Dual-Polarization Radar Observations of Deep Convection over Lake Victoria Basin in East Africa

Waniha, Pascal F.; Roberts, Rita D.; Wilson, James W.; Kijazi, Agnes Lawrence; Katole, Benedicto

doi:10.3390/atmos10110706

Cited by 10 publications

(14 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thus, extreme Lake Victoria lightning clusters form in an unstable environment with enhanced low-level moisture and large-scale low-level convergence. Local processes not resolved in a reanalysis dataset, such as outflow boundaries (Waniha et al 2019) or converging nocturnal land and mountain breezes, likely also aid in initiating these extreme clusters.…”

Section: Thunderstorm Initiationmentioning

confidence: 99%

“…Dual-polarimetric Doppler radars, a key observation component for thunderstorm nowcasting, are located along the northern (Entebbe, Uganda) and southern coasts of Lake Victoria (Mwanza, Tanzania) and to the southwest near Kigali, Rwanda. Archives of the radar volume scans are not available for the period analyzed in this paper, although a recent case study by Waniha et al (2019) using the Mwanza radar emphasized the role of gust fronts and other preexisting boundaries in initiating new convective storms over the lake. Precipitation radars aboard the Tropical Rainfall Measuring Mission (TRMM; Kawanishi et al 2000) and Global Precipitation Measurement (GPM; Skofronick-Jackson et al 2017) satellites and Lightning Imaging Sensors on board TRMM (TRMM-LIS; Christian et al 1999) and the International Space Station (ISS-LIS; Blakeslee et al 2014) have proved useful for process studies and in characterizing deep moist convection; however, these sensors only observe the region for 90 s or less during sporadic overpasses and thus do not observe the full convective life cycle.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Prolific Lightning and Thunderstorm Initiation over the Lake Victoria Basin in East Africa

Virts

Goodman²

2020

Monthly Weather Review

View full text Add to dashboard Cite

The Lake Victoria basin of East Africa is home to over 30 million people, over 200 000 of whom are employed in fishing or transportation on the lake. Approximately 3000–5000 individuals are killed by thunderstorms yearly, primarily by outflow winds and resulting large waves. Prolific lightning activity and thunderstorm initiation in the basin are examined using continuous total lightning observations from the Earth Networks Global Lightning Network (ENGLN) for September 2014–August 2018. Seasonal shifts in the intertropical convergence zone produce semiannual lightning maxima over the lake. Diurnally, solar heating and lake and valley breezes produce daytime lightning maxima north and east of the lake, while at night the peak lightning density propagates southwestward across the lake. Cluster analysis reveals terrain-related thunderstorm initiation hot spots northeast of the lake; clusters also initiate over the lake and northern lowlands. The most prolific clusters initiate between 1100 and 1400 LT, about 1–2 h earlier than the average cluster. Most daytime thunderstorms dissipate without reaching Lake Victoria, and annually 85% of clusters producing over 1000 flashes over Lake Victoria initiate in situ. Initiation times of prolific Lake Victoria clusters exhibit a bimodal seasonal cycle: equinox-season thunderstorms initiate most frequently between 2200 and 0400 LT, while solstice-season thunderstorms initiate most frequently from 0500 to 0800 LT, more than 12 h after the afternoon convective peak over land. More extreme clusters are more likely to have formed over land and propagated over the lake, including 36 of the 100 most extreme Lake Victoria thunderstorms. These mesoscale clusters are most common during February–April and October–November.

show abstract

Section: Thunderstorm Initiationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Prolific Lightning and Thunderstorm Initiation over the Lake Victoria Basin in East Africa

Virts

Goodman²

2020

Monthly Weather Review

View full text Add to dashboard Cite

show abstract

“…The first radar observations from the S‐band dual‐polarised radar in Mwanza (southern shore of Lake Victoria) operated by the Tanzania Meteorological Agency have been presented by Waniha et al . (2019), demonstrating the utility of the radar to identify convergence lines over the lake.…”

Section: Discussionmentioning

confidence: 99%

“…With radar, multiple scans could be used to study the 3D evolution of the circulations, especially convergence and storm structure. The first radar observations from the S-band dual-polarised radar in Mwanza (southern shore of Lake Victoria) operated by the Tanzania Meteorological Agency have been presented by Waniha et al (2019), demonstrating the utility of the radar to identify convergence lines over the lake.…”

Section: Discussionmentioning

confidence: 99%

“…The campaign was also associated with the HIGHWAY field campaign, which included two enhanced observation periods during March–May and July–August 2019. Among other data sources, observations were collected using ground‐based weather stations across the basin and radar located on the southern shore of the lake in Mwanza, Tanzania (Waniha et al ., 2019). HIGHWAY has also enhanced the long‐term collection of atmospheric data over East Africa to improve the quality of operational forecasts and increase climate monitoring.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Aircraft observations and sub‐km modelling of the lake–land breeze circulation over Lake Victoria

Woodhams

Barrett

Marsham

et al. 2021

Quart J Royal Meteoro Soc

View full text Add to dashboard Cite

The lake–land breeze circulation over Lake Victoria was observed in unprecedented detail with a research aircraft during the HyVic pilot flight campaign in January 2019. An evening and morning flight observed the lake and land breezes respectively under mostly dry conditions. The circulation was observed at various heights along a transect across the lake and onshore in Tanzania. Profiles of the lower troposphere were recorded by dropsondes over the lake and land. Convection‐permitting MetUM simulations with different horizontal grid‐spacings (including sub‐km) were run for the flight periods. During the evening flight, the aircraft crossed the lake breeze front over land at 1627 LT, approximately 50 km to the east of the lake shore, recording a 6 g·kg−1 decrease in specific humidity and reversal in wind direction over ∼5 km. During the morning flight, a shallow land breeze was observed across the eastern shore at 0545 LT. At least one region of increased and deeper moisture (previously seen in simulations but never observed) was sampled over the lake surface between 0527 and 0855 LT. This bulge of moisture was likely formed from the lifting of near‐surface moist air above the lake by low‐level convergence. The observations and model simulations suggest that low‐level convergence occurred at the leading edge of the land breeze, which had detached from the main land breeze and independently propagated westward across the lake with wave‐like characteristics. The MetUM simulations were able to reasonably reproduce the lake breeze front, bulge feature, and its propagation, which is a major achievement given the sparse observational data for model initialisation in this region. However, some timing, resolution and boundary‐layer depth biases require further investigation. Overall, this pilot campaign provided an unprecedented snapshot of the Lake Victoria lake–land breeze circulation and motivates a more comprehensive field campaign in the future.

show abstract

Evaluating synthetic aperture radar surface winds for convective squalls in the Gulf of Mexico

La,

Messager

2024

Quart J Royal Meteoro Soc

View full text Add to dashboard Cite

The detection and quantification of strong sea surface winds, reaching up to 25 m·s−1, whether associated with deep convection aloft or not, have been extensively discussed in previous studies. This method involves the combined observation of the same event from both low‐orbit altitude and geostationary (GEO) satellites. Strong surface winds observed by the Sentinel‐1 C‐band synthetic aperture radar (SAR) are robustly associated with deep convective clouds detected by GEO infrared sensors. The current paper aims to generalize the previous assessment of several convective wind events by collecting a larger dataset and comparing these data to in‐situ wind observations. To achieve this, we evaluated wind speeds retrieved from Sentinel‐1 SAR images against corresponding in‐situ wind measurements from all active buoys/stations in the Gulf of Mexico. Significant agreement between satellite‐based winds and in‐situ data was achieved, particularly for wind speeds exceeding 3 m·s−1, with even better agreement for wind speeds over 10 m·s−1. From this dataset, three specific convective cases were extracted to illustrate various stages of convective squall events: before, during, and after the occurrence of a squall peak. In each case, comparison with in‐situ measurements showed that SAR‐estimated wind speeds closely matched observed speeds, including the peak convective winds, which were estimated at 18.90 m·s−1 and measured at 20.69 m·s−1. Furthermore, combining these findings with GOES‐16 sequential images illustrates the temporal and spatial similarity between deep convection areas, estimated strong sea surface wind patterns, and measured wind speeds.

show abstract

Dual-Polarization Radar Observations of Deep Convection over Lake Victoria Basin in East Africa

Cited by 10 publications

References 17 publications

Prolific Lightning and Thunderstorm Initiation over the Lake Victoria Basin in East Africa

Prolific Lightning and Thunderstorm Initiation over the Lake Victoria Basin in East Africa

Aircraft observations and sub‐km modelling of the lake–land breeze circulation over Lake Victoria

Evaluating synthetic aperture radar surface winds for convective squalls in the Gulf of Mexico

Contact Info

Product

Resources

About