Variations in intensity and structure of a westward-propagating monsoon depression

The study deals with a monsoon depression which developed over the Bay of Bengal, moved westward across central India and turned into a mid-tropospheric disturbance (MTD) over the northeastern : corner of the Arabian Sea. Its interactions with the thermal fields associated with the basic monsoon, subtropical westerly troughs and a new depression over the Bay of Bengal are examined. Evidence suggests the involvement of all the three factors in causing the observed variations in its intensity and structure. The low pressure system turned into a mid-tropospheric disturbance when it re-entered the warm sector of the basic monsoon field and received increased warm advection from the north to the west of its centre and cold advection from the south to the east in mid-troposphere. The importance of thermal advection is confirmed by computation of a heat budget. The role of condensation heating is also briefly discussed.

Unusual weather over northwest & west India during November, 2010

lkekU;r% uoEcj dk eghuk /kwi ds fnuksa o fcuk ckfj'k okyk eghuk dgykrk gS vkSj uoEcj eghus ds chrus ds lkFk-lkFk mRrj if'peh Hkkjr ds eSnkuh Hkkxksa esa lqcg dh gYdh BaMd fy, ekSle lqgkouk jgrk gS fdUrq uoEcj 2010 ds nkSjku mRrj if'peh vkSj if'pe Hkkjr esa o"kkZ dh ckSNkjksa ds lkFk yEcs le; rd yxkrkj ckny Nk, jgs ftlds dkj.k ekSle vlkekU; jgkA bl vlkekU; ekSle ds fy, mRrjnk;h HkkSfrd izfØ;kvksa dk irk yxkus ds fy, bl 'kks/k i= esa bl ekg esa cuh flukfIVd fLFkfr;ksa dk foLr`r fo'ys"k.k fd;k x;k gSA bl v/;;u ls ;g irk pyk gS fd vjc lkxj esa xgu fuEu vonkc iz.kkyh dh mifLFkfr vkSj fupys Lrjksa esa if'peh gokvksa esa e/; {kksHkeaMyh; nzksf.k;ksa ds lkFk&lkFk iwohZ gokvksa esa mPp vk;keh nzksf.k;ksa dh ijLij fØ;kvksa ds dkj.k uoEcj ekg esa ekSle vlkekU; jgkA Generally, November is the dry month with sunny days and pleasant weather for plains of northwest & west India with a bit of early morning chill as the month progresses. But during November, 2010, there was unusual weather in the form of prolonged and persistent cloudy conditions with wet spell over northwest & west India. To find out the physical processes leading to this unusual weather, detailed analysis of synoptic conditions during the month has been carried out in this paper. This study reveals that the unusual weather that occurred in association with presence of an intense low pressure system in the Arabian Sea and interaction of high-amplitude troughs in easterlies in the lower levels with mid-tropospheric troughs in the westerlies.

A climatological feature with forecasting aspect of heavy rainfall events over Kolkata

In this paper an attempt has been made to study climatological characteristics and forecasting aspects of heavy rainfall over Kolkata for data of 34 years of period from 1974 to 2007. Total 184 events has been found out and the data set has been subjected to various types of analysis along with favourable synoptic system and critical index for occurrence of heavy rainfall over Kolkata. Average occurrence is found as 5.4 events per year. Monthly distribution shows maximum of 26% events in July followed by September 20%, August17% and June as 14%. Seasonal distribution naturally indicates maximum of 77% occurrence during monsoon followed by post-monsoon with 14% and pre-monsoon with 09 %. Synoptic analysis revealed that majority of heavy rainfall events occurred due to low pressure system (LPS). Study of 167 cases (during June to October) suggests that when any one of the favourable synoptic condition prevailed over the region and DPD-Wind-PW-WS index reaches a critical value, heavy to very heavy rain occurred over Kolkata and suburban areas.

Assessing the Reliability of Global Monsoon Low Pressure System Track Datasets for the East Asian Monsoon

Limited by the lack of atmospheric observation data over the ocean and the absence of a comprehensive set of track data for monsoon low pressure systems (MLPSs), an in-depth understanding of the activity of East Asian MLPSs has not been acquired. In recent years, advancements in satellite remote sensing and data assimilation techniques have enabled the creation of numerous high-resolution global reanalysis datasets. Additionally, with the improvement of tracking algorithms, two sets of global MLPS track data (HB2015 and VB2020) have been published. This study seeks to understand the fidelity of the two datasets with respect to the East Asian monsoon. The genesis location, movement path, and three-dimensional structure of the East Asian MLPSs obtained using HB2015 and VB2020 are compared, and the atmospheric circulation conditions of typical MLPSs are analyzed. The results show that both datasets are able to generate MLPSs with identical structure for the East Asian Monsoon, and they provide similar results in terms of the location and monthly frequency. Compared to the HB2015, the VB2020 adopts a more stringent set of thresholds for the determination of the MLPS genesis and extinction and a more rigorous tracking algorithm. Therefore, it yields a lower count of MLPSs with significantly shorter lifetimes. However, the MLPSs identified by the VB2020 all have cyclonic circulations in the proximity of their central areas as they continue their movement. In this sense, the results generated by the VB2020 are more consistent with the observed MLPSs and hence are more reliable. However, the tracking can end prematurely with this dataset.

Model Sensitivity Study of the Direct Radiative Impact of Saharan Dust on the Early Stage of Hurricane Earl

Current studies report inconsistent results about the impacts of Saharan dust on the development of African Easterly Waves (AEWs), the African Easterly Jet (AEJ), and tropical cyclones (TCs). We present a modeling case study to further elucidate the direct radiative impacts of dust on the early development stage of a TC. We conducted experiments using the Weather Research and Forecasting model coupled with chemistry (WRF-Chem-V3.9.1) to simulate Hurricane Earl (2010) which was influenced by the dusty Saharan Air Layer (SAL). We used the aerosol product from ECMWF MACC-II as the initial and boundary conditions to represent aerosol distribution, along with typical model treatment of its radiative and microphysical effects in WRF. Our simulations at 36-km resolution show that, within the first 36 h, the presence of dust weakens the low-pressure system over North Africa by less than 1 hPa and reduces its mean temperature by 0.03 K. Dust weakens and intensifies the AEJ at its core and periphery, respectively, with magnitudes less than 0.2 m/s. Dust slightly shifts the position of 600 hPa AEW to the south and reduces its intensity prior to impacting the TC. Finally, TC with dust remains weaker.

Relationship between large amounts of Cryptomeria japonica D. Don pollen dispersion and cold front passage

Recently, with the proliferation of automatic Cryptomeria japonica pollen monitors, it has become possible to obtain data measured simultaneously from multiple locations. The KH-3000 monitor used by the Pollen Observation System of the Japanese Ministry of the Environment, “Hanako-san”, and the “Pollen Robo” monitor created by Weathernews Inc. were installed in various places in the Tohoku region for collection of simultaneous pollen count data, and the results indicated that the period of the day when large amounts of C. japonica pollen were dispersed may be related to the passage of a cold front extending from a low pressure system. When the types of pollen dispersed on that day were examined under a microscope, most of them were C. japonica pollen. Therefore, we investigated the relationship between the periods of these two events, with transit time of the cold front determined from the point when the wind direction changed from eastward to westward. The area with a high concentration of C. japonica pollen moved from the Sea of Japan side to the Pacific Ocean side in conjunction with the movement of the front. In 40% of the cases, the highest dispersion of C. japonica pollen occurred at the same time as the front passed, and 90% of the cases were within two hours before or after the passage. The number of dispersions was high in the northern part of the Tohoku region close to the low pressure system at the end of the front and low in the southernmost part of the Tohoku region away from this system.

Associating Synoptic-Scale Weather Patterns with Aggregated Offshore Wind Power Production and Ramps

Large-scale weather patterns and their variability can influence both the amount of wind power production and its temporal variation, i.e., wind power ramps. In this study, we use a self-organizing map to cluster hourly sea level pressure into a discrete number of weather patterns. The dependency of wind power production and wind power ramps on these weather patterns is studied for the Belgian offshore wind farm fleet. A newly developed wavelet-surrogate ramp-detection algorithm is used for the identification of wind power ramps. It was observed that low-pressure systems, southwesterly and northeasterly wind flows are often associated with high levels of wind power production. Regarding wind power ramps, the type of transition between weather patterns was shown to determine whether ramp up or ramp down events would occur. Ramp up events tend to occur due to the transition from a high-pressure to a low-pressure system, or the weakening of the intensity of a deep low-pressure system. The reverse is associated with ramp down events.

The Synoptic Characteristics, Causes, and Mechanisms of Kahlaa Tornado in Iraq on 14th April 2016

In this study, an analysis of the synoptic characteristics, causes and mechanisms of Kahlaa tornado event was carried out. This tornado occurred on 10:30 UTC (1:30 pm Iraq Local Time) on 14 April 2016 to the north of Kahlaa town in Maysan governorate. We analyzed surface and upper charts, weather conditions, the damage indices, the dynamical features and the instability of the tornado. The analysis showed that there was a low pressure system which was an extension of the Monsoon low in addition to a supercell thunderstorm and a jet stream aloft. The cold trough and high relative vorticity at 500 hPa level, the humid warm wind blowing from the south and the dry cold wind from the north contributed to the initiation of the tornado. According to the damage amount, Kahlaa tornado can be classified as EF2 degree (considerable) on Enhanced Fujita scale. Three indices were calculated to estimate the instability of the tornado. The values of the convective available potential energy (CAPE), K-index, and lifted index were (≥2500 J/kg), (35.3 oC), and (-7), respectively. All these indices confirmed the instability required to form severe thunderstorm essential to tornado formation. Although the forecasting of tornadoes occurrence is difficult, there would be indications that may lead to expect of occurrence. These may include the availability of moisture, heat, and significant wind direction changes with altitude. However, the vital factors were the existence of high instability and a supercell thunderstorm.

The unusually long cold spell and the snowstorm Filomena over Spain in January 2021

<p>In January 2021, large parts of Spain were affected by an unusually long cold spell and exceptional snowfall associated with the winter storm Filomena. According to the Spanish weather service AEMET, snow heights of nearly 50 cm were registered in and around Madrid. During the days after Filomena, record-breaking low temperatures were measured at many stations.</p><p>Already during the days before the arrival of storm Filomena, anomalously cold temperatures at 850 hPa and night frosts at the surface prevailed over large parts of Spain. During these days in early January, the air flow towards Spain was predominantly northeasterly and advected cold air masses from Central Europe, as revealed by backward trajectories that were initialised near the surface over Spain. The land surface progressively cooled down during the days prior to the heavy snowfall, which then prevented the snow from melting when reaching the surface. Therefore, this cold spell preconditioning seems to be very important for the extreme consequences of the snowfall event.</p><p>The storm Filomena affected Spain between 8 and 10 January. It developed from a precursor low-pressure system between the Azores and Madeira. The precursor low-pressure system itself developed on 2 January 2021 between the northeastern US and Nova Scotia, rapidly intensified along a potential vorticity (PV) streamer and propagated southeastwards. Between 4 and 6 January, the cyclone, now located near the Azores, was associated with a PV cut-off and eventually decayed into multiple centres. Out of this decaying low-pressure system, Filomena developed and reached Spain on 8 January.</p><p>The most intense snowfall occurred on 9 January and affected large parts of Spain, except for southwestern Spain, where temperatures were too high and all precipitation fell as rain. Filomena was associated with an intense air mass boundary, with dry and cold air in the north and warm and humid air in the south. Equivalent potential temperature differences at 850 hPa across Spain exceeded 20 K. Along the warm frontal part of this air mass boundary, strong ascending airstreams, intensified by the dynamics of Filomena, led to cloud formation. Due to the unusually cold lowermost troposphere, snow was not melting before reaching the land surface, and the surface snow layer could therefore easily grow.</p><p>Overall, the combination of the already cold temperatures near the surface, the optimal position of the air mass boundary, and the dynamical forcing for ascent at this intense baroclinic zone associated with Filomena were essential ingredients for this extreme snow fall event to occur.</p>

Estimation of Design Parameters and Performance for a State-of-the-Art Turbofan

The aim of this study is to explore the possibility of matching a cycle performance model to public data on a state-of-the-art commercial aircraft engine (GEnx-1B). The study is focused on obtaining valuable information on figure of merits for the technology level of the low-pressure system and associated uncertainties. It is therefore directed more specifically towards the fan and low-pressure turbine efficiencies, the Mach number at the fan-face, the distribution of power between the core and the bypass stream as well as the fan pressure ratio. Available cycle performance data have been extracted from the engine emission databank provided by the International Civil Aviation Organization (ICAO), type certificate datasheets from the European Union Aviation Safety Agency (EASA) and the Federal Aviation Administration (FAA), as well as publicly available data from engine manufacturer. Uncertainties in the available source data are estimated and randomly sampled to generate inputs for a model matching procedure. The results show that fuel performance can be estimated with some degree of confidence. However, the study also indicates that a high degree of uncertainty is expected in the prediction of key low-pressure system performance metrics, when relying solely on publicly available data. This outcome highlights the importance of statistic-based methods as a support tool for the inverse design procedures. It also provides a better understanding on the limitations of conventional thermodynamic matching procedures, and the need to complement with methods that take into account conceptual design, cost and fuel burn.