Seasonal variations of surface duct conditions in Ngaoundere, North Cameroon

详细信息    查看全文

• 作者：Samuel Kaissassou ; André Lenouo ; Armand Nzeukou…
• 刊名：Meteorology and Atmospheric Physics
• 出版年：2015
• 出版时间：December 2015
• 年：2015
• 卷：127
• 期：6
• 页码：659-674
• 全文大小：4,988 KB
• 参考文献：Agusti AP, Beljaars A, Ahlgrimm M, Balsamo G, Bock O, Forbes R, Ghelli A, Guichard F, K?hler M, Meynadier R, Morcrettea JJ (2010) The ECMWF re-analysis for the AMMA observational campaign. Q J R Meteorol Soc 136:1457-472CrossRef
  Almond T, Clarke J (1983) Consideration of the usefulness of microwave propagation prediction methods on air-to-ground paths. Proc IEEE Part F 130:649-56
  Ao CO (2007) Effect of ducting on radio occultation measurements: an assessment based on high-resolution radiosonde soundings. Radio Sci 42:RS2008. doi:10.-029/-006RS003485 CrossRef
  Arya SP (1988) Introduction to micrometeorology. Academic Press
  Babin SM (1996) Surface duct height distributions for Wallops Island, Virginia, 1985-994. J Appl Meteorol 35:86-3CrossRef
  Barla MC (1986) Sur les indices de réfraction atmosphérique en Turquie. La Météorologie; VII 13:2-
  Battan LJ (1973) Radar observation of the atmosphere. University of Chicago Press
  Bean BR, Dutton EJ (1968) Radio meteorology. Dover
  Bech J, Bebbington DH, Codina B, Sairouni A, Lorente J (1998) Evaluation of atmospheric anomalous propagation conditions: an application for weather radars. Remote sensing for agriculture, ecosystems, and hydrology. In: Engman ET (ed) International Society for Optical Engineering (SPIE Proceedings vol. 3499), pp 111-13
  Bech J, Codina B, Lorente J, Bebbington D (2002) Monthly and daily variations of radar anomalous propagation conditions: how “normal-is normal propagation? In: Proceedings of Second European Conference of Radar Meteorology, Delft, Netherlands, ERAD Publication Ser vol. 1, Copernicus GmbH, pp 35-9
  Bech J, Gjertsen U, Haase G (2007) Modelling weather radar beam propagation and topographical blockage at northern high latitudes. Q J R Meteorol Soc 133:1191-204CrossRef
  Bluestein HB (1993) Observations and theory of weather systems. Vol II. Synoptic-dynamic meteorology in midlatitudes. Oxford University Press
  Born M, Wolf E (1999) Principles of optics, 7th edn. Cambridge University Press, New YorkCrossRef
  Borsum DL (1995) Doppler dilemma delineates danger from dirt. National Weather Service Western Region Technical Attachment 95-07, National Weather Service Field Office, Boise, ID, p 7. Available from National Weather Service Field Office, DOC/WASC, 3833 S. Development Ave., # 3807, Boise, ID 83705-5354
  Brooks IM, Goroch AK, Rogers DP (1999) Observations of strong radar ducts over the Persian Gulf. J Appl Meteorol 38:1293-310CrossRef
  Cook J (1991) A sensitivity study of weather data inaccuracies on evaporation duct height algorithms. Radio Sci 26:731-46CrossRef
  Craig KH, Hayton TG (1995) Climatic mapping of refractivity parameters from radiosonde data. In: Proceeding Conference 567 on Propagation Assessment in Coastal Environments, Bremerhaven, Germany, AGARD-NATO, 43, pp 1-4
  Dalmaz M (1977) Variation de la réfraction atmosphérique en fonction de la température à G?ztepe. La Météorologie; VI 10: 113-24
  Deniz A, Karaca M, Borhan Y (1997) A climatological study on the relationship between cyclone paths and air pollutants in Turkey. Environ Res Forum 7-:360-66
  Ding J, Fei J, Huang X et al (2013) Observational occurrence of tropical cyclone duct from dropsonde data. J Appl Meteorol Climatol 2013(52):1221-236CrossRef
  Dockery GD (1988) Modeling electromagnetic wave propagation in the troposphere using the parabolic equation. IEEE Trans Antennas Propag 36:1464-470CrossRef
  Erinc S (1984) Klimatoloji ve Metodlari (Methods of climatology). Gunay Matbaasi, p 540
  Falodun SE, Ajewole MO (2006) Radio refractive index in the lowest 100-m layer of the troposphere in Akure, South Western Nigeria. J Atmos Solar Terr Phys 68(2):236-43CrossRef
  Falodun SE, Okeke PO (2012) Radiowave propagation measurements in Nigeria (preliminary reports). Theor Appl Climatol 2013 113:127-35CrossRef
  Freehafer JE (1988) Tropospheric refraction. Propagation of short radio waves. In: Kerr DE (ed) Peninsula Publishing, pp 9-2
  Gossard EE (1977) Refractive index variance and its height distribution in different air masses. Radio Sci 12:89-05CrossRef
  Kadioglu M (1997) Trends in surface air temperature data over Turkey. Int J Climatol 17:511-20CrossRef
  Kaissassou S, Lenouo A, Tchaouwa C, Lopez P, Amadou TG (2015) Climatology of anomalous propagation radar over West Africa. J Atmos Solar Terr Phys 123(2015):1-2CrossRef
  Lenouo A (2012) Climatology of anomalous propagation radar over Douala, Cameroon. Meteorol Appl. doi:10.-002/?met.-321
  Lenouo A, Monkam D, Vondou DA, Tanessong RS, Mkankam Kamga F (2009) Analyse des conditions météorologiques pour la sécurité aérienne `a Douala. La Météorol 65:46-8CrossRef
  Lopez P (2009) A 5-year 40-km-resolution global climatology of superrefraction for ground-based weather radars. J Appl Meteorol Climatol 48:89-10CrossRef
  Mentes S, Kaymaz Z (2007) Investigation of surface duct conditions over Istanbul, Turkey.
• 作者单位：Samuel Kaissassou (1)
  André Lenouo (2)
  Armand Nzeukou (3)
  Clément Tchawoua (4)
  D. A. Vondou (1)
  
  1. LEMAP, Department of Physics, Faculty of Science, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon
  2. Department of Physics, Faculty of Science, University of Douala, P.O. Box 24157, Douala, Cameroon
  3. Laboratory of Industrial Systems and Environmental Engineering, Fotso Victor Technology Institute, University of Dschang, Dschang, Cameroon
  4. Laboratory of Mechanic, Department of Physics, Faculty of Science, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon
  
• 刊物类别：Earth and Environmental Science
• 刊物主题：Earth sciences
  Meteorology and Climatology
  Atmospheric Protection, Air Quality Control and Air Pollution
  Climate Change
  Mathematical Applications in Environmental Science
  Terrestrial Pollution
  Waste Water Technology, Water Pollution Control, Water Management and Aquatic Pollution
  
• 出版者：Springer Wien
• ISSN：1436-5065

文摘

The seasonal variations of refractivity gradients from 104 to 3000 m above ground level in the troposphere layer are presented based on observations from the radiosonde station located in Ngaoundere (13.5°E, 7.3°N), a middle belt savannah region of Cameroon. Six years (2006-011) of data from in situ measurements made by Agency for the Safety of Air Navigation in Africa and Madagascar (ASECNA) of the temperature, moisture, and pressure are used to determine the surface duct conditions over Ngaoundere region. Each time that a negative gradient from the Abel-retrieved refractivity profiles is seen, it implies the presence of a duct in this study. The occurrence of ducts strongly depends on the local climate and synoptic weather conditions which have an appreciable influence on the refractivity vertical profile, especially the seasonal north–south movement of the Inter Tropical Convergence Zone (ITCZ) which provides wet and dry seasons to the region. Monthly and seasonal variations of ducts were also determined from the measured data. The highest and the lowest occurrence rate of surface ducts were observed during the wet and the dry seasons, respectively. September appears as the month when most of the ducts occur at the rate of at least one duct per day. The median duct thickness and duct strength are high and strong during the wet season, whereas they are low and weak during the dry season. When the data are separated into stable and unstable atmospheric conditions, we noticed that surface duct characteristics show some seasonal differences. Surface ducts are found to be more frequent in a stable atmosphere than in an unstable atmosphere. Statistical results are discussed alongside with local meteorological conditions and weather systems affecting the town of Ngaoundere. Besides, comments are made on their prospective significance in the region. Responsible Editor: R. Roebeling.