Relationship Between Persistent Heavy Rain Events in the Huaihe River Valley and the Distribution Pattern of Convective Activities in the Tropical Western Pacific Warm Pool

Using daily outgoing long-wave radiation （OLR） data from the National Oceanic and Atmospheric Administration （NOAA） and the National Center for Environmental Prediction/National Center for Atmospheric Research （NCEP/NCAR） reanalysis data of geopotential height fields for 1979-2006, the relationship between persistent heavy rain events （PHREs） in the Huaihe River valley （HRV） and the distribution pattern of convective activity in the tropical western Pacific warm pool （WPWP） is investigated. Based on nine cases of PHREs in the HRV, common characteristics of the West Pacific subtropical high （WPSH） show that the northern edge of the WPSH continues to lie in the HRV and is associated with the persistent ＂north weak south strong＂ distribution pattern of convective activities in the WPWP. Composite analysis of OLR leading the circulation indicates that the response of the WPSH to OLR anomaly patterns lags by about 1-2 days. In order to explain the reason for the effects of the distribution pattern of convective activities in the WPWP on the persistent northern edge of the WPSH in the HRV, four typical persistent heavy and light rain events in the Yangtze River valley （YRV） are contrasted with the PHREs in the HRV. The comparison indicates that when the distribution pattern of the convective activities anomaly behaves in a weak （strong） manner across the whole WPWP, persistent heavy （light） rain tends to occur in the YRV. When the distribution pattern of the convective activities anomaly behaves according to the ＂north weak south strong＂ pattern in the WPWP, persistent heavy rain tends to occur in the HRV. The effects of the ＂north weak south strong＂ distribution pattern of convective activities on PHREs in the HRV are not obvious over the seasonal mean timescale, perhaps due to the non-extreme status of convective activities in the WPWP.

Interdecadal change of the connection between winter North Pacific Oscillation and summer precipitation in the Huaihe River valley

The relationship between the winter North Pacific Oscillation (NPO) and the following summer precipitation in the Huaihe River valley before and after the mid-1970s is investigated by using the Chinese 160-station precipitation data and NCEP/NCAR reanalysis data from 1951 to 2008.It is found that their linkage appears to have an apparent interdecadal variation.Before the mid-1970s, there was a prominent out-of-phase relationship between the winter NPO and the summer precipitation in the Huaihe River valley.However, such a relationship is significantly weakened afterwards.The change of atmospheric circulations related to the winter NPO before and after the mid-1970s is further addressed.Before the mid-1970s, a strong (weak) winter NPO was followed by the summer situations with anomalous low-level cyclonic (anticyclonic) circulation over the western Pacific and descending (ascending) over the Huaihe River valley.Meanwhile, the water vapor transporting to the Huaihe River valley was reduced (enhanced).These conditions are unfavorable (favorable) for the precipitation occurring in the Huaihe River valley, and thus the local precipitation was decreased (increased).After the mid-1970s, however, the impact of winter NPO on the summer atmospheric circulation system associated with the rainfall in the Huaihe River valley becomes diluted, thereby weakening its linkage to the summer precipitation in the Huaihe River valley.

Energy Budgets on the Interactions between the Mean and Eddy Flows during a Persistent Heavy Rainfall Event over the Yangtze River Valley in Summer 2010

In this study,a persistent heavy rainfall event（PHRE） that lasted for around 9 days（from 0000 UTC 17 to0000 UTC 26 June 2010） and caused accumulated precipitation above 600 mm over the Yangtze River valley,was reasonably reproduced by the advanced research WRF model.Based on the simulation,a set of energy budget equations that divided the real meteorological field into the mean and eddy flows were calculated so as to understand the interactions between the precipitation-related eddy flows and their background circulations（BCs）.The results indicated that the precipitation-related eddy flows interacted with their BCs intensely during the PHRE.At different layers,the energy cycles showed distinct characteristics.In the upper troposphere,downscaled energy cascade processes appeared,which favored the maintenance of upper-level eddy flows;whereas,a baroclinic energy conversion,which reduced the upper-level jet,also occurred.In the middle troposphere,significant upscaled energy cascade processes,which reflect the eddy flows＇ reactionary effects on their BCs,appeared.These effects cannot be ignored with respect to the BCs＇ evolution,and the reactionary effects were stronger in the dynamical field than in the thermodynamical field.In the lower troposphere,a long-lived quasi-stationary lower-level shear line was the direct trigger for the PHRE.The corresponding eddy flows were sustained mainly through the baroclinic energy conversion associated with convection activities.Alongside this,the downscaled energy cascade processes of kinetic energy,which reflect the direct influences of BCs on the precipitation-related eddy flows,were also favorable.A downscaled energy cascade of exergy also appeared in the lower troposphere,which favored the precipitation-related eddy flow indirectly via the baroclinic energy conversion.