Some aspects of the West African monsoon circulation As deduced from a geostationary satellite

This paper focusses on some aspects or the West African monsoonal circulation observed during the period 15 July-l0 August 1979 of the PGGE, as derived from the satellite cloud windvectors. Temporal averages of the computed winsfields reveal that the flow at the low level is southerly (monsoonal), and Its line of discontinuity with the continental northeasterly was found at approximately 16°-18°N, lying about 300 km south of the accepted mean position. At both the middle and upper tropospheres the flow is easterly with axis about 12o-14,N and, latitude 8 No respectively, such that it is a circulation south of the axis and northwards, it is anticyclonic. The satellite-observed tropospheric circulation IS then discussed in relation to the, weather manifestations over the sub-region typical of the July / August period. The mass fields obtained from our gridded satellite-winds indicate that inflow into the land area occur mainly at the lowest layer (1000:850 hPa), whereas at the upper, levels (that is, above 850 hPa) it is predominantly an outflow, The tropospheric average gives a net mass for divergence from within the area, The significance of this result in relation to the observed weather phenomenology of a temporary cessation of the monsoon precipitations occurring about the peak of the season IS also discussed.

EFFECT OF WESTWARD MOVING CLOUD ORGANISATIONS IN WEST AND NEAR EQUATORIAL PACIFIC OCEAN ON THE MONSOON RAINFALL OF INDIA

Th en: are various synoptic s)')leDls which affect the rainfall over India during southwest mansoonseason directly or indirectly. AJ'110 J12 them. one subject of interest is the westward movina cloud pulses over th eequatorial wt'sl Pacific region. An attempt h as been made to connect the satellite c10uJ pulses in the eq ua torial westPacific. ns seen in the INSAT· I geostationary satellite imageries. with the rai nfall of selected meteorological subqh·i~ on~ o f Ind ia v.tlkh an: seemingly affected by Ih ~'~ pulses.

Mapping Diurnal Variability of the Wintertime Pearl River Plume Front from Himawari-8 Geostationary Satellite Observations

the spatial pattern of the wintertime Pearl River plume front (PRPF), and its variability on diurnal and spring-neap time scales are characterized from the geostationary meteorological Himawari-8 satellite, taking advantage of the satellite’s unique 10-minutely sea surface temperature sequential images. Our findings suggest that the PRPF in winter consists of three subfronts: the northern one north of 22°N 20′, the southern one south of 21°N 40′, and the middle one between 22°N 20′ and 21°N 40′. The time-varying trend of the frontal intensity generally exhibits a strong-weak-strong pattern, with the weakest plume front occurring at about 06:00 UTC, which is closely associated with net surface heat flux over the region. The comparison in frontal variability between the spring and neap tides shows that the plume front during the spring tide generally tends to be more diffuse for the frontal probability, move further offshore for the frontal position, and be weaker for the frontal intensity than those found during the neap tide. These great differences largely depend on the tidally induced stronger turbulent mixing during the spring tide while the wind stress only plays a secondary role in the process. To best of our knowledge, the distinct diurnal variations in PRPF with wide coverage are observed for the first time. This study demonstrates that the Himawari-8 geostationary satellite has great potential in characterizing high-frequency surface thermal fronts in considerable detail.

Wolkenverfolgung: Vom Experiment zur Realität

<p>Die Wolkenverfolgung ist die einzige Möglichkeit zur Beobachtung der zeitlichen Entwicklung von Wolken und zur Quantifizierung der Veränderung ihrer physikalischen Eigenschaften während ihrer Lebensdauer (Seelig et al., 2021). Der Schlüssel dazu sind zeitaufgelöste Messungen von Instrumenten an Bord geostationärer Satelliten. Experimente mit atmosphärenähnlicher Konfiguration treiben die Entwicklung von Messmethoden und Alghoritmen unter Laborbedingungen voran. Heutzutage ist es z.B. möglich zweidimensionale, zeitlich und räumlich hochaufgelöste Geschwindigkeitsfelder auf Basis der Verschiebung kleinster Partikel zu messen (Seelig and Harlander, 2015; Seelig et al., 2018). Die Methodik der Partikelgeschwindigkeitsmessung dient als Anfangsbedingung zum Verfolgen dieser Partikel und kann auf troposphärische Wolken angewendet werden. Diese Präsentation stellt die Analogie von Experiment zur Realität vor, beschreibt das Verfahren der Partikelgeschwindigkeitsmessung und die Anwendung auf Daten geostationärer Satelliten.</p> <p><strong>Literatur:</strong></p> <p>Seelig, T., Deneke, H., Quaas, J., and Tesche, M.: Life cycle of shallow marine cumulus clouds from geostationary satellite observations, J. Geophys. Res.: Atmos., 126(22), e2021JD035577, https://doi.org/10.1029/2021JD035577, 2021.</p> <p>Seelig, T., Harlander, U., and Gellert, M.: Experimental investigation of stratorotational instability using a thermally stratified system: instability, waves and associated momentum flux, Geophys. Astrophys. Fluid Dyn., 112, 239-264, https://doi.org/10.1080/03091929.2018.1488971, 2018.</p> <p>Seelig, T. and Harlander, U.: Can zonally symmetric inertial waves drive an oscillating zonal mean flow?, Geophys. Astrophys. Fluid Dyn., 109, 541-566, https://doi.org/10.1080/03091929.2015.1094064, 2015.</p>