Lidar observations of a lot of sporadic sodium layers in mid‐latitude

Abstract

We have routinely observed mesosphenc Na layers since November 1991 with a Na ground-based lidar above Tokyo Metropolitan University (TMU) at Hachioji, Tokyo (35.6øN, 139.4øE) in mid-latitude. In the past, the sporadic Na layers have been observed commonly at lowand high-latitude lidar sites [Kwon et al., 1988; Batista et al., 1989; yon Zahn et al., 1987] but rarely observed a.t mid-latitude sites [Senfi et al., 1989]. Contrary to expectations, we could observe more than 100 events of the sporadic Na layers for two years from November 1991 until October 1993 in this mid-latitude lidar site, and the large sporadic Na layers had been observed especially during spring and summer. Most of these events were accompanied by sporadic E layers and the most enhancement of the sporadic E layers preceded that of the sporadic Na layers by 15 to 30 minutes. 98, 16,865-16,873, 1993. Hansen, G. and U. von Zahn, Sudden sodium layers in polar latitude, if. Atmos. Terr. Phys., 52, 585-608, 1990. Kane, T. J. and C. S. Gardner, Structure and seasonal variability of the nighttime mesospheric Fe layer at midlatitudes, J. Geophys. Res., 98, 16,875-16,886, 1993a. observations of large sporadic sodium layers, Geophys. Res. Lett., 16, 715-718, 1989. Smith, E. K., Temperature zone sporadic E maps (foEs>7MHz), Radio Sci. , 13, 571, 1978. yon Zahn, U. and T. L. Hansen, Sudden neutral sodium layers: A strong link to sporadic E layers, J. Atmos. Terr. Phys., 50, 93-104, 1988. von Zahn, U., P. von der Gathen, and G. Hansen, Forced release of sodium from upper atmospheric dust particles, Geophys.

Sporadic Ca and Ca<sup>+</sup> layers at mid-latitudes: Simultaneous observations and implications for their formation

“…11 (upper panel). The data from Nagasawa and Abo (1995) show a strong positive correlation between seasonal variations of Na s and E s . We compare their results with ours obtained at Juliusruh, Germany (54 • N, 13 • E) (Fig.…”

“…11. Seasonal variation of sporadic metal and electron layers: Na s and E s as observed above Tokyo (Nagasawa and Abo, 1995) (upper panel), Ca s and E s as observed above Kühlungsborn and Juliusruh, respectively (lower panel). The occurrence of strong sporadic Ca + s with number densities higher than 300 cm −3 is shown for comparison (lower panel).…”

“…So both Batista et al (1989) and Hansen and von Zahn (1990) reported on only weak seasonal variation of sporadic Na layer occurrence. Nagasawa and Abo (1995) gave the occurrence a total of 37 Na s above Tokyo, Japan (36 • N, 140 • E) on a monthly basis and compared this with the seasonal variation in occurrence of local sporadic E layers. Their observations are shown in Fig.…”

Lidar Observations of Sporadic Fe and Na Layers in the Mesopause Region over Equator

“…Usually, Nas has a thin layer with a width of 1-2 km, lasting for a few tens of minutes to several hours, and the ratio of peak Na density to the normal density is usually from three to five, occasionally, as large as ten (Nagasawa and Abo 1995). The appearance of such a sudden thin layer is also reported also in other metallic atoms, such as Fe and K (Bills R.E.…”

“…In the Southern hemisphere, longterm observations of the Na layer for over 15 years were made by Clemesha et al (1992). On the other hand, in the Northern mid-latitude, Nagasawa and Abo (1995) also have made long-term observations of the Na layer for over 10 years. Moreover, in addition to sodium, observations of the metallic species such as iron, potassium, lithium, calcium in atomic and ionic form (Fe, K, Li, Ca, Ca þ ) were successfully observed.…”