scholarly journals Coupling of the Localized Wind Wall at High Latitudes to the Lower Thermosphere by Neutral Cells

2020 ◽  
Vol 8 (3) ◽  
pp. 27
Author(s):  
Vin Bhatnagar
Keyword(s):  
Lower Thermosphere ◽  
High Latitudes

scholarly journals Retrieval of sodium number density profiles in the mesosphere and lower thermosphere from SCIAMACHY limb emission measurements

2016 ◽  
Vol 9 (1) ◽  
pp. 295-311 ◽  
Author(s):  
M. P. Langowski ◽  
C. von Savigny ◽  
J. P. Burrows ◽  
V. V. Rozanov ◽  
T. Dunker ◽  
...  
Keyword(s):  
Seasonal Variations ◽  
Lower Thermosphere ◽  
High Latitudes ◽  
Full Width ◽  
Half Maximum ◽  
Number Density ◽  
Data Set ◽  
Density Profiles ◽  
Atom Concentration ◽  
Mesosphere And Lower Thermosphere

Abstract. An algorithm has been developed for the retrieval of sodium atom (Na) number density on a latitude and altitude grid from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) limb measurements of the Na resonance fluorescence. The results are obtained between 50 and 150 km altitude and the resulting global seasonal variations of Na are analyzed. The retrieval approach is adapted from that used for the retrieval of magnesium atom (Mg) and magnesium ion (Mg+) number density profiles recently reported by Langowski et al. (2014). Monthly mean values of Na are presented as a function of altitude and latitude. This data set was retrieved from the 4 years of spectroscopic limb data of the SCIAMACHY mesosphere and lower thermosphere (MLT) measurement mode (mid-2008 to early 2012). The Na layer has a nearly constant peak altitude of 90–93 km for all latitudes and seasons, and has a full width at half maximum of 5–15 km. Small but significant seasonal variations in Na are identified for latitudes less than 40°, where the maximum Na number densities are 3000–4000 atoms cm−3. At middle to high latitudes a clear seasonal variation with a winter maximum of up to 6000 atoms cm−3 is observed. The high latitudes, which are only measured in the summer hemisphere, have lower number densities, with peak densities being approximately 1000 Na atoms cm−3. The full width at half maximum of the peak varies strongly at high latitudes and is 5 km near the polar summer mesopause, while it exceeds 10 km at lower latitudes. In summer the Na atom concentration at high latitudes and at altitudes below 88 km is significantly smaller than that at middle latitudes. The results are compared with other observations and models and there is overall a good agreement with these.

Solar cycle modulation of nighttime ozone near the mesopause as observed by MLS

2020 ◽  
Author(s):  
Jae N. Lee ◽  
Dong L. Wu
Keyword(s):  
Carbon Monoxide ◽  
Solar Cycle ◽  
Solar Radiation ◽  
Lower Thermosphere ◽  
Boreal Winter ◽  
High Latitudes ◽  
Ozone Maximum ◽  
Solar Cycle 24 ◽  
Cycle 24 ◽  
Single Oxygen

<p>Solar 11-year cycle variations of nighttime ozone near the secondary ozone maximum layer are analyzed with Aura Microwave Limb Sounder (MLS) observations since 2004 that covers complete solar cycle 24. Produced primarily from the recombination of molecular oxygen (O<sub>2</sub>) with single oxygen (O) transported from the lower thermosphere, the mesospheric nighttime ozone concentration is proportional to single oxygen density [O], of which the latter is modulated by UV solar cycle variations. MLS nighttime ozone and Solar Radiation and Climate Experiment (SORCE) Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) measured UV show a positive correlation in-phase with the solar cycle. The nighttime ozone correlates strongly with temperature but not monotonously positive nor negative. The slope and sign of the correlation depend on location and season. They are positively correlated in general except for the boreal winter high latitudes.  Because the nighttime [O<sub>3</sub>] depends strongly on [O] in the upper mesosphere, it is expected the nighttime [O<sub>3</sub>] would follow the [O] distributions, producing similar diurnal, seasonal, and solar-cycle variations, as well as latitudinal distributions as observed in Carbon Monoxide (CO) in the upper mesosphere.</p>

Concentrations of H2O and NO in the mesosphere and the lower thermosphere at high latitudes

1985 ◽  
Vol 47 (1-3) ◽  
pp. 291-300 ◽  
Author(s):  
K.U. Grossmann ◽  
W.G. Frings ◽  
D. Offermann ◽  
L. André ◽  
E. Kopp ◽  
...  
Keyword(s):  
Lower Thermosphere ◽  
High Latitudes

scholarly journals Global investigation of the Mg atom and ion layers using SCIAMACHY/Envisat observations between 70 km and 150 km altitude and WACCM-Mg model results

2014 ◽  
Vol 14 (2) ◽  
pp. 1971-2019 ◽  
Author(s):  
M. Langowski ◽  
C. von Savigny ◽  
J. P. Burrows ◽  
W. Feng ◽  
J. M. C. Plane ◽  
...  
Keyword(s):  
Lower Thermosphere ◽  
Equatorial Region ◽  
High Latitudes ◽  
Polar Night ◽  
Density Maximum ◽  
Vertical Column ◽  
Latitudinal Dependence ◽  
Vertical Column Density ◽  
Summer Maximum ◽  
Similar Peak

Abstract. Mg and Mg+ concentration fields in the upper mesosphere/lower thermosphere (UMLT) region are retrieved from SCIAMACHY/Envisat limb measurements of Mg and Mg+ dayglow emissions using a 2-D tomographic retrieval approach. The time series of monthly means of Mg and Mg+ for number density as well as vertical column density in different latitudinal regions are shown. Data from the limb mesosphere-thermosphere mode of SCIAMACHY/Envisat are used, which covers the 50 km to 150 km altitude region with a vertical sampling of 3.3 km and a highest latitude of 82°. The high latitudes are not covered in the winter months, because there is no dayglow emission during polar night. The measurements were performed every 14 days from mid-2008 until April 2012. Mg profiles show a peak at around 90 km altitude with a density between 750 cm−3 and 2000 cm−3. Mg does not show strong seasonal variation at mid-latitudes. The Mg+ peak occurs 5–15 km above the neutral Mg peak at 95–105 km. Furthermore, the ions show a significant seasonal cycle with a summer maximum in both hemispheres at mid- and high-latitudes. The strongest seasonal variations of the ions are observed at mid-latitudes between 20–40° and densities at the peak altitude range from 500 cm−3 to 6000 cm−3. The peak altitude of the ions shows a latitudinal dependence with a maximum at mid-latitudes that is up to 10 km higher than the peak altitude at the equator. The SCIAMACHY measurements are compared to other measurements and WACCM model results. In contrast to the SCIAMACHY results, the WACCM results show a strong seasonal variability for Mg with a winter maximum, which is not observable by SCIAMACHY, and globally higher peak densities. Although the peak densities do not agree the vertical column densities agree, since SCIAMACHY results show a wider vertical profile. The agreement of SCIAMACHY and WACCM results is much better for Mg+, showing the same seasonality and similar peak densities. However, there are the following minor differences: there is no latitudinal dependence of the peak altitude for WACCM and the density maximum, passing the equatorial region during equinox conditions, is not reduced as for SCIAMACHY.

scholarly journals Long-term studies of MLT summer length definitions based on mean zonal wind features observed for more than one solar cycle at mid- and high-latitudes in the northern hemisphere

2021 ◽  
Author(s):  
Juliana Jaen ◽  
Toralf Renkwitz ◽  
Jorge L. Chau ◽  
Maosheng He ◽  
Peter Hoffmann ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Zonal Wind ◽  
Large Scale ◽  
Southern Oscillation ◽  
Lower Thermosphere ◽  
Polar Vortex ◽  
Mean Value ◽  
High Latitudes ◽  
The Mean

Abstract. Specular meteor radars (SMRs) and partial reflection radars (PRRs) have been observing mesospheric winds for more than a solar cycle over Germany (~54 °N) and northern Norway (~69 °N). This work investigates the mesospheric mean zonal wind and the zonal mean geostrophic zonal wind from the Microwave Limb Sounder (MLS) over these two regions between 2004 and 2020. Our study focuses on the summer when strong planetary waves are absent and the stratospheric and tropospheric conditions are relatively stable. We establish two definitions of the summer length according to the zonal wind reversals: (1) the mesosphere and lower thermosphere summer length (MLT-SL) using SMR and PRR winds, and (2) the mesosphere summer length (M-SL) using PRR and MLS. Under both definitions, the summer begins around April and ends around mid-September. The largest year to year variability is found in the summer beginning in both definitions, particularly at high-latitudes, possibly due to the influence of the polar vortex. At high-latitudes, the year 2004 has a longer summer length compared to the mean value for MLT-SL, as well as 2012 for both definitions. The M-SL exhibits an increasing trend over the years, while MLT-SL does not have a well-defined trend. We explore a possible influence of solar activity, as well as large-scale atmospheric influences (e.g. quasi-biennial oscillations (QBO), El Niño-southern oscillation (ENSO), major sudden stratospheric warming events). We complement our work with an extended time series of 31 years at mid-latitudes using only PRR winds. In this case, the summer length shows a breakpoint, suggesting a non-uniform trend, and periods similar to those known for ENSO and QBO.

scholarly journals Variability of the nighttime OH layer and mesospheric ozone at high latitudes during northern winter: influence of meteorology

2010 ◽  
Vol 10 (21) ◽  
pp. 10291-10303 ◽  
Author(s):  
A. Damiani ◽  
M. Storini ◽  
M. L. Santee ◽  
S. Wang
Keyword(s):  
Carbon Monoxide ◽  
Lower Thermosphere ◽  
Complete Disappearance ◽  
High Latitudes ◽  
Atmospheric Conditions ◽  
Short Term ◽  
Lower Altitude ◽  
Additional Tool ◽  
The Third ◽  
Short Term Variability

Abstract. Analyses of OH zonal means, recorded at boreal high latitudes by the Aura Microwave Limb Sounder (MLS) in winters of 2005–2009, have shown medium- (weeks) and short- (days) term variability of the nighttime OH layer. Because of the exceptional descent of air from the mesosphere-lower thermosphere (MLT) region, medium-term variability occurred during February 2006 and February/March 2009. The layer normally situated at about 82 km descended by about 5–7 km, and its density increased to more than twice January values. In these periods and location the abundance of the lowered OH layer is comparable to the OH values induced by Solar Energetic Particle (SEP) forcing (e.g., SEP events of January 2005) at the same altitudes. In both years, the descent of the OH layer was coupled with increased mesospheric temperatures, elevated carbon monoxide and an almost complete disappearance of ozone at the altitude of the descended layer (which was not observed in other years). Moreover, under these exceptional atmospheric conditions, the third ozone peak, normally at about 72 km, is shown to descend about 5 km to lower altitude and increase in magnitude, with maximum values recorded during February 2009. Short-term variability occurred during Sudden Stratospheric Warming (SSW) events, in particular in January 2006, February 2008 and January 2009, when dynamics led to a smaller abundance of the OH layer at its typical altitude. During these periods, there was an upward displacement of the OH layer coupled to changes in ozone and carbon monoxide. These perturbations were the strongest during the SSW of January 2009; coincident upper mesospheric temperatures were the lowest recorded over the late winters of 2005–2009. Finally, the series of SSW events that occurred in late January/February 2008 induced noticeable short-term variability in ozone at altitudes of both the ozone minimum and the third ozone peak. These phenomena, confined inside the polar vortex, are an additional tool that can be used to investigate mesospheric vortex dynamics.

scholarly journals MIPAS observations of longitudinal oscillations in the mesosphere and the lower thermosphere: Part 1. Climatology of odd-parity daily frequency modes

2016 ◽  
Author(s):  
Maya García-Comas ◽  
Francisco González-Galindo ◽  
Bernd Funke ◽  
Angela Gardini ◽  
Aythami Jurado-Navarro ◽  
...  
Keyword(s):  
Lower Thermosphere ◽  
Lower Boundary ◽  
Daily Basis ◽  
High Latitudes ◽  
Quasi Biennial Oscillation ◽  
Propagating Waves ◽  
Single Instrument ◽  
First Time ◽  
Biennial Oscillation ◽  
Mlt Region

Abstract. MIPAS global sun-synchronous observations are almost locked in local time. Subtraction of the descending and ascending node measurements at each longitude only contain the longitudinal oscillations with odd daily frequencies nodd from a solar perspective at 10 A.M. Contributions of the background atmosphere, persistent (on a daily basis) longitudinal oscillations and tidal modes with even daily frequencies vanish. We have determined MIPAS temperature longitudinal oscillations with nodd and wavenumber k = 0–4 from 20 to 150 km from April 2007 to March 2012. To our knowledge, this is the first time temperature zonal oscillations are derived in this altitude range globally from a single instrument. The major findings are the detection of: (1) migrating tides at Northern and Southern high latitudes; (2) significant k = 1 activity at extra-tropical and high-latitudes, particularly in the SH; (3) k = 3 and k = 4 eastward propagating waves that penetrate in the lower thermosphere with a significantly larger vertical wavelength than in the mesosphere; (4) a quasi-biennial oscillation of the migrating tide mainly originated in the stratosphere and propagated to the MLT. MIPAS global measurements of longitudinal oscillations are useful for testing tide modeling in the MLT region and as a lower boundary of models extending higher up in the atmosphere.

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