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Hailstorm at Negrar (Verona, Italy), August 27, 1971
Agricultural Meteorology, 16(1976) 185--192 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
H A I L S T O R M A T N E G R A R ( V E R O N A , I T A L Y ) , A U G U S T 27, 1971
A. CASTALDO
Central Office of Agrarian Ecology (U. C.E.A.), Italian Ministry of Agriculture and Forestry, Rome (Italy) (Received July 15, 1974; accepted February 26, 1975)
ABSTRACT Castaldo, A., 1976. Hailstorm at Negrar (Verona, Italy), August 27, 1971. Agric. Meteorol.,16: 185--192. The importance of a specific description of hailstorms is obvious when the various scientific requirements are considered, and it is very important to know, in detail, the effects of such storms on material at ground level. An example is given of the application of the "hail-pad" method, used in a network of accurate gauges and supplemented by eye-observations to assess the impact of a heavy hailstorm within the Negrar (Verona, Italy) experimental area on August 27, 1971. The density of the observation network and the frequency of instrument distribution (at least one gauge per 0.5 km ~ Within the storm area) made possible a full description of the entire phenomenon. It was verified that the extent of the damage caused by this storm could be regarded as a function of the combined effects of the various factors which are involved in the quantitative evaluation of a hailstorm, and which determine the impact energy. INTRODUCTION The field research, carried o u t in 1 9 7 1 , was designed t o evaluate statistically t h e possible effects in t i m e and space o f the anti-hail devices used b y local f a r m e r s (Castaldo, 1972). Such investigations have p r o v i d e d a great deal o f i n f o r m a t i o n a b o u t hail damage. The n e t w o r k o f hail-pads (or hail indicators) and hail recorders (Vento, 1 9 7 2 ) is illustrated in Fig.1. This degree o f i n s t r u m e n t a t i o n p e r m i t t e d an e x a m i n a t i o n o f the variation o f the h a i l s t o r m p a r a m e t e r s on a very small scale, and f u r t h e r m o r e m a d e it possible t o evaluate the degree o f sampling e r r o r f r o m the significant variations in these p a r a m e t e r s t h r o u g h o u t the collected data. Such q u a n t i t a t i v e and qualitative i n f o r m a t i o n m u s t be regarded as essential for a n y valid c o n s i d e r a t i o n and evaluation o f the effectiveness o f anti-hail o p e r a t i o n s . The details w h i c h f o l l o w were o b t a i n e d f o l l o w i n g the installation o f a dense o b s e r v a t i o n a l a n d i n s t r u m e n t a l n e t w o r k covering the target area ( o f the
186 L E G E N D :
Q
LAUNCHINGRAMPS OFE.XPLOSIVEROCKETS
Q
HAILRECORDERS
N
/ J
_ _ _ HAll.AREA
c
/ / f
-
\
_
2-
So
zano
•
~
.Ta~islo
srl~l'O
~6eno~,a '-'-~w •l'tdJ Rgvenua ~Ch,ava. Wo.oo . ~ - Z -
0_
OxM
1i
2i
'4 I
P~
I~'~ •
Siena
,
Anco~
•
Fig.1. Experimental area of Negrar.
a t t e m p t e d protection) and the control area, and are concerned with hail falling on the morning of August 27, 1971, on a hill area of about 25 km 2 (see Fig.l) mainly cultivated in vineyards. The areas within this zone where rockets were fired are indicated by the striped areas in Fig.2; the figures within the launching-ramp symbols indicate the number which were exploded (see Table I); the area hit by the hailstorm is shown by the outline trace. The results of this particular case (of the rocket launching) alone can not be considered as statistically significant, and therefore no reliable deductions or final conclusions can be made. It is interesting to note that this form of hail defence was temporarily
187 TABLE I Numbers of exploded rockets Launching ramp No.
Exploded rockets
Launching ramp No.
Exploded rockets
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
6 8 6 5 5 8 1 8 9 0 6 3 5 6 4 0 6 2 5 4 9 2
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
0 6 0 1 9 5 4 0 10 0 5 5 4 0 2 7 8 4 5 8 0 5
s t o p p e d in 1 9 7 2 and it seems possible t h a t its use m a y be b e c o m i n g less frequent. DESCRIPTION OF THE HAILSTORM AND THE DATA OBTAINED At a b o u t 0 8 h 0 0 (C.L.T.) o n the d a y in question, a s t o r m belt was advancing t o w a r d s the hill research area, m o v i n g in a west to east d i r e c t i o n at a speed o f 3 0 - - 4 0 k m / h . A brief p e r i o d o f h e a v y rain o c c u r r e d , a c c o m p a n i e d b y a s h o w e r o f hailstones in the Valpolicella region in w h i c h t h e Negrar z o n e is situated. The electrical activity was relatively s u b d u e d and the surface wind speed, f r o m a n o r t h - n o r t h w e s t direction, was n o t very significant. Within the area o f hail, all the 34 hail indicators, and 8 (80%) o f the hail recorders were hit. The t y p e o f pads w h i c h were hit are s h o w n in Table II, while Table I I I gives details m e a s u r e d b y the hail recorders (Fig.3), indicating t h a t the d u r a t i o n o f the intense s e c t o r o f the s t o r m was s o m e 4 - - 7 rain. A t y p i c a l e x a m p l e o f the i n f o r m a t i o n p r o v i d e d b y one of the hail-pads is given in Table IV, w h i c h shows the d i m e n s i o n s o f the imprints f o u n d o n the
188
N .
Km
0.
OKm
!
zs 2
3
4
Fig.2. Overlap of the presumable lines of the hail-isoenergy on the area where the rockets explosion occurred.
light laminate surface of the pads, together with the value of the energy index in Joules per square metre. I This unit was selected following a calibration at the Central Office of Agrarian Ecology of the hail-pads fitted with the light laminate. This surface appeared to give the most valid set of results, and'~all the data in the present paper refer to observations deduced from such recordings. A similar energy index was calculated in this n~anner for each pad with the results given in Table V which also includes the number of dents of a diameter i exceeding 10 mm. It is important to take into account the fact that all the data obtained from the instruments were corroborated by interviews and cross-questions of onthe-spot observers soon after the event, and by examination of the hailstone
189
TABLE
II
Pads collected Pad No.
Frequency A*
1 2 3 4 5 6 7 8 9 10 11 12 13 14
+ + + + + + + + + + + + + +
15 16 17 18 19 20 21 22
+ + + + + + + +
23 24
+ +
25
+
26 27 28 29
+ + +
30 31 32 33 34
+ + + + +
Total
of type of dented B
C
D
pads E
Total
+ +
+
+ +
+ + + +
+
+ +
+ + + + +
+ +
+ + + + + +
+ + + +
+ +
+ +
2 3 3
+
2 3 2
+
*
34
2 1 3 3 3 3 2 1
+
+ +
2 2 1 3 3 2 2 3 4 2 3 1 3 2
1
+
4
4
+ + +
+ +
3 3 3 1 1
23
13
78
*A = horizontal; B = south-vertical; C = east-vertical; D = north-vertical; E = west-vertical
190 TABLE III Parameters collected by the hail recorders No.
1 2 3 4 5 6 7 8 9 10
Weight
Recording
(g)
begin
70 30 50 60 120 80
end
no recording very confused recording very confused recording 8.08 8.13 very confused recording unsynchronized clock 8.08 8.12 unsynchronized clock 8.08 8.15 unsynchronized clock
Water from hail collected (cm 3)
Water from rain collected (cm 3)
200 20 100 100 130 30 100 60 220 150
1,250 900 750 1,000 1,150 750 620 1,000 1,300 1,050
samples. Finally, t h e s t o r m analysis was c o m p l e t e d b y use o f r a d a r i n f o r m a t i o n f r o m t h e O b s e r v a t o r y o f T o r r i c e l l a I! o f V e r o n a a n d k n o w l e d g e o f t h e s y n o p t i c m e t e o r o l o g i c a l situation. DISCUSSION T h e c a l c u l a t i o n of the e n e r g y i n d e x e s f o r each p a d s h o w n in T a b l e V enables p r o b a b l e lines o f e q u a l e n e r g y t o be d r a w n u p o v e r the area as illustrated in Fig.2. This d i a g r a m indicates t h e c o n s i d e r a b l e v a r i a t i o n s o f e n e r g y values over q u i t e a small r e s t r i c t e d area. C o n s i d e r a t i o n s o f the o v e r l a p (Castaldo a n d V e n t o , 1 9 7 3 ) in this figure b e t w e e n t h e h o p e d - f o r " p r o t e c t i o n " a n d t h e o b s e r v e d i n c i d e n c e are interesting, b u t it is b y n o m e a n s possible t o d r a w a n y f i r m c o n c l u s i o n s f r o m t h e d a t a c o n c e r n i n g one isolated incident; r e p e a t e d results f r o m a series o f such d e t a i l e d o b s e r v a t i o n s are r e q u i r e d t o establish statistical validity. ACKNOWLEDGEMENTS H e a r t y t h a n k s are d u e t o P r o f e s s o r E. Rosini f o r his valuable suggestions a n d t o Dr. D. V e n t o f o r his l a b o r i o u s and indispensable c o l l a b o r a t i o n t h r o u g h o u t t h e p e r i o d o f this s t u d y , as well as t o A. Bellecci, A. Carnevali, C. F r a n k a n d R. Salgari, w h o w e r e p a r t o f a g r o u p o p e r a t i n g in the Hail O b s e r v a t o r y , T o r r i c e l l a II, o f V e r o n a , f o r t h e i r valuable h e l p in the installation o f t h e surv e y n e t w o r k a n d in t h e c o l l e c t i o n o f the data, a n d to Dr. C. Gagliardi for his s u p e r v i s i o n in t h e t r a n s l a t i o n o f this paper.
191
Fig,3. H a i l r e c o r d e r used b y t h e U.C.E.A. a n d c o n s t r u c t e d by t h e firm S.I.A.P. ( F o t . G. Bellecci ).
T A B L E IV N u m b e r o f d e n t s s u b d i v i d e d i n t o d i m e n s i o n classes, a n d p e r t i n e n t e n e r g y i n d e x D e n t s o n h a i l p a d No. 4* ( 2 2 2 " ) : < 5 mm
5--10 mm
10--15 mm
15--20 mm
20--25 mm
25--30 mm
32
18
6
1
1
1
Energy index ( J / m 2) 349,4
* Panel h o r i z o n t a l (A). T h e i n c l i n a t i o n o f the h a i l s t o r m regarding t h e vertical d i r e c t i o n is < 7 °.
192 TABLE V Energy i n d e x calculated for t h e single hailpad. T h e i n c l i n a t i o n o f t h e h a i l s t o r m regarding t h e vertical d i r e c t i o n is < 7 ° Pad No.
Energy index ( J / m 2)
Number dents > 10 m m
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
0.6 6.2 2.8 349.4 12.5 6.0 462.0 320.8 31.0 45.9 121.1 21.9 26.4 63.0 9.7 21.3 116.8 59.1 48.4 117.4 65.1 40.9 80.9 77.4 24.9 14.0 47.0 25.9 5.3 44.9 31.6 5.6 27.6 0.6
0 0 0 9 0 0 13 2 2 2 3 1 1 2 0 1 4 2 2 5 3 3 3 3 1 1 3 1 0 2 1 0 1 0
REFERENCES Castaldo, A., 1972. A statistical m e t h o d of c o n t r o l of the results in an anti-hail e x p e r i m e n t Riv. Ital. Geofis. 2 1 ( 3 / 4 ) . Castaldo, A. a n d V e n t o , D. 1973. Sul r i l e v a m e n t o delle g r a n d i n a t e per il c o n t r o l l o dei m e t o d i di p r e v e n z i o n e . Riv. Ital. Geofis., 2 2 ( 5 / 6 ) . C h a n g n o n Jr., S. A., 1964. Surface features of t w o intersecting h a i l s t o r m s - Nubila, 6(1). C h a n g n o n Jr., S. A., N o t e o n H a i l s t o r m Size D i s t r i b u t i o n . Ill. State Water Surv., U r b a n a , Ill. V e n t o , D., 1972. The d e t e r m i n a t i o n of t h e i m p a c t energy of the hail. Riv. Ital. Geofis., 21(1/2).
H A I L S T O R M A T N E G R A R ( V E R O N A , I T A L Y ) , A U G U S T 27, 1971
A. CASTALDO
Central Office of Agrarian Ecology (U. C.E.A.), Italian Ministry of Agriculture and Forestry, Rome (Italy) (Received July 15, 1974; accepted February 26, 1975)
ABSTRACT Castaldo, A., 1976. Hailstorm at Negrar (Verona, Italy), August 27, 1971. Agric. Meteorol.,16: 185--192. The importance of a specific description of hailstorms is obvious when the various scientific requirements are considered, and it is very important to know, in detail, the effects of such storms on material at ground level. An example is given of the application of the "hail-pad" method, used in a network of accurate gauges and supplemented by eye-observations to assess the impact of a heavy hailstorm within the Negrar (Verona, Italy) experimental area on August 27, 1971. The density of the observation network and the frequency of instrument distribution (at least one gauge per 0.5 km ~ Within the storm area) made possible a full description of the entire phenomenon. It was verified that the extent of the damage caused by this storm could be regarded as a function of the combined effects of the various factors which are involved in the quantitative evaluation of a hailstorm, and which determine the impact energy. INTRODUCTION The field research, carried o u t in 1 9 7 1 , was designed t o evaluate statistically t h e possible effects in t i m e and space o f the anti-hail devices used b y local f a r m e r s (Castaldo, 1972). Such investigations have p r o v i d e d a great deal o f i n f o r m a t i o n a b o u t hail damage. The n e t w o r k o f hail-pads (or hail indicators) and hail recorders (Vento, 1 9 7 2 ) is illustrated in Fig.1. This degree o f i n s t r u m e n t a t i o n p e r m i t t e d an e x a m i n a t i o n o f the variation o f the h a i l s t o r m p a r a m e t e r s on a very small scale, and f u r t h e r m o r e m a d e it possible t o evaluate the degree o f sampling e r r o r f r o m the significant variations in these p a r a m e t e r s t h r o u g h o u t the collected data. Such q u a n t i t a t i v e and qualitative i n f o r m a t i o n m u s t be regarded as essential for a n y valid c o n s i d e r a t i o n and evaluation o f the effectiveness o f anti-hail o p e r a t i o n s . The details w h i c h f o l l o w were o b t a i n e d f o l l o w i n g the installation o f a dense o b s e r v a t i o n a l a n d i n s t r u m e n t a l n e t w o r k covering the target area ( o f the
186 L E G E N D :
Q
LAUNCHINGRAMPS OFE.XPLOSIVEROCKETS
Q
HAILRECORDERS
N
/ J
_ _ _ HAll.AREA
c
/ / f
-
\
_
2-
So
zano
•
~
.Ta~islo
srl~l'O
~6eno~,a '-'-~w •l'tdJ Rgvenua ~Ch,ava. Wo.oo . ~ - Z -
0_
OxM
1i
2i
'4 I
P~
I~'~ •
Siena
,
Anco~
•
Fig.1. Experimental area of Negrar.
a t t e m p t e d protection) and the control area, and are concerned with hail falling on the morning of August 27, 1971, on a hill area of about 25 km 2 (see Fig.l) mainly cultivated in vineyards. The areas within this zone where rockets were fired are indicated by the striped areas in Fig.2; the figures within the launching-ramp symbols indicate the number which were exploded (see Table I); the area hit by the hailstorm is shown by the outline trace. The results of this particular case (of the rocket launching) alone can not be considered as statistically significant, and therefore no reliable deductions or final conclusions can be made. It is interesting to note that this form of hail defence was temporarily
187 TABLE I Numbers of exploded rockets Launching ramp No.
Exploded rockets
Launching ramp No.
Exploded rockets
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
6 8 6 5 5 8 1 8 9 0 6 3 5 6 4 0 6 2 5 4 9 2
23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
0 6 0 1 9 5 4 0 10 0 5 5 4 0 2 7 8 4 5 8 0 5
s t o p p e d in 1 9 7 2 and it seems possible t h a t its use m a y be b e c o m i n g less frequent. DESCRIPTION OF THE HAILSTORM AND THE DATA OBTAINED At a b o u t 0 8 h 0 0 (C.L.T.) o n the d a y in question, a s t o r m belt was advancing t o w a r d s the hill research area, m o v i n g in a west to east d i r e c t i o n at a speed o f 3 0 - - 4 0 k m / h . A brief p e r i o d o f h e a v y rain o c c u r r e d , a c c o m p a n i e d b y a s h o w e r o f hailstones in the Valpolicella region in w h i c h t h e Negrar z o n e is situated. The electrical activity was relatively s u b d u e d and the surface wind speed, f r o m a n o r t h - n o r t h w e s t direction, was n o t very significant. Within the area o f hail, all the 34 hail indicators, and 8 (80%) o f the hail recorders were hit. The t y p e o f pads w h i c h were hit are s h o w n in Table II, while Table I I I gives details m e a s u r e d b y the hail recorders (Fig.3), indicating t h a t the d u r a t i o n o f the intense s e c t o r o f the s t o r m was s o m e 4 - - 7 rain. A t y p i c a l e x a m p l e o f the i n f o r m a t i o n p r o v i d e d b y one of the hail-pads is given in Table IV, w h i c h shows the d i m e n s i o n s o f the imprints f o u n d o n the
188
N .
Km
0.
OKm
!
zs 2
3
4
Fig.2. Overlap of the presumable lines of the hail-isoenergy on the area where the rockets explosion occurred.
light laminate surface of the pads, together with the value of the energy index in Joules per square metre. I This unit was selected following a calibration at the Central Office of Agrarian Ecology of the hail-pads fitted with the light laminate. This surface appeared to give the most valid set of results, and'~all the data in the present paper refer to observations deduced from such recordings. A similar energy index was calculated in this n~anner for each pad with the results given in Table V which also includes the number of dents of a diameter i exceeding 10 mm. It is important to take into account the fact that all the data obtained from the instruments were corroborated by interviews and cross-questions of onthe-spot observers soon after the event, and by examination of the hailstone
189
TABLE
II
Pads collected Pad No.
Frequency A*
1 2 3 4 5 6 7 8 9 10 11 12 13 14
+ + + + + + + + + + + + + +
15 16 17 18 19 20 21 22
+ + + + + + + +
23 24
+ +
25
+
26 27 28 29
+ + +
30 31 32 33 34
+ + + + +
Total
of type of dented B
C
D
pads E
Total
+ +
+
+ +
+ + + +
+
+ +
+ + + + +
+ +
+ + + + + +
+ + + +
+ +
+ +
2 3 3
+
2 3 2
+
*
34
2 1 3 3 3 3 2 1
+
+ +
2 2 1 3 3 2 2 3 4 2 3 1 3 2
1
+
4
4
+ + +
+ +
3 3 3 1 1
23
13
78
*A = horizontal; B = south-vertical; C = east-vertical; D = north-vertical; E = west-vertical
190 TABLE III Parameters collected by the hail recorders No.
1 2 3 4 5 6 7 8 9 10
Weight
Recording
(g)
begin
70 30 50 60 120 80
end
no recording very confused recording very confused recording 8.08 8.13 very confused recording unsynchronized clock 8.08 8.12 unsynchronized clock 8.08 8.15 unsynchronized clock
Water from hail collected (cm 3)
Water from rain collected (cm 3)
200 20 100 100 130 30 100 60 220 150
1,250 900 750 1,000 1,150 750 620 1,000 1,300 1,050
samples. Finally, t h e s t o r m analysis was c o m p l e t e d b y use o f r a d a r i n f o r m a t i o n f r o m t h e O b s e r v a t o r y o f T o r r i c e l l a I! o f V e r o n a a n d k n o w l e d g e o f t h e s y n o p t i c m e t e o r o l o g i c a l situation. DISCUSSION T h e c a l c u l a t i o n of the e n e r g y i n d e x e s f o r each p a d s h o w n in T a b l e V enables p r o b a b l e lines o f e q u a l e n e r g y t o be d r a w n u p o v e r the area as illustrated in Fig.2. This d i a g r a m indicates t h e c o n s i d e r a b l e v a r i a t i o n s o f e n e r g y values over q u i t e a small r e s t r i c t e d area. C o n s i d e r a t i o n s o f the o v e r l a p (Castaldo a n d V e n t o , 1 9 7 3 ) in this figure b e t w e e n t h e h o p e d - f o r " p r o t e c t i o n " a n d t h e o b s e r v e d i n c i d e n c e are interesting, b u t it is b y n o m e a n s possible t o d r a w a n y f i r m c o n c l u s i o n s f r o m t h e d a t a c o n c e r n i n g one isolated incident; r e p e a t e d results f r o m a series o f such d e t a i l e d o b s e r v a t i o n s are r e q u i r e d t o establish statistical validity. ACKNOWLEDGEMENTS H e a r t y t h a n k s are d u e t o P r o f e s s o r E. Rosini f o r his valuable suggestions a n d t o Dr. D. V e n t o f o r his l a b o r i o u s and indispensable c o l l a b o r a t i o n t h r o u g h o u t t h e p e r i o d o f this s t u d y , as well as t o A. Bellecci, A. Carnevali, C. F r a n k a n d R. Salgari, w h o w e r e p a r t o f a g r o u p o p e r a t i n g in the Hail O b s e r v a t o r y , T o r r i c e l l a II, o f V e r o n a , f o r t h e i r valuable h e l p in the installation o f t h e surv e y n e t w o r k a n d in t h e c o l l e c t i o n o f the data, a n d to Dr. C. Gagliardi for his s u p e r v i s i o n in t h e t r a n s l a t i o n o f this paper.
191
Fig,3. H a i l r e c o r d e r used b y t h e U.C.E.A. a n d c o n s t r u c t e d by t h e firm S.I.A.P. ( F o t . G. Bellecci ).
T A B L E IV N u m b e r o f d e n t s s u b d i v i d e d i n t o d i m e n s i o n classes, a n d p e r t i n e n t e n e r g y i n d e x D e n t s o n h a i l p a d No. 4* ( 2 2 2 " ) : < 5 mm
5--10 mm
10--15 mm
15--20 mm
20--25 mm
25--30 mm
32
18
6
1
1
1
Energy index ( J / m 2) 349,4
* Panel h o r i z o n t a l (A). T h e i n c l i n a t i o n o f the h a i l s t o r m regarding t h e vertical d i r e c t i o n is < 7 °.
192 TABLE V Energy i n d e x calculated for t h e single hailpad. T h e i n c l i n a t i o n o f t h e h a i l s t o r m regarding t h e vertical d i r e c t i o n is < 7 ° Pad No.
Energy index ( J / m 2)
Number dents > 10 m m
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
0.6 6.2 2.8 349.4 12.5 6.0 462.0 320.8 31.0 45.9 121.1 21.9 26.4 63.0 9.7 21.3 116.8 59.1 48.4 117.4 65.1 40.9 80.9 77.4 24.9 14.0 47.0 25.9 5.3 44.9 31.6 5.6 27.6 0.6
0 0 0 9 0 0 13 2 2 2 3 1 1 2 0 1 4 2 2 5 3 3 3 3 1 1 3 1 0 2 1 0 1 0
REFERENCES Castaldo, A., 1972. A statistical m e t h o d of c o n t r o l of the results in an anti-hail e x p e r i m e n t Riv. Ital. Geofis. 2 1 ( 3 / 4 ) . Castaldo, A. a n d V e n t o , D. 1973. Sul r i l e v a m e n t o delle g r a n d i n a t e per il c o n t r o l l o dei m e t o d i di p r e v e n z i o n e . Riv. Ital. Geofis., 2 2 ( 5 / 6 ) . C h a n g n o n Jr., S. A., 1964. Surface features of t w o intersecting h a i l s t o r m s - Nubila, 6(1). C h a n g n o n Jr., S. A., N o t e o n H a i l s t o r m Size D i s t r i b u t i o n . Ill. State Water Surv., U r b a n a , Ill. V e n t o , D., 1972. The d e t e r m i n a t i o n of t h e i m p a c t energy of the hail. Riv. Ital. Geofis., 21(1/2).