Upper-air Sounding Data Research Articles

半乾燥地域で夕方に観測された水蒸気圧の顕著なピークについて

Significant evening peaks were observed in the diurnal variations of vapor pressure over an oasis surrounded by desert in the north-west part of China. They appeared not only in the surface layer measurement but also in the upper air soundings below 500 m. According to the surface flux measurements, it was observed that sensible heat flux was much stronger over the desert than over the oasis during the daytime. The upper-air sounding data shows that the oasis is a cool and moist island capped by dry and hot air which would be advected from the surrounding desert. In these situations, upper-layer convective mixing is considered to be much stronger than in the lower cool island, and this can lead to water vapor flux divergence in the afternoon. In the evening, convective mixing, which is suggested by the sensible heat flux from the ground, decreases over the desert and in the upper layer over the oasis. It was observed that evapotranspiration from the surface still continues upward. It is suggested that water vapor flux convergence can occur near the oasis surface.

Convective Stabilization in Midlatitudes

Abstract The upper-air sounding data from PRE-STORM are used to investigate the convective stabilization effect on the large-scale atmosphere. To facilitate comparison between different stages of cumulus convection, the data are divided into four categories: environment, presystem, insystem, and postsystem. It is found that the convective available potential energy of the atmosphere is reduced substantially after cumulus convection, most of which is consumed during the transition from presystem to insystem. Examination of the temperature and moisture changes during cumulus convection suggests that cooling and drying in the subcloud layer are the most important factors in stabilizing the atmosphere. In general, virtual potential temperature profiles in all categories are close to reversible moist adiabats below the 600-mb level and nearly parallel to moist pseudoadiabats above it. The effect of entrainment on parcel buoyancy is also studied. It is found that a small amount of entrainment of ambient air can...

マイクロ波放射計と8.6mm波レーダーによる中層層状雲の氷晶化度の観測

Middle-level stratiform clouds associated with cyclones were observed in spring 1985 simultaneously by a 19.35 GHz microwave radiometer and an 8.6mm-radar. The vertically integrated liquid-water content was estimated by analysing the data of the microwave radiometer together with upper-air sounding data, and the vertically integrated ice content was estimated from radar-echo intensity. Structure and precipitation formation in middle-level stratiform clouds were studied, especially their degree of glaciation which is defined by the ratio of vertically integrated ice content to the total amount of condensed water (the sum of vertically integrated liquid-water and ice).Analysed cases are divided into two types of clouds (type-A and type-B). Type-A clouds showed a low degree of glaciation, a large amount of integrated liquid-water, and a comparatively thin and weak radar-echo layer only at middle levels. The degree of glaciation in three cases was slightly less than 10% and an average and the total amount of condensed water was about 55mg/cm2 . Type-B clouds had a deep and intensive radar-echo layer, whose tops were far above middle levels. The degree of glaciation in three cases was about 65% on average and the total amount of condensed water was about 40mg/cm2. The degree of glaciation was significantly different between the two types, though total condensed-water amounts were comparable.The structure and precipitation formation processes of the two types of clouds can be summarized as follows. The type-A cloud is a one-layer middle-level cloud. Ice particles are initiated near its top where the air temperature is not low enough to allow a sufficient number of ice-nuclei to be activated. The glaciation process is not efficient though the supercooled water content is large due to strong updraft in it. On the other hand, the type-B cloud is composed of an upper-level cloud and a middle-level cloud which seem to have formed independently. Ice particles supplied by the upper-level cloud promote the glaciation in the middle-level cloud. By comparing glaciation proceses in two types of clouds we showed quantitatively that only a middle-level stratiform cloud could not produce solid precipitation efficiently, even though it contains a large amount of super-cooled water, unless an upper-level cloud supplies sufficient ice particles to it.

Scale-Controlled Objective Analysis

Abstract The major topic of this paper is the resolvable spatial scales that can be analyzed by statistical interpolation of an undersampled dataset. The inquiry was motivated by the need to design the most appropriate procedures for spatial analysis of the upper-air sounding data from the GARP Atlantic Tropical Experiment. A reliable representation of horizontal scales in the analyzed wind fields was a matter of utmost concern, since the derived fields of vorticity, divergence and vertical motion were also of vital interest. To achieve our goal, it was found that the traditional promise of statistical interpolation had to be reexamined. The main conclusions of this theoretical inquiry are (i) resolvable scales are determined by the geometrical distribution of observing stations; (ii) precise knowledge of the second-moment statistics improves the analysis by de-aliasing the amplitudes of resolvable scales, but has no effect on the definition of resolvable scales; (iii) residual effects of unresolvable sig...

Response of Stratified Flow in the Lee of the Olympic Mountains

The behavior of stratified air flowing around an isolated mountain is dependent on an internal Froude number (F), which indicates the relative importance of upstream velocity and vertical stratification. Three cases of the flow in the lee of the Olympic Mountains in the State of Washington are studied where the measured F was in the range 1.0–1.4 but apparently dominated by stable stratification. This study combined measurements of spatial variation of low-level winds and other parameters from a NOAA P-3 research aircraft with a dense network of surface stations including eight meteorological buoys and six upper-air stations. Results from these cases show the presence of an area of light winds in the lee of the Olympic Mountains. The characteristics of the flow are shown to be similar to laboratory results for low Froude number flow around an isolated obstacle where the flow is confined to quasi-horizontal planes. These cases are contrasted with a situation which led to the formation of a mesoscale low-pressure area and high surface winds in the lee of the mountains. The latter case was the Hood Canal Bridge storm on 13 February 1979 where local winds in the lee of the Olympic Mountains were in excess of 50 m s−1. The flow at the surface was produced by down-pressure-gradient acceleration in the confined channels of Puget Sound toward the orographically produced low-pressure center. The measured internal Froude number in this situation was 4.6, and the pressure fields are shown to agree with the linear hydrostatic model developed by Smith (1980) for F > 1. It is suggested that the Froude number calculated from routine, upper-air sounding data is an index that forecasters can use to determine the potential for severe wind conditions over the inland waters of Puget Sound.