Showing papers on "Convective available potential energy published in 2018"

Atmospheric conditions associated with heavy precipitation events in comparison to seasonal means in the western mediterranean region

Abstract: The autumn atmospheric conditions associated with Heavy Precipitation Events (HPEs) in the western mediterranean region and differences with respect to the seasonal-mean conditions are investigated. Seasonal high-resolution simulations from the regional climate model COSMO-CLM covering the autumn periods of 2011 and 2012 are used. Atmospheric conditions at five different subdomains surrounding the western Mediterranean are considered, namely France, Italy (North and South), Spain, and North Africa. During HPEs, moisture and instability sources are located generally upstream of the target area over the sea, being transported by fast low-level winds towards the HPE areas. Concentration of high humidity over land and initiation of convection are highly related to the orography in the area. Stronger convective precipitation events occur at mid-level elevations rather than at higher altitudes. The significant increase in atmospheric moisture and instability, identified prior to HPEs, builds up in two different time lengths: atmospheric moisture increase could be traced back to at least 6–24 h before the initiation stage of the event, whereas an increase of Convective Available Potential Energy (CAPE) is detected in the hours prior to the event during the mature stage. The most intense HPEs are in general associated with higher values of integrated water vapour, CAPE, and low-level and mid-tropospheric wind speed. During HPEs in all subdomains, the dominant precipitation peak occurs between 1200 and 1800 UTC suggesting that convective precipitation prevails in most HPEs. The diurnal cycle of integrated water vapour during the mature stage of HPEs shows that the atmosphere remains wetter than average for most of the period and that only a decrease is seen after the afternoon precipitation peak. Negligible CAPE characterizes mean-seasonal conditions while the classical diurnal cycle with the peak in the early afternoon and much higher mean values occur during HPE events. Despite significant differences in the precipitation distribution and characteristics of the investigated subdomains, similar mechanisms are identified in relation to HPE environments and considerable contrasts compared to the mean-seasonal conditions.

Climatic factors contributing to long-term variations in surface fine dust concentration in the United States

Abstract: . High concentrations of dust particles can cause respiratory problems and increase non-accidental mortality. Studies found fine dust (with an aerodynamic diameter of less than 2.5 µ m) is an important component of the total PM 2.5 mass in the western and central US in spring and summer and has positive trends. This work examines climatic factors influencing long-term variations in surface fine dust concentration in the US using station data from the Interagency Monitoring Protected Visual Environments (IMPROVE) network during 1990–2015. The variations in the fine dust concentration can be largely explained by the variations in precipitation, surface bareness, and 10 m wind speed. Moreover, including convective parameters such as convective inhibition (CIN) and convective available potential energy (CAPE) that reveal the stability of the atmosphere better explains the variations and trends over the Great Plains from spring to fall. While the positive trend of fine dust concentration in the southwestern US in spring is associated with precipitation deficit, the increase in fine dust over the central Great Plains in summer is largely associated with enhanced CIN and weakened CAPE, which are caused by increased atmospheric stability due to surface drying and lower-troposphere warming. The strengthening of the Great Plains low-level jet also contributes to the increase in fine dust concentration in the central Great Plains in summer via its positive correlation with surface winds and negative correlation with CIN. Summer dusty days in the central Great Plains are usually associated with a westward extension of the North Atlantic subtropical high that intensifies the Great Plains low-level jet and also results in a stable atmosphere with subsidence and reduced precipitation.

Role of moisture patterns in the backbuilding formation of HyMeX IOP13 heavy precipitation systems

Abstract: Mediterranean regions are regularly affected by heavy convective precipitation. During the Hydrological Cycle in the Mediterranean Experiment Intensive Observation Period 13 (HyMeX-IOP13), the multi-platform observation strategy allowed analysing the backbuilding convective systems which developed on 14 October 2012 as well as the associated moisture structures in the environment upstream of convection. The numerical simulation at 2.5-km horizontal resolution succeeds in reproducing the location and time evolution of the observed heavy precipitation systems and the main characteristics of the marine air mass. Convection develops in Southeastern France over the foothills closest to the coast when a moist conditionally unstable marine boundary layer topped by particularly dry air masses is advected inland. Cold air formed by evaporative cooling under the precipitating cells flows down the valleys slowly shifting the location of the backbuilding convective cells from the mountainsides to the coast and over the sea. Surface observations confirm that these simulated backbuilding mechanisms describe realistically the processes involved in the maintenance of the heavy precipitation event. A lagrangian analysis shows that the moisture supply to the convective system is provided by the moist conditionally unstable marine boundary layer while the dry air masses above are involved in the cold pool formation. Four days before the event, both, the dry and the moist air masses, come from the Atlantic Ocean in the lower half of the troposphere. The dry air mass involved in the cold pool formation results from both the advection of mid-level air masses and the drying of low-level air masses lifted up over Spain. For the moist air mass feeding the backbuilding convective systems, most of the air parcels overpass France before travelling almost 48 hours in the lowest 1000m above the Mediterranean. About 50 % of the moisture supply to the precipitating system originates from the evaporation over the sea.

Simulated precipitation diurnal cycles over East Asia using different CAPE-based convective closure schemes in WRF model

Abstract: Closure assumption in convection parameterization is critical for reasonably modeling the precipitation diurnal variation in climate models. This study evaluates the precipitation diurnal cycles over East Asia during the summer of 2008 simulated with three convective available potential energy (CAPE) based closure assumptions, i.e. CAPE-relaxing (CR), quasi-equilibrium (QE), and free-troposphere QE (FTQE) and investigates the impacts of planetary boundary layer (PBL) mixing, advection, and radiation on the simulation by using the weather research and forecasting model. The sensitivity of precipitation diurnal cycle to PBL vertical resolution is also examined. Results show that the precipitation diurnal cycles simulated with different closures all exhibit large biases over land and the simulation with FTQE closure agrees best with observation. In the simulation with QE closure, the intensified PBL mixing after sunrise is responsible for the late-morning peak of convective precipitation, while in the simulation with FTQE closure, convective precipitation is mainly controlled by advection cooling. The relative contributions of different processes to precipitation formation are functions of rainfall intensity. In the simulation with CR closure, the dynamical equilibrium in the free troposphere still can be reached, implying the complex cause-effect relationship between atmospheric motion and convection. For simulations in which total CAPE is consumed for the closures, daytime precipitation decreases with increased PBL resolution because thinner model layer produces lower convection starting layer, leading to stronger downdraft cooling and CAPE consumption. The sensitivity of the diurnal peak time of precipitation to closure assumption can also be modulated by changes in PBL vertical resolution. The results of this study help us better understand the impacts of various processes on the precipitation diurnal cycle simulation.

Convective environment in pre-monsoon and monsoon conditions over the Indian subcontinent: the impact of surface forcing

Abstract: . Thermodynamic soundings for pre-monsoon and monsoon seasons from the Indian subcontinent are analysed to document differences between convective environments. The pre-monsoon environment features more variability for both near-surface moisture and free-tropospheric temperature and moisture profiles. As a result, the level of neutral buoyancy (LNB) and pseudo-adiabatic convective available potential energy (CAPE) vary more for the pre-monsoon environment. Pre-monsoon soundings also feature higher lifting condensation levels (LCLs). LCL heights are shown to depend on the availability of surface moisture, with low LCLs corresponding to high surface humidity, arguably because of the availability of soil moisture. A simple theoretical argument is developed and showed to mimic the observed relationship between LCLs and surface moisture. We argue that the key element is the partitioning of surface energy flux into its sensible and latent components, that is, the surface Bowen ratio, and the way the Bowen ratio affects surface buoyancy flux. We support our argument with observations of changes in the Bowen ratio and LCL height around the monsoon onset, and with idealized simulations of cloud fields driven by surface heat fluxes with different Bowen ratios.

Early Warnings of Severe Convection Using the ECMWF Extreme Forecast Index

Abstract: ECMWF provides the ensemble-based extreme forecast index (EFI) and shift of tails (SOT) products to facilitate forecasting severe weather in the medium range. Exploiting the ingredients-based method of forecasting deep moist convection, two parameters, convective available potential energy (CAPE) and a composite CAPE–shear parameter, have been recently added to the EFI/SOT, targeting severe convective weather. Verification results based on the area under the relative operating characteristic curve (ROCA) show high skill of both EFIs at discriminating between severe and nonsevere convection in the medium range over Europe and the United States. In the first 7 days of the forecast ROCA values show significant skill, staying well above the no-skill threshold of 0.5. Two case studies are presented to give some practical considerations and discuss certain limitations of the EFI/SOT forecasts and how they could be overcome. In particular, both convective EFI/SOT products are good at providing guidance f...

On the role of convective available potential energy (CAPE) in tropical cyclone intensification

Abstract: This study addresses the role of convective available potential energy (CAPE) in the intensification of simulated tropical cyclones. Additionally, it also examines the ‘wind-induced surface heat ex...

A representation of the collisional ice break-up process in the two-moment microphysics LIMA v1.0 scheme of Meso-NH

Abstract: . The paper describes a switchable parameterization of collisional ice break-up (CIBU), an ice multiplication process that fits in with the two-moment microphysical Liquid Ice Multiple Aerosols (LIMA) scheme. The LIMA scheme with three ice types (pristine cloud ice crystals, snow aggregates, and graupel hail) was developed in the cloud-resolving mesoscale model (Meso-NH). Here, the CIBU parameterization assumes that collisional break-up is mostly efficient for the small and fragile snow aggregate class of particles when they are hit by large, dense graupel particles. The increase of cloud ice number concentration depends on a prescribed number (or a random number) of fragments being produced per collision. This point is discussed and analytical expressions of the newly contributing CIBU terms in LIMA are given. The scheme is run in the cloud-resolving mesoscale model (Meso-NH) to simulate a first case of a three-dimensional deep convective event with heavy production of graupel. The consequence of dramatically changing the number of fragments produced per collision is investigated by examining the rainfall rates and the changes in small ice concentrations and mass mixing ratios. Many budgets of the ice phase are shown and the sensitivity of CIBU to the initial concentration of freezing nuclei is explored. The scheme is then tested for another deep convective case where, additionally, the convective available potential energy (CAPE) is varied. The results confirm the strong impact of CIBU with up to a 1000-fold increase in small ice concentrations, a reduction of the rainfall or precipitating area, and an invigoration of the convection with higher cloud tops. Finally, it is concluded that the efficiency of the ice crystal fragmentation needs to be tuned carefully. The proposed parameterization of CIBU is easy to implement in any two-moment microphysics scheme. It could be used in this form to simulate deep tropical cloud systems where anomalously high concentrations of small ice crystals are suspected.

A statistical model for isolated convective precipitation events

Abstract: To study the diurnal evolution of the convective cloud field, we develop a precipitation cell tracking algorithm which records the merging and fragmentation of convective cells during their life cycles, and apply it on large eddy simulation (LES) data. Conditioning on the area covered by each cell, our algorithm is capable of analyzing an arbitrary number of auxiliary fields, such as the anomalies of temperature and moisture, convective available potential energy (CAPE) and convective inhibition (CIN). For tracks that do not merge or split (termed "solitary"), many of these quantities show generic, often nearly linear relations that hardly depend on the forcing conditions of the simulations, such as surface temperature. This finding allows us to propose a highly idealized model of rain events, where the surface precipitation area is circular and a cell's precipitation intensity falls off linearly with the distance from the respective cell center. The drop-off gradient is nearly independent of track duration and cell size, which allows for a generic description of such solitary tracks, with the only remaining parameter the peak intensity. In contrast to the simple and robust behavior of solitary tracks, tracks that result from merging of two or more cells show a much more complicated behavior. The most intense, long lasting and largest tracks indeed stem from multi-mergers - tracks involved in repeated merging. Another interesting finding is that the precipitation intensity of tracks does not strongly depend on the absolute amount of local initial CAPE, which is only partially consumed by most rain events. Rather, our results speak to boundary layer cooling, induced by rain re-evaporation, as the cause for CAPE reduction, CIN increase and shutdown of precipitation cells.

Elevated Potential Instability in the Comma Head: Distribution and Development

Abstract: The development of elevated potential instability within the comma head of a continental winter cyclone over the north-central United States is examined using a 63-h Weather Research and Forecasting (WRF) Model simulation. The simulation is first compared to the observed cyclone. The distribution of most unstable convective available potential energy (MUCAPE) within the comma head is then analyzed. The region with positive MUCAPE was based from 2- to 4-km altitude with MUCAPE values up to 93 J kg−1. Backward trajectories from five sublayers within the region of elevated convection in the comma head were calculated to investigate how elevated potential instability developed. Air in the lowest sublayer, the source air for convective cells, originated 63 h earlier near Baja California at elevations between 2.25- and 2.75-km altitude. Air atop the layer where convection occurred originated at altitudes between 9.25 and 9.75 km in the Arctic, 5000 km away from the origin of air in the lowest sublayer. ...

Sensitivity of convective precipitation to soil moisture and vegetation during break spell of Indian summer monsoon

Abstract: Indian summer monsoon rainfall is characterized by large intra-seasonal fluctuations in the form of active and break spells in rainfall. This study investigates the role of soil moisture and vegetation on 30-h precipitation forecasts during the break monsoon period using Weather Research and Forecast (WRF) model. The working hypothesis is that reduced rainfall, clear skies, and wet soil condition during the break monsoon period enhance land-atmosphere coupling over central India. Sensitivity experiments are conducted with modified initial soil moisture and vegetation. The results suggest that an increase in antecedent soil moisture would lead to an increase in precipitation, in general. The precipitation over the core monsoon region has increased by enhancing forest cover in the model simulations. Parameters such as Lifting Condensation Level, Level of Free Convection, and Convective Available Potential Energy indicate favorable atmospheric conditions for convection over forests, when wet soil conditions prevail. On spatial scales, the precipitation is more sensitive to soil moisture conditions over northeastern parts of India. Strong horizontal gradient in soil moisture and orographic uplift along the upslopes of Himalaya enhanced rainfall over the east of Indian subcontinent.

Classification and Diurnal Variations of Precipitation Echoes Observed by a C-band Vertically-Pointing Radar in Central Tibetan Plateau during TIPEX-III 2014-IOP

Abstract: This study investigates classification and diurnal variations of the precipitation echoes over the central Tibetan Plateau based on the observations collected from a C-band vertically-pointing frequency-modulated continuous-wave (C-FMCW) radar during the Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX-III) 2014-Intensive Observation Period (2014-IOP). The results show that 51.32% of the vertical profiles have valid echoes with reflectivity > –10 dBZ, and 35.06% of the valid echo profiles produce precipitation at the ground (precipitation profiles); stratiform precipitation with an evident bright-band signature, weak convective precipitation, and strong convective precipitation account for 52.03%, 42.98%, and 4.99% of the precipitation profiles, respectively. About 59.84% of the precipitation occurs in the afternoon to midnight, while 40.16% of the precipitation with weaker intensity is observed in the nocturnal hours and in the morning. Diurnal variation of occurrence frequency of precipitation shows a major peak during 2100–2200 LST (local solar time) with 59.02% being the stratiform precipitation; the secondary peak appears during 1300–1400 LST with 59.71% being the weak convective precipitation; the strong convective precipitation occurs mostly (81.83%) in the afternoon and evening with two peaks over 1200–1300 and 1700–1800 LST, respectively. Starting from approximately 1100 LST, precipitation echoes develop with enhanced vertical air motion, elevated echo top, and increasing radar reflectivity. Intense upward air motion occurs most frequently in 1700–1800 LST with a secondary peak in 1100–1400 LST, while the tops of precipitation echoes and intense upward air motion reach their highest levels during 1600–1800 LST. The atmospheric conditions in the early morning are disadvantageous for convective initiation and development. Around noon, the convective available potential energy (CAPE) increases markedly, convective inhibition (CIN) is generally small, and a super-dry-adiabatic layer is present near the surface (0–400 m). In the early evening, some larger values of CAPE, level of neutral buoyancy, and total precipitable water are present, suggesting more favorable thermodynamic and water vapor conditions.

Characterizing the Impact of Aerosols on Pre-Hurricane Sandy

Abstract: This study focuses on the role that African dust over the Atlantic had on the persistence of the tropical system that eventually became Hurricane Sandy in October 2012. On October 8, a Saharan dust event in the Mauritania region of West Africa transported significant amounts of mineral dust into the troposphere and along the path of an easterly wave created by a break in the Intertropical Convergence Zone (ITCZ). The Terra/Aqua-MODIS satellite observations clearly define the spatial distribution of the coarse/fine aerosols, while the CALIPSO observations of the total attenuated backscatter at 532 nm provide a detailed view of the vertical structure and aerosol types in the dust-laden layer. European Centre for Medium-Range Weather Forecasts and Modern-Era Retrospective Analysis for Research and Applications, Version 2 reanalysis data show the distribution of aerosols along the path of the pre-Sandy wave as well as a second wave that formed north of the ITCZ under different condition. The second wave, which started in an area of relatively larger aerosol optical depth (AOD), moved into an area with abnormally low convective available potential energy and AOD, subsequently dying out, while the wave that became Sandy had light aerosol loading (AOD between 0.15–0.5) along a majority of its path. The evidence suggests that aerosols played a nontrivial role in the maintenance of this system until it moved into an environment favorable for cyclogenesis.

Observation of Temperature Profiles of Kototabang (Bukittinggi-West Sumatera Indonesia) Using Radiosonde and Rain Event Identification

Abstract: We recorded temperature profiles of Kototabang (West Sumatera-Indonesia) in a four days observation using Radio Acoustic Sounding System (RASS) and Radiosonde. The activity was carried out in August 2016, on a research cooperation framework of National Institute of Aeronautics and Space (LAPAN), Indonesia and Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Japan. The current article discussed the temperature profile based on 12 times launch of Radiosonde, Convective Available Potential Energy (CAPE) estimation and its relationship with rain events, while the temperature profile based on RASS was discussed in another report. CAPE is the amount of energy an air parcel would have if lifted to a certain distance vertically through the atmosphere. CAPE is effectively the positive buoyancy of an air parcel and is an indicator of atmospheric instability, related to convection clouds. If there is not enough water vapour present, there is no ability for condensation, and therefore, storms, clouds, and rain will not form. CAPE is calculated as the area of positive region in the thermodynamic diagram or through relationships with virtual temperature. On August 30, 2016, at 08 LT, the range of temperatures based on Radiosonde measurements was recorded from 294.9°K at ground level to 186.5°K at an altitude of 26.8 km. The temperature range varied with time. CAPE based on Radiosonde data ranged from 0 to 5075.2 Jkg-1 within 30 August 2016 until 2 September 2016. The maximum CAPE value occurred on August 30, 2016 at 15.34 LT. Large CAPE (> 2000 Jkg-1) was coincident with rain events.

Dynamic and Thermodynamic Mechanisms for the Onset of the Southeastern United States Convective Season

Abstract: The southeastern United States (SE US) receives ample precipitation year-round. In the winter , precipitation primarily comes from synoptic-scale baroclinic systems and cold fronts. Meanwhile , precipitation in the summer over the SE US is primarily the result of convection. With this shift from the winter to summertime precipitation regimes , spring is the transition period to the convective season , and this transition occurs rather abruptly. This shift can be described as a sudden increase in precipitation from isolated precipitation features (IPF) while precipitation from mesoscale precipitation features (MPF) stays relatively unchanged over the SE US. IPF is defined as small , short-lived , and spatially heterogeneous features while MPF is defined as larger , well-organized , and generally longer-lived precipitating features. To study the springtime transition to the convective season , the SE US was split into twenty-seven 2°x2° boxes. Precipitation data for March-August from the National Mosaic and Multi-Sensor Quantitative Precipitation Estimation (QPE) (NMQ) for the years 2009-2012 is used to determine onset using an objective method based on IPF precipitation in each of the twenty-seven boxes for each year and for the four-year average. Meteorological data from the North American Regional Reanalysis (NARR) is analyzed to determine potential dynamic and thermodynamic mechanisms that cause onset of the convective season in the SE US. Thermodynamic variables analyzed include convective available potential energy (CAPE) , surface temperature , and specific humidity. Dynamic variables analyzed include 500 hPa geopotential height , mean sea level pressure (MSLP) , and 850 hPa wind speed and direction. Daily composites of NARR are generated for May and June , while pentad average composites are generated for April-July for each year. Pentad averages of IPF will be created using the NMQ dataset to determine the pentad of onset. Three different sensitivity tests are also conducted to determine how sensitive onset is to the threshold criteria used to determine onset. It was found that the timing of onset varies from year to year , and there is no regional progression of onset in the SE US. Along with that , IPF behavior varies quite greatly across the SE US. Despite this variation in onset timing within the four years and variation in IPF behavior across the SE US , there are similarities in meteorological conditions in the pentads immediately leading up to and during onset. The North Atlantic Subtropical High (NASH) becomes established over the SE US one to two pentads before onset , priming the atmosphere for onset by bringing warm air and moisture from the Gulf of Mexico into the SE US. As the NASH becomes established , CAPE and specific humidity increase over the SE US , providing instability and moisture for IPF precipitation to develop over the SE US. At 500 hPa , either a ridge or zonal flow is present over the SE US at the time of onset , which aids in the NASH staying established over the SE US. The results of this research have begun to provide a new framework to better understand precipitation variability in the SE US.

Dynamic Ensemble Analysis of Frontal Placement Impacts in the Presence of Elevated Thunderstorms during PRECIP Events

Abstract: The Program for Research on Elevated Convection with Intense Precipitation (PRECIP) field campaign sampled 10 cases of elevated convection during 2014 and 2015. These intense observing periods (IOP) mostly featured well-defined stationary or warm frontal zones, over whose inversion elevated convection would form. However, not all frontal zones translated as expected, with some poleward motions being arrested and even returning equatorward. Prior analyses of the observed data highlighted the downdrafts in these events, especially diagnostics for their behavior: the downdraft convective available potential energy (DCAPE) and the downdraft convective inhibition (DCIN). With the current study, the DCAPE and DCIN are examined for four cases: two where frontal motion proceeded poleward, as expected, and two where the frontal motions were slowed significantly or stalled altogether. Using the Weather Research and Forecasting (WRF) model, a multi-model ensemble was created for each of the four cases, and the best performing members were selected for additional deterministic examination. Analyses of frontal motions and surface cold pools are explored in the context of DCAPE and DCIN. These analyses further establish the DCAPE and DCIN, not only as a means to classify elevated convection, but also to aid in explaining frontal motions in the presence of elevated convection.

Objective Definition of Climatologically Homogeneous Areas in the Southern Balkans Based on the ERA5 Data Set

Abstract: An objective definition of climatologically homogeneous areas in the southern Balkans is attempted with the use of daily 0.25° × 0.25° ERA5 meteorological data of air temperature, dew point, zonal and meridional wind components, Convective Available Potential Energy, Convective Inhibition, and total cloud cover. The classification of the various grid points into climatologically homogeneous areas is carried out by applying Principal Component Analysis and K-means Cluster Analysis on the mean spatial anomaly patterns of the above parameters for the 10-year period of 2008 to 2017. According to the results, 12 climatologically homogenous areas are found. From these areas, eight are mainly over the sea and four are mainly over the land. The mean intra-annual variations of the spatial anomalies of the above parameters reveal the main climatic characteristics of these areas for the above period. These characteristics refer, for example, to how much warmer or cloudy the climate of a specific area is in a specific season relatively to the rest of the geographical domain. The continentality, the latitude, the altitude, the orientation, and the seasonal variability of the thermal and dynamic factors affecting the Mediterranean region are responsible for the climate characteristics of the 12 areas and the differences among them.

Kinetic energy budget of active summer monsoon on Southeast Asia

Abstract: In this paper present and show kinetic energy and convective available potential energy (CAPE) on active summer monsoon on May to August from 1981 to 1990. Result show that kinetic energy usually appear over Bay of Bengal and India area. Because of zonal and meridional components are flow through India area that active monsoon is happen. However, kinetic energy is less available potential energy. The distribution of CAPE in summer and the value of high CAPE located between the equator and 20°N and low CAPE located below equator. The pattern CAPE position distribution fluctuates as an inter-tropical convergence zone.

calculation system for convective available potential energy using radiometer and calculation method for convective available potential energy using the same

Abstract: The present invention relates to a calculation system for convective available potential energy and a calculation method for convective available potential energy using the same and, more specifically, relates to a calculation system and a method for convective available potential energy using a radiometer. The present invention provides the calculation system for convective available potential energy using a radiometer and the method using the same, wherein the calculation system comprises: a convective available potential energy (CAPE) input data generating unit collecting radiometer data in a radiometer and AWS data in an AWS to generate CAPE input data; and a CAPE calculation unit calculating CAPE with the CAPE input data. Therefore, according to the present invention, the radiometer is used to easily and accurately calculate convective available potential energy.

Numerical Model and Forecasting Potential of Aircraft Weather Hazards over Kenya

Abstract: The study investigated the forecasting potential of aircraft weather hazards over Kenya using numerical model. The various causes of accidents/incidents were identified using analyzed investigated weather-related aviation hazards data obtained from Kenya Civil Aviation Authority database system from 2008 through 2014. The parameters analyzed included the Winds, Temperature, Relative humidity, Convective Available Potential Energy (CAPE), Lifted Index (LI) and Dew Point Temperature. Their combined effect was able to provide the means of identifying the areas of strong convection. The model was run on a grid point distance resolution of 10 km and runs finite differencing scheme, based on Taylor series. Grid Analysis and Display System (GrADS) which is embedded on the model upon installation, was used as the default post processing tool. Key findings revealed that Wind, Fog, Turbulence, Heavy rain showers, and low ceiling influenced aircraft operations. It was shown that the majority of the hazards were linked with cumulonimbus clouds. Landing phase of flight affected aviation most.

Convective Available Potential Energy Variability over India

Abstract: The convection developed due to temperature and moisture stratification in the atmosphere is main cause for precipitation and can be measured with Convective available potential energy (CAPE). Convection takes place before monsoon starts and as it is measured in CAPE reaches to maximum value at a place and after monsoon ends CAPE takes minimum value. In this way we have a cycle of convection over the year. There is variation in convection from station to station. In this study we have inspected dominant frequency components in CAPE for 15 meteorological station over India by applying EMD and Lomb-Scargle periodogram (LSP) algorithm for a period of 30 years (1987-2016) using Integrated Global Radiosonde Archive (IGRA) radiosonde data. We have observed significant variation in periodicity of convective activity for different stations. We have observed regional (3-4 months), semiannual (6 months), annual (12 months), quasibiennial (20-35 months), ENSO (40-80 months), solar cycles (100-140 months), periodicities.