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Free Content Some features of columnar aerosol optical depth, ozone and precipitable water content observed over land during the INDOEX-IFP99

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Abstract Columnar aerosol optical depth (AOD), ozone and precipitable water content measurements have been made under different atmospheric conditions on a total of 46 days at the Indian Institute of Tropical Meteorology (IITM), Pune during the Intensive Field Phase (IFP) of the Indian Ocean Experiment INDOEX (January-March 1999). These observations have been obtained using two compact, on-line, multi-band solar radiometers (MICROTOPS-II) simultaneously. The results indicate higher aerosol optical depth (more than double) on hazy days as compared to clear stable days. Further increase in aerosol optical depth and markable changes in the size spectrum are also noticed during the occasions of smoke particles' emission from combustion processes in proximity to the experimental site and high water content in the atmosphere. Size spectra of aerosols exhibit characteristic bimodal distribution with mode radii between 0.1 and 1.0 μm on the days associated with hazy-sky conditions and combustion activity. However, the mean aerosol optical depth over the entire IFP shows almost exponential decrease with increase in wavelength, and corresponding size spectrum portrays power law distribution, which may be due to the averaging effect of time variations such as forenoon, afternoon and day-to-day. Moreover, the daily values of columnar aerosol optical depth and water content show almost similar variations. Besides an increasing trend in the total column ozone variations throughout the period of study, it shows opposite variation with those observed in AOD and water content. These interesting features reveal the influence of water content on the growth processes of aerosol particles, and relationship between the increase in aerosol extinction and reduction in ozone amount and vice versa. The columnar aerosol optical depth or content or loading during the IFP99 exhibit higher values as compared to those during the First Field Phase (FFP98).

Messungen der optischen Dicke auf Grund von Aerosolen (Aerosol Optical Depth, AOD), des Ozons und des niederschlagbaren Wassers in einer Luftsäule wurden an insgesamt 46 Tagen unter verschiedenen Atmosphärenbedingungen vorgenommen. Dies geschah am Indian Institute of Tropical Meteorology (IITM) in Poona, während der Intensiv-Feldphase (IFP) des Indian Ocean Experiments INDOEX (Januar-März 1999). Die Beobachtungen wurden mittels zweier kompakter, direkt messender Mehrband Solar-Radiometer (MICROTOPS-II) gleichzeitig aufgezeichnet. Die Ergebnisse zeigen, dass an dunstigen Tagen die optische Dicke auf Grund von Aerosolen mehr als doppelt so groß wie an Tagen mit gleichbleibend klarer Luft war. Die Größenspektren der Aerosole zeigen die charakteristische bimodale Verteilung mit den Modalwerten zwischen 0.1 und 10 μm an dunstigen Tagen, an denen auch erhöhter Eintrag durch Verbrennung vorlag. Die täglichen AOD- und Wassergehaltswerte zeigen fast gleiche Variabilität. Neben einem Zunahmetrend der Variationen im Gesamtozongehalt der Luftsäule während des gesamten Untersuchungszeitraums gibt es umgekehrte Verläufe bei der AOD und dem Wassergehalt. Diese interessanten Erscheinungen legen den Einfluss des Wassergehalts auf Aerosol-Wachstumsprozesse offen. Dazu gibt es Wechselbeziehungen zwischen der Zunahme der Aerosol-bedingten Extinktion und der Ozonreduktion. Im Vergleich zur ersten Feldphase (First Field Phase, FFP98) wurden während der IFP99 höhere Werte der AOD in der Luftsäule oder der Belastung der Luft registriert.


Document Type: Research Article


Affiliations: Indian Institute of Tropical Meteorology, Pune, India

Publication date: 2001-03-01

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