We present an extensive data set of simultaneous temperature and wind measurements in the Arctic middle atmosphere. It consists of more than 300 h of Doppler Rayleigh lidar observations obtained ...during three January seasons (2012, 2014, and 2015) and covers the altitude range from 30 km up to about 85 km. The data set reveals large year-to-year variations in monthly mean temperatures and winds, which in 2012 are affected by a sudden stratospheric warming. The temporal evolution of winds and temperatures after that warming are studied over a period of 2 weeks, showing an elevated stratopause and the reformation of the polar vortex. The monthly mean temperatures and winds are compared to data extracted from the Integrated Forecast System of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Horizontal Wind Model (HWM07). Lidar and ECMWF data show good agreement of mean zonal and meridional winds below ≈ 55 km altitude, but we also find mean temperature, zonal wind, and meridional wind differences of up to 20 K, 20 m s−1, and 5 m s−1, respectively. Differences between lidar observations and HWM07 data are up to 30 m s−1. From the fluctuations of temperatures and winds within single nights we extract the potential and kinetic gravity wave energy density (GWED) per unit mass. It shows that the kinetic GWED is typically 5 to 10 times larger than the potential GWED, the total GWED increases with altitude with a scale height of ≈ 16 km. Since temporal fluctuations of winds and temperatures are underestimated in ECMWF, the total GWED is underestimated as well by a factor of 3–10 above 50 km altitude. Similarly, we estimate the energy density per unit mass for large-scale waves (LWED) from the fluctuations of nightly mean temperatures and winds. The total LWED is roughly constant with altitude. The ratio of kinetic to potential LWED varies with altitude over 2 orders of magnitude. LWEDs from ECMWF data show results similar to the lidar data. From the comparison of GWED and LWED, it follows that large-scale waves carry about 2 to 5 times more energy than gravity waves.
This paper presents a method to calculate the harmonic content of stator vibrations and acoustic noise resulting from radial force excitations in switched reluctance machines (SRM). The method is ...based on a thin cylinder approximation of the stator. The eigen modes are represented by their transmission impedance. The spectral composition of the vibrations can be calculated using superposition of the eigen modes and vibrations caused by all phases of the SRM.
We present a new method for calculating backscatter ratios of the stratospheric sulfate aerosol (SSA) layer from daytime and nighttime lidar measurements. Using this new method we show a first ...year-round dataset of stratospheric aerosol backscatter ratios at high latitudes. The SSA layer is located at altitudes between the tropopause and about 30 km. It is of fundamental importance for the radiative balance of the atmosphere. We use a state-of-the-art Rayleigh-Mie-Raman lidar at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) station located in northern Norway (69.sup.â N, 16.sup.â E; 380 m a.s.l.). For nighttime measurements the aerosol backscatter ratios are derived using elastic and inelastic backscatter of the emitted laser wavelengths 355, 532 and 1064 nm. The setup of the lidar allows measurements with a resolution of about 5 min in time and 150 m in altitude to be performed in high quality, which enables the identification of multiple sub-layers in the stratospheric aerosol layer of less than 1 km vertical thickness.
This paper presents the design and an encoder-based starting strategy for a low-cost single-phase switched reluctance machine (SRM). The single-phase SRM cannot produce a continuous torque over one ...revolution. Therefore, applications that do not require a continuous torque, e.g., pumps and fans, are especially suitable. Another issue of single-phase machines is start up. The starting direction is affected by the initial rotor position. Due to the functional concept of SRM the machine produces no torque at aligned and unaligned position of the rotor and consequently, cannot be started from these positions. To start up from every rotor position a saturation-based starting method is used. The design of the rotor with the saturable area is shown and the principles of an encoder-based starting strategy for a fast start-up under 0.5 s are introduced. Finally, the build prototype and experimental results of the starting strategy are shown.
Noctilucent clouds (NLC) have been observed by a Rayleigh/Mie/Raman (RMR) lidar in Northern Norway (69N,16E) capable to measure the aerosol backscatter coefficients at three wavelengths (355
nm, 532
...nm, 1064
nm) and since 1998 also under sunlight conditions. For strong noctilucent cloud events the three backscatter coefficients are used to calculate the parameters of a monomodal particle distribution describing the observed optical properties. We deduce the radius of the particle size distribution, the width, and the average number density of the particle ensemble. To minimize the smearing by a changing structure of the noctilucent clouds we use the lowest possible time and altitude resolutions, which are 14 and 150
min, respectively. Using this, the vertical structure of the particle properties below and above the peak is investigated. From a statistical comparison of the observed ratios of backscatter coefficients we find that under the assumption of spherical particles the lognormal distribution describes the optical properties of NLC above ALOMAR better than the Gaussian distribution. If the optical analysis is extended to aspherical particles then both Gaussian and lognormal distribution can sufficiently describe the optical properties when the axis ratio of the particles is allowed to vary from 1/10 to 10. Using the traditional optical model but the new data inversion method on the summer 1998 NLC data leads to the same results found by von Cossart et al. von Cossart, G., Fiedler, J., von Zahn, U. Size distributions of NLC particles as determined from 3-colour observations of NLC by ground-based lidar, Geophys. Res. Lett., 26 (11), 1513–1516. doi: 10.1029/1999GL900226, 1999. Using the new optical model we find that independent of the assumed particle shape the average size of strong NLCs above ALOMAR in 2005 is 47
±
3
nm for spheroids or cylinders with Gaussian distribution while it is 54
±
3
nm for the same particles but assuming a lognormal size distribution. The distribution widths are
s
=
16
±
1
nm or
σ
=
1.25
±
0.03 for Gaussian or lognormal distribution while the particle number-density is
N
=
120
cm
−3 for both cases. This comparison shows that the combination of three widely separated wavelengths used in backscatter geometry allows a robust measurement of the particle size. We recommend performing the sensitivity test of the deduced particle properties on the particle shape also for other optical instruments sounding the NLC particle sizes.
Noctilucent clouds (NLCs) occur during summer from midlatitudes to high latitudes. They consist of
nanometer-sized ice particles in an altitude range from 80 to 90 km and are
sensitive to ambient ...temperature and water vapor content, which makes them a
suitable tracer for variability on all timescales. The data set acquired by
the ALOMAR Rayleigh–Mie–Raman (RMR) lidar covers 21 years and is
investigated regarding tidal signatures in NLCs. For the first time solar and
lunar tidal parameters in NLCs were determined simultaneously from the same
data. Several NLC parameters are subject to persistent mean variations
throughout the solar day as well as the lunar day. Variations with lunar time
are generally smaller compared to variations with solar time. NLC occurrence
frequency shows the most robust imprint of the lunar semidiurnal tide. Its
amplitude is about 50 % of the solar semidiurnal tide, which is
surprisingly large. Phase progressions of NLC occurrence frequency indicate
upward propagating solar tides. Below 84 km altitude the corresponding
vertical wavelengths are between 20 and 30 km. For the lunar semidiurnal
tide phase progressions vary symmetrically with respect to the maximum of the
NLC layer.
Noctilucent clouds (NLC) are mesospheric ice clouds occurring in the summer hemisphere at high latitudes and an altitude of about 83km. This region is the coldest of the earth’s atmosphere and is ...characterized by the presence of wave interaction and dissipation. The processes involved here lead to a variety of structures and instabilities that become visible in noctilucent clouds and are observed by different instruments. In this work high-resolution lidar measurements are used to give a wide overview of the structures at small scales below the Brunt–Väisälä period of ∼5min. For the first time a large amount of NLC profiles from lidar with a temporal resolution of 1s is analyzed in detail, covering about 1400h during the summer from 2011 to 2018. A new categorization focusing on small-scale structures is introduced, and occurrence statistics for these categories in the season of 2014 are performed. Both wave structures with periods below 10min and thin layers of <100m thickness are commonly found. When taking simultaneous wind measurements into account, we find that structures often are advected by the wind.
•Novel lidar measurements of noctilucent clouds (NLC) with 1s and 25m resolution.•First time observation of very thin NLC layers with thickness < 100m.•NLC are highly dynamic on small scales and often multi-layered.•We introduce a new categorization of NLC based on small-scale structures.•NLC structures are often advected by the wind.
Noctilucent clouds (NLC) are measured by the Rayleigh/Mie/Raman-lidar at the ALOMAR research facility in Northern Norway (69°N, 16°E) since 1994. The data set contains about 2860h of NLC detections ...and is investigated for the first time regarding trends. NLC properties depend on cloud brightness which is taken into account by the use of several cloud classes, related to brightness ranges. For NLC brighter than the long-term detection limit and strong NLC, respectively, the trend terms show increasing occurrence frequency (+9%/dec and+5%/dec) and brightness (+1.7×10−10 m−1 sr−1/dec and +1.5×−10 m−1 sr−1/dec) from 1998 to 2015. In the same period the altitude of faint and long-term limit clouds decreases (−66m/dec and −108m/dec). Over the entire time period of 22 years strong clouds show an increasing altitude by +76m/dec. NLC properties are affected differently by solar and atmospheric parameters. In general, Lyman-α and stratospheric ozone impact all three NLC parameters, temperature at 83km impacts mainly the NLC altitude. Time series of RMR lidar and SBUV satellite instruments match best for NLC occurrence frequency and brightness when restricting SBUV to the morning data at longitudes around ALOMAR (64–74°N, 8–24°E/0–9LT). This suggests longitudinal dependent trends, which is confirmed by trend investigations of longitudinal subsets of the SBUV data set.
•First trend investigation of the 22 years NLC data set at ALOMAR.•NLC occur more often and are getting brighter since 1998.•Altitudes of strong clouds increase by only few meters per year since 1994.•NLC trends might depend on longitude.
This paper describes the technical specifications of the extensions made to the middle-atmospheric lidar facility at the Leibniz Institute of Atmospheric Physics in Kühlungsborn, Germany (54.12° N, ...11.77° E). The upgrade complements the existing daylight-capable Rayleigh–Mie–Raman (RMR) temperature lidar with a nighttime-only RMR wind–temperature lidar. The new system comprises an independent lidar with laser, telescopes, and detectors, which is synchronized with and adapted to the (old) temperature lidar. As a result, with the combination of RMR lidars the atmosphere is probed with three (vertical and tilted) beams. This work intends to highlight the recent innovations in the construction of a Doppler–Rayleigh lidar system using the single-edge iodine-cell technique, which allows for the simultaneous measurement of wind, temperature, and aerosols. We will detail supporting subsystems that allow for a high degree of lidar automation and concisely provide key technical information about the system that will support readers in the development of additional RMR wind–temperature lidar systems. We show an example of time-resolved temperature and wind soundings reaching up to ∼ 90 km. These data agree well with ECMWF-IFS profiles between 35 and ∼ 50 km but show a much larger variability above. In the companion article, we will present the algorithm design and uncertainty budgets associated with the data processing chain.
In this paper we present a new description of statistical probability density functions
(pdfs) of polar mesospheric clouds (PMCs). The analysis is based on observations of
maximum backscatter, ice ...mass density, ice particle radius, and number density of ice
particles measured by the ALOMAR Rayleigh–Mie–Raman lidar for all PMC seasons from 2002
to 2016. From this data set we derive a new class of pdfs that describe the statistics of
PMC events that is different from previous statistical methods using the approach of an
exponential distribution commonly named the g distribution. The new analysis describes
successfully the probability distributions of ALOMAR lidar data. It turns out that the
former g-function description is a special case of our new approach. In general the new statistical function can be
applied to many kinds of different PMC parameters, e.g., maximum backscatter, integrated
backscatter, ice mass density, ice water content, ice particle radius, ice particle
number density, or albedo measured by satellites. As a main advantage the new method
allows us to connect different observational PMC distributions of lidar and satellite
data, and also to compare with distributions from ice model studies. In particular, the
statistical distributions of different ice parameters can be compared with each other on
the basis of a common assessment that facilitates, for example, trend analysis of PMC.
PDF
