[1] The new NRLMSISE-00 empirical atmospheric model extends from the ground to the exobase and is a major upgrade of the MSISE-90 model in the thermosphere. The new model and the associated NRLMSIS database now include the following data: (1) total mass density from satellite accelerometers and from orbit determination (including the Jacchia and Barlier data sets), (2) temperature from incoherent scatter radar covering 1981-1997, and (3) molecular oxygen number density, [O 2 ], from solar ultraviolet occultation aboard the Solar Maximum Mission. A new component, ''anomalous oxygen,'' allows for appreciable O + and hot atomic oxygen contributions to the total mass density at high altitudes and applies primarily to drag estimation above 500 km. Extensive tables compare our entire database to the NRLMSISE-00, MSISE-90, and Jacchia-70 models for different altitude bands and levels of geomagnetic activity. We also explore scientific issues related to the new data sets in the NRLMSIS database. Especially noteworthy is the solar activity dependence of the Jacchia data, with which we study a large O + contribution to the total mass density under the combination of summer, low solar activity, high latitude, and high altitude. Under these conditions, except at very low solar activity, the Jacchia data and the Jacchia-70 model indeed show a significantly higher total mass density than does MSISE-90. However, under the corresponding winter conditions, the MSIS-class models represent a noticeable improvement relative to Jacchia-70 over a wide range of F 10.7 . Considering the two regimes together, NRLMSISE-00 achieves an improvement over both MSISE-90 and Jacchia-70 by incorporating advantages of each.
No abstract
Radiations of solar origin penetrating below 85 km in the terrestrial atmosphere are: (1) X rays of λ<10 A; (2) Lyman α; and (3) wavelengths greater than 1800 A. These radiations can ionize: (1) molecular nitrogen and oxygen; (2) nitric oxide; and (3) various atoms such as sodium and calcium. Molecular oxygen and nitrogen are also ionized by cosmic rays. The negative ion to electron ratio is important below 70 km and affects the electron distribution below that altitude. It is possible to explain normal conditions of ionization by cosmic rays and Lyman α. Conditions due to solar flares must be explained by X rays. Above 85 km, the behavior of the ionization is related to the formation of the E layer.
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 mean Mg and Mg + number density and vertical column density in different latitudinal regions are presented. Data from the limb mesosphere-thermosphere mode of SCIAMACHY/Envisat are used, which cover the 50 to 150 km altitude region with a vertical sampling of ≈ 3.3 km and latitudes up to 82• . The high latitudes are not observed 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 1500 cm −3 . Mg does not show strong seasonal variation at latitudes below 40 • . For higher latitudes the density is lower and only in the Northern Hemisphere a seasonal cycle with a summer minimum is observed. The Mg + peak occurs 5-15 km above the neutral Mg peak altitude. These ions have a significant seasonal cycle with a summer maximum in both hemispheres at mid and high latitudes. The strongest seasonal variations of Mg + are observed at latitudes between 20 and 40• and the density at the peak altitude ranges from 500 cm −3 to 4000 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. The WACCM results show a significant seasonal variability for Mg with a summer minimum, which is more clearly pronounced than for SCIAMACHY, and globally a higher peak density than the SCIAMACHY results. Although the peak density of both is not in agreement, the vertical column density agrees well, because SCIAMACHY and WACCM profiles have different widths. The agreement between SCIAMACHY and WACCM results is much better for Mg + with both showing the same seasonality and similar peak density. However, there are also minor differences, e.g. WACCM showing a nearly constant altitude of the Mg + layer's peak density for all latitudes and seasons.
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