Latitudinal variations of neutral wind structures in the lower thermosphere for the March equinox period

Neutral winds in the lower thermosphere (95–$\text{130}\text{km}$) measured during the March equinox period (1991–1992) by ground-based incoherent scatter radars at Arecibo (18°N), Millstone Hill (42.5°N), and Sondrestrom (67°N) and by the space-based wind imaging interferometer (WINDII) are compared and show overall good agreement but some differences. At 18°N, the wind field in the altitude region of 95–$\text{110}\text{km}$ displays prevailing upward propagating diurnal tides with wavelengths of about $\text{22}\text{km}$. The diurnal structure is affected by the semidiurnal tide resulting in regular minima separated by 11–$\text{12}\text{h}$. At altitudes above $\text{110}\text{km}$, the diurnal tide dominant wind structure changes to the semidiurnal tide dominant structure as illustrated clearly by WINDII data with $\text{24}\text{h}$ coverage. Winds at 42.5°N and 67°N show similar structures in which winds at 105–$\text{115}\text{km}$ are generally anti-sunward. Daytime ISR winds show prevailing upward propagating semidiurnal tides with wavelengths of 35–$\text{70}\text{km}$. Winds from WINDII reveal the existence of the in situ thermospheric diurnal tide with amplitudes comparable to those of the semidiurnal tide. The superimposition of the two tides result in a wind field stronger during daytime than during nighttime at mid- and high-latitudes. Geomagnetic influence on neutral winds is negligible at low- and mid-latitudes under solar quiet conditions, but is observed at high-latitudes, where wind vectors follow a clockwise one-cell pattern at altitudes above about $\text{118}\text{km}$ in geomagnetic coordinates. Most recent simulations for the three latitudes provided by the NCAR thermosphere/ionosphere/mesosphere electrodynamics general circulation model are compared to the observations. The results at low- and mid-latitudes agree well with the observed winds in both wind structures and magnitudes, and reveal details of wave transition. Simulations for high-latitudes are less satisfactory, and require further improvements.     

Rayleigh lidar temperature measurements in the upper troposphere and lower stratosphere

A single-wavelength Rayleigh lidar system has been used to measure the temperatures in the upper troposphere and lower stratosphere in the night in the altitude range from about 8 to $\text{30}\text{km}$. The temperature derivation is based on an inversion algorithm of the pure Rayleigh backscatter. Calculations include the derivation of the air molecular concentration by an iterative method and the backscattered signals corrected by the background aerosol, which is now found to be low and stable. The uncertainties in estimating the temperature using this method are discussed in detail.The temperature profiles and the tropopause characteristics derived by using the lidar measurements are compared with the radiosonde data. Good agreement is found between these two measurements revealing the potential of this method. The comparison with radiosonde data shows that the lidar measured tropopause temperature is lower by $\text{0.8±1.5}\text{K}$ and the tropopause height is higher by $\text{0.45±0.8}\text{km}$ than the radiosonde measurements. The climatology of local tropopause (24.57°N,121.13°E) is briefly discussed in terms of a double tropopause formation and seasonal variations of the tropopause height and temperature.