Wyniki wyszukiwania - BazTech

Ograniczanie wyników

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: pora deszczowa

Sortuj według:

Ogranicz wyniki do:

Tropospheric features associated with the onset and cessation of the rainy season in Iran

Asakereh Hossein, Masoodian Sayed Abolfazl, Tarkarani Fatemeh, Zandkarimi Soma

Acta Geophysica

2023

Vol. 71, no. 2

1063--1084

In the present study, according to a provided definition of the widespread rainy season (WRS), the onset of the WRS (OWRS) and the cessation of the WRS (CWRS) occurred in three and four phases, respectively. The phases of the OWRS (26 Sep, 5 Nov, and 15 Dec) were related to the interaction of the sub-polar low pressure (central pressure lower than 996 hpa) and the Siberian high pressure (central pressure higher than 1020 hpa) at the tropospheric lower level and the ridge of Arabia at the 500 hpa (higher than 5850 m). Thus, the eastward-moving of the Mediterranean cyclones (the number of cyclones from the first to the third phase was 264, 245, and 407, respectively) bred the positive moisture flux convergence and reduced the outgoing long waves radiation (OLR) values to about 240 W/M2. Simultaneous with the northward shift of the sub-polar low pressure and penetrating the Siberian high pressure to the west of Iran and the extension of 300-hpa jet stream, the next phase of the OWRS appeared in the southern regions. The four phases of the CWRS (6 Oct, 31 Dec, 5 Mar, and 3 Apr) commenced with the strength (central pressure higher than 1032 hpa) and expansion of the Siberian high pressure, concurrent with the formation of high pressure in the northwest of Iran, followed by the second phase on the Iranian coast of the Caspian Sea. The reduction in gradients of 500 hpa height in the latitude of 20–40 N was associated with increased zonal wind in the longitude of 40 E toward the east and the weakening of the jet stream at 300 hpa. In addition to increasing the OLR (more than 250 W/m2 ), the thermal low pressure, positive values of meridian wind, and negative values of zonal wind over Iran led to the transfer of the characteristics of the adjacent desert, and the maximum OLR planetary belt moved toward the country. Contrary to previous studies, which attributed the onset and cessation of the rainy season to a few atmospheric features, the results of the current study suggest that the onset and cessation of the rainy season resulted from a very complex interaction of several tropospheric factors and geographical features of different regions. This interaction, primarily in geographically diverse realms (e.g., Iran), leads to complicated spatial patterns of the onset and cessation of the rainy season.

Physicochemical changes and abundance of freshwater snails in Anambra River (Nigeria) during the rainy season

Okoye Charles Obinwanne, Echude Daniel, Chiejina Chike Obinna, Andong Felix Atawal, Okoye Kingsley Chukwuebuka, Ugwuja Samuel Ejike, Ezeonyejiaku Chigozie Damian, Eyo Joseph

Ecological Chemistry and Engineering. S

2022

Vol. 29, nr 2

169--181

Rapid diversification is a way of responding to environmental change for freshwater organisms. This work examined the physicochemical changes and abundance of freshwater snails in Anambra River (Nigeria) during the rainy season. Field studies were conducted fortnightly from June to August 2019 at three stations of the river namely: Otuocha (station I), Otunsugbe (station II), and Ukwubili (station III) about 8.35 kilometers apart from each other. A scoop net of 2 cm mesh size and handpicking was used to sample freshwater snails randomly and water samples were taken to the laboratory for physicochemical analysis. A total of 896 freshwater snails belonging to 6 species (Afropomus balanoidea, Pomacea maculata, Lymnea stagnalis, Lanistes ovum, Pila wernei, and Saulea vitrea) were collected. Pomacea maculata was the most dominant species with a relative abundance of 45.87 %, while Saulea vitrea was the least dominant species with a relative abundance of 2.34 %. There was a significant negative correlation between dissolved oxygen and Pomacea maculate (r = –0.877, p = 0.002) and a positive correlation between dissolved oxygen and Stagnalis lymnea (r = 0.840, p = 0.005). The diversity of species was highest at Otuocha (1.171) followed by Ukwubili (1.133) and Otunsugbe (0.856) with average mean temperatures of (23.1 ±0.1) °C, (27.30 ±0.00) °C, and (26.80 ±0.03) °C respectively. The distribution of freshwater snails was influenced by the physicochemical variability of Anambra River during the rainy season. Therefore, further studies for a longer time and different seasons to examine the impact of physicochemical changes on the snail distribution are encouraged.