Segmentation of PMSE data using random forests

EISCAT VHF radar data are used for observing, monitoring, and understanding Earth’s upper atmosphere. This paper presents an approach to segment Polar Mesospheric Summer Echoes (PMSE) from datasets obtained from EISCAT VHF radar data. The data consist of 30 observations days, corresponding to 56,250 data samples. We manually labeled the data into three different categories: PMSE, Ionospheric background, and Background noise. For segmentation, we employed random forests on a set of simple features. These features include: altitude derivative, time derivative, mean, median, standard deviation, minimum, and maximum values corresponding to neighborhood sizes ranging from 3 by 3 to 11 by 11 pixels. Next, in order to reduce the model bias and variance, we employed a method that decreases the weight applied to pixel labels with large uncertainty. Our results indicate that, first, it is possible to segment PMSE from the data using random forests. Second, the weighted-down labels technique improves the performance of the random forests method

A case study of a sporadic sodium layer observed by the ALOMAR Weber Na lidar

Several possible mechanisms for the production of sporadic sodium layers have been discussed in the literature, but none of them seem to explain all the accumulated observations. The hypotheses range from direct meteoric input, to energetic electron bombardment on meteoric smoke particles, to ion neutralization, to temperature dependent chemistry. The varied instrumentation located on Andøya and near Tromsø in Norway gives us an opportunity to test the different theories applied to high latitude sporadic sodium layers. We use the ALOMARWeber sodium lidar to monitor the appearance and characteristics of a sporadic sodium layer that was observed on 5 November 2005. We also monitor the temperature to test the hypotheses regarding a temperature dependent mechanism. The EISCAT Tromsø Dynasonde, the ALOMAR/UiO All-sky camera and the SKiYMET meteor radar on Andøya are used to test the suggested relationships of sporadic sodium layers and sporadic E-layers, electron precipitation, and meteor deposition during this event. We find that more than one candidate is eligible to explain our observation of the sporadic sodium layer

Spatial and temporal variability in MLT turbulence inferred from in situ and ground-based observations during the WADIS-1 sounding rocket campaign

In summer 2013 the WADIS-1 sounding rocket campaign was conducted at the Andøya Space Center (ACS) in northern Norway (69° N, 16° E). Among other things, it addressed the question of the variability in mesosphere/lower thermosphere (MLT) turbulence, both in time and space. A unique feature of the WADIS project was multi-point turbulence sounding applying different measurement techniques including rocket-borne ionization gauges, VHF MAARSY radar, and VHF EISCAT radar near Tromsø. This allowed for horizontal variability to be observed in the turbulence field in the MLT at scales from a few to 100 km. We found that the turbulence dissipation rate, ε varied in space in a wavelike manner both horizontally and in the vertical direction. This wavelike modulation reveals the same vertical wavelengths as those seen in gravity waves. We also found that the vertical mean value of radar observations of ε agrees reasonably with rocket-borne measurements. In this way defined 〈εradar〉 value reveals clear tidal modulation and results in variation by up to 2 orders of magnitude with periods of 24 h. The 〈εradar〉 value also shows 12 h and shorter (1 to a few hours) modulations resulting in one decade of variation in 〈εradar〉 magnitude. The 24 h modulation appeared to be in phase with tidal change of horizontal wind observed by SAURA-MF radar. Such wavelike and, in particular, tidal modulation of the turbulence dissipation field in the MLT region inferred from our analysis is a new finding of this work

Impacts of a sudden stratospheric warming on the mesospheric metal layers

We report measurements of atomic sodium, iron and temperature in the mesosphere and lower thermosphere (MLT) made by ground-based lidars at the ALOMAR observatory (69°N, 16°E) during a major sudden stratospheric warming (SSW) event that occurred in January 2009. The high resolution temporal observations allow the responses of the Na and Fe layers to the SSW at high northern latitudes to be investigated. A significant cooling with temperatures as low as 136 K around 90 km was observed on 22 − 23 January 2009, along with substantial depletions of the Na and Fe layers (an ~80% decrease in the column abundance with respect to the mean over the observation period). The Whole Atmosphere Community Climate Model (WACCM) incorporating the chemistry of Na, Fe, Mg and K, and nudged with reanalysis data below 60 km, captures well the timing of the SSW, although the extent of the cooling and consequently the depletion in the Na and Fe layers is slightly underestimated. The model also predicts that the perturbations to the metal layers would have been observable even at equatorial latitudes. The modelled Mg layer responds in a very similar way to Na and Fe, whereas the K layer is barely affected by the SSW because of the enhanced conversion of K+ ions to K atoms at the very low temperatures

Corrigendum to "Development of the mesospheric Na layer at 69 degrees N during the Geminids meteor shower 2010", published in Ann.Geophys., 31, 61-73, 2013

No abstract available

Derivation of vertical wavelengths of gravity waves in the MLT-region from multispectral airglow observations

We present the derivation of gravity wave vertical wavelengths from OH airglow observations of different vibrational transitions. It utilizes small phase shifts regularly observed between the OH(3-1) and OH(4-2) intensities in the spectra of the GRIPS (GRound-based Infrared P-branch Spectrometer) instruments, which record the OH airglow emissions in the wavelength range from 1.5  μm to 1.6  μm simultaneously. These phase shifts are interpreted as being due to gravity waves passing through the OH airglow layer and affecting individual vibrational transitions at slightly different times due to small differences in their emission heights. The results are compared with co-located observations of the Na-Lidar measurements acquired between 2010 and 2014 at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR, 69.28° N, 16.01° E), Norway. This comparison shows best agreement if the mean height difference of the OH(3-1) and OH(4-2) emission is assumed to be 540 m (1σ = 160 m). The results are also compared with co-located observations of the OH(6-2)- and O2b(0-1)-transitions by means of spectrometer observations (TANGOO instrument, Tilting-filter spectrometer for Atmospheric Nocturnal Ground-based Oxygen & hydrOxyl emission measurements) performed from 2013 until 2016 at Oberpfaffenhofen (48.08° N, 11.27° E), Germany. For approximately 40% of all wave events observed with GRIPS in the period range from 0.25 h to 17 h, a quantitative estimate of the phase relationship between the OH(3-1) and OH(4-2) intensities can be retrieved from the spectra allowing derivation of vertical wavelengths. The retrieval performs best for wave periods below two hours (80% success rate) and worse for periods above ten hours (successful in less than 10% of the cases). The average wavelength determined from 102 events amounts to 22.9 km (1σ: 9.0 km). The corresponding mean wavelength determined from the TANGOO observations amounts to 22.6 km ± 10.5 km, if a mean separation of 6.5 km is assumed for the height difference between the OH(6-2) and O2b(0-1)-transitions.</p

Localized mesosphere-stratosphere-troposphere radar echoes from the E region at 69 degrees N: Properties and physical mechanisms

We present the first observations, to our knowledge, of a new class of high‐latitude mesosphere‐stratosphere‐troposphere radar echoes from the E region as observed with the Arctic Lidar Observatory for Middle Atmosphere Research wind radar during the period 2004–2008. These echoes occur primarily during the summer months and in the altitude range from 93 to 114 km, with a pronounced peak of maximum occurrence at about 100 km. The echoes are rather short with typical durations of ∼20 min, with some examples lasting as long as 3 h. The echoes typically cover only a few hundred meters in the vertical and show both small Doppler velocities (±1–2 m/s) as well as very narrow spectral widths (just a few meters per second when converted to Doppler velocities). The echoes are highly aspect sensitive indicative of a specular‐scattering mechanism and reveal a distinct diurnal variation with maxima of occurrence around noon and midnight. The latter is related to the semidiurnal tidal components of the zonal and meridional wind where times of occurrence correspond to large values of corresponding vertical wind shears. Considering possible physical mechanisms, turbulence with large Schmidt number scatter is likely ruled out as is auroral backscatter. Finally, a strong case for a close correspondence of the echoes to sporadic E layers is presented on the basis of comparisons to ionosonde data, occurrence patterns of sporadic layers, simultaneous and common volume lidar measurements of a sporadic Fe layer, as well as simultaneous measurements of sporadic E layers with the European Incoherent Scatter UHF radar at a horizontal distance of 130 km. Applying the theory of partial reflections to the observed electron density gradients, we are able to demonstrate that the observed echo strengths can likely be explained on the basis of this scattering mechanism