scholarly journals The Role of Aerosols in Convective Processes during the Midsummer Drought in the Caribbean

2015 ◽  
Vol 2015 ◽  
pp. 1-16 ◽  
Author(s):  
Nathan Hosannah ◽  
Hamed Parsiani ◽  
Jorge E. González
Keyword(s):  
Heavy Precipitation ◽  
Atmospheric Modeling ◽  
Dew Point ◽  
Saharan Dust ◽  
Convective Precipitation ◽  
Precipitation Event ◽  
Atmospheric Conditions ◽  
Cloud Resolving Model ◽  
The Caribbean

Saharan dust (SD) heavily impacts convective precipitation in the Caribbean. To better understand the role of SD in precipitation development during the midsummer drought (MSD), an observational campaign, centered at the city of Mayagüez, Puerto Rico (18.21 N, 67.13 W), between 3 June and 15 July 2014, was conducted in order to select a range of atmospheric conditions to be simulated using the Regional Atmospheric Modeling System (RAMS) cloud resolving model under “no SD” and “SD” conditions. The events included one dry day with moderate-heavy SD, one localized moderate rainfall event with moderate SD, one island-wide light precipitation event with heavy SD, and one island-wide heavy precipitation event with light-moderate SD. Model results show that (1) precipitation results are improved when compared with observation with the presence of SD, (2) precipitation, cloud fraction, dew point temperatures, and humidity are significantly reduced under SD conditions, (3) precipitation can occur when SD is removed for a dry day, (4) there is evidence of rain being delayed due to the presence of SD without rainfall intensity or accumulation increases, (5) liquid mixing ratio increases of up to 1.4 g kg−1occur in the absence of SD, and (6) vertical wind increases of up to 0.8 m s−1occur in the absence of SD.

scholarly journals Parameter Modulation of Madden-Julian Oscillation Behaviors in BCC_CSM1.2: The Key Role of Moisture-Shallow Convection Feedback

Atmosphere ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 241 ◽  
Author(s):  
Kai Huang ◽  
Hong-Li Ren ◽  
Xiangwen Liu ◽  
Pengfei Ren ◽  
Yuntao Wei ◽  
...  
Keyword(s):  
Lower Troposphere ◽  
Latin Hypercube Sampling ◽  
Heavy Precipitation ◽  
Convective Precipitation ◽  
Physical Parameters ◽  
Madden Julian Oscillation ◽  
Shallow Convection ◽  
Climate System Model ◽  
New Strategy

To reveal key parameter-related physical mechanisms in simulating Madden-Julian Oscillation (MJO), seven physical parameters in the convection and cloud parameterization schemes of Beijing Climate Center Climate System Model (BCC_CSM1.2) are perturbed with Latin hypercube sampling method. A new strategy is proposed to select runs with good and poor MJO simulations among 85 generated ones. Outputs and parameter values from good and poor simulations are composited separately for comparison. Among the seven chosen parameters, a decreased value of precipitation efficiency for shallow convection, higher values of relative humidity threshold for low stable clouds and evaporation efficiency for deep convective precipitation are crucial to simulate a better MJO. Changes of the three parameters act together to suppress heavy precipitation and increase the frequency of light rainfall over the Indo-Pacific region, supplying more moisture in low and middle troposphere. As a result of a wetter lower troposphere ahead of the MJO main convection, the low-level moisture preconditioning along with the leading shallow convection tends to be enhanced, favorable for MJO’s further development and eastward propagation. The MJO’s further propagation across the Maritime Continent (MC) in good simulations is accompanied with more land precipitation dominated by shallow convection. Therefore, the above-mentioned three parameters are found to be crucial parameters out of the seven ones for MJO simulation, providing an inspiration for better MJO simulation and prediction with this model. This work is valuable as it highlights the key role of moisture-shallow convection feedback in the MJO dynamics.

scholarly journals Contrasting stable water isotope signals from convective and large-scale precipitation phases of a heavy precipitation event in southern Italy during HyMeX IOP 13: a modelling perspective

2019 ◽  
Vol 19 (11) ◽  
pp. 7487-7506
Author(s):  
Keun-Ok Lee ◽  
Franziska Aemisegger ◽  
Stephan Pfahl ◽  
Cyrille Flamant ◽  
Jean-Lionel Lacour ◽  
...  
Keyword(s):  
Large Scale ◽  
Cold Front ◽  
Heavy Precipitation ◽  
Convective Precipitation ◽  
Water Isotopes ◽  
Precipitation Event ◽  
Stable Water Isotopes ◽  
Heavy Precipitation Event ◽  
The North ◽  
Upper Level

Abstract. The dynamical context and moisture transport pathways embedded in large-scale flow and associated with a heavy precipitation event (HPE) in southern Italy (SI) are investigated with the help of stable water isotopes (SWIs) based on a purely numerical framework. The event occurred during the Intensive Observation Period (IOP) 13 of the field campaign of the Hydrological Cycle in the Mediterranean Experiment (HyMeX) on 15 and 16 October 2012, and SI experienced intense rainfall of 62.4 mm over 27 h with two precipitation phases during this event. The first one (P1) was induced by convective precipitation ahead of a cold front, while the second one (P2) was mainly associated with precipitation induced by large-scale uplift. The moisture transport and processes responsible for the HPE are analysed using a simulation with the isotope-enabled regional numerical model COSMOiso. The simulation at a horizontal grid spacing of about 7 km over a large domain (about 4300 km ×3500 km) allows the isotopes signal to be distinguished due to local processes or large-scale advection. Backward trajectory analyses based on this simulation show that the air parcels arriving in SI during P1 originate from the North Atlantic and descend within an upper-level trough over the north-western Mediterranean. The descending air parcels reach elevations below 1 km over the sea and bring dry and isotopically depleted air (median δ18O ≤-25 ‰, water vapour mixing ratio q≤2 g kg−1) close to the surface, which induces strong surface evaporation. These air parcels are rapidly enriched in SWIs (δ18O ≥-14 ‰) and moistened (q≥8 g kg−1) over the Tyrrhenian Sea by taking up moisture from surface evaporation and potentially from evaporation of frontal precipitation. Thereafter, the SWI-enriched low-level air masses arriving upstream of SI are convectively pumped to higher altitudes, and the SWI-depleted moisture from higher levels is transported towards the surface within the downdrafts ahead of the cold front over SI, producing a large amount of convective precipitation in SI. Most of the moisture processes (i.e. evaporation, convective mixing) related to the HPE take place during the 18 h before P1 over SI. A period of 4 h later, during the second precipitation phase P2, the air parcels arriving over SI mainly originate from north Africa. The strong cyclonic flow around the eastward-moving upper-level trough induces the advection of a SWI-enriched African moisture plume towards SI and leads to large-scale uplift of the warm air mass along the cold front. This lifts moist and SWI-enriched air (median δ18O ≥-16 ‰, median q≥6 g kg−1) and leads to gradual rain out of the air parcels over Italy. Large-scale ascent in the warm sector ahead of the cold front takes place during the 72 h preceding P2 in SI. This work demonstrates how stable water isotopes can yield additional insights into the variety of thermodynamic mechanisms occurring at the mesoscale and synoptic scale during the formation of a HPE.

scholarly journals Evaluation of surface properties and atmospheric disturbances caused by post-dam alterations of land use/land cover

2014 ◽  
Vol 18 (9) ◽  
pp. 3711-3732 ◽  
Author(s):  
A. T. Woldemichael ◽  
F. Hossain ◽  
R. Pielke Sr.
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Energy Budget ◽  
Atmospheric Modeling ◽  
Dew Point ◽  
Precipitation Event ◽  
Land Use Land Cover ◽  
River Watershed ◽  
Precipitation Patterns ◽  
Lulc Changes

Abstract. This study adopted a differential land-use/land-cover (LULC) analysis to evaluate dam-triggered land–atmosphere interactions for a number of LULC scenarios. Two specific questions were addressed: (1) can dam-triggered LULC heterogeneities modify surface and energy budget, which, in turn, change regional convergence and precipitation patterns? (2) How extensive is the modification in surface moisture and energy budget altered by dam-triggered LULC changes occurring in different climate and terrain features? The Regional Atmospheric Modeling System (RAMS, version 6.0) was set up for two climatologically and topographically contrasting regions: the American River watershed (ARW), located in California, and the Owyhee River watershed (ORW), located in eastern Oregon. For the selected atmospheric river precipitation event of 29 December 1996 to 3 January 1997, simulations of three pre-defined LULC scenarios are performed. The definition of the scenarios are (1) the "control" scenario, representing the contemporary land use, (2) the "pre-dam" scenario, representing the natural landscape before the construction of the dams and (3) the "non-irrigation" scenario, representing the condition where previously irrigated landscape in the control is transformed to the nearby land-use type. Results indicated that the ARW energy and moisture fluxes were more extensively affected by dam-induced changes in LULC than the ORW. Both regions, however, displayed commonalities in the modification of land–atmosphere processes due to LULC changes, with the control–non-irrigation scenario creating more change than the control–pre-dam scenarios. These commonalities were: (1) the combination of a decrease in temperature (up to 0.15 °C) and an increase at dew point (up to 0.25 °C) was observed; (2) there was a larger fraction of energy partitioned to latent heat flux (up to 10 W m−2) that increased the amount of water vapor in the atmosphere and resulted in a larger convective available potential energy (CAPE); (3) low-level wind-flow variation was found to be responsible for pressure gradients that affected localized circulations, moisture advection and convergence. At some locations, an increase in wind speed up to 1.6 m s−1 maximum was observed; (4) there were also areas of well-developed vertical motions responsible for moisture transport from the surface to higher altitudes that enhanced precipitation patterns in the study regions.

scholarly journals The Role of Moisture Pathways on Snowfall Amount and Distribution in the Payette Mountains of Idaho

2020 ◽  
Vol 148 (5) ◽  
pp. 2033-2048
Author(s):  
Matthew D. Cann ◽  
K. Friedrich
Keyword(s):  
Sierra Nevada ◽  
Central Valley ◽  
Heavy Precipitation ◽  
The United States ◽  
The Other ◽  
Atmospheric Conditions ◽  
Intermountain West ◽  
The Pacific ◽  
Precipitation Events

Abstract The pathways air travels from the Pacific Ocean to the Intermountain West of the United States are important for understanding how air characteristics change and how this translates to the amount and distribution of snowfall. Recent studies have identified the most common moisture pathways in the Intermountain West, especially for heavy precipitation events. However, the role of moisture pathways on snowfall amount and distribution in specific regions remains unclear. Here, we investigate 24 precipitation events in the Payette Mountains of Idaho during January–March 2017 to understand how local atmospheric conditions are tied to three moisture pathways and how it impacts snowfall amount and distribution. During one pathway, southwesterly, moist, tropical air is directed into the Central Valley of California where the air is blocked by the Sierra Nevada, redirected northward and over lower terrain north of Lake Tahoe into the Snake River Plain of Idaho. Other pathways consist of unblocked flows that approach the coast of California from the southwest and then override the northern Sierra Nevada and southern Cascades, and zonal flows approaching the coast of Oregon overriding the Oregon Cascades. Air masses in the Payette Mountains of Idaho associated with Sierra-blocked flow were observed to be warmer, moister, and windier compared to the other moisture pathways. During Sierra-blocked flow, higher snowfall rates, in terms of mean reflectivity, were observed more uniformly distributed throughout the region compared to the other flows, which observed lower snowfall rates that were predominantly collocated with areas of higher terrain. Of the total estimated snowfall captured in this study, 67% was observed during Sierra-blocked flow.

scholarly journals Future extreme precipitation intensities based on historic events

2017 ◽  
Author(s):  
Iris Manola ◽  
Bart van den Hurk ◽  
Hans De Moel ◽  
Jeroen Aerts
Keyword(s):  
Extreme Precipitation ◽  
Impact Analysis ◽  
Numerical Models ◽  
Summer Precipitation ◽  
Heavy Precipitation ◽  
Dew Point ◽  
Precipitation Event ◽  
Intensity Changes ◽  
Historic Data ◽  
Nwp Model

Abstract. In a warmer climate, it is expected that precipitation intensities will increase, and form a considerable risk of high impact of precipitation extremes. This study applies three methods to transform a historic extreme precipitation event in the Netherlands to a similar event in a future warmer climate, thus compiling a future weather scenario. The first method uses an observation-based non-linear relation between the hourly observed summer precipitation and the antecedent dew-point temperature (the Pi-Td relation). The second method simulates the same event by using the convective-permitting NWP model Harmonie, for both present day and future warm conditions. The third method is similar to the first method, but applies a simple linear delta transformation to the historic data by using indicators from The Royal Netherlands Meteorological Institute (KNMI) '14 climate scenarios. A comparison of the three methods shows comparable intensity changes, ranging from below the Clausius-Clapeyron (CC) scaling to a 3 times CC increase per degree of warming. In the NWP model, the position of the events is somewhat different, due to small wind and convection changes, the intensity changes somewhat differ with time, but the total spatial area covered by heavy precipitation does not change with the temperature increase. The Pi-Td method is simple and time-efficient, compared to numerical models. The outcome can be used directly for hydrological and climatological studies, and for impact analysis, such as flood-risk assessments.

scholarly journals Assessing atmospheric moisture effects on heavy precipitation during HyMeX IOP16 using GPS nudging and dynamical downscaling

2020 ◽  
Vol 20 (10) ◽  
pp. 2753-2776
Author(s):  
Alberto Caldas-Alvarez ◽  
Samiro Khodayar
Keyword(s):  
Mediterranean Region ◽  
Air Entrainment ◽  
Heavy Precipitation ◽  
Western Mediterranean ◽  
Convective Precipitation ◽  
Precipitation Event ◽  
Small Scale ◽  
Atmospheric Moisture ◽  
Large Variability ◽  
The Mediterranean

Abstract. Gaining insight into the interaction between atmospheric moisture and convection is determinant for improving the model representation of heavy precipitation, a weather phenomenon that causes casualties and monetary losses in the western Mediterranean region every year. Given the large variability of atmospheric moisture, an accurate representation of its distribution is expected to reduce the errors related to the representation of moist convective processes. In this study, we use a diagnostic approach to assess the sensitivity of convective precipitation and underlying mechanisms during a heavy precipitation event (Hydrological cycle in the Mediterranean eXperiment Intensive Observation Period; HyMeX IOP16) to variations of the atmospheric moisture spatio-temporal distribution. Sensitivity experiments are carried out by nudging a homogenized data set of the Global Positioning System-derived zenith total delay (GPS-ZTD) with sub-hourly temporal resolution (10 min) in 7 and 2.8 km simulations with the COnsortium for Small-scale MOdeling in CLimate Mode (COSMO-CLM) model over the western Mediterranean region. The analysis shows that (a) large atmospheric moisture amounts (integrated water vapour; IWV ∼ 40 mm) precede heavy precipitation in the affected areas. This occurs 12 h prior to initiation over southern France and 4 h over Sardinia, north-eastern Italy and Corsica, which is our main study area. (b) We found that the moisture is swept from the Atlantic by a westerly large-scale front associated with an upper level low on the one hand and evaporated from the Mediterranean Sea and north Africa on the other. The latter moisture transport occurs in the 1 to 4 km layer. (c) COSMO-CLM overestimated the atmospheric humidity over the study region (Corsica), and this was, to a good extent, corrected by the GPS-ZTD nudging. This reduced maximum precipitation (−49 % for 7 km and −16 % for 2.8 km) drastically, considerably improving the precipitation representation in the 7 km simulation. The convection-permitting simulation (2.8 km) without the GPS-ZTD nudging already did a good job in representing the precipitation amount. (d) The two processes that exerted the largest control on precipitation reduction were the decrease of atmospheric instability over Corsica (convective available potential energy; CAPE −35 %) and the drying of the lower free troposphere bringing additional dry air entrainment. In addition, the 7 km simulation showed a weakening of the represented low-pressure system and the associated cyclonic wind circulation. This ultimately reduced the intensity and number of convective updrafts represented over the island. These results highlight the large impact exerted by moisture corrections on precipitating convection and the chain of processes leading to it across scales.

scholarly journals The heavy precipitation event of 14–15 October 2018 in the Aude catchment: a meteorological study based on operational numerical weather prediction systems and standard and personal observations

2021 ◽  
Vol 21 (3) ◽  
pp. 1135-1157
Author(s):  
Olivier Caumont ◽  
Marc Mandement ◽  
François Bouttier ◽  
Judith Eeckman ◽  
Cindy Lebeaupin Brossier ◽  
...  
Keyword(s):  
Numerical Weather Prediction ◽  
Weather Prediction ◽  
Heavy Precipitation ◽  
Convective Precipitation ◽  
Precipitation Event ◽  
Synoptic Situation ◽  
Heavy Precipitation Event ◽  
Cold Air ◽  
Numerical Weather ◽  
Prediction Systems

Abstract. The case of the heavy precipitation event on 14 and 15 October 2018 which has led to severe flash flooding in the Aude watershed in south-western France is studied from a meteorological point of view using deterministic and probabilistic numerical weather prediction systems, as well as a unique combination of observations from both standard and personal weather stations. This case features typical characteristics of Mediterranean heavy precipitation events such as its classic synoptic situation and its quasi-stationary convective precipitation that regenerates continuously, as well as some peculiarities such as the presence of a former hurricane and a pre-existing cold air mass close to the ground. Mediterranean Sea surface temperature and soil moisture anomalies are briefly reviewed, as they are known to play a role in this type of hydrometeorological events. A study of rainfall forecasts shows that the event had limited predictability, in particular given the small size of the watersheds involved. It is shown that the stationarity of precipitation, whose estimation benefits from data from personal stations, is linked to the presence near the ground of a trough and a strong potential virtual temperature gradient, the stationarity of both of which is highlighted by a combination of observations from standard and personal stations. The forecast that comes closest to the rainfall observations contains the warmest, wettest, and fastest low-level jet and also simulates near the ground a trough and a marked boundary between cold air in the west and warm air in the east, both of which are stationary.

scholarly journals The heavy precipitation event of 14–15 October 2018 in the Aude catchment: A meteorological study based on operational numerical weather prediction systems and standard and personal observations

2020 ◽  
Author(s):  
Olivier Caumont ◽  
Marc Mandement ◽  
François Bouttier ◽  
Judith Eeckman ◽  
Cindy Lebeaupin Brossier ◽  
...  
Keyword(s):  
Numerical Weather Prediction ◽  
Weather Prediction ◽  
Heavy Precipitation ◽  
Convective Precipitation ◽  
Precipitation Event ◽  
Synoptic Situation ◽  
Heavy Precipitation Event ◽  
Cold Air ◽  
Numerical Weather ◽  
Prediction Systems

Abstract. The case of the heavy precipitation event on 14 and 15 October 2018 which has led to severe flash flooding in the Aude watershed in south-western France is studied from a meteorological point of view using deterministic and probabilistic numerical weather prediction systems, as well as a unique combination of observations from both standard and personal weather stations. This case is typical of Mediterranean heavy precipitation events due to its classic synoptic situation and its quasi-stationary convective precipitation that regenerates continuously, but with some peculiarities such as the presence of a former hurricane and a pre-existing cold air mass close to the ground. It is shown that the positive Mediterranean sea surface temperature anomaly may have played an aggravating role in the amount of precipitation that poured into the Aude basin. On the other hand, soil moisture does not seem to have played a significant role. A study of rainfall forecasts shows that the event had limited predictability, in particular given the small size of the watersheds involved. It is shown that the stationarity of precipitation, whose estimation benefits from data from personal stations, is linked to the presence near the ground of a trough and a strong potential virtual temperature gradient, the stationarity of both of which is highlighted by a combination of observations from standard and personal stations. The forecast that comes closest to the rainfall observations contains the warmest, wettest and fastest low-level jet and also simulates near the ground a trough and a marked boundary between cold air in the west and warm air in the east, both of which are stationary.

scholarly journals A New Parameterization of the Accretion of Cloud Water by Graupel and Its Evaluation through Cloud and Precipitation Simulations

2019 ◽  
Vol 76 (2) ◽  
pp. 381-400 ◽  
Author(s):  
Han-Gyul Jin ◽  
Hyunho Lee ◽  
Jong-Jin Baik
Keyword(s):  
Collection Efficiency ◽  
Precipitation Amount ◽  
Cloud Droplet ◽  
Convective Cloud ◽  
Heavy Precipitation ◽  
Cloud Water ◽  
The Other ◽  
Precipitation Event ◽  
Cloud Droplets ◽  
Cloud Resolving Model

Abstract A new parameterization of the accretion of cloud water by graupel for use in bulk microphysics schemes is derived by analytically integrating the stochastic collection equation (SCE). In this parameterization, the collection efficiency between graupel particles and cloud droplets is expressed in a functional form using the data obtained from a particle trajectory model by a previous study. The new accretion parameterization is evaluated through box model simulations in comparison with a bin-based direct SCE solver and two previously developed accretion parameterizations that employ the continuous collection equation and a simplified SCE, respectively. Changes in cloud water and graupel mass contents via the accretion process predicted by the new parameterization are closest to those predicted by the direct SCE solver. Furthermore, the new parameterization predicts a decrease in the cloud droplet number concentration that is smaller than the decreases predicted by the other accretion parameterizations, consistent with the direct SCE solver. The new and the other accretion parameterizations are implemented into a cloud-resolving model. Idealized deep convective cloud simulations show that among the accretion parameterizations, the new parameterization predicts the largest rate of accretion by graupel and the smallest rate of accretion by snow, which overall enhances rainfall through the largest rate of melting of graupel. Real-case simulations for a precipitation event over the southern Korean Peninsula show that among the examined accretion parameterizations, the new parameterization simulates precipitation closest to observations. Compared to the other accretion parameterizations, the new parameterization decreases the fractions of light and moderate precipitation amounts and increases the fraction of heavy precipitation amount.

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