scholarly journals Influences of Lake Malawi on the spatial and diurnal variability of local precipitation

2019 ◽  
Vol 23 (7) ◽  
pp. 2795-2812 ◽  
Author(s):  
Shunya Koseki ◽  
Priscilla A. Mooney
Keyword(s):  
Diurnal Cycle ◽  
Water Resource Management ◽  
Moisture Flux ◽  
Atmospheric Model ◽  
Lake Malawi ◽  
Land Breeze ◽  
Surrounding Area ◽  
Breeze Circulation ◽  
Flux Divergence ◽  
Diurnal Variability

Abstract. We investigate how the intensity and spatial distribution of precipitation vary around Lake Malawi on a diurnal timescale, which can be valuable information for water resource management in tropical south-eastern African nations. Using a state-of-the-art satellite product and regional atmospheric model, the well-defined diurnal cycle is detected around Lake Malawi with harmonic and principle component analyses: the precipitation is intense during midnight to morning over Lake Malawi and the precipitation peaks in the daytime over the surrounding area. This diurnal cycle in the precipitation around the lake is associated with the lake–land breeze circulation. Comparisons between the benchmark simulation and an idealized simulation in which Lake Malawi is removed reveal that the diurnal variations in precipitation are substantially amplified by the presence of Lake Malawi. This is most evident over the lake and surrounding coastal regions. Lake Malawi also enhances the lake–land breeze circulation; the nocturnal lakeward land breeze generates surface convergence effectively and precipitation intensifies over the lake. Conversely, the daytime landward lake breeze generates the intense divergence over the lake and precipitation is strongly depressed over the lake. The lake–land breeze and the background vapour enriched by Lake Malawi drive primarily a diurnal variation in the surface moisture flux divergence/convergence over the lake and surrounding area which contributes to the diurnal cycle of precipitation in this region.

scholarly journals Observed and modeled diurnal variations around Lake Malawi

2019 ◽  
Author(s):  
Shunya Koseki ◽  
Priscilla A. Mooney
Keyword(s):  
Diurnal Cycle ◽  
Water Resource Management ◽  
Sensible Heat Flux ◽  
Moisture Flux ◽  
Lake Malawi ◽  
Diurnal Variations ◽  
Land Breeze ◽  
Surrounding Area ◽  
Breeze Circulation ◽  
Flux Divergence

Abstract. We investigate how the intensity and spatial distribution of precipitation varies around Lake Malawi on a diurnal time scale, which can be valuable information for water resource management in tropical southeastern African nations. Using a state-of-the-art satellite product and regional atmospheric model, the well-defined diurnal cycle is detected around Lake Malawi with harmonic and principle component analyses: the precipitation is intense during midnight to morning over Lake Malawi and the precipitation peaks in the daytime over the surrounding area. This diurnal cycle in the precipitation around the lake is associated with the lake-land breeze circulation. Comparisons between the benchmark simulation and an idealized simulation in which Lake Malawi is removed, reveals that the diurnal variations in the precipitation are substantially amplified by the presence of Lake Malawi. This is most evident over the lake and relatively surrounding coastal regions. Lake Malawi also enhances the lake-land breeze circulation; the nocturnal lakeward land breeze generates the surface convergence effectively and the precipitation intensifies over the lake. Conversely, the daytime landward lake breeze generates the intense divergence over the lake and the precipitation is strongly depressed over the lake. The lake surface helps to create the thermal contrast between the lake and land and consequently the local lake-land breeze system is maintained via sensible heat flux. The lake-land breeze and the background water vapour enriched by Lake Malawi drives dominantly a diurnal variation in the surface moisture flux divergence/convergence over the lake and surrounding area and consequently, contributes to the diurnal cycle of the precipitation.

scholarly journals The influence of sea- and land-breeze circulations on the diurnal variability of precipitation over a tropical island

2017 ◽  
Author(s):  
Lei Zhu ◽  
Zhiyong Meng ◽  
Fuqing Zhang ◽  
Paul M. Markowski
Keyword(s):  
Diurnal Variation ◽  
Numerical Simulations ◽  
Diurnal Cycle ◽  
Lower Troposphere ◽  
Sea Breeze ◽  
Hainan Island ◽  
Dominant Factor ◽  
Land Breeze ◽  
Moist Convection ◽  
Diurnal Variability

Abstract. This study examines the diurnal variation of precipitation over Hainan Island in the South China Sea using gauge observations from 1950 to 2010 and CMORPH satellite estimates from 2006 to 2015, as well as numerical simulations. Precipitation is most significant from April to October, and exhibits a strong diurnal cycle resulting from land/sea breeze circulations. More than 60 % of the total annual precipitation over the island is attributable to the diurnal cycle, with a significant monthly variability as well. The CMORPH and gauge datasets agree well, except that the CMORPH data underestimates precipitation and has a 1-h delay of peaks. The diurnal cycle of the rainfall and the related land/sea breeze circulations during May and June were well captured by convection-allowing numerical simulations with WRF, which were initiated from 10-year average ERA-interim reanalysis, despite slightly overall overestimation and 1-h delay of the rainfall peak. The diurnal precipitation is due to a diurnal cycle of moist convection, which initiates around noontime owing to low-level convergence associated with the sea breeze circulation. The precipitation intensifies rapidly thereafter and peaks in the afternoon with the collisions of sea breeze fronts from different sides of the island. Cold pools of the convective storms contribute to the inland propagation of the sea breeze. The precipitation dissipates quickly in the evening owing to the cooling and stabilization of the lower troposphere and decrease of boundary-layer moisture. Interestingly, the rather high island orography is not a dominant factor in the diurnal variation of the precipitation over the island.

scholarly journals The influence of sea- and land-breeze circulations on the diurnal variability in precipitation over a tropical island

2017 ◽  
Vol 17 (21) ◽  
pp. 13213-13232 ◽  
Author(s):  
Lei Zhu ◽  
Zhiyong Meng ◽  
Fuqing Zhang ◽  
Paul M. Markowski
Keyword(s):  
Diurnal Variation ◽  
Numerical Simulations ◽  
Diurnal Cycle ◽  
Wrf Model ◽  
Lower Troposphere ◽  
Sea Breeze ◽  
Dominant Factor ◽  
Land Breeze ◽  
Moist Convection ◽  
Diurnal Variability

Abstract. This study examines the diurnal variation in precipitation over Hainan Island in the South China Sea using gauge observations from 1951 to 2012 and Climate Prediction Center MORPHing technique (CMORPH) satellite estimates from 2006 to 2015, as well as numerical simulations. The simulations are the first to use climatological mean initial and lateral boundary conditions to study the dynamic and thermodynamic processes (and the impacts of land–sea breeze circulations) that control the rainfall distribution and climatology. Precipitation is most significant from April to October and exhibits a strong diurnal cycle resulting from land–sea breeze circulations. More than 60 % of the total annual precipitation over the island is attributable to the diurnal cycle with a significant monthly variability. The CMORPH and gauge datasets agree well, except that the CMORPH data underestimate precipitation and have a 1 h peak delay. The diurnal cycle of the rainfall and the related land–sea breeze circulations during May and June were well captured by convection-permitting numerical simulations with the Weather Research and Forecasting (WRF) model, which were initiated from a 10-year average ERA-Interim reanalysis. The simulations have a slight overestimation of rainfall amounts and a 1 h delay in peak rainfall time. The diurnal cycle of precipitation is driven by the occurrence of moist convection around noontime owing to low-level convergence associated with the sea-breeze circulations. The precipitation intensifies rapidly thereafter and peaks in the afternoon with the collisions of sea-breeze fronts from different sides of the island. Cold pools of the convective storms contribute to the inland propagation of the sea breeze. Generally, precipitation dissipates quickly in the evening due to the cooling and stabilization of the lower troposphere and decrease of boundary layer moisture. Interestingly, the rather high island orography is not a dominant factor in the diurnal variation in precipitation over the island.

Modulation of the Diurnal Cycle of Rainfall Associated with the MJO Observed by a Dense Hourly Rain Gauge Network at Sarawak, Borneo

2013 ◽  
Vol 26 (13) ◽  
pp. 4858-4875 ◽  
Author(s):  
Hironari Kanamori ◽  
Tetsuzo Yasunari ◽  
Koichiro Kuraji
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Coastal Region ◽  
Daily Rainfall ◽  
Sea Breeze ◽  
Moisture Flux ◽  
Rain Gauge ◽  
Flux Divergence ◽  
Interior Region ◽  
Rain Gauge Network

Abstract This study investigates spatiotemporal characteristics of the diurnal cycle (DC) of rainfall over Sarawak in northwest Borneo Island, associated with large-scale intraseasonal disturbances represented by the Madden–Julian oscillation (MJO). This is accomplished using a dense hourly rain gauge network and satellite data. The spatial pattern of the DC is classified into two major groups, coastal and interior regions, based on remarkable differences in rainfall peak times and amplitudes. Amplitudes of the DC and daily rainfall amount increase in active MJO phases at all sites, but the MJO has a stronger effect in the coastal region than the interior region. This modulation of rainfall by the MJO disturbance is largely attributed to rainfall frequency in the interior region, but to both frequency and intensity of rainfall in the coastal region. The low-level westerly wind anomaly enhances convergence, the land–sea breeze, and a midnight rainfall peak in the coastal region during the active MJO phase. Analysis of moisture flux divergence and moist static instability suggests the different dynamics of this modulation of the DC between coastal and interior regions.

scholarly journals The effect of coastal upwelling on the sea-breeze circulation at Cabo Frio, Brazil: a numerical experiment

1998 ◽  
Vol 16 (7) ◽  
pp. 866-871 ◽  
Author(s):  
S. H. Franchito ◽  
V. B. Rao ◽  
J. L. Stech ◽  
J. A. Lorenzzetti
Keyword(s):  
Coastal Upwelling ◽  
Surface Wind ◽  
Three Dimensional ◽  
Sea Breeze ◽  
Atmospheric Model ◽  
Ocean Model ◽  
Breeze Circulation ◽  
Mesoscale Meteorology ◽  
Forcing Function ◽  
Cabo Frio

Abstract. The effect of coastal upwelling on sea-breeze circulation in Cabo Frio (Brazil) and the feedback of sea-breeze on the upwelling signal in this region are investigated. In order to study the effect of coastal upwelling on sea-breeze a non-linear, three-dimensional, primitive equation atmospheric model is employed. The model considers only dry air and employs boundary layer formulation. The surface temperature is determined by a forcing function applied to the Earth's surface. In order to investigate the seasonal variations of the circulation, numerical experiments considering three-month means are conducted: January-February-March (JFM), April-May-June (AMJ), July-August-September (JAS) and October-November-December (OND). The model results show that the sea-breeze is most intense near the coast at all the seasons. The sea-breeze is stronger in OND and JFM, when the upwelling occurs, and weaker in AMJ and JAS, when there is no upwelling. Numerical simulations also show that when the upwelling occurs the sea-breeze develops and attains maximum intensity earlier than when it does not occur. Observations show a similar behavior. In order to verify the effect of the sea-breeze surface wind on the upwelling, a two-layer finite element ocean model is also implemented. The results of simulations using this model, forced by the wind generated in the sea-breeze model, show that the sea-breeze effectively enhances the upwelling signal.Key words. Meteorology and atmospheric dynamics (mesoscale meteorology; ocean-atmosphere interactions) · Oceanography (numerical modeling)

scholarly journals The diurnal cycle of cloud profiles over land and ocean between 51° S and 51° N, seen by the CATS spaceborne lidar from the International Space Station

2018 ◽  
Vol 18 (13) ◽  
pp. 9457-9473 ◽  
Author(s):  
Vincent Noel ◽  
Hélène Chepfer ◽  
Marjolaine Chiriaco ◽  
John Yorks
Keyword(s):  
High Altitude ◽  
International Space Station ◽  
Diurnal Cycle ◽  
Space Station ◽  
Cloud Fraction ◽  
Vertical Profiles ◽  
Diurnal Variability ◽  
International Space ◽  
Low Level ◽  
Diurnal Cycles

Abstract. We document, for the first time, how detailed vertical profiles of cloud fraction (CF) change diurnally between 51∘ S and 51∘ N, by taking advantage of 15 months of measurements from the Cloud-Aerosol Transport System (CATS) lidar on the non-sun-synchronous International Space Station (ISS). Over the tropical ocean in summer, we find few high clouds during daytime. At night they become frequent over a large altitude range (11–16 km between 22:00 and 04:00 LT). Over the summer tropical continents, but not over ocean, CATS observations reveal mid-level clouds (4–8 km above sea level or a.s.l.) persisting all day long, with a weak diurnal cycle (minimum at noon). Over the Southern Ocean, diurnal cycles appear for the omnipresent low-level clouds (minimum between noon and 15:00) and high-altitude clouds (minimum between 08:00 and 14:00). Both cycles are time shifted, with high-altitude clouds following the changes in low-altitude clouds by several hours. Over all continents at all latitudes during summer, the low-level clouds develop upwards and reach a maximum occurrence at about 2.5 km a.s.l. in the early afternoon (around 14:00). Our work also shows that (1) the diurnal cycles of vertical profiles derived from CATS are consistent with those from ground-based active sensors on a local scale, (2) the cloud profiles derived from CATS measurements at local times of 01:30 and 13:30 are consistent with those observed from CALIPSO at similar times, and (3) the diurnal cycles of low and high cloud amounts (CAs) derived from CATS are in general in phase with those derived from geostationary imagery but less pronounced. Finally, the diurnal variability of cloud profiles revealed by CATS strongly suggests that CALIPSO measurements at 01:30 and 13:30 document the daily extremes of the cloud fraction profiles over ocean and are more representative of daily averages over land, except at altitudes above 10 km where they capture part of the diurnal variability. These findings are applicable to other instruments with local overpass times similar to CALIPSO's, such as all the other A-Train instruments and the future EarthCARE mission.

scholarly journals The Atmospheric Water Balance over the Semiarid Murray–Darling River Basin

2008 ◽  
Vol 9 (3) ◽  
pp. 521-534 ◽  
Author(s):  
Clara Draper ◽  
Graham Mills
Keyword(s):  
Surface Water ◽  
Water Balance ◽  
River Basin ◽  
Moisture Flux ◽  
Limited Area ◽  
Consecutive Series ◽  
Atmospheric Water ◽  
Flux Divergence ◽  
Murray Darling Basin ◽  
Moisture Flux Divergence

Abstract The atmospheric water balance over the semiarid Murray–Darling River basin in southeast Australia is analyzed based on a consecutive series of 3- to 24-h NWP forecasts from the Australian Bureau of Meteorology’s Limited Area Prediction System (LAPS). Investigation of the LAPS atmospheric water balance, including comparison of the forecast precipitation to analyzed rain gauge observations, indicates that the LAPS forecasts capture the general qualitative features of the water balance. The key features of the atmospheric water balance over the Murray–Darling Basin are small atmospheric moisture flux divergence (at daily to annual time scales) and extended periods during which the atmospheric water balance terms are largely inactive, with the exception of evaporation, which is consistent and very large in summer. These features present unique challenges for NWP modeling. For example, the small moisture fluxes in the basin can easily be obscured by the systematic errors inherent in all NWP models. For the LAPS model forecasts, there is an unrealistically large evaporation excess over precipitation (associated with a positive bias in evaporation) and unexpected behavior in the moisture flux divergence. Two global reanalysis products (the NCEP Reanalysis I and the 40-yr ECMWF Re-Analysis) also both describe (physically unrealistic) long-term negative surface water budgets over the Murray–Darling Basin, suggesting that the surface water budget cannot be sensibly diagnosed based on output from current NWP models. Despite this shortcoming, numerical models are in general the most appropriate tool for examining the atmospheric water balance over the Murray–Darling Basin, as the atmospheric sounding network in Australia has extremely low coverage.

scholarly journals Characterizing the diurnal cycle of South Atlantic stratocumulus cloud properties from satellite retrievals

2018 ◽  
Author(s):  
Chellappan Seethala ◽  
Jan Fokke Meirink ◽  
Ákos Horváth ◽  
Ralf Bennartz ◽  
Rob Roebeling
Keyword(s):  
Diurnal Variation ◽  
Biomass Burning ◽  
Diurnal Cycle ◽  
Near Infrared ◽  
South Atlantic ◽  
Radiation Budget ◽  
Ozone Monitoring Instrument ◽  
Liquid Water Path ◽  
Diurnal Variability ◽  
Late Afternoon

Abstract. Marine stratocumulus (Sc) clouds play an essential role in the earth radiation budget. Here, we compare liquid water path (LWP), optical thickness (COT), and effective radius (CER) retrievals from two years of collocated Spinning Enhanced Visible and InfraRed Imager (SEVIRI), MODerate resolution Imaging Spectroradiometer (MODIS), and Tropical Rainfall Measuring Mission Microwave Imager (TMI) observations, estimate the effect of biomass burning smoke on passive imager retrievals, as well as evaluate the diurnal cycle of South Atlantic marine Sc clouds. The effect of absorbing aerosols from biomass burning on the retrievals was investigated using aerosol index (AI) obtained from the Ozone Monitoring Instrument (OMI). SEVIRI and MODIS LWPs were found to decrease with increasing AI relative to TMI LWP, consistent with well-known negative visible/near-infrared retrieval biases in COT and CER. In the aerosol-affected months of July–August–September, SEVIRI LWP – based on the 1.6-µm CER – was biased low by 14 g m−2 (~ 16 %) compared to TMI in overcast scenes, while MODIS LWP showed a smaller low bias of 4 g m−2 (~ 5 %) for the 1.6-µm channel and a high bias of 8 g m−2 (~ 10 %) for the 3.7-µm channel compared to TMI. Neglecting aerosol-affected pixels reduced the mean SEVIRI-TMI LWP bias considerably. On a two-year data base, SEVIRI LWP had a correlation with TMI and MODIS LWP of about 0.86 and 0.94, respectively, and biases of only 4–8 g m−2 (5–10 %) for overcast cases. The SEVIRI LWP diurnal cycle was in good overall agreement with TMI except in the aerosol-affected months. Both TMI and SEVIRI LWP decreased from morning to late afternoon, after which a slight increase was observed. Terra and Aqua MODIS mean LWPs also suggested a similar diurnal variation. The relative amplitude of the two-year mean and seasonal mean LWP diurnal cycle varied between 35–40 % from morning to late afternoon for overcast cases. The diurnal variation in SEVIRI LWP was mainly due to changes in COT, while CER showed only little diurnal variability.

scholarly journals Coupling of Precipitation and Cloud Structures in Oceanic Extratropical Cyclones to Large-Scale Moisture Flux Convergence

2018 ◽  
Vol 31 (23) ◽  
pp. 9565-9584 ◽  
Author(s):  
Sun Wong ◽  
Catherine M. Naud ◽  
Brian H. Kahn ◽  
Longtao Wu ◽  
Eric J. Fetzer
Keyword(s):  
Large Scale ◽  
Moisture Flux ◽  
Extratropical Cyclones ◽  
Flux Divergence ◽  
Moisture Flux Convergence ◽  
Convective Clouds ◽  
Moisture Advection ◽  
Deep Convective Clouds ◽  
Stratiform Clouds ◽  
High Level

Precipitation (from TMPA) and cloud structures (from MODIS) in extratropical cyclones (ETCs) are modulated by phases of large-scale moisture flux convergence (from MERRA-2) in the sectors of ETCs, which are studied in a new coordinate system with directions of both surface warm fronts (WFs) and surface cold fronts (CFs) fixed. The phase of moisture flux convergence is described by moisture dynamical convergence Qcnvg and moisture advection Qadvt. Precipitation and occurrence frequencies of deep convective clouds are sensitive to changes in Qcnvg, while moisture tendency is sensitive to changes in Qadvt. Increasing Qcnvg and Qadvt during the advance of the WF is associated with increasing occurrences of both deep convective and high-level stratiform clouds. A rapid decrease in Qadvt with a relatively steady Qcnvg during the advance of the CF is associated with high-level cloud distribution weighting toward deep convective clouds. Behind the CF (cold sector or area with polar air intrusion), the moisture flux is divergent with abundant low- and midlevel clouds. From deepening to decaying stages, the pre-WF and WF sectors experience high-level clouds shifting to more convective and less stratiform because of decreasing Qadvt with relatively steady Qcnvg, and the CF experiences shifting from high-level to midlevel clouds. Sectors of moisture flux divergence are less influenced by cyclone evolution. Surface evaporation is the largest in the cold sector and the CF during the deepening stage. Deepening cyclones are more efficient in poleward transport of water vapor.

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