An analytical study of easterly waves over southern peninsular India during the northeast monsoon 2010

Easterly wave characteristics over southern peninsular India during the northeast monsoon season of 2010 are examined by means of synergetic analysis involving synoptic, statistical and numerical methods. NCEP 6-hourly reanalysis datasets of zonal and meridional winds, vertical velocity, temperature and net long wave radiation at 2.5° × 2.5° grid resolution for the period 20th October to 31st December, 2010 form the main database for the analysis. During this period, 3 easterly waves could be identified to have passed over this region and the time period of these waves are determined to be 4.2 days (4.5 days) by statistical methods (synoptic methods). The speed of movement, wavelength and amplitude of the waves are determined to be 7.28 ms-1, 2800 km and 6.7 ms-1 respectively. While rising motion is observed at most of the tropospheric levels over and behind the trough, subsidence occurs ahead of the trough. Divergence is noted over and behind the trough at upper troposphere while convergence occurs in the lower to mid-troposphere. Concomitantly warming is noted ahead of the trough while colder anomalies are noted in the lower levels over and behind the trough.

Importance of meridional winds in. forecasting sub-regional summer monsoon rainfall

ABSTRACT. Based on 35 years' (1959-1993) data, the zonal and meridional wind components of selected Indian RS/RW statiomupto 100 hPa level were analysed for the pre-monsoon months of April and May in order to associate them with sub-regional monsoon rainfall of northeast India. Composite values of monsoon rainfall and meridional components for May for excess and deficient yean have revealed that anomaly of meridional components for the middle and upper troposphere is northerly/southerly preceding excees/deficient monsoon year. The meridional winds at most of the levels of Delhi and some of the levels of Jodhpur Nagpur, Bombay and Madras for the month of May showed significant correlations (significant at 0.1% to 5% level of significance) with sub-divisional monsoon rainfall in northeast India. The temporal behaviour of correlation coefficients for Punjab and Haryana for 16 and 20-year sliding windows has exhibited rasonable temporal stability except for first few years. Multiple rearession equations for 30 and 35 year period for Haryana, Punjab and contiguous northweat India were also developed. The regression model for Punjab sub-division has shown quite good results for the independent period.

Investigation of Atmospheric Conditions Associated with a Storm Surge in the South-West of Iran

Severe thunderstorms are often accompanied by strong vertical air currents, temporary wind gusts, and heavy rainfall. The development of this atmospheric phenomenon over tropical shallow water zones, such as bays, can lead to intensification of atmospheric disturbances and produce a small-scale storm surge. Here, the storm surge that occurred on 19 March 2017 in the Persian Gulf coastal area has been investigated. Air temperature, precipitation, mean sea level pressure, wave height, wind direction, wind speed, geopotential height, zonal components, meridional winds, vertical velocity, relative humidity, and specific humidity obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) and Global Forecast System (FNL) were used to implement the Weather Research and Forecasting (WRF) model. The results showed that the main cause of the storm surge was the occurrence of a supercell thunderstorm over the Persian Gulf. The formation of this destructive phenomenon resulted from a downburst under Cumulonimbus cloud and high-velocity air subsidence, after collision with the sea surface coinciding with the high tide. This caused a severe, yet temporary, gust, which in turn caused the creation of the four waves of 3.1 m height along the coast of Bandar Dayyer.

Research of sources and distribution of suspended matter in Omega Bay (Crimea) based on expeditional data and numerical simulation

The regularities of the suspended matter distribution in the system of wind currents from the area of bottom elevation along the Omega Bay are revealed. Observational data show that in the region of bottom elevation there is a topographic quasi-stationary eddy cell accumulating pollutants. Based on numerical modeling, it is revealed that the meridional winds of all directions contribute to the transfer of the suspended matter from the area of elevation to the western coast of the bay to the beach area, to a small coastal area with a characteristic bend of the coastline. The most significant suspended matter flows are generated by northeasterly and southeasterly winds. With a westerly wind, the main flow of suspended matter is directed to the eastern coast of the bay. The weak easterly winds, typical for Sevastopol, do not cause the removal of suspended matter from the central area of the investigated bay.

Investigation of Atmospheric Conditions Associated with a Storm Surge in the South-West of Iran

Severe thunderstorms are often accompanied by strong vertical air currents, temporary wind gusts, and heavy rainfall. The development of this atmospheric phenomenon over tropical shallow water zones, such as bays, can lead to intensification of atmospheric disturbances and produce a small-scale storm surge. Here, the storm surge that occurred on 19 March 2017 in the Persian Gulf coastal area has been investigated. Air temperature, precipitation, mean sea level pressure, wave height, wind direction, wind speed, geopotential height, zonal components, meridional winds, vertical velocity, relative humidity, and specific humidity obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF (and Global Forecast System (FNL) were used to implement the Weather Research and Forecasting (WRF) model. The results showed that the main cause of the storm surge was the occurrence of a supercell thunderstorm over the Persian Gulf. The formation of this destructive phenomenon resulted from a downburst under Cumulonimbus cloud and high-velocity air subsidence, after collision with the sea surface coinciding with the high tide. This caused a severe, yet temporary, gust, which in turn caused the creation of the four waves of 3.1 m height along the coast of Bandar Dayyer.

Estimating zonal Ekman transport along coastal Senegal during passage of Hurricane Fred, 30–31 August 2015

We examine the role of zonal Ekman transport along the coast of Senegal on 30 August 2015 when the tropical disturbance associated with Tropical Cyclone Fred was located to the west of Senegal, causing considerable coastal damage in the southern Senegal–Gambia domain (south of Dakar, Senegal). Ten-meter winds from three Weather Research and Forecast model simulations were used to estimate zonal Ekman transport, when the maximum values were found on 30 August. These simulations are in agreement with limited coastal observations showing increasing southerly wind speeds during 30 August but overestimated relative to the three coastal stations. The strong meridional winds translate into increased zonal Ekman transport to the coast of Senegal on 30 August and are likely responsible for some coastal flooding. Ekman transport along the coast contributes significantly to the water-level variations during swell events. The use of a coupled ocean model will improve the estimates of Ekman transport along the Guinea-Senegalese coast. The observed damage suggests that artificial and natural barriers (mangroves) should be strengthened to protect coastal communities in Senegal.

Validation of wind measurements of two mesosphere–stratosphere–troposphere radars in northern Sweden and in Antarctica

Two atmospheric VHF radars: ESRAD (Esrange MST radar) located near Kiruna in the Swedish Arctic and MARA (Moveable Atmospheric Radar for Antarctica) at the Indian research station Maitri in Antarctica perform wind measurements in the troposphere and lower stratosphere on a regular basis. We compared horizontal winds at altitudes between about 0.5 and 14 km derived from the radar data using the full correlation analysis (FCA) technique with radiosonde observations and models. The comparison with 28 radiosondes launched from January 2017 to August 2019 showed that ESRAD underestimates the zonal and meridional winds by about 8 % and 25 %, respectively. This is likely caused by the receiver group arrangement used for the FCA together with a high level of non-white noise. A similar result was found when comparing with the regional numerical weather prediction model HARMONIE-AROME (Bengtsson et al., 2017) for the period September 2018–May 2019. The MARA winds were compared with winds from radiosondes for the period February–October 2014 (291 occasions). In contrast to ESRAD, there is no indication that MARA underestimates the winds compared to the sondes. The mean difference between the radar and radiosonde winds is close to zero for both zonal and meridional components. The comparison of MARA with the ECMWF ERA5 reanalysis for January–December 2019 reveals good agreement with the mean difference between 0.1 and −0.5 m/s depending on the component and season. The random errors in the wind components (standard deviations over all estimates in 1 h averages) are typically 2–3 m/s for both radars. Standard deviation of the differences between radars and sondes are 3–5 m/s.

Impacts of Detoured Madden-Julian Oscillations on the South Pacific Convergence Zone

Madden-Julian Oscillations (MJOs) are a major component of tropical intraseasonal variabilities. There are two paths for MJOs across the Maritime Continent; one is a detoured route into the Southern Hemisphere and the other one is around the equator across the Maritime Continent. Here, it is shown that the detoured and non-detoured MJOs have significantly different impacts on the South Pacific convergence zone (SPCZ). The detoured MJOs trigger strong cross-equatorial meridional winds from the Northern Hemisphere into the Southern Hemisphere. The associated meridional moisture and energy transports due to the background states carried by the intraseasonal meridional winds are favorable for reinforcing the SPCZ. In contrast, the influences of non-detoured MJOs on either hemisphere or the meridional transports across the equator are much weaker. The detoured MJOs can extend their impacts to the surrounding regions by shedding Rossby waves. Due to different background vorticity during detoured MJOs in boreal winter, more ray paths of Rossby waves traverse the Maritime Continent connecting the southern Pacific Ocean and the eastern Indian Ocean, but far fewer Rossby wave paths traverse Australia. Further studies on such processes are expected to contribute to a better understanding of extreme climate and natural disasters on the rim of the southern Pacific and Indian Oceans.

Meridional Changes in Satellite Chlorophyll and Fluorescence in Optically-Complex Coastal Waters of Northern Patagonia

Northern Patagonia is one of the largest estuarine systems worldwide. It is characterized by complex geography, including islands, peninsulas, channels, and fjords. Here, the Inner Sea of Chiloé (ISC) is the largest estuarine system extending about 230 km in the meridional direction. Phytoplankton’s long-term dynamics and the main physical drivers of their variability are not well understood yet. Time-space fluctuations of Chlorophyll-a (Chl-a) and Chlorophyll fluorescence (nFLH) within the ISC and their association with meteorological and oceanographic processes were analyzed using high resolution (1000 m) satellite data (2003–2019). Our results revealed a meridional Chl-a and nFLH gradient along the ISC, with higher concentrations north of the Desertores islands where the topography promotes a semi-closed system with estuarine characteristics yearlong. Satellite Chl-a and nFLH were characterized by asynchronous seasonal cycles (nFLH peaks in fall) that differed from the southern ISC where the maximum Chl-a and nFLH occurs in spring-summer. The adjacent coastal ocean influences the southern ISC, and thus, the Chl-a and nFLH variability correlated well with the seasonal variation of meridional winds. The northern ISC was clearly influenced by river discharges, which can bias the Chl-a retrievals, decoupling the annual cycles of Chl-a and nFLH. In situ data from a buoy in Seno Reloncaví reaffirmed this bias in satellite Chl-a and a higher correlation with nFLH, by which the construction of a local Chl-a algorithm for northern Patagonia is essential.