Temperature oscillations observed in the stable boundary layer over four different underlying surfaces

Nocturnal temperature is crucial in stability determination, as well as parameterization in numerical models. In the present research, data from four tall towers are used to investigate the temperature oscillations observed in the stable boundary layer, including the 307-m Boseong Tower on the southern coast of Korea, a 100-m tower in a grassland area of northern China, a 70-m tower in a desert area in northwestern China, and the 32S-m Beijing Tower. Large temperature oscillations, with amplitudes of about 2℃ and periods of several minutes to tens of minutes, are detected. Using the empirical mode decomposition method working as a high-pass filter, the oscillations of temperature are extracted from the original non-stationary and nonlinear temperature data. The daily variations and vertical distribution of the temperature oscillations are discussed. Generally strong temperature oscillations are found at tens of meters high during nighttime in the coastal area, in the steppe, and in the desert, when stable conditions have formed. Much weaker nocturnal temperature oscillations are observed in Beijing, where the large heat capacity of buildings and streets and artificial heat sources prevent the boundary layer conditions from becoming stable. Static stability expressed by the Brunt-Vaisala frequency is found to be an important factor for such temperature oscillation events, which is worthy of model parameterization.

Mesoscale Vegetation-Breeze Circulations and Their Impact on Boundary Layer Structures at Night

The impact of well watered mesoscale wheat over mid-latitude arid areas on mesoscale boundary layer structures (MBLS) and climate has been investigated in the study .using a mesoscale biophysical, meteorological model (BM) developed in the current study. The BM is composed of six modules:mesoscale atmospheric module, soil module, vegetation module, snow-atmosphere interaction module, underlying surface meteorology module and subgrid scale flux parameterization module. The six modules constitute an interacting system by supplying boundary conditions to each other.The investigation indicates that a horizontal pressure gradient associated with mesoscale perturbations in temperature and humidity is created during the day, which results from more water transpired from the vegetation canopy (VC) and evaporated from underlying wet soil. Non-classical mesoscale circulations (called as vegetation-breeze) are forced by the pressure perturbations with wind speeds about 5 m / s, flowing from the VC to the adjacent bare soil in the low boundary layer.Specific attention in the study is given to study the MBLS at night caused by the interactions between these mesoscale vegetation-breezes.The impacts of the VC's scale and atmospheric background thermal stability (ABTS) on these thermally forced mesoscale vegetation-breezes are also investigated.

Role of the Nocturnal Low-level Jet in the Formation of the Morning Precipitation Peak over the Dabie Mountains

The diurnal variation of precipitation over the Dabie Mountains(DBM) in eastern China during the 2013 mei-yu season is investigated with forecasts of a regional convection-permitting model. Simulated precipitation is verified against surface rain-gauge observations. The observed morning precipitation peak on the windward(relative to the prevailing synoptic-scale wind) side of the DBM is reproduced with good spatial and temporal accuracy. The interaction between the DBM and a nocturnal boundary layer low-level jet(BLJ) due to the inertial oscillation mechanism is shown to be responsible for this precipitation peak. The BLJ is aligned with the lower-level southwesterly synoptic-scale flow that carries abundant moisture.The BLJ core is established at around 0200 LST upwind of the mountains. It moves towards the DBM and reaches maximum intensity at about 70 km ahead of the mountains. When the BLJ impinges upon the windward side of the DBM in the early morning, mechanical lifting of moist air leads to condensation and subsequent precipitation.

Lidar Measurements of Aerosols in the Tropical Atmosphere

Measurements of atmospheric aerosols and trace gases using the laser radar (lidar) techniques, have been in progress since 1985 at the Indian Institute of Tropical Meteorology, Pune (18°32'N, 73°51'E, 559 m AMSL), India. These observations carried out during nighttime in the lower atmosphere (up to 5.5 km AGL), employing an Argon ion / Helium-Neon lidar provided information on the nature, size, concentration and other characteristics of the constituents present in the tropical atmosphere. The time-height variations in aerosol concentration and associated layer structure exhibit marked differences between the post-sunset and pre-sunrise periods besides their seasonal variation with maximum concentration during pre-monsoon / winter and minimum concentration during monsoon months. These observations also revealed the influence of the terrain of the experimental site and some selected meteorological parameters on the aerosol vertical distributions. The special observations of aerosol vertical profiles obtained in the nighttime atmospheric boundary layer during October 1986 through September 1989 showed that the most probable occurrence of mixing depth lies between 450 and 550 m, and the multiple stably stratified aerosol layers present above the mixing depth with maximum frequency of occurrence at around 750 m. This information on nighttime mixing depth / stable layer derived from lidar aerosol observations showed good agreement with the height of the ground-based shear layer / elevated layer observed by the simultaneously operated sodar at the lidar site.