Relationship between the Upper-level Winds and the Horizontal Movement of Localized Heavy Rainfall in the Afternoon of Summer Days around Tokyo

This study analyses the spatial and temporal distribution of heavy rainfall events (HREs) and its associated circulation anomalies over Tanzania during March to May (MAM) rainfall season of 1980–2010. A total of 822 HREs were revealed, concentrated over the northern sector (NS) of the country. Years with anomalous HREs are associated with low-level westerly convergence, advection of moisture from both the Indian Ocean and Congo basin, an upper warm temperature anomaly (UWTA), intensified and well-positioned Intertropical Convergence Zone (ITCZ), and pronounced rising motion since the ascending limb of the Walker type of circulation is centered over Tanzania. The analysis of the UWTA in this study has brought a key factor in exploring the possible likely cause and improved early warning system for the HREs during the MAM rainfall season in Tanzania. Making use of the thermal wind equation and the velocity divergent form of the continuity equation (DFCE), we found that the UWTA results into an upper-level horizontal wind divergence which significantly accelerates vertical ascent, deepening the surface low pressure for an enhanced convective process and HREs formation.

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Mesoscale Convective Systems: A Case Scenario of the ‘Heavy Rainfall’ Event of 15–20 January 2013 over Southern Africa

Climate ◽

10.3390/cli7060073 ◽

2019 ◽

Vol 7 (6) ◽

pp. 73

Author(s):

Modise Wiston ◽

Kgakgamatso Marvel Mphale

Keyword(s):

Atlantic Ocean ◽

Southern Africa ◽

Heavy Rainfall ◽

Rainfall Event ◽

Mesoscale Convective Systems ◽

Heavy Rainfall Event ◽

Convergence Zone ◽

Convective Systems ◽

Mesoscale Convective ◽

Upper Level

Southern east Africa is prone to some extreme weather events and interannual variability of the hydrological cycle, including tropical cyclones and heavy rainfall events. Most of these events occur during austral summer and are linked to shifts in the intertropical convergence zone, changes in El Niño Southern Oscillation signatures, sea surface temperature and sea level pressure. A typical example include mesoscale convective systems (MCSs) that occur between October and March along the eastern part, adjacent to the warm waters of Mozambique Channel and Agulhas Current. In this study we discuss a heavy rainfall event over southern Africa, focusing particularly on the period 15–20 January 2013, the period during which MCSs were significant over the subcontinent. This event recorded one of the historic rainfalls due to extreme flooding and overflows, loss of lives and destruction of economic and social infrastructure. An active South Indian Convergence Zone was associated with the rainfall event sustained by a low-level trough linked to a Southern Hemisphere planetary wave pattern and an upper-level ridge over land. In addition, also noteworthy is a seemingly strong connection to the strength of the African Easterly Jet stream. Using rainfall data, satellite imagery and re-analysis (model processed data combined with observations) data, our analysis indicates that there was a substantial relation between rainfall totals recorded/observed and the presence of MCSs. The low-level trough and upper-level ridge contributed to moisture convergence, particularly from tropical South East Atlantic Ocean, which in turn contributed to the prolonged life span of the rainfall event. Positive temperature anomalies favored the substantial contribution of moisture fluxes from the Atlantic Ocean. This study provides a contextual assessment of rainfall processes and insight into the physical control mechanisms and feedback of large-scale convective interactions over tropical southern Africa.

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Very heavy rainfall over Punjab, Himachal Pradesh and Haryana during 24-27 September 1988- case study

MAUSAM ◽

10.54302/mausam.v47i3.3741 ◽

2021 ◽

Vol 47 (3) ◽

pp. 269-274

Author(s):

D. S. DESAI ◽

N. B. TRADE ◽

M. G. HUPRIKAR

Keyword(s):

Heavy Rainfall ◽

Himachal Pradesh ◽

Low Level ◽

Westerly Trough ◽

Upper Level

Heavy to exceptionally very heavy rainfall over Haryana Punjab and Himachal Pradesh during 24-27 September 1988 was associated with the low level easterly trough which was overlain by upper level diffluent westerly trough. The case study of this phenomenon is reported here.

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Role of baroclinic trough in triggering vertical motion during summertime heavy rainfall events in Korea

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0216.1 ◽

2021 ◽

Cited By ~ 1

Author(s):

Chanil Park ◽

Seok-Woo Son ◽

Jung-Hoon Kim

Keyword(s):

Heavy Rainfall ◽

Vertical Motion ◽

The West ◽

Rainfall Events ◽

Synoptic Conditions ◽

Upper Level ◽

Diabatic Forcing ◽

Upper Level Jet ◽

Q Vector ◽

Heavy Rainfall Events

AbstractThe nature of the vertical motion responsible for the summertime (June–September) heavy rainfall events (HREs) in Korea is quantitatively examined. By compositing 318 HREs in 1979–2018, it is found that the synoptic conditions of the HREs are typically characterized by a developing surface cyclone with a southwesterly low-level jet on its southeastern flank and an upper-level trough to the west of the HREs. This baroclinic environment allows for well-organized vertical motion over Korea at the equatorward side of the upper-level jet entrance. The relative importance of dynamic and diabatic forcings in driving the vertical motion is further quantified by solving the quasi-geostrophic omega equation. It turns out that the dynamic forcing, defined as Q-vector convergence, is comparable to the diabatic forcing in the developing stage of the HREs. The diabatic forcing, however, becomes more important in the mature stage as latent heating rapidly increases. The decomposition of Q-vector into the transverse and shearwise components reveals that the dynamic uplift is largely caused by the shearwise Q-vector convergence which is closely related to the developing trough in the upper-to-middle troposphere on the west of the HREs. This result indicates that the HREs in Korea are organized by the baroclinic trough coupled to moist processes, with a minor contribution of the thermally-direct secondary circulation at the entrance region of the upper-level jet.

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Development and Evaluation of Mei-Yu Season Quantitative Precipitation Forecasts in Taiwan River Basins Based on a Conceptual Climatology Model

Weather and Forecasting ◽

10.1175/waf-d-11-00098.1 ◽

2012 ◽

Vol 27 (3) ◽

pp. 586-607 ◽

Cited By ~ 5

Author(s):

Chung-Chieh Wang ◽

Chu-Ying Kung ◽

Cheng-Shang Lee ◽

George Tai-Jen Chen

Keyword(s):

Heavy Rainfall ◽

Statistical Tests ◽

River Basins ◽

Short Wave ◽

Rain Gauge ◽

Quantitative Precipitation Forecasts ◽

Southern Taiwan ◽

Upper Level ◽

Central Weather Bureau ◽

Rainfall Climatology

Abstract Using rain gauge data during 134 mei-yu frontal cases in May–June 1991–2006, a rainfall climatology in relation to the positions of fronts every 0.5° in Taiwan is obtained, showing widespread precipitation with maxima over windward mountain slopes associated with frontal passages. For six major river basins, rainfall characteristics and synoptic factors are further analyzed to build a conceptual climatology model for short-term quantitative precipitation forecasts (QPFs). The four basins in central–southern Taiwan exhibit increased heavy-rainfall frequencies (>25%) roughly from 2° south to 1° north of the front, while the two basins in northern Taiwan have lower frequencies with different characteristics mainly due to the differences in their topography. The synoptic factors in the checklist employed by the Central Weather Bureau and important to heavy rainfall are identified for each of the six basins through statistical tests and their threat score (TS). These factors include those related to mei-yu fronts, low-level jets and moisture, upper-level divergence–diffluence, and short-wave troughs. A conceptual climatology model that uses both synoptic and probability forecasting guidance is developed, and in practice the average rainfall climatology is replaced by one obtained for heavy-rainfall periods if either of the two guidance schemes indicates heavy-rainfall possibility. This model for 0–6- and 0–12-h QPFs is also evaluated for its usefulness using cases during the 2007–08 seasons. With typical TSs of 0.2–0.3 (for heavy rainfall), this approach outperforms simple climatology in all six basins especially toward higher thresholds (about 20–50 mm) and for 12-h events, where it also shows advantages over model QPFs in southern Taiwan. Thus, the model can provide useful information for operational use.

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The influence of the coastal front on heavy rainfall events along the east coast

10.32469/10355/79565 ◽

2019 ◽

Author(s):

◽

Chasity B. Henson

Keyword(s):

Tropical Cyclone ◽

Heat Release ◽

Latent Heat ◽

Heavy Rainfall ◽

East Coast ◽

Latent Heat Release ◽

Rainfall Events ◽

Upper Level ◽

Heavy Rainfall Events ◽

Frontal Boundary

Coastal fronts are commonly found along the East Coast of the United States and can often be associated with intense rainfall and flooding due to elevated convection on the cold side of the boundary. Five heavy rainfall events ([greater to or equal than] 250 mm 24 hr-1) during the fall months along the East Coast were investigated using numerical weather prediction (NWP) models to determine the influence of an upper-level trough/cut-off low, an offshore tropical cyclone, a frontal boundary, and a moisture plume on the intense precipitation. Using experimental NWP simulations, it was determined that the tropical cyclone had an impact on the moisture plume and subsequent location of precipitation due to an associated deformation zone. The tropical cyclone prolonged the events by 6 hours, but inhibited the amount of moisture and resulting precipitation by deterring southeasterly flow. Evaporation from precipitation (surface heat fluxes) contributed to less than 25% (33%) of the precipitation, while latent heat release had the largest impact on the rain totals due to positive feedback from convection and an influence on the frontal boundary. Terrain also impacted the frontal boundary in each event, altering precipitation totals. Parcel trajectories confirmed regions of frontogenesis to be the main source of lift for the release of gravitational instability and convective initiation in each event, while the extratropical cyclone provided upper-level support for ascent and organized the plume of deep tropospheric moisture perpendicular to the front. Three of the five events lasted multiple days due to negative PV advection by the irrotational wind, in response to latent heat release in the region of convection, acting to slow the propagation of the upper-level low.

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Synoptic environment associated with heavy rainfall events on the coastland of Northeast Brazil

Advances in Geosciences ◽

10.5194/adgeo-35-73-2013 ◽

2013 ◽

Vol 35 ◽

pp. 73-78 ◽

Cited By ~ 11

Author(s):

P. T. Oliveira ◽

K. C. Lima ◽

C. M. Santos e Silva

Keyword(s):

Coastal Area ◽

Heavy Rainfall ◽

Daily Rainfall ◽

South Atlantic Convergence Zone ◽

Rain Gauge ◽

Economic Losses ◽

Heavy Rainfall Event ◽

Northeast Brazil ◽

Daily Data ◽

Upper Level

Abstract. Northeast Brazil (NEB) has an extensive coastal area, often hit by natural disasters that bring many social and economic losses. The objective of this work was to study the synoptic environment associated with a heavy rainfall event (HRE) on the coastland of NEB. We used daily rainfall data for coastal area of NEB between the states of Rio Grande do Norte and Bahia, divided into two subregions: north and south coastland. This data was obtained from the hydrometeorological network managed by the Agência Nacional de Águas and the daily data reanalysis from the ERAInterim. For the selection of HRE the technique of quantiles was used, thus defined HRE where at least one rain gauge recorded rainfall above 95th percentile. The interannual distribution of events showed occurrence maximum in La Niña years and minimal in El Niño years. The results suggest that the HRE were formed mainly due to the action of upper-level cyclonic vortex, in hight levels, and due to the action to South Atlantic convergence zone, in low levels.

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Causes of the upper-level warm temperature anomaly (UWTA) associated with March–May heavy rainfall in Tanzania

Atmospheric Research ◽

10.1016/j.atmosres.2020.105016 ◽

2020 ◽

Vol 242 ◽

pp. 105016

Author(s):

Kantamla Biseke Mafuru ◽

Tan Guirong

Keyword(s):

Heavy Rainfall ◽

Temperature Anomaly ◽

Warm Temperature ◽

Upper Level

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Synoptic Environments Associated with the Training of Convective Cells

Weather and Forecasting ◽

10.1175/2009waf2222275.1 ◽

2010 ◽

Vol 25 (2) ◽

pp. 446-464 ◽

Cited By ~ 5

Author(s):

Ryan P. Aylward ◽

Jamie L. Dyer

Keyword(s):

Extreme Precipitation ◽

Heavy Rainfall ◽

Precipitable Water ◽

Moisture Convergence ◽

Convective Storms ◽

Warm Sector ◽

Upper Level ◽

Convective Cells

Abstract Many studies have been done on synoptically forced systems and heavy rainfall, but little research has gone into the forecasting of training convective storms specifically in a synoptically forced environment. Training convective storms are recognized as the propagation of convective cells repeatedly over the same location. The research in this paper examines 38 separate synoptically forced convective extreme precipitation training (SCEPT) events to find trends and consistencies in their synoptic environments. Three separate cases were found in which a SCEPT event occurred: closed upper-level trough (CULL), upper-level trough (ULT), and 850-hPa trough–low (850TL). Each event occurred in areas of precipitable water greater than 36.42 mm (1.43 in.), near maximums of 850-hPa moisture convergence and 700-hPa upward vertical velocities, under the 850-hPa jet, and in the warm sector of a midlatitude cyclone. CULL and ULT events occurred in strongly forced synoptic environments where 500- and 300-hPa troughs were evident and generally positively tilted. Little upper-level forcing, above 700 hPa, was found in 850TL events.

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The Secondary Low and Heavy Rainfall Associated with Typhoon Mindulle (2004)

Monthly Weather Review ◽

10.1175/2007mwr2069.1 ◽

2008 ◽

Vol 136 (4) ◽

pp. 1260-1283 ◽

Cited By ~ 27

Author(s):

Cheng-Shang Lee ◽

Yi-Chin Liu ◽

Fang-Ching Chien

Keyword(s):

Heavy Rainfall ◽

Numerical Study ◽

North Coast ◽

Mountain Range ◽

Mountain Area ◽

The North ◽

Main Circulation ◽

Upper Level ◽

The Taiwan Strait ◽

Strong Vorticity

Abstract This paper presents an observational and numerical study of Typhoon Mindulle (2004) as it affected Taiwan. Mindulle made landfall on the east coast of Taiwan at 1500 UTC 1 July 2004, and after 13 h, it exited Taiwan from the north coast. Severe rainfall (with a maximum amount of 787 mm) occurred over central-southwestern Taiwan on 2 July 2004. During the landfall of Mindulle’s main circulation, a secondary low formed over the Taiwan Strait. However, the secondary low, after it developed significantly (vorticity exceeded 5 × 10−4 s−1 over a 30-km radius), did not replace the original center as was observed in many other storms. Instead, it moved inland and dissipated after the original center redeveloped near the north coast of Taiwan. In this study, the evolution of the secondary low, the redevelopment of the primary center, and the processes leading to the severe rainfall were examined. Results showed that the processes leading to the formation and the development of the secondary low were similar to those described in previous studies. These processes include the leeside subsidence warming, the horizontal transport of vorticity around the northern tip of the Central Mountain Range (CMR), and the overmountain upper-level vorticity remnant. However, because of the northward track, Mindulle preserved some strong vorticity on the eastern slope of the CMR. This strong vorticity remnant was steered northward over the ocean offshore from the north coast where the redevelopment of the primary center occurred. This “quasi-continuous track” of Mindulle has not been documented in previous studies. The vortex interaction between the redeveloped primary center and the secondary low resulted in the northeastward movement of the secondary low, which then dissipated after making landfall. Analyses also showed that even though heavy rainfall would occur over the mountain area when only the southwesterly flow prevailed, as on 3 July 2004, Typhoon Mindulle and the secondary low provided extra convergence that resulted in the west–east-oriented convective bands. These convective bands and the orographic lifting of the circulation associated with the secondary low resulted in the heavy rainfall over the central-western plains area.

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