Seasonal variations of the Na and Fe layers at the South Pole and their implications for the chemistry and general circulation of the polar mesosphere

Abstract

[1] Lidar observations, conducted at the South Pole by University of Illinois researchers, are used to characterize the seasonal variations of mesospheric Na and Fe above the site. The annual mean layer abundances are virtually identical to midlatitude values, and the mean centroid height is just 100 m higher for Na and 450 m higher for Fe compared with 40°N. The most striking feature of the metal profiles is the almost complete absence of Na and Fe below 90 km during midsummer. This leads to summertime layers with significantly higher peaks, narrower widths, and smaller abundances than are observed at lower latitudes. The measurements are compared with detailed chemical models of these species that were developed at the University of East Anglia. The models accurately reproduce most features of these observations and demonstrate the importance of rapid uptake of the metallic species on the surfaces of polar mesospheric clouds and meteoric smoke particles. The models show that vertical downwelling in winter, associated with the meridional circulation system, must be less than about 1 cm s À1 in the upper mesosphere in order to avoid displacing the minor constituents O, H, and the metal layers too far below 85 km. They also show that an additional source of gas-phase metallic species, that is comparable to the meteoric input, is required during winter to correctly model the Na and Fe abundances. This source appears to arise from the wintertime convergence of the meridional flow over the South Pole.

Retrieval of global mesospheric sodium densities from the Odin satellite

“…This loss of atomic Na is expected from the temperaturedependence of the mesospheric Na chemistry as discussed by Plane et al [1999]. Note that the summertime minimum is even more pronounced near 60°N, most likely because of the uptake of Na species onto ice particles above 80 km [Gardner et al, 2005].…”

Simultaneous, common‐volume lidar observations and theoretical studies of correlations among Fe/Na layers and temperatures in the mesosphere and lower thermosphere at Boulder Table Mountain (40°N, 105°W), Colorado

“…In fact, previous observations have shown that the associated correlation coefficients among temperature, Fe and Na densities are often quite high (absolute values greater than 0.7) but the sign can vary rapidly near the peaks of the Na and Fe layers [Gardner and Liu, 2010;Gardner et al, 2005;Chen and Yi, 2011]. For chemically active constituents such as Fe and Na, the fluctuations arise from purely dynamical effects associated with wave-induced displacement, as well as chemical effects associated with the perturbed production and loss reactions involving the species.…”

“…The ratios between these two channels are used to derive the Fe temperature in the MLT region by employing the Boltzmann technique [Gelbwachs, 1994;Chu et al, 2002]. Over the last decade, this lidar has been deployed to the Pacific Ocean, the North Pole, the South Pole, and Rothera, Antarctica, under harsh environment [Chu et al, 2000;Gardner et al, 2001Gardner et al, , 2005Gardner et al, , 2011], so we must refurbish and upgrade the lidar to restore and enhance its capabilities before deploying it to McMurdo, Antarctica, in November 2010 [Chu et al, 2011a]. Such refurbishment and upgrade along with extensive sky tests were conducted at the University of Colorado [Z. , which led to the Boulder observations in 2010.…”

“…Unfortunately, observations of multiple species are rare, although general properties of Fe and Na layers have been reported by several groups independently [Tilgner and von Zahn, 1988;Plane et al, 1999;States and Gardner, 1999;Raizada and Tepley, 2003;Gardner et al, 2011] and by a few correlative observations Gardner et al, 1993Gardner et al, , 2005. The lidar group at Wuhan has undertaken extensive simultaneous Fe and Na observations with broadband resonance lidars [Yi et al, 2008[Yi et al, , 2009.…”

“…The metal layers are affected by complex dynamical and chemical processes in the MLT region. Wave-induced vertical transport of atmospheric species through mixing, displacement, and advection [Gardner and Liu, 2010], in combination with chemistry and meteor input [Plane, 2012] as well as (horizontal) meridional transport [Marsh, 2011;Gardner et al, 2005], controls the abundance and structure of the metal layers in the MLT. While advective transport (upward in summer and downward in winter) is important in the seasonal variations of metal layers, eddy transport, dynamical transport, and chemical transport play crucial roles in the short-term (within a night) temporal variations of metal layer density [Gardner and Liu, 2010].…”