Thursday, February 21, 2008

A wind and wave atlas for the Mediterranean Sea

Well one of my favorite subjects, that has a major impact on the maritime community, rogue waves. Here is a interesting report on wind speed and wave height measurements provided by ERS-1.

Luigi Cavaleri

ISMAR, S.Polo 1364 , 30125 Venezia, Italy


Long term climatological data over the sea are much in demand for a number of reasons, ranging from pure scientific knowledge to the more important applications of, e.g., safety at sea and the design of sea structures. Till 15 years ago the only practical sources of the long term data required for a meaningful statistics was the collection of visual observations done from ships at sea. Starting from 1991 two new sources of data started to be available. The launch of ERS-1, and soon after of Topex-Poseidon, offered an unprecedented continuous flow of wind speed and wave height measurements. At the same time the improvements in computer power and numerical modelling led to a continuous synoptic description, typically at 6-hour interval, of the distribution of wind and wave characteristics at sea.

These two sources offered a wealth of data and today quite reliable statistics exist in the open oceans. However, the situation is less favourable in the inner seas. Here the global meteorological models exhibit a steady underestimate of the wind speeds, that in turn leads to an underestimate of the associated modelled wave heights. On the other hand the strong spatial gradients that characterise the basins with a complicated geometry, as in our case the Mediterranean Sea, imply that the spatial resolution of the altimeter ground tracks is not sufficient to provide the necessary details.

The solution lies in the complementary use of both the altimeter and the modelled data. The latter ones provide the background information, very dense in time and space, that is then calibrated using the information derived from the altimeters. This is done determining for each grid point, at 0.5 degree intervals, the series of co-located values, model and altimeter, for both wind speed and wave height. Provided the necessary reliability checks are satisfied, for each point and each parameter the best-fit slopes of the co-located data provide the correction coefficients of the model data. After some spatial averaging to avoid unrealistic local variability, long term time series of calibrated wind and wave fields have been obtained. These have been used to derive multiple long term statistics, both at synoptic and point levels. All these results have been made available in the MEDATLAS atlas of the Mediterranean Sea, available in both paper (A3) and interactive CD formats.

The results have also allowed a check of the correctness of the wind speed and wave height altimeter measurements. The direct relationship existing between these two quantities implies a consistency between their statistics. This is obviously present in the original data that are model derived, and it should be expected also in the calibrated data. On the contrary we have found that the calibrated wind speed values are lower than expected from the calibrated wave heights. As the latter ones have also been verified versus accurate buoy data, we suggest that the algorithm used to derive the altimeter wind speed provides values lower than the actual truth. ( Full paper ) pdf format.

Severe Weather Awareness Week

Tornado drill alert, Severe Weather Awareness Week

The week of Feb. 24 through Mar. 1 has been designated as “Severe Weather Awareness Week” in the state of Texas. During this week, all National Weather Service offices serving the Lone Star State will be actively involved in promoting severe weather awareness.

In addition, the NWS office in Houston/Galveston will be participating in a region-wide tornado drill for southeast Texas. At approximately 10 a.m. on Wednesday, Feb. 27, the Houston/Galveston NWS office will issue a mock tornado warning for all 23 counties in southeast Texas. The warning will be issued through broadcast on the NOAA All Hazards Weather Radio. This will give government agencies, businesses, schools and other interested parties an opportunity to practice their emergency operation plans for tornados.

If you have any questions regarding “Severe Weather Awareness Week” or the mock tornado drill, contact Gene Hafele via email at or call 281-337-5074, ext. 223.

Arkansas Severe Weather Awareness Week Feb. 25-29th

Arkansas Governor Mike Beebe has joined the National Weather Service and the Arkansas Department of Emergency Management to urge the citizens of Arkansas to prepare for the severe weather season.

The Governor has proclaimed February 25-29, 2008 as "Severe Weather Awareness Week" in Arkansas.

Governor Beebe is encouraging citizens to use the week to review severe weather safety rules and to understand the hazards associated with severe thunderstorms.

Arthur Rabjohn CEM

A powerful earthquake of 7.6 magnitude, 30km deep struck off the coast of Sumatra, Indonesia, prompting tsunami warnings. There are reports of at least 3 deaths. The tremor was centred about 319km west-southwest of Medan, Sumatra. The earthquake could generate a tsunami.

PHILIPPINES: Flash floods have killed at least 10 people in the central Philippines and forced tens of thousands to evacuate. Three people were injured. Nearly 140,000 people have been affected as collapsed bridges, landslides and floodwaters isolated Eastern Samar province.

PHILIPPINES: An earthquake measuring 5.6 on the Richter scale occurred west of the Philippine Batan Islands Wednesday. The earthquake hit at 0:59 a.m. Wednesday (1659 Tuesday GMT), with the epicentre initially determined to be 20.3 degrees north latitude and 121.1 degrees east longitude, about 270 km south southeast of Kaohsiung, a major town in the south of the China's Taiwan. There were no immediate reports of casualties or damages.

BOLIVIA: More than 58,000 families are affected by flooding. Hundreds are suffering from waterborne diseases and acute diarrhoea. Around 52 people have died, eight are missing and more than 616,000 hectares of crops destroyed as rivers burst their banks. The region most affected is Beni, but water levels are starting to drop in the city of Trinidad.

MOZAMBIQUE: Tropical Cyclone Ivan has weakened after killing 11 people in Madagascar, but could still cause torrential rains in Mozambique and flood many rivers in Madagascar. Cyclone Ivan was expected to lash Mozambique with heavy rains when it reached land on Tuesday as it was moving at a speed of 190 km/h.


Chicago Maritime Festival - February 23

February 23 the Chicago Maritime Society will host the 6th annual Chicago Maritime Festival. Since the first festival in 2003, Torresen Marine has been a proud sponsor, providing support services to the event.

If you are in the Chicago area, please consider attending this event and learning more about our maritime heritage.

10:00 AM - 4:30 PM:
Seminars, workshops, exhibits, etc.
Common Times, in cooperation with the Chicago History Museum and The Chicago Maritime Society presents an international gathering to celebrate Chicago’s diverse marine community and maritime heritage. Daytime activities include seminars, workshops, lectures, films, and exhibits on a broad range of topics such as underwater archeology, the Eastland, the Endurance, lighthouses, ballads, shanties, life at sea, model shipbuilding, environmental issues, boating safety, weather, shipwrecks, diving, art, canoes, voyaging, and tall ships. There will also be some activities for children. Admission: $10.00 Adults, children 12 and under free.

7:00 -10:30 PM:
Maritime Music Concert

An international concert will feature critically acclaimed performers from around the country and across the sea including Dick Holdstock and Allan MacLeod (England, Scotland), Northern Neck Chantey Singers (Virginia), Debra Cowen (Massachusetts), Walter Askew (California), Tom and Chris Kastle (Chicago) and others. Admission: $20.00.

Concert and daytime activities: $25.00. ($20.00 by February 15, 2007). 10% discount for CHM or CMS members. For more information or to purchase tickets visit or call 773-774-7216.