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Sardeshmukh, Prashant D.; Hoskins, Brian J.
doi: 10.1002/qj.49711146802pmid: N/A
The mean vorticity balances in the tropical atmosphere during December 1982 to February 1983, a season of extraordinary anomalies associated with the warming of the east equatorial Pacific Ocean, are determined using the 6‐hourly initialized and objectively analysed observations archived at the European Centre for Medium Range Weather Forecasts. the budgets are evaluated at one upper (150 mb) and one lower (850 mb) tropospheric level, with particular emphasis on the balance at 150 mb, near the level of maximum outflow associated with organized deep convection in the tropics.
doi: 10.1002/qj.49711146803pmid: N/A
Air parcel trajectories are calculated for the mid‐stratosphere using data from the stratospheric sounding unit on board NOAA‐6. In the analysis method all the orbital data for each 24 h period are combined into a single global analysis. Three trajectory methods are used‐isobaric, isentropic and quasi‐isentropic‐and the results are compared and contrasted. For the quasi‐isentropic method a radiation model is used, via the thermodynamic equation, to imply cross‐isentrope flow at regular intervals along the trajectory. the positions of the parcels, computed using the three methods, are found in general to be in good agreement when projected on to a horizontal plane. However, the altitude varies according to the trajectory method used and changes by about 1 km along a quiescent trajectory and as much as 2 km along a disturbed trajectory, during a 10‐day period. This has important implications in the study of chemistry along parcel trajectories during disturbed periods since the temperature‐ and pressure‐dependent reactions will proceed at different rates under the different assumptions. Also, the high lapse rate in the vertical mixing ratio profile of ozone implies that the detailed photochemistry will depend critically on the height of the air parcel.
doi: 10.1002/qj.49711146804pmid: N/A
By the use of stratospheric height and temperature field data obtained from the TIROS satellite, dynamical interaction between planetary waves and mean zonal winds in the stratosphere is investigated. Special attention is paid to differences between northern and southern hemispheres. an analysis is made for pressure levels from 70 to 0.4 mb during the period from June 1981 to May 1982. Eliassen‐Palm (E‐P) flux diagnostics are used as a powerful and useful tool to investigate the wave‐mean flow interaction.
Clough, S. A.; Grahame, N. S.; O'Neill, A.
doi: 10.1002/qj.49711146805pmid: N/A
Maps of Ertel's potential vorticity, Q, are computed on an isentropic surface in the middle of the stratosphere. They are derived using data from stratospheric sounding units on board NOAA satellites. the reliability of the maps is demonstrated mainly by conservation of Q that is shown in successive analyses, and by the close agreement obtained using independent data from two satellites.
Al‐Ajmi, D. N.; Harwood, R. S.; Miles, T.
doi: 10.1002/qj.49711146806pmid: N/A
This paper presents a case study of a wave‐mean flow interaction, or minor warming, near the southern hemisphere stratopause for 15‐30 July 1974. the analysis is based mainly on data from the selective chopper radiometer carried by Nimbus 5.
doi: 10.1002/qj.49711146807pmid: N/A
Results are presented from an observational study of the mid‐latitude atmospheric boundary layer over the sea. the data were obtained mainly by instrumented aircraft as part of the Joint Air‐Sea Interaction Experiment (JASIN).
Mishra, S. K.; Patwardhan, M. D.; George, L.
doi: 10.1002/qj.49711146808pmid: N/A
A primitive equation barotropic stability analysis of the 700 mb zonal wind profile over the Arabian Sea was performed for each day between 10 and 14 June 1979, during the onset phase of the monsoon. the flow was found to become progressively more unstable with the passage of time. the most unstable inviscid primitive equation mode has an e‐folding time of 3.1 days, a wavelength of 3500 km and a westward phase speed of 1.9ms‐1.
doi: 10.1002/qj.49711146809pmid: N/A
The interaction of a polar trough with a polar front can lead to a characteristic satellite cloud pattern commonly referred to as an instant occlusion. the detailed structure and development of an event rather resembling an instant occlusion is analysed in this paper using routine data supplemented by additional radiosondes, soundings and cloud imagery from NOAA‐7 and Meteosat, and radar network pictures. the event presented differs from an instant occlusion as described by Anderson and others in that a band of polar front cloud developed simultaneously with the band of cloud associated with the polar trough rather than being a pre‐existing feature. Thus we refer to it under the different name of pseudo‐occlusion in order to keep this distinction in mind. A conceptual model of the pseudo‐occlusion is developed in which the key elements are (i) a moist, relatively warm, low‐level jet associated with the polar trough, referred to as the ‘polar trough conveyor belt’, and (ii) a major upper‐level jet streak associated with the polar front, referred to as the ‘polar front conveyor belt’. the two conveyor belts intersect almost at right angles. Precipitation associated with the polar front is predominantly from stratiform cloud, whereas that associated with the polar trough is a mixture of stratiform and convective. Just on the poleward side of the upper jet the cloud top drops abruptly. Here, dry air having recently descended beneath the tropopause fold, suppresses the depth of the moist air associated with the polar trough conveyor belt. This leads to a minimum in the intensity of precipitation between the rain areas associated with the trough and the front. Although the air overrunning the trough just on the poleward side of the polar front is dry as a result of earlier descent, the air in this location is likely to have begun ascending as part of the indirect circulation in the exit region of the upper level jet streak. the polar trough low‐level jet probably forms part of this circulation.
Herzegh, Paul H.; Hobbs, Peter V.
doi: 10.1002/qj.49711146810pmid: N/A
Ice particle size spectra measured by optical particle size spectrometers during airborne sampling of clouds associated with several frontal precipitation systems in the Pacific Northwest are presented and discussed. In the majority of the spectra measured, the concentration densities of particles <2 mm in diameter deviated significantly below or above the exponential curve fitting larger diameters (we term these sub‐exponential and super‐exponential spectra, respectively). Sub‐exponential spectra were found to be dominant in regions of weak stratiform cloud, where liquid water was scarce. Super‐exponential spectra were dominant in convective regions between the ‐1 and ‐9°C levels, where supercooled liquid water was present in amounts up to 0.2 gm‐3. Exponential spectra were dominant in convective regions at the ‐11 °C level and above.
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