Characteristics of the sporadic Na layers observed during the Airborne Lidar and Observations of Hawaiian Airglow/Airborne Noctilucent Cloud (ALOHA/ANLC‐93) campaigns

Abstract

Abstract. We summarize the characteristics of the 43 sporadic Na (Na0 layers observed by the airborne Na density and the Haleakala Na wind/temperature lidars during the Airborne Lidar and Observations of Hawaiian Airglow/Airborne Noctilucent Cloud (ALOHA/ANLC-93) campaigns. Na• layers are clearly not a local phenomenon since the horizontal extents varied from approximately 25 to almost 1600 km with a mean of 440 km. For the majority of the Na• layers observed above Haleakala, the temperatures were significantly warmer than the mean. The average enhancement was 12.9øK or about 6%. The temperature variations typically led the Na• density variations in time and on average reached their maximum values approximately 0.7 km below and 23 min before the Na• maxima. However, the maximum temperatures and Na• densities were only weakly correlated. Strong vertical shears in the horizontal winds were observed during the majority of the Na• events. The average maximum total shear was approximately equal to the shear instability limit of 42 rn s -• km -•. The maximum shears were located on average about 0.5 km below the Na• layer. In most cases the meridional shears were significantly stronger than the zonal shears. The maximum total shears were generally directed to the N-NE and to the south. The strong temperature and wind perturbations observed during the majority of the events suggest that gravity waves play an important role in Na• formation, although the exact nature of that role remains unclear.

A statistical study of sporadic sodium layer observed by Sodium lidar at Hefei (31.8° N, 117.3° E)

“…An airborne lidar (ALOHA90) has also been used to show that an SSL in the Pacific equatorial region extended for more than 1800 km (Kane et al, 1991). Another airborne observation (ALOHA/ANLC-93) showed that the horizontal extents varied from approximately 25 to almost 1600 km with a mean of 440 km (Qian et al, 1998). Recently, satelliteborne measurements illustrated that most SSLs were much more prevalent in the Southern Hemisphere, with a horizontal extent of less than 300 km (Fan et al, 2007).…”

“…More extensive studies on SSLs by lidars were conducted after the observation by Von Zahn and Hansen (1988) (e.g. Kwon et al, 1988;Batista et al, 1989;Senft et al, 1989;Kane et al, 1991;Gardner et al, 1993;Clemesha, 1995;Clemesha et al, 1998;Qian et al, 1998;Gong et al, 2002;Clemesha et al, 2004;Williams et al, 2006Williams et al, , 2007Fan et al, 2007;Nesse et al, 2008;Vishnu Prasanth et al, 2007;Yi et al, 2007;Heinrich et al, 2008). Sporadic sodium layers have been studied for more than 20 years.…”

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

“…Still, a strong link between the neutral and the ionized sporadic metal layers is generally assumed (e.g. Alpers et al, 1993;Qian et al, 1998). For the case of Ca atoms and Ca + ions, this link can be studied time-resolved by ground-based lidar observations.…”

A case study on generation mechanisms of a sporadic sodium layer above Tromsø (69.6° N) during a night of high auroral activity

“…Clemesha et al (1999) mentioned that the median value was about 420 km as a typical horizontal dimension at São Jose dos Campos. SSLs that extended farther than 1000 km were also observed by an airborne lidar (e.g., Kane et al, 1991;Gu et al, 1995;Qian et al, 1998). SSLs have concentrations about 2-10 times higher than that of the background normal sodium layer (cf.…”