scholarly journals Long-term variability of mean winds in the mesosphere and lower thermosphere at low latitudes

2012 ◽  
Vol 117 (A10) ◽  
pp. n/a-n/a ◽  
Author(s):  
N. Venkateswara Rao ◽  
T. Tsuda ◽  
D. M. Riggin ◽  
S. Gurubaran ◽  
I. M. Reid ◽  
...  
Keyword(s):  
Lower Thermosphere ◽  
Low Latitudes ◽  
Mesosphere And Lower Thermosphere

scholarly journals Climatologies and long-term changes in mesospheric wind and wave measurements based on radar observations at high and mid latitudes

2019 ◽  
Vol 37 (5) ◽  
pp. 851-875 ◽  
Author(s):  
Sven Wilhelm ◽  
Gunter Stober ◽  
Peter Brown
Keyword(s):  
Kinetic Energy ◽  
Gravity Waves ◽  
Lower Thermosphere ◽  
Atmospheric Parameters ◽  
Amplitude Response ◽  
Wave Measurements ◽  
Long Term Changes ◽  
The Mean ◽  
Mesosphere And Lower Thermosphere

Abstract. We report on long-term observations of atmospheric parameters in the mesosphere and lower thermosphere (MLT) made over the last 2 decades. Within this study, we show, based on meteor wind measurement, the long-term variability of winds, tides, and kinetic energy of planetary and gravity waves. These measurements were done between the years 2002 and 2018 for the high-latitude location of Andenes (69.3∘ N, 16∘ E) and the mid-latitude locations of Juliusruh (54.6∘ N, 13.4∘ E) and Tavistock (43.3∘ N, 80.8∘ W). While the climatologies for each location show a similar pattern, the locations differ strongly with respect to the altitude and season of several parameters. Our results show annual wind tendencies for Andenes which are toward the south and to the west, with changes of up to 3 m s−1 per decade, while the mid-latitude locations show smaller opposite tendencies to negligible changes. The diurnal tides show nearly no significant long-term changes, while changes for the semidiurnal tides differ regarding altitude. Andenes shows only during winter a tidal weakening above 90 km, while for the Canadian Meteor Orbit Radar (CMOR) an enhancement of the semidiurnal tides during the winter and a weakening during fall occur. Furthermore, the kinetic energy for planetary waves showed strong peak values during winters which also featured the occurrence of sudden stratospheric warming. The influence of the 11-year solar cycle on the winds and tides is presented. The amplitudes of the mean winds exhibit a significant amplitude response for the zonal component below 82 km during summer and from November to December between 84 and 95 km at Andenes and CMOR. The semidiurnal tides (SDTs) show a clear 11-year response at all locations, from October to November.

scholarly journals Global change induced trends in ion composition of the troposphere to the lower thermosphere

2008 ◽  
Vol 26 (5) ◽  
pp. 1181-1187 ◽  
Author(s):  
G. Beig
Keyword(s):  
Middle Atmosphere ◽  
Anthropogenic Activities ◽  
Lower Thermosphere ◽  
Cluster Ions ◽  
Atmospheric Density ◽  
Mesosphere And Lower Thermosphere ◽  
Induced Changes ◽  
Positive Ion ◽  
Mlt Region

Abstract. In this paper a brief overview of the changes in atmospheric ion compositions driven by the human-induced changes in related neutral species, and temperature from the troposphere to lower thermosphere has been made. It is found that ionic compositions undergo significant variations. The variations calculated for the double-CO2 scenario are both long-term and permanent in nature. Major neutrals which take part in the lower and middle atmospheric ion chemical schemes and undergo significant changes due to anthropogenic activities are: O, O2, H2O, NO, acetonitrile, pyridinated compounds, acetone and aerosol. The concentration of positive ion/electron density does not change appreciably in the middle atmosphere but indicates a marginal decrease above about 75 km until about 85 km, above which the magnitude of negative trend decreases and becomes negligible at 93 km. Acetonitrile cluster ions in the upper stratosphere are likely to increase, whereas NO+ and NO+(H2O) in the mesosphere and lower thermosphere (MLT) region are expected to decrease for the double CO2 scenario. It is also found that the atmospheric density of pyridinated cluster ions is fast rising in the troposphere.

scholarly journals Ozone and temperature decadal responses to solar variability in the mesosphere and lower thermosphere, based on measurements from SABER on TIMED

2016 ◽  
Vol 34 (1) ◽  
pp. 29-40 ◽  
Author(s):  
F. T. Huang ◽  
H. G. Mayr ◽  
J. M. Russell III ◽  
M. G. Mlynczak
Keyword(s):  
Solar Cycle ◽  
Multiple Regression ◽  
Solar Maximum ◽  
Lower Thermosphere ◽  
Correlation Coefficients ◽  
Solar Variability ◽  
Broadband Emission ◽  
Low Latitudes ◽  
Mesosphere And Lower Thermosphere ◽  
Temperature Responses

Abstract. We have derived ozone and temperature responses to solar variability over a solar cycle, from June 2002 through June 2014, 50 to 100 km, 48° S to 48° N, based on data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite. Results with this extent of coverage in the mesosphere and lower thermosphere have not been available previously. A multiple regression is applied to obtain responses as a function of the solar 10.7 cm flux (solar flux units, sfu). Positive responses mean that they are larger at solar maximum than at solar minimum of the solar cycle. From  ∼  80 to 100 km, both ozone and temperature responses are positive for all latitudes and are larger than those at lower altitudes. From  ∼  80 to 100 km, ozone responses can exceed 10 % (100 sfu)−1, and temperature responses can approach 4 °K. From 50 to  ∼  80 km, the ozone responses at low latitudes ( ∼  ±35°) are mostly negative and can approach  ∼  negative 3 % (100 sfu)−1. However, they are mostly positive at midlatitudes in this region and can approach  ∼  2 % (100 sfu)−1. In contrast to ozone, from  ∼  50 to 80 km, the temperature responses at low latitudes remain positive, with values up to  ∼  2.5 K (100 sfu)−1, but are weakly negative at midlatitudes. Consequently, there is a systematic and robust relation between the phases of the ozone and temperature responses. They are positively correlated (in phase) from  ∼  80 to 100 km for all latitudes and negatively correlated (out of phase) from  ∼  50 to 80 km, also for all latitudes. The negative correlation from 50 to 80 km is maintained even though the ozone and temperature responses can change signs as a function of altitude and latitude, because the corresponding temperature responses change signs in step with ozone. This is consistent with the idea that dynamics have the larger influence between  ∼  80 and 100 km, while photochemistry is more in control from  ∼  50 to 75 km. The correlation coefficients between the solar 10.7 cm flux and the ozone and temperature themselves from 2012 to 2014 are positive (negative) in regions where the responses are positive (negative). This supports our results since the correlations are independent of the multiple regression used to derive the responses. We also compare with previous results.

scholarly journals A review of recent MLT studies at low latitudes

2004 ◽  
Vol 22 (9) ◽  
pp. 3261-3275 ◽  
Author(s):  
B. R. Clemesha
Keyword(s):  
Lower Thermosphere ◽  
Temperature Structure ◽  
Mesopause Region ◽  
The Pacific ◽  
Low Latitudes ◽  
Long Term Trends ◽  
The Caribbean ◽  
Temperature Inversions ◽  
Mlt Region

Abstract. Recent years have shown a continuing interest in studies of the mesosphere-lower thermosphere region at low latitudes, with more than 50 papers dealing specifically with this area published over the past 5 years. Experimental ground-based work has been carried out mainly in South America and the Caribbean, India and the Pacific areas. Subjects of interest include gravity waves, tides and planetary waves, the temperature structure of the mesopause region, with special reference to temperature inversions and the two-level mesopause, sporadic neutral layers and their relationship with ionized layers, the possible effects of the micrometeoroid influx, and long-term trends in the MLT region. Experimental techniques in use include MF, MST and meteor radar, lidar, airglow (including satellite-borne limb-scanning measurements) and rocket-borne instruments. Airglow imaging has shown itself to be a particularly useful technique, mainly for studying gravity wave propagation in the MLT region. This paper will present highlights of recent work and will discuss some of the problems which remain to be resolved.

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