Precipitation Type Classification of Micro Rain Radar Data Using an Improved Doppler Spectral Processing Methodology

This paper describes a methodology for processing spectral raw data from Micro Rain Radar (MRR), a K-band vertically pointing Doppler radar designed to observe precipitation profiles. The objective is to provide a set of radar integral parameters and derived variables, including a precipitation type classification. The methodology first includes an improved noise level determination, peak signal detection and Doppler dealiasing, allowing us to consider the upward movements of precipitation particles. A second step computes for each of the height bin radar moments, such as equivalent reflectivity (Ze), average Doppler vertical speed (W), spectral width (σ), the skewness and kurtosis. A third step performs a precipitation type classification for each bin height, considering snow, drizzle, rain, hail, and mixed (rain and snow or graupel). For liquid precipitation types, additional variables are computed, such as liquid water content (LWC), rain rate (RR), or gamma distribution parameters, such as the liquid water content normalized intercept (Nw) or the mean mass-weighted raindrop diameter (Dm) to classify stratiform or convective rainfall regimes. The methodology is applied to data recorded at the Eastern Pyrenees mountains (NE Spain), first with a detailed case study where results are compared with different instruments and, finally, with a 32-day analysis where the hydrometeor classification is compared with co-located Parsivel disdrometer precipitation-type present weather observations. The hydrometeor classification is evaluated with contingency table scores, including Probability of Detection (POD), False Alarm Rate (FAR), and Odds Ratio Skill Score (ORSS). The results indicate a very good capacity of Method3 to distinguish rainfall and snow (PODs equal or greater than 0.97), satisfactory results for mixed and drizzle (PODs of 0.79 and 0.69) and acceptable for a reduced number of hail cases (0.55), with relatively low rate of false alarms and good skill compared to random chance in all cases (FAR 0.70). The methodology is available as a Python language program called RaProM at the public github repository

Vertical structure and microphysical observations of winter precipitation in an inner valley during the Cerdanya-2017 field campaign

Precipitation processes at windward and leeward sides of the mountains have been object of study for many decades. Instead, inner mountain valleys, where usually most mountain population lives, have received considerably less attention. This article examines precipitation processes during a winter field campaign in an inner valley of the Pyrenees (NE Spain) using, among other instruments, a K-band vertically pointing Doppler radar (Micro Rain Radar) and a laser-based optical disdrometer (Parsivel). A decoupling is found between the stalled air of the valley and the air of the free atmosphere above the mountain crest level, evidenced by an increase of turbulence and spectral width of precipitation particles. Wind shear layer may promote riming and aggregation of the ice and snow particles. Two main rainfall regimes are found during the campaign: (1) stratiform rainfall mostly produced by water vapour deposition processes, although sometimes riming and aggregation become important, and (2) weak convection with slight dominance of collision-coalescence processes. Precipitation characteristics at the bottom of the valley show typical continental features such as low Liquid Water Content, despite the valley is only about 100 km from the sea. This study demonstrates that inner valley may present distinct precipitation features with respect to windward and leeward precipitation

Characteristics of lightning flashes generating dancing sprites above thunderstorms

During the night of October 29-30, 2013, a low-light video camera at Pic du Midi (2877 m) in the French Pyrénées, recorded TLEs above a very active storm over the Mediterranean Sea. The minimum cloud top temperature reached -73 °C at ~1600 UTC while its cloud to ground (CG) flash rate reached ~30 fl min-1. Some sprite events with long duration are classified as dancing sprites. We analyze in detail the temporal evolution and estimated location of sprite elements for two cases of these events. They consist in series of sprite sequences with a duration that exceeds 1 second. By associating the cloud structure, the lightning activity, the electric field radiated in a broad range of low frequencies and the current moment waveform of the lightning strokes, some findings are highlighted: (i) In each series, successive sprite sequences reflect the occurrence time and location of individual positive lightning strokes across the stratiform region. (ii) The longer time-delayed (> 20 ms) sprite elements correspond to the lower impulsive charge moment changes (iCMC) of the parent stroke (< 200 C km) and they are shifted few tens of kilometres from their SP+CG stroke. However, both short and long time-delayed sprite elements also occur after strokes that produce a large iCMC and that are followed by a continuing current. (iii) The long time-delayed sprite elements produced during the continuing current correspond to surges in the current moment waveform. They occur sometimes at an altitude apparently lower than the previous short time-delayed sprite elements, possibly because of the lowered altitude of the ionosphere potential. (iv) The largest and brightest sprite elements produce significant current signatures, visible when their delay is not too short (~3-5 ms).Preprin

Multi-instrumental analysis of large sprite events and of their producing storm in southwestern France

During the night of 01-02 September, 2009, several TLEs including 3 halos and 16 distinct sprites were observed above a storm in north-western Mediterranean Sea with a camera at Pic du Midi (42.93° N, 0.14° E, 2877 m). Some of the sprites were especially large with vertical and horizontal extension estimated at about 70 km and 80 km, respectively. The TLE sequence lasted about one hour during a storm which developed 9 hours earlier over northern Spain in a very unstable atmosphere (CAPE at about 2000 J kg-1). The storm was characterized by a very circular shape and a size of about 250×250 km2 (cloud top temperature lower than -30°C) when the TLEs were produced (0209-0307 UT). The cloud to ground (CG) flash rate was large (45 min-1) one hour before the first TLE was detected and very low ( 5 ms) was observed for the electric field in ELF range in the cases of the very large sprites. Data from a VLF receiver shows the association between large sprites and early VLF signal perturbations.Postprint (published version

Kinematics and microphysics of MAP-IOP3 event from radar observations and Meso-NH simulations

International audienceThis paper presents a kinematic and microphysical study of the MAP-IOP3 orographic precipitation event performed with radar observations and Meso-NH numerical simulations. Studies relying on both observations and mesoscale model simulations are of great interest for achieving a better understanding of intense precipitation events. Despite some slight discrepancies between radar observations and numerical outputs in the present work, both emphasize the same phenomena. The merging of two convective cells, which is an important mechanism to locally enhance precipitation is shown. Beyond Meso-NH outputs and radar observations similarities, the Meso-NH model completes and precises qualitative conclusions inferred from radar observations. In particular, it permits to identify and quantify the microphysical processes involved in the triggering and development of the orographic precipitation. The computation of hydrometeor mixing ratio and microphysical budgets highlights the convective nature of the IOP3 precipitation, which is characterized by efficient microphysical mechanisms such as heavy riming, warm coalescence, and melting of heavy particles (graupel and hail). More precisely, the initiation of the system is associated with warm microphysics whereas the development of the system and enhancement of rain involve graupel and hail

Influence of drizzle on Z-M relationships in warm clouds.

This paper addresses the sensitivity of the relationships between radar reflectivity (Z) and liquid water content (M) for liquid water clouds to microphysical drizzle parameters by means of simulated radar observation at a frequency of 3 GHz of modeled cumulus clouds. A power law relationship for non drizzling clouds with water content as high as 3 gm− 3: Zc = 0.026 Mc1.61 is numerically derived and agreed with previous empirical relationships relative to cumulus and stratocumulus. This relationship is then used to explore the influence of drizzle on the correlation between radar reflectively and water content. Due to their large diameters with respect to cloud droplets, drizzle sized drops dominate radar reflectivity but do not carry the cloud water content so that reflectivity and liquid water content are expected to be not correlated in clouds containing drizzle. It is shown that for congestus or extreme congestus cumuli, microphysical conditions for which the Zc–Mc relationship can be used with a tolerance of 5 and 10% are provided whereas for humilis or mediocris cumuli, the presence of drizzle breaks down the Zc–Mc relationship whatever the situations

Kinematics and microphysics of MAP-IOP3 event from radar observations and Meso-NH simulations

International audienceThis paper presents a kinematic and microphysical study of the MAP-IOP3 orographic precipitation event performed with radar observations and Meso-NH numerical simulations. Studies relying on both observations and mesoscale model simulations are of great interest for achieving a better understanding of intense precipitation events. Despite some slight discrepancies between radar observations and numerical outputs in the present work, both emphasize the same phenomena. The merging of two convective cells, which is an important mechanism to locally enhance precipitation is shown. Beyond Meso-NH outputs and radar observations similarities, the Meso-NH model completes and precises qualitative conclusions inferred from radar observations. In particular, it permits to identify and quantify the microphysical processes involved in the triggering and development of the orographic precipitation. The computation of hydrometeor mixing ratio and microphysical budgets highlights the convective nature of the IOP3 precipitation, which is characterized by efficient microphysical mechanisms such as heavy riming, warm coalescence, and melting of heavy particles (graupel and hail). More precisely, the initiation of the system is associated with warm microphysics whereas the development of the system and enhancement of rain involve graupel and hail

Dynamics and microphysics of orographic precipitation during MAP IOP3

A dynamical and microphysical four-dimensional study of an intense orographic precipitating system is carried out in the frame of MAP IOP3 (25–26 September 1999). High precipitation opportunely occurred in the range of the Swiss operational Doppler radar at Monte Lema (Switzerland), the US SPOL polarimetric Doppler radar and the French Ronsard Doppler radar both located near Lago Maggiore (Italy). Radar data have been combined to deduce four-dimensional precipitation and wind fields during the most intense precipitation period (1600–2000 UTC on 25 September). The organization and evolution of the microphysical field have been obtained through an analysis of SPOL polarimetric data: nine hydrometeor classes (light, moderate and heavy rain, hail, rain–hail and graupel–hail mixtures, dry and wet snow, and ice crystals) are inferred by means of a fuzzy-logic method initially developed by Vivekanandan et al.The temporal mean study of reflectivity fields reveals that the precipitation presents a convective pattern and is primarily located on the foothills and over the first mountain. Mean microphysical fields reveal rain below the 0 °C level, wet snow, ice crystals and dry snow above with an embedded 2 km deep layer of graupel–hail mixture. This suggests convective microphysical processes.Temporal series of precipitation and wind fields are then analysed in order to characterize in detail the organization and evolution of the system. Three stages were identified: first an elongated structure growing and intensifying over the lake while moving towards the Alps, then a spreading of the system over the mountains and finally a weakening over Lago Maggiore and the mountains. It has to be noted that the lake and the first mountainous peaks were important factors in the generation and the intensification of convective cells: the lake acts as a secondary moisture source which can favour local convection, and mountainous slopes favour updraughts which permit a downwind extension of the system by ejection of precipitating particles according to the fountain particles concept. Finally, through a temporal and spatial microphysical study, coalescence below the 0 °C level, riming and freezing above, are concluded to be the major processes in the formation of intense precipitation. The essential role of ice phase in the formation and enhancement of precipitation has been highlighted

Multi-instrumental analysis of large sprite events and of their producing storm in southwestern France

During the night of 01-02 September, 2009, several TLEs including 3 halos and 16 distinct sprites were observed above a storm in north-western Mediterranean Sea with a camera at Pic du Midi (42.93° N, 0.14° E, 2877 m). Some of the sprites were especially large with vertical and horizontal extension estimated at about 70 km and 80 km, respectively. The TLE sequence lasted about one hour during a storm which developed 9 hours earlier over northern Spain in a very unstable atmosphere (CAPE at about 2000 J kg-1). The storm was characterized by a very circular shape and a size of about 250×250 km2 (cloud top temperature lower than -30°C) when the TLEs were produced (0209-0307 UT). The cloud to ground (CG) flash rate was large (45 min-1) one hour before the first TLE was detected and very low ( 5 ms) was observed for the electric field in ELF range in the cases of the very large sprites. Data from a VLF receiver shows the association between large sprites and early VLF signal perturbations

Dancing sprites: detailed analysis of two case studies

On 29–30 October 2013, a low-light video camera installed at Pic du Midi (2877¿m), recorded transient luminous events above a very active storm over the Mediterranean Sea. The minimum cloud top temperature reached -73°C, while its cloud to ground (CG) flash rate exceeded 30¿fl¿min-1. Some sprite events have long duration and resemble to dancing sprites. We analyze in detail the temporal evolution and estimated location of two series of sprite sequences, as well as the cloud structure, the lightning activity, the electric field radiated in a broad range of low frequencies, and the current moment waveform of the lightning strokes. (i) In each series, successive sprite sequences reflect time and location of corresponding positive lightning strokes across the stratiform region. (ii) The longer time-delayed (>20¿ms) sprite elements correspond to the lower impulsive charge moment changes (iCMC) of the parent strokes (<200¿C¿km), and they are shifted few tens of kilometers from their SP¿+¿CG stroke. However, both short and long time-delayed sprite elements also occur after strokes that produce a large iCMC and that are followed by a continuing current. (iii) The long time-delayed sprite elements during the continuing current correspond to surges in the current moment waveform. They occur sometimes at an altitude apparently lower than the previous short time-delayed sprite elements, possibly because of changes in the local conductivity. (iv) The largest and brightest sprite elements produce significant current signatures, visible when their delay is not too short (~3–5¿ms).Peer Reviewe