Microphysical Properties of Maritime Squall Line Observed on June 2, 2008 in Taiwan

Abstract

The physical characteristics of rain are reflected by the shape of the raindrop size distribution (RDSD). Specifically, the RDSD is the result of different precipitation formation processes. We measured the RDSD at the surface in heavy rainfall during SoWMEX/TiMREX (2008) in Taiwan. The heavy rainfall was characterized by a squall line accompanied by trailing stratiform precipitation, and it was partitioned into three regions based on radar reflectivity patterns: convective line, stratiform, and reflectivity trough. The convective line was further partitioned into the convective center, leading edge, and trailing edge using a threshold rainfall intensity of 20 mm h -1 .The leading edge, which belongs to the convective line, had upward motion from the surface and contained many small drops. The leading edge was characterized by a small median volume diameter (D 0 ) and a linear shape of gamma RDSD. In the convective center, a strong updraught rose to the top of the cell with time, and many large drops over 4 mm were observed. The convective center, which had large D 0 and normalized intercept parameter (N W ), was characterized by an upward convex shape of gamma RDSD. The range of raindrop diameter decreased toward the trailing edge, with no updraught or only weak updraughts at high altitudes. The trailing edge had large shape and slope parameters, along with a more upward convex shape of gamma RDSD. A bright band was observed in the stratiform region with continual downward motion from the bright band to the surface, even though the intensity became weak. In the stratiform region, D 0 and N W were small and the gamma RDSD had an upward convex shape.The different RDSDs in each region of a maritime squall line suggest the existence of different cloud microphysical processes described by the change of RDSD parameters: the coalescence process induces an increase of D 0 and shape parameter and a decrease of N W , while the break-up process induces a decrease of D 0 and an increase of N W .In comparison with other maritime storms, the convective center has small log 10 N W and large D m value. And the convective edge region is positioned between convective center and stratiform region in the D m -log 10 N W scatter plot.

Evolution of microphysical structure of a subtropical squall line observed by a polarimetric radar and a disdrometer during OPACC in Eastern China

“…As the squall line passes the PARSIVEL, the convective region of the squall line is subdivided into three segments: LE, CC, and TE, as illustrated in Figure using the criteria in Jung et al . []. For LE, the concentration of raindrops is the lowest among the three segments with the maximum drop diameter ( D max ) ~4 mm (Figure a).…”

“…Disdrometers and polarimetric radars have been extensively used to derive DSDs and other microphysical properties, including mass‐weighted diameter ( D m ), logarithmic normalized intercept (log 10 N w ), and liquid water content (LWC), respectively [ Bringi et al ., ; Rosenfeld and Ulbrich , ]. The DSD characteristics of squall lines have been studied in many field campaigns throughout the world, such as the South China Sea Monsoon Experiment (SCSMEX) in Asia [ Wang and Carey , ], the African Monsoon Multidisciplinary Analysis (AMMA) in Mexico [ Evaristo et al ., ], the Midlatitude Continental Convective Clouds Experiment (MC3E) in the United States [ Wang et al ., ], and the Southwest Monsoon Experiment/Terrain‐influenced Monsoon Rainfall Experiment (SoWMEX/TiMREX) in Taiwan [ Jung et al ., ]. Early studies used ground‐based disdrometers to derive DSDs within passing squall lines and revealed DSDs in three regions, convection, transition, and stratiform [e.g., Uijlenhoet et al ., ].…”

“…The DSD characteristics within the convection region of a squall line in nearby Taiwan were further divided into three different regions, leading edge (LE), the convective center (CC), and the trailing edge (TE) [ Jung et al ., ]. The CC is defined as the region where rainfall rate exceeds 20 mm h −1 , while LE and TE sandwiched CC.…”

Controls on phase composition and ice water content in a convection-permitting model simulation of a tropical mesoscale convective system

“…This is due to the reduction in the riming of cloud water by graupel compared to the accretion of cloud water by rain. The large IWC in the downdraught regions of the warmer temperature regime is where graupel is expected, which is often located behind and below the convective updraughts (Barnes and Houze, 2014), where the suggestion is that these larger particles help to generate downdraughts through mass loading (Franklin et al, 2005;Jung et al, 2012). This argument is supported by analysis of the downdraught IWC that shows that the majority of the ice in the downdraughts is graupel.…”

A Comparison Study of Summer Season Raindrop Size Distribution Between Palau and Taiwan, Two Islands in Western Pacific

“…In all rain rate classes, Palau rainfall has higher values of N w , μ, and Λ and Taiwan rainfall has higher D m values. Similar type of results were reported by Jung et al (2012) for a squall line in south Taiwan. They found higher (lower) values of D m (N w , μ, and Λ) in convective region of the Taiwan squall line than tropical oceanic storms.…”