Diurnal temperature variations in the lower troposphere as measured by an all-day-operational pure rotational Raman lidar

Abstract

We describe a pure rotational Raman lidar for measuring the all-day temperature profiles in the lower troposphere. The lidar is made up of a frequency-tripled Nd:YAG laser at 354.82 nm with ∼250mJ pulse energy at the 30 Hz repetition rate, a 200 mm receiving telescope, and narrow-band interference-filter-based detection optics. The lidar performance is shown by measured examples. Under clear sky conditions, with an integration time of 60 min and a vertical resolution of 90 m, the 1-σ statistical uncertainty does not exceed 1 K up to the altitude of ∼4.1km during nighttime, while the corresponding altitude is ∼2.3km at noon. The diurnal temperature variation characteristics have been revealed by the lidar measurements with the 1-σ statistical uncertainty <1K between altitudes ranging from 0.6 to ∼2.0km at Wuhan, China (30.53°N, 114.37°E). The atmospheric temperature shows a strong diurnal oscillation and moderate semidiurnal oscillation at altitudes 0-1.4 km for two days in July 2019 (July period), 0-1.4 km for four days in September 2019 (September period), and 0-0.8 km for three days in January 2018 (January period), respectively. The mean diurnal and semidiurnal amplitudes of the nine days are respectively ∼1.4K and ∼0.5K at the 0.6 km altitude, while the corresponding surface values are ∼4.2K and ∼1.4K, respectively. The diurnal amplitudes tend to weaken with increasing altitude. At altitudes >0.6km, the diurnal amplitude in the September period is less than that in the July period, but greater than that in the January period. The phase delays of the diurnal oscillations are ∼3h in the July period, 5-6 h in the September period, and 5-7 h in the January period compared to those at the surface, respectively. Both the diurnal amplitudes and phase delays indicate a possible seasonal dependence.