Structure and seasonal variations of the nocturnal mesospheric K layer at Arecibo

Abstract

We present the seasonal variations of the nocturnal mesospheric potassium (K) layer at Arecibo, Puerto Rico (18.35°N, 66.75°W) from 160 nights of K Doppler lidar observations between December 2003 and January 2010, during which the solar activity is mostly low. The background temperature is also measured simultaneously by the lidar and shows a strong semiannual oscillation with maxima occurring during equinoxes at all altitudes. The annual mean K density profile is approximately Gaussian with a peak altitude of 91.7 km. The K column abundance and the centroid height have strong semiannual variations, with maxima at the solstices. Both parameters are negatively correlated to the mean background temperature with a correlation coefficient < −0.5. The root‐mean‐square (RMS) width has a distinct annual oscillation with the largest width occurring in May. The seasonal variation of the centroid height is similar to that of the Fe layer at the same site. The seasonal temperature variation indicates significant enhanced wave‐induced downward transport for both species during spring and autumn. This explains the metal layer centroid height and column abundance variations at Arecibo and provides a general mechanism to account for the seasonal variations in the centroid height of all metal species measured at low‐latitude and midlatitude sites.

Observations and Modeling of Potassium Emission in the Terrestrial Nightglow

“…In this respect, the variability of the potassium (K) layer is different from that of sodium (Na), the next lighter alkali metal. While Na exhibits a dominant annual oscillation (AO) with a maximum in late autumn/early winter in both hemispheres at nonequatorial latitudes (Fan et al, ; Gardner et al, ; Langowski et al, ; States & Gardner, ; Yi et al, ), the K layer at all latitudes is characterized by a pronounced semiannual oscillation (SAO) with maxima around the solstices (Dawkins et al, ; Eska et al, ; Friedman et al, ; Lautenbach et al, ; Wang et al, ; Yue et al, ). Plane et al () explain these differences by a nearly temperature‐independent cycling between K and the main neutral reservoir species KHCO 3 .…”

“…Since the first use of laser light for its activation by Felix et al (), the lidar technique is the preferred method for ground‐based studies of the K layer. Nevertheless, observations extending for more than a year are limited to a few stations in the Northern Hemisphere: Longyearbyen at 78°N (Höffner & Lübken, ), Kühlungsborn at 54°N (Lautenbach et al, ; von Zahn & Höffner, ; Eska et al, ), Beijing at 40°N (Wang et al, ), and Arecibo at 18°N (Friedman et al, ; Yue et al, ). In addition, nearly global daytime retrievals of the K layer density profile were obtained from K(D 1 ) resonance fluorescence measurements made by the limb‐scanning Optical Spectrograph and Infrared Imaging System (OSIRIS) onboard the Odin satellite for the period from 2004 to 2013 (Dawkins et al, , ).…”

Long-term Lidar Observations of the Gravity Wave Activity near the Mesopause at Arecibo

“…The Arecibo K Doppler lidar probes the potassium D1 line to deduce the potassium density and neutral air temperature simultaneously by employing the three-frequency technique (e.g., Friedman and Chu, 2007;Friedman et al, 2003). The temperature was obtained at 0.45/0.9 km vertical and 10/30 minutes temporal resolution, respectively (Friedman and Chu, 2007;Yue et al, 2017), and we unify them into profiles with resolutions of 0.9 km and 30 minutes in vertical and temporal dimensions, respectively. This data processing excludes the perturbations relevant to gravity waves with vertical wavelengths and observed periods less than 1.8 km and 1 hour, respectively.…”

“…Their exclusion may bias the deduced gravity wave associated potential energy estimations towards mid-and low-frequency gravity waves. The root mean square (RMS) temperature errors is about 2 to 3 K at the peak of the K density layer and increase to about 10 K at the edge of the layer around 85 and 100 km (Friedman and Chu, 2007;Yue et al, 2017).…”

“…Such measurements of atmospheric temperature have been conducted with the K Doppler lidar located at the Arecibo Observatory (18.35°N, 66.75°W), Puerto Rico (Friedman and Chu, 2007;Yue et al, 2013Yue et al, , 2016Yue et al, , 2017. Since December 2003, the Arecibo Observatory K Doppler lidar has operated routinely, producing high-quality temperature data.…”