An investigation of clear air stratification with radar and elevated instruments

Abstract

A study o.f radar reflectio.ns within the clear air Qf the IQwer trQPQsphere has bee n carried Qut Qver two. prQIQnged intervals. A specially designed radar Qperating at 7000 MHz has been used fo.r this purpQse, with its statio.nary antennas directed vertICally Into. the layer Qf fflctlOnal onfluence. An Interpretatio.n o.f these radar QbservatiQns has been made with the aid Qf synQptic weather infQrmatiQn, to. indicate that the incidence Qf reflectio.ns varies with the type Qf air mass and with the degree Qf dampness Qf the underlying gro.und. The distributiQn Qf reflecting centers generally has a maximum at a height Qf 300 m, but this distributiQn is altered by the intrusiQn Qf a weather fro.nt. These reflectIng ce nters appear to. be small departures in air refractivity within hQrizo.ntallayers that a~e o.nly a fe,,: centimeters in vertical depth and that are either flat o.r weakly CQncave dQwnwards, extendIng Qver hQflzontal distances Qf at least a few meters. The need fQr further infQrmatio.n Qn the air structure to. supPQrt these radar QbservatiQns has led to. a program Qf special instrument develQpment. Included are a ballQQn-bQrne refractQmeter and te mperature sQnde which have a rapid reSPQnse and a high degree Qf spatial resQluti Qn, and a smQke-generating no.se CQne fQr IQW level rQckets. Prelimin~ry Qbservatio.ns have been carried Qut with these instruments to. assess their capabilities, and SQme detruls o.n the smo.ke trail analysis are given in this paper. Inspec tiQn Qf the s mQke trails indicates lo.calized layers Qf turbulence and rapid diffusiQn within dee per layers Qf laminar translatiQn. . It appears t~at averaging tim es. in excess Qf 20 min are required to. o.btain SQme mean wind-speed prQfiles. The vertical extent Qf velo.Clty inhQmQgeneities is no.t small as co.mpared with their hQrizQntal extent, and the law o.f diffusio.n generally is different at levels abQve and belQw 300 m.