University of Ferrara Department of Physics and Earth Sciences

Leo Pio D'Adderio

PhD Student 27th cycle - Ferrara, December 3rd, 2013

Precipitation fine structure

University of Ferrara

Department of Physics and

Earth Sciences

Leo Pio D'Adderio PhD Student 27th cycle - Ferrara, December 3rd, 2013

Work done

• Study of precipitation characteristics over Tibetan plateau during monsoon

season with particular interest on variation of drop size distribution (DSD) with

respect to altitude and latitude.

• Detection of breakup occurrence studying DSD shape to recognize the process

regardless the physical principle of the instrument.

• Study of the vertical variability of DSD.

• Start of a cooperation with NASA to deepen these studies in order to find new

DSD parameterization in presence of breakup situations, for a direct application

in rain retrieval from DPR (to be launched next year).


Precipitation properties over Tibetan Plateau

• 37 rain events during monsoon season were collected from 2 measurement sites:

Linzhi 3300 m a.s.l. and Lhasa 3600 m a.s.l.

• Five case studies (from stratiform to mixed stratiform/convective to deep

convective) have been analyzed in terms of rainfall rate and DSD evolution.

• All minutes with rainfall rate higher than 0.1 mm/h have been analyzed in terms

of DSD trend as function of rainfall rate intensity and in terms of Z-R

relationship.

To completion of CEOP-AEGIS Project an overall study on the precipitation

properties over Tibetan Plateau has been carried out.


Two case studies

5th September 2010, Linzhi

mixed

• Long-lasting precipitation event with two intensity peaks at the beginning

and at the end of event (data are averaged over 5 minutes);

• The central part of event has statiform characteristics with exponential

DSD;

• The peaks reveal different cloud structure, with breakup evident for the

ending peak while is absent for the beginning peak.


Two case studies

28th July 2010, Linzhi

convective

• Short convective precipitation event (data are averaged over 2 minutes);

• For the higher intensity minutes the presence of breakup is evident with an

increase of drop number around 2.5 mm;

• For both cases the maximum dimension reached by drop does not exceed 4

mm of diameter.


Integral parameters

• Change DSD shape and concavity moving from light rain to heavy rain

• Very low b term in 𝑍 = 𝐴𝑅𝑏 relationship it means limited presence of

large drops

• From case studies: confirmation that drops reach smaller dimension with respect

to sea level

• From case studies: easier reaching of breakup situation due to the higher drops

kinetic energy


Automatic recognizing of breakup occurrence in DSD

Numerical simulations Experimental data

Pratt and Barros, 2007

Willis and Tattelman,

1988

• Agreement between numerical and experimental

results;

• DSD shows two or three peaks depending on

breakup kernel used;

• The peak around 2.5 mm is a strong feature that

is absent when only coalescence contribute in

DSD formation;

• The more recent parameterizations show two

peak only (McFarquhar, 2004).


How to recognize breakup situations from DSD spectra

DSD technique (DS) minutes with RR higher than 8 mmh-1 are selected;

the point by point DSD spectrum ascending normalized derivative between

1.55 mm and 2.45 mm diameter is calculated (see figure below);

the point by point DSD spectrum descending normalized derivative for

diameters higher than 2.45 mm is calculated;

the ten minutes with the highest sum of renormalized ascending and

descending derivative value are considered as breakup minutes;

the central diameter of diametral class with the maximum descending

derivative is considered as breakup diameter;

finally the mean breakup diameter, with its standard deviation, is estimated

for each measuring site.


The selected Pludix

power spectra and

the corresponding

DSDs for breakup

occurrence.The selected DSDs by

the DS technique for

breakup occurrence for

the same site.

Breakup: power spectra vs DSD spectra


Breakup recognizing

Two main aims:

Distinguish breakup situation from no-breakup situation;

Estimate the breakup diameter.

The algorithm recognizes the breakup situations, but is not yet able to determine

automatically which DSD shape marks the transition from breakup to no-breakup

and vice versa future studies;

The estimated breakup diameter on the whole dataset shows a decrease with

altitude.


NASA collaboration

A recent collaboration with NASA gives me the possibility to access to a very

extended disdrometric database;

Different measuring sites: Iowa (Ifloods, ~41000 mins), Finland (Lpvex, ~8100

mins), Italy/France (Hymex ~10300 mins), Oklahoma (Mc3e, ~10000 mins);

The aim is to study a different parameterization for breakup DSD, with respect to

that used at the moment, for radar/satellite retrieval.

These studies and collaboration are in the

frame of Global Precipitation

Measurement (GPM) mission.

The new parameterization can be used to

analyze data from the first space-borne

Ku/Ka-band Dual-frequency Precipitation

Radar (DPR).


First results

The developed algorithm applied to the

whole dataset well identifies the breakup

situations (reddish lines).

The correlation coefficient between

measured DSD and Gamma

distribution assumes very low values

for breakup minutes.

Does a different distribution fit better

these situations?


MRR

The Micro Rain Radar (MRR) is a vertical radar Doppler that investigates the

atmosphere up to 6000 m above it.

It allows to have instantaneous vertical reconstruction of rain properties (DSD, rainfall

rate, reflectivity, liquid water content, etc.).

Data from 2 MRR installed at La Sapienza (Rome) and Trafoi (1570m a.s.l., Trentino

Alto Adige) they investigated 1000 m of atmosphere.

We are able to cover about 3000 m of atmosphere.

The MRR measurement can be used to check the results found NB: it has to

be take into account the differences due to climatology, season, etc.


Vertical structure

Better spatial resolution than the others operational radars;

Possibility to study the variations of rain properties in a limited portion of

atmosphere;

Possibility to study sudden variations especially during more intense

precipitation (left figure).


Integral parameters

Measurement with rainfall rate higher than 0.2 mm/h are considered for both

sites;

A and b terms of Z-R relationship are calculated as function of altitude;

The trend shows a strong decrease of A term with altitude, with values lower

for Tafoi site:

The same trend is found for b term, with the highest elevation in strong

agreement with results found.


Runoff studies

Conclusion of collaboration with Engineering Department of University of

Cagliari;

The fall velocity measurement of drops in accelerations were used to rescale

the rain simulator measurement.

The DSD obtained by rain

simulator are similar to those of

natural rain.

The rain simulator has been used to

study the runoff as function of soil

moisture and rainfall intensity.

High impact of initial soil moisture on the surface runoff process;

Lower rainfall rate increase the ponding time and decrease the surface runoff.


Summary and perspectives

To conclusion of CEOP-AEGIS project microphysics precipitation properties

over Tibetan Plateau during monsoon season have been analyzed;

Different datasets are used to study the DSD properties during breakup situations;

An automatic algorithm to recognize these situations and estimate the breakup

diameter analyzing DSD directly is under developing;

A collaboration with NASA, in the frame of GPM mission, is started; the aim is

study the possibility of a new parameterization of breakup DSD to apply to

radar/satellite retrieval (in particular for the first dual frequency radar);

Conclusion of collaboration with Engineering Department of University of

Cagliari published paper “On the estimation of surface runoff through a

new plot scale rainfall simulator in Sardinia, Italy.”

Documents

University of Ferrara Department of Physics and Earth Sciences