from those of similar waves at middle and low latitudes. The azimuthal dependence of the wave propagation direction is consistent with the theory of wave filtration by a background wind in the middle atmosphere. Probable sources of the waves are mountain ranges located at a distance of 200 km east of the observation site. Somewhat greater values of the mean wavelength and wave propagation velocities than those recorded at lower latitudes may be due to the lower loss of energy and velocity of the waves during their propagation from the source to the mesosphere, although other causes are not ruled out. Ripple-type waves have the same direction of propagation as band-type waves.     

Semidiurnal thermal tide in the mesopause region over Yakutia

The study is based on measuring fluctuations of the intensity and rotational temperatures of the molecular emissions of hydroxyl OH(6,2) and the first atmospheric band of oxygen O₂(0–1), excited at approximately 87 and 95 km, respectively. The measurements are conducted at Maimaga station (63°N, 129.5°E), located 150 km north of Yakutsk. The semidiurnal tide parameters were obtained using the database compiled from 1999 to 2005. The data obtained from October to March were analyzed. The measurements conducted during 214 nights were used to determine the semidiurnal tide parameters. The wave amplitude at the height of the molecular oxygen emission (～95 km) is 8 K, which is larger than the amplitude at the height of the hydroxyl emission (～87 km) by approximately 2 K. Except November, the 12-h oscillation at the height of molecular oxygen excitation leads the oscillation at the height of hydroxyl excitation. On average, the phase is ～5.7 h at the OH emission height and ～6.4 h at the O₂ emission height. We note that an abrupt increase in the tide amplitude in March at the molecular oxygen height can be related to a seasonal decrease in the so-called “wave” turbopause height.     

An extreme flood caused by a heavy snowfall over the Indigirka River basin in Northeastern Siberia

Flooding is one of the greatest disasters that produces strong effects on the ecosystem and livelihoods of the local population. Flood frequency is expected to increase globally making its risk assessment an urgent issue. In spring-summer 2017, an extreme flooding occurred in the Indigirka River lowland of Northeastern Siberia that inundated a large area. In this study, the extent and climatic drivers of the flooding were determined using the results of field observations, satellite images, and climate reanalysis dataset, and its possible effects on the ecosystem were discussed. In 2017, a significant lowland area of around 16,016 km² was covered with water even in July, which was 5,217 km² (around 4% of the total area) greater than the water-covered area in 2015 when usual hydrological condition in the area was observed. The hydrographic signature obtained for the Indigirka River water level in 2017 was unusual. Although the water level rose sharply at the end of May (which was typical for the Arctic region), it did not fall afterwards and even increased again to an annual daily maximum value in the middle of July. The climate reanalysis dataset obtained for the temporal–spatial variations of snow water equivalent, snowmelt, and runoff over the lowland revealed that a large amount of snowmelt runoff in June and July 2017 produced a large water-covered area and unusually high river water levels that lasted until summer. Snow depth from winter to spring was largest in 2017 over the period from 2009 to 2017, and the surface of the lower reach of the lowland was partially covered with snow even in the end of June due to the extreme snowfall that occurred in October 2016. Such unusual hydrological conditions waterlogged most trees over the lowland, which caused serious ecosystem devastation and changes in the material cycle.     

Comparison of ground-based and satellite measurements of atmospheric temperature in the mesopause region in high-latitude eastern Siberia

The mesopause kinetic temperature at an altitude of 87 km measured with a SABER broadband radiometer installed on the TIMED satellite and the hydroxyl molecule rotational temperature measured with a ground-spectrograph installed in high-latitude eastern Siberia (Maimaga optical station; φ = 63°N, λ = 129.5°E) are compared. The data of the observations performed from 2002 to 2006 have been analyzed. The temperatures measured during the satellite passes at distances not larger than 300 km from the intersection of the spectrograph sighting line with the hydroxyl emitting layer (∼87 km) have been compared. An analysis of 130 cases of coincident measurements indicated that the average hydroxyl molecule rotational temperatures are systematically lower than the average kinetic temperature at an altitude of the hydroxyl layer measured with SABER by 4.4 K (with a standard deviation of 11.4 K). A seasonal dependence is observed regarding the difference between the ground-based and satellite measurements. The difference decreases from 10 K in January to zero towards March. However, the time variations in the temperature obtained with the ground-based device and on the satellite are similar. Based on the performed analysis, it has been concluded that a series of hydroxyl rotational temperatures can be used to study temperature variations on different time scales, including long-term trends at the temperature emission altitude (∼87 km).     

Detection of short-period global waves from nightglow observations

Atmospheric temperature oscillations at similar frequencies have been detected in the spectra of variations in the rotational temperatures of the OH and O₂ nighttime emissions, simultaneously observed at two spaced stations in the range of periods ～1–3 h. These oscillations are probably caused by global waves: short-period solar tides and/or free oscillations of the atmosphere.