Extreme Orographic Rains from Streams of Moist Marine Layer Wind Systems with a Possible Geoengineering Application

This study covers four parts. The first part describes the heaviest rains at Waialeale Mountains of the Kauaʻi Island of Hawaii. The second part describes a numerical modelling of the daily heavy rains at Waialeale during undisturbed weather days. A third part of this study explores other parts of the world where certain thresholds, such as a Baines number and a triple product (suggested by a microphysical cloud resolving model) call for the possibility of heavy rains. The fourth part suggests that with a proper shape of the mountain, models predict heavy rains in regions, which satisfy the two numbers, during days of no rains. We show that strong trades and monsoonal winds carry huge amounts of moisture in the marine layer next to the ocean surface that has the capability for yielding, under proper conditions, large amounts of orographic rains. Hawaiian rainfall has been studied by a number of authors; these include studies on rainfall variability, mesoscale modelling, trade wind inversion, humidity profiles, and topographic effects [1-5]. These study have provided important background for the orographic rains of Hawaii. Mount Waialeale (or Waialeale) is a volcanic mountain on the island of Kaua’i in the Hawaiian Islands. The name Waialeale means “rippling water” or “overflowing water” in Hawaiian language. The Waialeale mountain formed some 6 million years ago from a volcanic eruption, with a conical shape, whose east face eroded somewhat with time [6-8]. This is a small size mountain; its height and width are around 1.5 km and 22 km, respectively. Figure 1 illustrates its plan view and a photograph of the (eastward) windward front face. A rain gauge placed over a region of the Waialeale mountain in 2007, where visual observations showed most frequent rains and measured the world’s highest rains, nearly 400 to 430 inches of rain per year. In later date new places have emerged that are now at the top of the list of highest rains per year and Waialeale mountain has presently moved down to the 8th position in the list (study conducted by “worldatlas” http://www.worldatlas.com/articles/the-ten-wettest-places-inthe-world.html). Waialeale is an isolated heavy rainfall center over a small region, by the mountain, that occupies nearly a two-and-a-half-mile square area. Roughly 70 percent of that rain comes from days of undisturbed weather and passage of streams of stratocumulus and a few towering cumuli that interact with the Waialeale mountains. In this study the term “undisturbed weather” is used to define periods when the trades (or the winter monsoon flows), at the 850 hPa level, carry no storms on the synoptic or mesoscales. These trade winds (or north-east flows) resemble the climatological mean flows for that month. During such periods of undisturbed weather, often surges are present in the trades. Using a very high resolution cloud resolving mesoscale model, these heavy rains are modeled. Other Hawaiian Islands do have taller mountains but the shapes of the mountains are not as favorable as the Waialeale for such annual rainfall totals. When the volcanic eruptions first formed the conical shaped Waialeale Volume 1 Issue 7 2017