Climatological Variations in the Upper Atmosphere and Ionosphere II
Presiding: R A Akmaev, University of Colorado; G M Keating, George Washington University
SA52A-01 10:30h
Long-Term Trends in foF2: A Comparison of Various Methods
Results of various authors on long-term trends in foF2, i.e. in the maximum electron density in the ionosphere, and their interpretation do not reveal a consistent pattern. Therefore a joint analysis of one carefully selected data set was performed by five teams, which used different approaches to trend determination. High-quality data of station Juliusruh (54.6N, 13.4E) for noon (average from 10-14 UT) with a small number of gaps were used. The data covered the period of two solar cycles from minimum to minimum (1976-1996). Data gaps were filled in by interpolation using Juliusruh measurements at other times and measurements of neighbor stations. Juliusruh is relatively sensitive to geomagnetic activity as an almost subauroral station, which might play some role in interpretation of trend results. Various methods provide results, which differ to some extent. Even when one co-author applies various modifications of his method,the results differ. Another source of differences are various ways of removal (or at least large suppression) of effects of solar (and geomagnetic) activity. Also interpretation is not unique - co-authors consider either the long-term change in geomagnetic activity, or greenhouse effect to be predominantly responsible for trends. Nevertheless, there is some output from the joint analysis. All trends are either negative or insignificant. Data corrections with sunspot number (R), F10.7 adjusted to the Sun-Earth distance, and observed F10.7 result in somewhat different trends; the observed F10.7 appears to be the best correcting factor. The Juliusruh dip angle increased over the period 1976-1996 from 68.6 to 68.8 deg, but the possible impact of that increase is negligibly small and it would make the trend more positive. The paper will present results in more detail.
SA52A-02 INVITED 10:45h
Trends in Ionospheric Data: Techniques and Results
Increases in greenhouse gases are expected to affect the entire atmosphere including the ionosphere. Long-term, hiqh quality data from the ionosonde network are examined to determine if trends are detectable. Techniques used to screen the data for problems will be briefly reviewed. The statistical techniques employed to look for trends were developed to take into account the non-linear nature of ionospheric response to solar forcings. These techniques will be summarized. Trend results from at least four international locations show that the trends vary by season, time of day and location. These results will be presented and the largest sources of uncertainties will be outlined.
SA52A-03 11:00h
Ionospheric climatology and model from long-term databases of worldwide incoherent scatter radars
Long-term databases of worldwide incoherent scatter radars are utilized to study ionospheric climatology and create empirical models for electron density, ion and electron temperatures, and ion drifts. These radars, including, from magnetic north to south and east to west, EISCAT Svalbard Radar (Norway), Soundrestrom Radar (Greenland), EISCAT Tromso Radars (Norway), Millstone Hill Radar (USA), St. Santin Radar (France), Shigaraki Middle and Upper atmosphere (MU) Radar (Japan) and Arecibo Radar (Puerto Rico), are able to characterize diurnal, seasonal, and solar cycle variations of height dependent ionospheric strctures in a broad latitude and longitude area. In these huge databases, available through the MADRIGAL system (http://www.openmadrigal.org), the data cover generally 1-2 solar cycles, and for Millstone Hill and Arecibo they span nearly 3 solar cycles. Based on these data, our systematical analyses result in a comprehensive overview of various features of the ionosphere and series of web-based empirical models (http://www.haystack.mit.edu/madrigal/Models/). This presentation will review local models for each site and discuss the ionospheric climatology, with emphasis on the development of annual/semiannual electron density variations with latitudes and longitudes, and on ionospheric thermal status at midlatitudes. This presentation will also explore the long-term trend of ionospheric electron density and ion temperature variations from Millstone Hill observations.
http://www.haystack.mit.edu/madrigal/Models/
SA52A-04 11:15h
The climatology of the quiet nighttime low-latitude ionosphere
Long term measurement datasets have recently become available from several satellite missions. The TOPEX satellite obtains the total electron content (TEC) from ~1200 km orbit and the DMSP satellites measure the in-situ ion densities at ~800 km, while the GUVI instrument onboard the TIMED satellite retrieves the electron density profile below ~550 km altitude. TOPEX and TIMED are slowly precessing satellites that are able to obtain complete local time observations approximately every two months. The DMSP satellites are sun-synchronous and sample the ionosphere at least 4 discrete local times. This rich dataset allows us to examine a climatological picture of the nighttime low-latitude ionosphere. In this paper we describe the structure of the nighttime ionosphere as observed by three different sets of measurements, including the latitudinal separation of the equatorial arcs, the asymmetry of the peak densities as a function of longitude and local time. We also will compare these results with those from the IRI model. The observed climatology is essential for understanding low-latitude electrodynamics.
SA52A-05 11:30h
Ionospheric Storms Climatology, an Oxymoron?
The physical processes responsible of the ionospheric response during disturbed conditions are diverse, mixed and complex. They include the development of neutral composition bulges, rapid changes in equatorial electrodynamics, the substantial movement of the trough by high latitude processes. The complexity of these interactions makes it difficult to model the ionospheric response to perturbed conditions, but some level of success has been reached recently. We will explore the common repeatable features that appear from storm to storm, the so-called "storm climatology", that are clearly shown in the results of the empirical modeling of the ionospheric foF2 parameter. More recent results from the initial steps toward the empirical modeling of the Total Electron Content show similar features.
SA52A-06 11:45h
Insuring Data Quality in Long Term Observations of Geocoronal Hydrogen Emissions
Long term data sets are required to investigate sources of natural variability in the upper atmosphere. Understanding the influence of sources of natural variaibility such as the solar cycle is needed to characterize the thermosphere + exosphere, to understand coupling processes between atmospheric regions, and to isolate signatures of natural variability from those due to human caused change. Multi-year comparisons of thermospheric + exospheric H-alpha emissions require cross-calibrated and well-understood instrumentation, a stable calibration source, reproducible observing conditions, separation of the terrestrial from the galactic emission line, and consistent data analysis accounting for differences in viewing geometry. We discuss how we address these criteria in the acquisition and analysis of a midlatitude geocoronal H-alpha column emission data set now spanning two solar cycles and taken mainly from Wisconsin and Kitt Peak, Arizona. These data show a statistically significant variation over the solar cycle with higher intensities observed during solar maximum conditions. We also discuss results and outstanding challenges for increasing the accuracy and use of these observations.