Probing the mesopause region thermal and dynamical structure above Fort Collins, Colorado, using a novel sodium Doppler lidar: evolution and results

Abstract

ABSTRACT Continued hardware upgrades have permitted extension of th e Colorado State University (CSU) sodium fluorescence doppler temperature/wind lidar to two-beam operation overall full diurnal cycles. The lidar utilizes the abundance of neutral sodium atoms in the mesopause region to probe the sodium D 2 A transition at 3 pre-sel ected frequencies. Range-gated ratios of the returns at the 3 frequencies are then used to deduce temperature and ho rizontal wind profiles with different time resolutions, dependent on signal-to-noise ratio of the returns. From these measurements, atmospheric convective and dynamic stability can be assessed via the Brunt -Vaisala frequency and gradient Richardson number. The mesopause region is a crucial coupling region between the lower and upper atmosphere. The coupling occurs via waves-which consist of perturbations to the temperature and wind fields. Metal fluorescence lid ars are the only ground-based instrument able to simultaneously measure vertical profiles of mesopause temperatures and winds, thereby maximizing geophysical information obtained. This paper outlines major hardware upgrades leading to the current lidar capabilities, in addition to measurement methodology. Sample seasonal te mperature and wind statistics, taken from April 2002-May 2003, will then be provided, followed by samples from a 12-mont h seasonal statistical study of derived parameters such as wind shears, Brunt-Vaisala frequency, and Richardson number. Keywords: mesopause, MLT, sodium fluorescence lidar, climatology, atmospheric stability, Brunt-Vasaila frequency, Richardson number