Potential vorticity(PV)has been widely applied as a tracer because of its property of conservation in frictionless,dry adiabatic flow.However,PV itself is more effective in describing the slow-manifold flow at large scale.Therefore,we wish to find a materially conserved invariant other than PV to diagnose severe weather such as growing and mature tropical cyclones,whose velocity and dynamic pressure vary rapidly and locally.Starting from the absolute motion equation after elimination of the pressure gradient term by introducing moist entropy and moist enthalpy,the baroclinic Ertel-Rossby invariant(ERI)in moist flow is derived by the Weber transformation.Furthermore,the material conservation property of moist ERI is proven.Besides the traditional moist potential vorticity(MPV)term,the invariant includes the moisture factor that is excluded in dry ERI and the term related to gradients of pressure,kinetic energy and potential energy that reflects the"fast-manifold"property.Therefore,it is more complete to describe the fast motions off the slow manifold for severe weather than is the MPV term.The moist ERI is then applied to diagnose a triple-typhoon system,and is compared with MPV and dry ERI.Contrastive analysis shows that moist ERI is a better tool to diagnose the movements and intensity variations of several coexisting typhoons.The moist ERI can signify the movement and development of a multi-typhoon system.It has wide application prospects for a real moist atmosphere.
This study produced a novel characterization of the troposphere-to-stratosphere transport(TST) over the Asian monsoon region during boreal summer,using a comprehensive analysis of 60-day backward trajectories initialized in the stratosphere.The trajectory datasets were derived from the high-resolution Lagrangian particle dispersion model(FLEXPART) simulation driven by the wind fields acquired from the National Center for Environmental Prediction(NCEP).The results indicate that the distribution of residence time(tTST) of tropopause-crossing trajectories in the lowermost stratosphere represents a horizontal signature of the Asian summer monsoon.Vertically,the distribution of tTST can be roughly separated into two layers:a consistent lower layer with tTST <5 days forming a narrow band,corresponding to a layer～3 km thick following the location of the tropopause,and an upper layer at a larger distance from the local tropopause.The maximum residence time was～20 days,especially within the Asian high anticyclone consistent with its confinement effects.In general,the overall geographical distribution of dehydration points was not coincident with the location of tropopause crossing.TST trajectories,which were initialized in the stratosphere,underwent their Lagrangian cold points mostly in the tropics and subtropics 1-4 days after the TST event;they were characterized by a wide range of temperature differences,with a mean value of 3-12 K.The vertical extent of the influence of tropospheric intrusion on the Asian monsoon region in the stratosphere exhibited a peak at～16.5-18.5 km,and the uppermost height was～21 km.
The study presented herein investigated the main characteristics of carbon monoxideintraseasonal variability and evaluated its possible impact factors using the upper troposphere and lowerstratosphere (UT/LS) Aura Microwave Limb Sounder (MLS) observations over Tibetan Plateau and itsadjacent areas in summer (June to August) of 2005 and 2006. Observations show a persistent constituentextreme extending up into the UT/LS throughout summer, as well as a temporally reversed phase variationbetween the carbon monoxide and ozone in UT/LS. The intraseasonal oscillations (ISOs) of carbonmonoxide during summer are investigated by using methods of wavelet and band pass filter analysis. It isfound that ISOs over the Tibetan Plateau have periods of 10 to 20 days and 30 to 60 days. The formermainly appeared in upper troposphere while the latter in lower stratosphere. Further analysis shows thatthese two periods of ISOs in UT/LS are mainly in phase to the activities of convection over the south of theplateau and the variation of South Asia High, respectively. The above two factors and their dynamicalcoupling may be responsible for the tracer ISOs at different levels.
