Jasmine Field Report 1 May 11, 1999 Chris Fairall, Peter Hacker, Yolande Serra, Peter Webster Following a week of loading and installing equipment in Singapore, the NOAA R/V Ronald H. Brown departed at 4 pm on April 30 to embark on the main phase of the Joint Air Sea Monsoon Experiment (JASMINE). JASMINE is a 40-day study of air-sea interaction and its relationship to monsoon variability in the Indian Ocean and Bay of Bengal involving scientists from four NOAA research laboratories, eight universities, and four countries. A 'pre-JASMINE' preliminary survey of the experimental area was conducted by the ship in mid-April. The principal investigators are Chris Fairall from the NOAA Environmental Technology Laboratory, Peter Hacker from the University of Hawaii, Yolande Serra from the University of Washington, and Peter Webster from the University of Colorado. Why are we are in the Indian Ocean making measurements of the ocean and the atmosphere? This is the part of the world that is influenced by the South Asian monsoon. Between late May and September strong moisture laden winds blow into the continental regions bringing copious rainfall. This rainfall is important as the countries that surround the Indian Ocean rim are essentially agrarian and good rains mean good crops and good crops means food. Furthermore, more than 60 % of the world's population lives under the influence of the monsoon. However, the monsoons sometimes fail and during any rainy season there are short term droughts called "monsoon breaks". Some of us believe that these variations in rainfall (either from month-to-month or year-to-year) can be forecast with sufficient lead time that the farmers can alter their crop plans if they expect a drought or anticipate a flood. Furthermore, we believe that the key to being able to forecast the variations of the monsoon lies in the manner that the ocean and the atmosphere interact. Hence the Joint Air-Sea Monsoon Interaction Experiment project where we are looking for the first time at the influence of the Indian Ocean on the monsoon. The Ronald H. Brown is NOAA's newest research vessel and she has been heavily instrumented for oceanic and atmospheric observations. Standard systems on the Brown include a state-of-the-art scanning Doppler weather radar, a satellite data receiver, a Doppler acoustic ocean current profiler, oceanic and atmospheric CO2 concentration measurements, a radiosonde launch system, and a Sea Beam sonar (for mapping ocean bottom terrain). The scientific party has added three Doppler radars for wind and cloud information, microwave radiometers to determine total column atmospheric water vapor and liquid concentrations, an air-sea flux measurement system, radiometers to measure incoming solar and infrared heat flux, and a high-accuracy dual-sensor conductivity-temperature-depth (CTD) ocean profiling system. Two types of drifting buoy oceanic measurement units will be deployed at selected locations. After leaving Singapore we headed towards the equator to enter the Indian Ocean between Java and Sumatra where we passed by the crater of Krakatoa (a volcano that exploded in the late 1800s). This early part of the trip was marked by nice weather and a variety of interesting sights from 'stilt cities' on the water to a flight of huge bats. From there, we headed west and then north west until we reached the equator. Off the coast of Sumatra we encountered rather disturbed weather with showers and towering cumulonimbus clouds. These were associated with the southern hemisphere intertropical convergence zone which stretches across the Indian Ocean along about 5S at this time of the year. In the next few weeks the convection and heavy rains will be more to the north of the equator as the south west monsoon sets in. Near the equator, the winds were very light and the seas almost flat except for a swell which gave the impression of the whole ocean heaving up and down like a large jello. We have been tracking along 89E and have gone as far as 13N. During the time, the rain fall has decreased and there has been little cumulus cloud, just an overcast of high level cirrus clouds some 10 km (33,000ft) above the surface. The winds have freshened to about 10 m/s (20-25 mph) and the seas are quite choppy with white caps. As we headed up 89E, we have been taking atmospheric and oceanic measurements. We measure the temperature of the ocean from the surface to 500 m as well as its salt content and the currents. We also measure the temperature and the moisture content of the atmosphere from the ocean surface to above the tropopause, some 18-20 km above us. But most importantly, we measure the heat and momentum exchanges between the ocean and the atmosphere so that we can understand how the ocean and the atmosphere interact. We are now "on station" for the next 5 days near 12N, 89E. This is just the type of weather that we need: no convection or very strong winds and lots of sunlight to heat the ocean. The reason why we like this type of weather is that we want to see how the upper ocean responds to continual heating from the sun. Later, when we return to the same spot in two weeks, and after rainfall and strong storms have stirred up the ocean, we will be able to compare we will be able to deduce the impact that the storms have had on the ocean. A group from The University of Hawaii is conducting the oceanographic observations on the JASMINE cruise. During the pre-JASMINE cruise, 7-22 April 1999, 44 CTD stations were completed along a survey line from 5S to 16.5N along 88E. In addition, continuous acoustic Doppler current profiler (ADCP) and near-surface thermosalinograph data (water temperature and salinity) were obtained while underway. Seven surface drifters supplied by the University of California at San Diego (UCSD) were deployed to measure near-surface currents and temperatures. The pre-JASMINE data were obtained during an active period of the pre-southwest monsoon season, with strong south-westerly winds driving eastward currents and forming deep near-surface mixed layers in the near-equatorial band. During the ongoing JASMINE cruise, 5-10 May, 39 CTD stations and continuous ADCP and thermosalinograph measurements have been completed along the south-to-north survey line within the Bay of Bengal sector. In addition, six surface drifters and one SOLO float (UCSD) have been deployed. The remarkable difference between the two surveys is the reversal of the equatorial currents, with the currents now flowing strongly to the west in the equatorial band. The two sections conducted as part of JASMINE are the first ever meridional sections of the combined upper ocean temperature, salinity and velocity fields during the pre- and monsoon onset periods in the Bay of Bengal sector. In this data sparse region of the world's oceans, these data will provide essential information on the upper ocean structure and variability and its relationship to atmospheric forcing during the monsoon onset period. The showcase instrument for the study of powerful rainstorms associated with the monsoon is the ship's C-band Doppler radar. The C-band radar radiates at a frequency of 5600 MHz or with a wavelength of about 5 cm. The radar beam is about 1 degree wide. This region of the electromagnetic spectrum sees the larger water droplets in the atmosphere, allowing us to detect rain and snow. The radar is alternating between two basic scan types for Jasmine, a surveillance scan and a volume scan. The 1 degree radar beam sweeps 360 degrees around the ship at an angle of less than 1 degree from the horizon for the surveillence scan. The range of this scan is about 0.5 - 250 km. The volume scan is a series of 360 degree sweeps between about 0.5 degrees and 30 degrees from the horizon with an extra sweep at 80 degrees for comparison with upward looking shipboard instruments also measuring at cloud properties. The volume scan set provides a three dimensional picture of the rainy areas, indicating both the intensity of the rain and the along-beam velocity of the air mass within these areas. This scan has a range of about 0.5 - 120 km. For our first leg of Jasmine from 5 S to 13.5 N along 89 E, we have not encountered any organized rain events. As discussed above, we are here just before the expected onset of the monsoon season. The radar primarily picks up isolated towering rain clouds attaining altitudes anywhere from 8 - 16 km or greater. The 1 degree width of this radar beam is smaller than the previous 1.5 degree beam radar taken to sea on the Ronald Brown in 1997 on a trip to the equatorial East Pacific. This narrower beam allows us to see smaller cloud systems. It is hard to say whether such systems are more common over the Indian Ocean than over the East Pacific Ocean, or whether our this newer radar is just allowing us to detect these systems. Such questions will likely be answered upon analysis of the data back home. The air-sea flux system has been running smoothly since we left, packing in about 400 mb of data every day. Unlike most past cruises, we have assembled a large number of different sensors to measure each variable. This gives us redundancy and cross checking. For example, we are recording 12 different measurements for near-surface humidity, 9 for air temperature, 3 for CO2 concentration, 3 for water temperature, and 3 for relative wind speed. We also have 4 different measurements of downward solar heat flux and 2 of downward atmospheric IR heat flux. So far the biggest surprise in these measurements has been the large increase of downward IR heat flux in the presence of low clouds and storms. In the tropical western Pacific warm pool, this increase is 5-10 W/m^2 while here in the Indian Ocean it has been 40-60 W/m^2. Right now don't know why this occurs, but we believe the explanation will be revealed in later analysis of the radiosonde temperature and humidity profiles. At this writing, we have just begun the first of two planned 'star' surveys. These are 5-day transects of the region in a 5-pointed star pattern about 50 in diameter. Our intention is to obtain one star pattern before the monsoon onset and then get a second with strong winds and heavy precipitation during the first monsoon cycle. So far, the atmosphere has consented to follow our plans by providing clear weather and weak convection for the first half of our study. Stay tuned for our next update in a couple of weeks. Some sample data from early JASMINE. Press.=atmospheric pressure at the surface Tair=air temperature RH=relative humidity Wspd=wind speed in nautical miles per hour Wdir =wind direction (from) Latitude/Longitude=position (519.7279 is 5 deg. 79.7279 minutes, minus sign means south of equator) Tsea=temperature of seawater at 5 m depth Date Hour Press. Tair RH WSpd WDir Latitude Longitude Tsea Millibar deg C % Kts deg dddmm.mmm deg C 5/4 1 1010.0 28.2 80 7.6 148 -519.7279 9706.3829 29.09 5/4 10 1007.2 28.1 80 5.4 126 -511.6182 9549.2952 29.23 5/4 16 1009.9 28.5 79 6.5 135 -503.2369 9430.9046 29.34 5/4 18 1008.7 28.3 80 5.1 147 -500.4593 9405.1191 29.23 5/4 22 1008.1 26.0 90 6.8 116 -437.6834 9337.6233 29.25 5/5 2 1009.7 28.3 81 6.7 119 -406.5403 9306.5331 29.24 5/5 6 1008.4 28.4 80 5.4 98 -338.5921 9238.5646 29.44 5/5 10 1006.9 27.8 81 3.3 100 -306.9892 9206.8906 29.54 5/5 14 1009.6 28.3 79 4.4 128 -239.3354 9139.3260 29.50 5/5 19 1008.4 27.2 87 4.3 148 -200.6514 9100.6872 29.63 5/5 23 1008.2 25.3 86 5.1 132 -133.7945 9034.1784 29.42 5/6 0 1008.6 27.0 84 3.9 140 -129.8700 9029.9128 29.38 5/6 2 1009.7 27.3 86 4.4 152 -113.9174 9013.9110 29.47 5/6 7 1008.5 28.4 75 2.3 125 -37.7137 8937.6449 29.39 5/6 11 1006.9 29.1 68 2.6 65 7.3141 8907.2434 29.62 5/6 14 1008.8 28.4 76 1.5 193 14.3417 8859.9832 29.51 5/6 23 1007.2 28.2 74 1.2 309 136.0732 8900.0171 29.53 5/7 3 1008.9 28.5 77 2.3 277 215.1747 8900.0101 29.40 5/7 22 1006.7 28.1 81 6.0 261 500.5890 8900.0046 29.20 5/8 3 1009.6 28.7 79 7.4 242 555.1909 8859.9889 29.04 5/8 6 1007.4 28.6 79 5.8 245 619.6500 8900.0339 29.11 5/8 10 1006.0 28.7 76 8.5 229 700.0142 8900.0145 29.04 5/8 18 1007.6 28.5 79 7.7 215 811.5048 8859.9176 28.96 5/8 23 1007.1 28.4 81 7.4 233 859.9332 8900.0713 29.10 5/9 2 1009.0 28.8 82 8.1 229 929.9986 8859.9193 29.03 5/9 6 1007.2 29.1 81 7.3 213 1000.0813 8859.9411 29.33 5/9 10 1004.4 29.2 78 9.2 214 1043.3510 8852.6551 29.41 5/9 14 1007.7 29.2 82 4.2 220 1125.8442 8845.6748 29.80 5/9 19 1006.3 29.3 79 5.7 240 1210.2207 8845.0341 29.85 5/9 23 1006.1 29.3 82 8.2 223 1252.3535 8844.7923 30.00 5/10 2 1008.1 29.5 80 6.2 260 1321.9246 8844.9853 29.68 5/10 7 1006.0 29.5 80 8.9 244 1245.8824 8844.9859 30.13 5/10 10 1003.9 29.5 80 9.6 239 1210.1723 8845.0619 29.93 5/10 11 1004.6 29.5 79 8.2 244 1159.9566 8845.0576 29.98 5/10 14 1006.1 29.5 79 7.2 246 1154.7613 8829.1358 30.02 5/10 19 1005.8 29.1 80 7.0 230 1150.3729 8841.2183 29.98 5/10 23 1005.9 29.0 79 5.9 246 1156.5166 8830.7968 29.88