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.

scholarly journals Long-term Measurements of Nighttime LF Radio Wave Reflection Heights over Central Europe

2005 ◽  
Vol 3 ◽  
pp. 427-430
Author(s):  
C. Jacobi ◽  
D. Kürschner
Keyword(s):  
Middle Atmosphere ◽  
Low Frequency ◽  
Radio Waves ◽  
Quasi Biennial Oscillation ◽  
Reflection Height ◽  
Stratospheric Wind ◽  
E Region ◽  
Long Term Trends ◽  
Cooling Trend

Abstract. The nighttime ionospheric absolute reflection height of low-frequency (LF) radio waves at oblique incidence has been measured continuously since late 1982 using 1.8kHz sideband phase comparisons between the sky wave and the ground wave of a commercial 177kHz LF transmitter. The dataset allows the analysis of long-term trends and other regular variations of the reflection height. Beside the clear signal of the 11-year solar cycle a quasi-biennial oscillation is visible in LF reflection heights, which is correlated to the equatorial stratospheric wind field. A long-term decreasing reflection height trend is found, confirming results from other measurements and theoretical estimations. The results can be interpreted as a long-term decrease of the height levels of fixed electron density in the lower E region, reflecting a long-term cooling trend of the middle atmosphere.

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 Estimation of ionospheric reflection height using long wave propagation

2019 ◽  
Vol 17 ◽  
pp. 205-212
Author(s):  
Dieter Keuer
Keyword(s):  
Low Frequency ◽  
Measuring Method ◽  
Radio Waves ◽  
Reflection Point ◽  
Sph Method ◽  
Long Wave ◽  
Reflection Height ◽  
Daily Series ◽  
Method Show

Abstract. Phase height measurements of low frequency radio waves are used to study the long-term variability of the mesosphere over Europe. Phase height measurements use a characteristic pattern in field strength registration of radio waves interpreted as phase relations between sky wave and surface wave to obtain the apparent height of the reflection point, the Standard Phase Height (SPH). Based on this SPH-method a homogenized daily series was generated since 1959 at Kühlungsborn. Improvements of the measuring method show that the signal is significantly influenced by lower atmospheric layers. Mesospheric reflection is not the exclusive source of the measured behavior. Tropospheric influence can not be neglected. Taking this into account one has to conclude that the strong coherency of the SPH data to mesospheric heights is not as significant as previously assumed.

scholarly journals Trends in MLT region winds and planetary waves, Collm (52° N, 15° E)

2008 ◽  
Vol 26 (5) ◽  
pp. 1221-1232 ◽  
Author(s):  
Ch. Jacobi ◽  
P. Hoffmann ◽  
D. Kürschner
Keyword(s):  
Time Lag ◽  
Lower Thermosphere ◽  
Solar Flux ◽  
Time Interval ◽  
Period Range ◽  
Before And After ◽  
Wind Measurements ◽  
Long Term Trends ◽  
Climatic Transition

Abstract. Long-period oscillations in the period range 2–30 days, interpreted as planetary wave (PW) signatures, have been analysed using daily mesosphere/lower thermosphere wind measurements near 90 km over Collm (52° N, 15° E) in the time interval 1980–2005. Interannual and interdecadal variability of PW are found. Since the 1990s, a tendency for larger zonal amplitudes compared to meridional ones has been observed, i.e. some long-term trends are visible, which are positive in the zonal component, but negative in the meridional component. There is a tendency of the trend to be non-linear for waves with periods lower than 7 days, so that a climatic transition appears around 1990, with smaller changes before and after that time. A solar cycle effect on PW is weak, but there is a tendency for a positive correlation between solar flux and wave activity, if a time lag of PW activity with respect to the solar flux of about 2 years is taken into consideration.

scholarly journals Survey of electron density changes in the daytime ionosphere over the Arecibo observatory due to lightning and solar flares

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Caitano L. da Silva ◽  
Sophia D. Salazar ◽  
Christiano G. M. Brum ◽  
Pedrina Terra
Keyword(s):  
Electron Density ◽  
Solar Flares ◽  
Low Frequency ◽  
Lower Ionosphere ◽  
Weather Conditions ◽  
Optical Observations ◽  
Radio Waves ◽  
D Region ◽  
E Region ◽  
Arecibo Observatory

AbstractOptical observations of transient luminous events and remote-sensing of the lower ionosphere with low-frequency radio waves have demonstrated that thunderstorms and lightning can have substantial impacts in the nighttime ionospheric D region. However, it remains a challenge to quantify such effects in the daytime lower ionosphere. The wealth of electron density data acquired over the years by the Arecibo Observatory incoherent scatter radar (ISR) with high vertical spatial resolution (300-m in the present study), combined with its tropical location in a region of high lightning activity, indicate a potentially transformative pathway to address this issue. Through a systematic survey, we show that daytime sudden electron density changes registered by Arecibo’s ISR during thunderstorm times are on average different than the ones happening during fair weather conditions (driven by other external factors). These changes typically correspond to electron density depletions in the D and E region. The survey also shows that these disturbances are different than the ones associated with solar flares, which tend to have longer duration and most often correspond to an increase in the local electron density content.

scholarly journals Repeat station data compared to a global geomagnetic field model

2013 ◽  
Vol 55 (6) ◽  
Author(s):  
Monika Korte ◽  
Vincent Lesur
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Global Model ◽  
Time Interval ◽  
Night Time ◽  
Core Field ◽  
Repeat Station ◽  
Station Data ◽  
Long Term Trends

<p>Geomagnetic repeat station surveys with local variometers for improved data reductions have been carried out in Germany for about ten years. For nearly the same time interval the satellites Ørsted and CHAMP have provided a good magnetic field data coverage of the whole globe. Recent global field models based on these satellite data together with geomagnetic observatory data provide an improved description of the core field and secular variation. We use the latest version of the GFZ Reference Internal Magnetic Model to compare the magnetic field evolution predicted by that model between 2001 and 2010 to the independent repeat station data collected over the same time interval in Germany. Estimates of crustal bias at the repeat station locations are obtained as averages of the residuals, and the scatter or trend around each average provides information about influences in the data from field sources not (fully) described by the global model. We find that external magnetic field signal in the order of several nT, including long-term trends, remains both in processed annual mean and quiet night time repeat station data. We conclude that the geomagnetic core field secular variation in this area is described to high accuracy (better than 1 nT/yr) by the global model. Weak long-term trends in the residuals between repeat station data and the model might indicate induced lithospheric anomalies, but more data are necessary for a robust analysis of such signals characterized by very unfavorable signal-to-noise ratio.</p>

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.

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