Estimating Tropical Cyclone Precipitation from Station Observations

In this paper, an objective technique for estimating the tropical cyclone （TC） precipitation from station observations is proposed. Based on a comparison between the Original Objective Method （OOM） and the Expert Subjective Method （ESM）, the Objective Synoptic Analysis Technique （OSAT） for partitioning TC precipitation was developed by analyzing the western North Pacific （WNP） TC historical track and the daily precipitation datasets. Being an objective way of the ESM, OSAT overcomes the main problems in OOM, by changing two fixed parameters in OOM, the thresholds for the distance of the absolute TC precipitation （D0） and the TC size （D1）, into variable parameters.Case verification for OSAT was also carried out by applying CMORPH （Climate Prediction Center MORPHing technique） daily precipitation measurements, which is NOAA＇s combined satellite precipitation measurement system. This indicates that OSAT is capable of distinguishing simultaneous TC precipitation rain-belts from those associated with different TCs or with middle-latitude weather systems.

Investigation on the Sediment Characteristics of the Electrostatic Cyclonic Precipitator

In order to find out the relationship between the sediment characteristics and collecting efficiency of the electrostatic cyclonic precipitator, an online study for the sediment characteristics of electrostatic cyclonic precipitator had been done with Kompton back scatter method, with the collecting efficiency tested at the same time. And the relationship between the sediment characteristics and the collecting efficiency was gotten. The sediment thickness increased with time extended and the concentration increased when the inlet velocity was fixed. The collecting efficiency increased with the inlet velocity increased, but dropped with the concentration increased. When the concentration and inlet velocity were fixed, the collecting efficiency drop a little with the increase of sediment thickness. The sediment would decrease the corona current in the collecting filed, which would make the electrostatic effect fall, then made the collecting efficiency drop a little.

Contribution of Winter SSTA in the Tropical Eastern Pacific to Changes of Tropical Cyclone Precipitation over Southeast China

Tropical cyclone precipitation(TCP)accounts for 10%-40%of the boreal summer precipitation that occurs over Southeast China(SEC),causing flood disasters and serious damage.On the decadal scale,TCP increases significantly in SEC while TC frequency decreases in the western North Pacific(WNP)during 1980-2019.Therefore,variations in TCP and the corresponding physical mechanism are investigated in this study.First,an empirical statistical method is introduced to quantify the TCP amount based on accumulated cyclone energy(ACE)and TC frequency with the TCP anomaly decomposed into three items(rainfall frequency,rainfall intensity,and nonlinear item).ACE,as the integration of TC intensity and frequency,is a more effective index than TC frequency for depicting the characteristics of TCP because the contribution of rainfall frequency represented by ACE is higher than that of TC frequency.Then,the physical mechanism affecting the WNP TC activities and TCP in SEC are inspected.Positive sea surface temperature anomaly(SSTA)over the tropical eastern Pacific(TEP)in winter can trigger variations of air-sea interaction over the tropical Pacific,including low-level divergent winds,mid-tropospheric descent flows,high-level convergent winds coupled with negative anomalies of vorticity and humidity over the tropical western Pacific(TWP)in the next summer.These dynamic conditions provide unfavorable environments for TC activities in the WNP and constrain TCP in SEC.Furthermore,more significantly negative SSTA events in the TEP facilitate enhanced ACE along with positive relative vorticity,relative humidity,and upwelling vertical winds anomalies over the coast of SEC after 1998,which is a reasonable explanation for the increasing TCP in SEC.

Relationship of tropical-cyclone-induced remote precipitation with tropical cyclones and the subtropical high

This study concerns the precipitation induced by a tropical cyclone （TC） before the TC arrives, which will be referred to as TC remote precipitation （TRP）. Based on the distribution characteristics of the non-rotational wind and the divergent-wind vertical circulation related to TC, the subtropical high, and TRP of 45 TRP events during June, July, and August of 2000-2009, the relationships among these three entities （TC, subtropical high, and TRP） can be categorized into four patterns. The first pattern accounts for the highest proportion of the TRP events （59%）, and a conceptual model is then provided for this pattern. The primary characteristics of this model are as follows： TC, the subtropical high, and TRP can interact with each other through the divergent-wind secondary circulation at both sides of the ridge line of the subtropical high （between the subtropical high and TC, and between the subtropical high and TRP）. At the upper level （150 or 200 hPa）, the northward non-rotational wind from the TC converged toward the subtropical high ridge line and subsided, and at 950 hPa the divergent wind from the ridge line of the subtropical high converged toward TC; these constructed the secondary circulation between TC and the subtropical high. In the meantime, the southward non- rotational wind at the upper level （150 or 200hPa） from TRP and the divergent wind at 950hPa from the subtropical high ridge line toward TRP constructed the secondary circulation between TRP and the subtropical high. As TC and TRP interacted with each other, the subtropical high ridge line was usually under the down- draft area of the whole atmosphere. The other three patterns are different from the first pattern mainly in terms of the intensity and position of the non-rotational-wind secondary circulation. The numerical simulation of the Beijing 7.21 rainstorm confirmed the relationship amongTC, the subtropical high, and TRP, indicating that when the interaction weakened, the TRP also weakened.

Estimation of mean water vapour residence time during tropical cyclones using a Lagrangian approach

Tropical cyclone(TC)-related rainfall mostly depends on the atmospheric moisture uptake from local and remote sources.In this study,the mean water vapour residence time(MWVRT)was computed for precipitation related to TCs in each basin and on a global scale by applying a Lagrangian moisture source diagnostic method.According to our results,the highest MWVRT was found for the TCs over the South Indian Ocean and South Pacific Ocean basins(~3.08 days),followed by the Western North Pacific Ocean,Central and East North Pacific Ocean,North Indian Ocean,and North Atlantic Ocean basins(which exhibited values of 2.98,2.94,2.85,and 2.72 days,respectively).We also found a statistically significant(p<0.05)decrease in MWVRT,at a rate of~2.4 h/decade in the North Indian Ocean and~1.0 h/decade in the remaining basins.On average,the MWVRT decreased during the 24 h before TCs made landfall,and the atmospheric parcels precipitated faster after evaporation when TCs moved over land than over the ocean.Further research should focus on the relationship between global warming and MWVRT of atmospheric parcels that precipitate over TC positions.