A research progress review on regional extreme events

An extreme （weather and climate） event does not only mean that an extreme occurs at a location, but more generally it can impact a certainarea and last a certain period of time, which is defined as a regional extreme event （REE） with a certain impacted area and duration. The conceptof REE has been defined to allow mainly objective assessment of the events without a pre-determined boundary and duration. This paper reviewsthe studies on REEs published during the past 20 years, especially recent years. Mainly in view of methodology, these studies can be divided intothree types studies focusing on spatial simultaneity, studies focusing on temporal persistence, and studies identifying REEs. The methodsidentifying REEs include two kinds, e.g., type-I methods stressing REE＇s temporal persistence within a relatively certain area and type-IImethods focusing on catching a complete REE. Identification methods proposed in this paper could provide valuable information for variouspurposes, such as real-time monitoring, estimating long-term changes, mechanism diagnosis, forecasting study and even attribution analysis.Research on REEs is important for objectively defining extreme weather and climate events, which depends on the spatial and temporal scales ofinterest. Such an objective definition will support ongoing climate monitoring and improve the assessment of how regional extreme events havechanged over time.

Validation of Aura Microwave Limb Sounder water vapor and ozone profiles over the Tibetan Plateau and its adjacent region during boreal summer

We present validation studies of MLS V2.2 and V3.3 water vapor(WV) and ozone profiles over the Tibetan Plateau(Naqu and Lhasa) and its adjacent region(Tengchong) respectively by using the balloon-borne Cryogenic Frost point Hygrometer and Electrochemical Concentration Cell ozonesonde. Coincident in situ measurements were selected to compare the MLS V2.2 and V3.3 WV and ozone profiles for understanding the applicability of the two version MLS products over the region. MLS V2.2 and V3.3 WV profiles respectively show their differences within ?2.2±15.7%(n=74) and 0.3±14.9%(n=75) in the stratosphere at and above 82.5 h Pa. Accordingly, at 100 h Pa, the altitude approaching the tropopuase height, differences are within 9.8± 46.0%(n=18) and 23.0±45.8%(n=17), and they are within 21.5±90.6%(n=104) and 6.0±83.4%(n=99) in upper troposphere. The differences of MLS ozone are within ?11.7±16.3%(n=135, V2.2) and 15.6±24.2%(n=305, V3.3) at and above 82.5 h Pa. At 100 h Pa, they are within ?3.5±54.4%(n=27) and ?8.7±41.6%(n=38), and within 18.0±79.1%(n=47) and 34.2±76.6%(n=160) in the upper troposphere. The relative difference of MLS WV and ozone profile has significant oscillation and scatter at upper troposphere and lower stratosphere partly due to the stronger gradients of WV and ozone concentrations here as well the linear interpolation of sonde data for the intercomparison. At and below 70 h Pa, the relative differences of MLS ozone are significantly larger over Lhasa during the Tibetan Plateau "ozone valley" season, which is also the Asian Summer Monsoon period. The MLS ozone differences over the three sites are similar in their vertical distributions during that period. A simple linear correlation analysis between MLS and sonde profiles indicates that the sensitivity of MLS profile products is related to concentrations at each pressure level. The MLS V3.3 product sensitivity is slightly improved for WV at and above 82.5 h Pa, whereas it is not obvious for ozone. The possible factors contributing to the differences of the MLS profile products of WV and ozone are discussed.