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.

scholarly journals Low-frequency lower E-region wind and reflection height measurements as sensor for climate variability

2008 ◽  
Vol 6 ◽  
pp. 331-335 ◽  
Author(s):  
C. Jacobi
Keyword(s):  
Oblique Incidence ◽  
Lower Thermosphere ◽  
Low Frequency ◽  
Time Interval ◽  
Radio Waves ◽  
Reflection Height ◽  
E Region ◽  
Long Term Trends ◽  
Mlt Region

Abstract. Measurements of reflection heights of low-frequency (LF) radio waves at oblique incidence and estimates of mesosphere/lower thermosphere (MLT) region horizontal winds applying the D1 spaced receiver method on LF field strength registrations are analyzed with respect to possible long-term trends and interdecadal variability in the time interval from ~1980 to date. While no clear signal of mesospheric height trend is registered during the last two decades, significant trends of MLT horizontal winds are found. These trends are non-linear, in particular a change of trends around 1990 is found, which is probably connected with changes in tropospheric and stratospheric conditions at that time.

Solar cycle dependence and long-term trends in the wind field of the mesosphere/lower thermosphere

1997 ◽  
Vol 59 (5) ◽  
pp. 497-509 ◽  
Author(s):  
J. Bremer ◽  
R. Schminder ◽  
K.M. Greisiger ◽  
P. Hoffmann ◽  
D. Kürschner ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Wind Field ◽  
Lower Thermosphere ◽  
Long Term Trends ◽  
Cycle Dependence

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 Long-term lidar observations of the gravity wave activity near the mesopause at Arecibo

2019 ◽  
Vol 19 (5) ◽  
pp. 3207-3221
Author(s):  
Xianchang Yue ◽  
Jonathan S. Friedman ◽  
Qihou Zhou ◽  
Xiongbin Wu ◽  
Jens Lautenbach
Keyword(s):  
Gravity Wave ◽  
Lower Thermosphere ◽  
Strong Support ◽  
Temporal Correlation ◽  
Temperature Inversion ◽  
Dynamical Instability ◽  
Temperature Structure ◽  
Mesopause Region ◽  
Mean Temperature ◽  
Lidar Observations

Abstract. Using 11-year-long K Doppler lidar observations of temperature profiles in the mesosphere and lower thermosphere (MLT) between 85 and 100 km, conducted at the Arecibo Observatory, Puerto Rico (18.35∘ N, 66.75∘ W), seasonal variations of mean temperature, the squared Brunt–Väisälä frequency, N2, and the gravity wave potential energy (GWPE) are estimated in a composite year. The following unique features are obtained. (1) The mean temperature structure shows similar characteristics to an earlier report based on a smaller dataset. (2) Temperature inversion layers (TILs) occur at 94–96 km in spring, at ∼92 km in summer, and at ∼91 km in early autumn. (3) The first complete range-resolved climatology of GWPE derived from temperature data in the tropical MLT exhibits an altitude-dependent combination of annual oscillation (AO) and semiannual oscillation (SAO). The maximum occurs in spring and the minimum in summer, and a second maximum is in autumn and a second minimum in winter. (4) The GWPE per unit volume reduces below ∼97 km altitude in all seasons. The reduction of GWPE is significant at and below the TILs but becomes faint above; this provides strong support for the mechanism that the formation of upper mesospheric TILs is mainly due to the reduction of GWPE. The climatology of GWPE shows an indeed pronounced altitudinal and temporal correlation with the wind field in the tropical mesopause region published in the literature. This suggests the GW activity in the tropical mesopause region should be manifested mainly by the filtering effect of the critical level of the local background wind and the energy conversion due to local dynamical instability.

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