Cloud seeding over Tasmania : a long-term evaluation and modelling plausibility study
Initially, an analysis of cloud seeding activity for the period 1960-2005 over a hydro-electric catchment (target) area located in central Tasmania is presented. The analysis is performed using a double ratio on monthly area averaged rainfall for the months May-October. Results indicate that increas...
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Monash University. Faculty of Science. School of Mathematical Sciences
2010
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ftmonashul:monash:34907 2023-05-15T18:24:49+02:00 Cloud seeding over Tasmania : a long-term evaluation and modelling plausibility study Morrison, Anthony Edward Principal Supervisor: Steven Thomas Siems 2010 http://arrow.monash.edu.au/hdl/1959.1/192123 eng eng Monash University. Faculty of Science. School of Mathematical Sciences Open access: open access to thesis full text. This thesis is protected by copyright. Copyright in the thesis remains with the author. The Monash University ARROW Repository has a non-exclusive licence to publish and communicate this thesis online. Cloud seeding Numerical modelling Southern Ocean Tasmania Modis satellite thesis thesis(doctorate) 2010 ftmonashul 2017-10-02T22:44:30Z Initially, an analysis of cloud seeding activity for the period 1960-2005 over a hydro-electric catchment (target) area located in central Tasmania is presented. The analysis is performed using a double ratio on monthly area averaged rainfall for the months May-October. Results indicate that increases in monthly precipitation are observed within the target area relative to nearby controls during periods of cloud seeding activity. Ten independent tests were performed and all double ratios found are above unity with values that range from 5-14%. Nine out of ten confidence intervals are entirely above unity and overlap in the range of 6-11%. Nine tests obtain levels of significance greater than the 0.05 level. If the Bonferroni adjustment is made to account for multiple comparisons, six tests are found to be significant at the adjusted alpha level. Secondly, the cloud structure associated with two frontal passages/cloud seeding events over the Southern Ocean and Tasmania is investigated. The Weather Research and Forecasting (WRFV2.2.1) model is evaluated using remote sensed and in-situ observations within the post frontal airmass. The evaluated cases are then used to investigate numerically the prevalence of supercooled and mixed phase clouds over Tasmania and the ocean to the west. The simulations produce marine stratocumulus like clouds with maximum heights of between 3 and 5km. These are capped by weak temperature and strong moisture inversions. When the inversion is at temperatures warmer than -10 C, WRF produces wide spread supercooled cloud fields with little glaciation. This is consistent with the limited in-situ observations. When the inversion is at higher altitudes, allowing cooler cloud tops, glaciated (and to a lesser extent mixed phase) clouds are more common. The sensitivity of the simulations to certain bulk microphysical assumptions is explored, the findings indicate the results are relatively insensitive to the parameters investigated. Finally, a MODIS based climatology of Southern Ocean clouds south of mainland Australia is presented, for the region 30-60S and 100-160E. Particular emphasis is placed on observations of supercooled clouds. Results are compared with those from the North Pacific region (30-60N, 160-220E) as a point of comparison. The findings presented are consistent with an earlier study by cite{Mace_cloudsat}, between 40-60% of clouds that exist over the Southern Ocean west of Tasmania are low with tops <3km and cloud top temperatures ~0 C. Supercooled clouds are more common at the high latitudes, the island of Tasmania (situated in the lower latitude bands) modifies clouds sufficiently so that these resemble more closely those within the higher latitude bands. Little annual variability is observed. The North Pacific region resembles the Southern Ocean, however a greater seasonal variability is observed. In general, a supercooled cloud top is observed ~20% of the total time over the Southern Ocean and North Pacific. Mixed phase clouds are more rare, occurring <10% of the total time. Over western Tasmania, supercooled clouds exist ~25% of the time during winter months. Doctoral or Postdoctoral Thesis Southern Ocean Unknown Pacific Southern Ocean |
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Open Polar |
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ftmonashul |
language |
English |
topic |
Cloud seeding Numerical modelling Southern Ocean Tasmania Modis satellite |
spellingShingle |
Cloud seeding Numerical modelling Southern Ocean Tasmania Modis satellite Morrison, Anthony Edward Cloud seeding over Tasmania : a long-term evaluation and modelling plausibility study |
topic_facet |
Cloud seeding Numerical modelling Southern Ocean Tasmania Modis satellite |
description |
Initially, an analysis of cloud seeding activity for the period 1960-2005 over a hydro-electric catchment (target) area located in central Tasmania is presented. The analysis is performed using a double ratio on monthly area averaged rainfall for the months May-October. Results indicate that increases in monthly precipitation are observed within the target area relative to nearby controls during periods of cloud seeding activity. Ten independent tests were performed and all double ratios found are above unity with values that range from 5-14%. Nine out of ten confidence intervals are entirely above unity and overlap in the range of 6-11%. Nine tests obtain levels of significance greater than the 0.05 level. If the Bonferroni adjustment is made to account for multiple comparisons, six tests are found to be significant at the adjusted alpha level. Secondly, the cloud structure associated with two frontal passages/cloud seeding events over the Southern Ocean and Tasmania is investigated. The Weather Research and Forecasting (WRFV2.2.1) model is evaluated using remote sensed and in-situ observations within the post frontal airmass. The evaluated cases are then used to investigate numerically the prevalence of supercooled and mixed phase clouds over Tasmania and the ocean to the west. The simulations produce marine stratocumulus like clouds with maximum heights of between 3 and 5km. These are capped by weak temperature and strong moisture inversions. When the inversion is at temperatures warmer than -10 C, WRF produces wide spread supercooled cloud fields with little glaciation. This is consistent with the limited in-situ observations. When the inversion is at higher altitudes, allowing cooler cloud tops, glaciated (and to a lesser extent mixed phase) clouds are more common. The sensitivity of the simulations to certain bulk microphysical assumptions is explored, the findings indicate the results are relatively insensitive to the parameters investigated. Finally, a MODIS based climatology of Southern Ocean clouds south of mainland Australia is presented, for the region 30-60S and 100-160E. Particular emphasis is placed on observations of supercooled clouds. Results are compared with those from the North Pacific region (30-60N, 160-220E) as a point of comparison. The findings presented are consistent with an earlier study by cite{Mace_cloudsat}, between 40-60% of clouds that exist over the Southern Ocean west of Tasmania are low with tops <3km and cloud top temperatures ~0 C. Supercooled clouds are more common at the high latitudes, the island of Tasmania (situated in the lower latitude bands) modifies clouds sufficiently so that these resemble more closely those within the higher latitude bands. Little annual variability is observed. The North Pacific region resembles the Southern Ocean, however a greater seasonal variability is observed. In general, a supercooled cloud top is observed ~20% of the total time over the Southern Ocean and North Pacific. Mixed phase clouds are more rare, occurring <10% of the total time. Over western Tasmania, supercooled clouds exist ~25% of the time during winter months. |
author2 |
Principal Supervisor: Steven Thomas Siems |
format |
Doctoral or Postdoctoral Thesis |
author |
Morrison, Anthony Edward |
author_facet |
Morrison, Anthony Edward |
author_sort |
Morrison, Anthony Edward |
title |
Cloud seeding over Tasmania : a long-term evaluation and modelling plausibility study |
title_short |
Cloud seeding over Tasmania : a long-term evaluation and modelling plausibility study |
title_full |
Cloud seeding over Tasmania : a long-term evaluation and modelling plausibility study |
title_fullStr |
Cloud seeding over Tasmania : a long-term evaluation and modelling plausibility study |
title_full_unstemmed |
Cloud seeding over Tasmania : a long-term evaluation and modelling plausibility study |
title_sort |
cloud seeding over tasmania : a long-term evaluation and modelling plausibility study |
publisher |
Monash University. Faculty of Science. School of Mathematical Sciences |
publishDate |
2010 |
url |
http://arrow.monash.edu.au/hdl/1959.1/192123 |
geographic |
Pacific Southern Ocean |
geographic_facet |
Pacific Southern Ocean |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_rights |
Open access: open access to thesis full text. This thesis is protected by copyright. Copyright in the thesis remains with the author. The Monash University ARROW Repository has a non-exclusive licence to publish and communicate this thesis online. |
_version_ |
1766205739166072832 |