TRACKING PULSES OF THE MADDEN-JULIAN OSCILLATION
By Long, Charles N | |
Proquest LLC |
A field campaign in the
From time to time, the tropical atmosphere feels the pulses of extraordinary strong deep convection and rainfall that repeat every 30-90 days. They come from the Madden-Julian oscilla- tion (MJO; Madden and Julian 1971, 1972). The MJO is identified as a large-scale [O(1,000 km)] region of abnormal deep convective cloud and rainfall propagating eastward at on average 5 m s-1 together with its associated fields of wind, humidity, and temperature. Its cloud and rainfall signature is prominent usually from the Indian to the west- ern Pacific Oceans. Its wind signals may move circumequatorially. During its life cycle, the MJO inf luences global weather and climate (Zhang 2013). This has motivated growing interest in its real-time monitoring (Wheeler and Hendon 2004) and forecasts (Gottschalck et al. 2010). Tremendous efforts have been made to improve our knowledge of the MJO from viewpoints of observations, numerical modeling, and theories (Zhang 2005; Lau and Waliser 2012). While there has been progress in MJO prediction (Bechtold et al. 2008; Vitart and
Our global climate predic- tion and projection will rely on models with parameterized convection in the foreseeable future. Improved simulations of the MJO will continue to serve as a benchmark of the advance- ment and development of model cumulus parameterizations. Development of physical param- eterizations in numerical models has been a long, painstaking endeavor. It has greatly benefited from observations of past field campaigns in the tropics (e.g., GATE, TOGA COARE; see ap- pendix for acronym expansions). The stunning lack of in situ ob- servations in the region of the tropical
An internationally cooperative field campaign was operated in 2011-12 (see sidebar on participating pro- grams) to investigate physical processes of the MJO in the central equatorial IO, with components in the tropical western Pacific and intervening Maritime Continent area. With advanced observing technology, this field campaign tracked the intraseasonal pulses of the MJO at its infant and mature stages. This article summarizes the scientific rationale, hypotheses, objectives, experimental design and operation, and preliminary results of this field campaign.
Scientific rAtionAle, hypotheSeS, And objectiVeS. Convective initiation of the MJO (referred to here as MJO initiation) over the IO conceptually consists of three stages (Stephens et al. 2004). The first is a pre-onset stage. Atmospheric deep convection is generally suppressed in a large area except in the ITCZ when it is present south of the equator. There can be precipitating and nonprecipitating shallow clouds and occasionally isolated deep convective cloud. SST is relatively high and surface wind weak. The second is an onset stage. Deep convection gradually becomes more active and widespread in a basin-scale area. A convective envelope of the MJO is thus formed. Its eastward movement signifies the commencement of a new MJO event. The final one is a post-onset stage. After deep convections move eastward, convectively suppressed condition returns and prevails again over a large area. Strong westerly wind reigns at the surface and low levels, and SST reaches its minimum. This post-onset stage eventually turns into another pre-onset stage as surface westerlies give away to easterlies and SST gradually increases. There are many mysteries in convective initiation of the MJO. What determines the time scales of the post- and pre-onset stages, which make the MJO episodic? What are the key factors for the transition from the pre-onset to onset stages? What makes the large-scale convective envelope move east- ward and thus inaugurates a new MJO event?
To efficiently address these and other questions regarding MJO initiation using field observations, three hypotheses were proposed which focused on processes local to the tropical IO:
* Hypothesis I: Deep convection can be organized into an MJO convective envelope only when the lower-tropospheric moist layer has become suf- ficiently deep over a region of the MJO scale; the pace at which this moistening occurs determines the duration of the pre-onset stage.
* Hypothesis II: Specific convective populations at different stages are essential for MJO initiation.
* Hypothesis III: The barrier layer, wind- and shear- driven mixing, shallow thermocline, and mixing layer entrainment all play essential roles in MJO initiation over the IO by controlling the upper- ocean heat content and sea surface temperature and thereby surface f lux feedback.
Hypothesis I is built upon the abundant literature on the sensitivity of convection to environmental moisture (Brown and Zhang 1997; Raymond 2001;
Hypothesis II advances the conventional thinking of convection versus no convection or shallow versus deep convection during MJO initiation to a holistic view of cloud population evolution, including pre- cipitating and nonprecipitating clouds of all sizes, depths, and degrees of organization. The MJO life cycle features a rich variability of different types of clouds (Lau and Wu 2010; Riley et al. 2011; Del Genio et al. 2012). Shallow and congestus clouds, in addition to their possible role of moistening the lower tropo- sphere as discussed earlier, provide low-level heating, when they precipitate, that induces low-level large- scale moisture convergence (Zhang and Hagos 2009), which helps maintain small or negative gross moist stability (Neelin and Held 1987; Raymond et al. 2009) and thereby convective development of the MJO. The essential role of low-level heating in the MJO has been suggested in theoretical studies (Wu 2003; Khouider and Majda 2006) and demonstrated in numerical simulations (Li et al. 2009). Upper-level heating due to stratiform precipitation may generate instabilities that help trigger new convection through interaction with equatorial waves (Mapes 2000;
Hypothesis III targets some of the unique features of the IO (see sidebar on the uniqueness of the
These hypotheses were proposed to be tested using field observations. Many other possible mecha- nisms for MJO initiation that cannot be effectively addressed by field observation were not included in these hypotheses. A combination of observations collected during the field campaign and large-scale data (e.g., global reanalyses, satellite data) is needed to investigate all aspects of MJO initiation.
The overarching goal of the 2011-12 MJO field campaign was to expedite our understanding of the MJO, especially its initiation processes, and our efforts to improve simulation and prediction of the MJO. Its specific objectives were to
* collect observations that are urgently needed to advance our understanding of the processes key to MJO initiation and propagation;
* identify critical deficiencies in numerical models that are responsible for their low prediction skill and poor simulations of the MJO;
* provide unprecedented observations to assist the broad community effort toward improving model parameterizations; and
* provide guiding information to enhance MJO monitoring and prediction capacities for delivering better climate prediction and assessment products on intraseasonal time scales for risk management and decision making over the global tropics.
The field campaign was integrated with modeling, data analysis, and real-time forecast to help accom- plish these objectives.
DeSiGn And operAtion of the cAmpAiGn. Based on the pilot studies (see sidebar on pilot studies), the 2011-12 MJO field campaign was designed to ensure a sufficient length to capture the full initiation cycle of at least one MJO event by the following observing components (Fig. 1):
(i) two quadrilateral sounding arrays for adequate atmospheric budget estimates, embedded in a broad sounding network from
(ii) multiple radars of different wavelength to sample the full spectrum of cloud population during all stages of MJO initiation;
(iii)simultaneous and continuous observations of atmospheric and upper-ocean profiles to measure coherent and coupled air-sea variability at time scales from turbulence to the MJO;
(iv) identical twin sites in the IO (Addu Atoll) and western Pacific (<location>Manus Island) to sample the same MJO event at its initiation and mature stages; and
(v) an aircraft operation to sample the atmospheric and oceanic boundary layers and large-scale vari- ability between atoll and ship sites.
Studies on the MJO mean seasonal cycle (Zhang and Dong 2004; Matthews 2008) indicated that main MJO initiation activity takes place in the central IO from October to March, with the highest occurrence probability near the equator in October-January. Accordingly, the field campaign covered three nested periods (Fig. 2):
* special observing period (SOP), 1 October-
* intensive observing period (IOP), 1 October 2011-15 January 2012; and
* extended observing period (EOP), 1 October 2011-31 March 2012
The SOP was designed to obtain high-resolution data to capture the diurnal cycle of convective activity with the maximum observing capacity. All instruments deployed during the field campaign oper- ated during the SOP. The transition from a quadrilateral to triangle array south of the equator because of the departure of a ship and the completion of the aircraft opera- tion marked the end of the SOP. All other instruments continued to operate after the SOP until the end of the IOP. Beyond the IOP, almost identical instruments at the IO site of Addu Atoll and the western Pacific site of
More detailed descriptions of each campaign com- ponent are given below. Detailed information on the measurement systems is given in Tables ES1-ES5 in the electronic supplement.
Soundings. Central to the campaign were two quad- rilateral sounding arrays over the central equatorial IO (outlined by dashed lines in Fig. 1). Their main mission was to observe the evolution of atmospheric vertical structures in wind, temperature, humidity, energy, and moisture budgets using radiosondes. The southern array was formed by two islands at
Surrounding the two quadrilater- al sounding arrays is a broad sound- ing network that includes sites over
Radars. Accompanying the sounding arrays and equally essential to the field campaign was a radar network. It included three radar sites in the IO (Addu Atoll, NE, and SE) and one in the western Pacific (
Addu Atoll, which occupied the vertex of both the northern and southern arrays, was selected as a "radar supersite" where a unique radar triad consisting of the S-PolKa, SMART-R, and KAZR was deployed (Fig. 3).
The KAZR is a profiling Doppler radar that oper- ates at a Ka band (8.6-mm wavelength). Located at the
The S-PolKa is an advanced dual-polarimetric, dual-wavelength (10 cm for S band and 0.8 cm for Ka band) radar. It was located near the wharf of
The SMART-R is a scanning Doppler system that operates at C band (5-cm wavelength). It was located on
This radar triad at Addu Atoll provided unprec- edented observations of the entire tropical cloud population, including precipitating and nonprecipi- tating shallow cumulus clouds, midlayer altostratus and altocumulus, convective congestus, isolated deep convective clouds, upper-level anvil and cirrus clouds, mesoscale convective systems, and hydrometer types. The regular horizontal PPI scans of S-PolKa and SMART-R provided a mesoscale context for the KAZR data collection. The RHI scans of the S-PolKa and SMART-R radars over the KAZR extended vertical profiles of reflectivity measured by the KAZR into altitudes above precipitation where the KAZR signal is attenuated, yielding vertical profiles of reflectivity over the KAZR site for both raining and nonraining clouds. These three radars in com- bination covered both nonprecipitating and (lightly and heavily) precipitating clouds, thus producing a merged cloud-precipitation product specifically tailored for model evaluation (Feng et al. 2009).
The other two radar sites were onboard R/V Mirai at SE and Revelle at NE, where C-band scan- ning Doppler radars and vertically pointing W-band (3.2-mm wavelength) Doppler radars were deployed. Radar observations from Revelle and Mirai captured cloud population during contrasting large-scale con- vective conditions (see "general conditions during the campaign" section).
At Addu Atoll, a multichannel scanning micro- wave radiometer was deployed next to the S-PolKa for humidity and liquid water retrievals during the IOP. Microwave radiometers of two and three channels operating in vertically pointing mode were deployed at the airport site near the KAZR to retrieve column water vapor and liquid water. At Diego Garcia, the southwestern corner of the southern intensive array, a 915-MHz wind profiler, a ceilometer, a surface meteorological station, and a whole-sky camera were deployed in addition to radiosondes.
In addition, X-band (3.22-cm wavelength) and C-band radars were deployed onboard one research airplane and W-band radars were onboard another airplane.
Ships, moorings, and floats. Four research vessels were deployed during the field campaign: R/V Roger Revelle (
Time series of upper- ocean structures were mea- sured by CTD profiler and shipboard ADCP from R/Vs Roger Revelle, Mirai, and
Several additional and special observations were made onboard R/V Revelle. A thermistor chain was deployed during her legs 2 and 3 to measure detailed temperature structure and evolution in the upper 10 m with a 0.25-m vertical resolution and extremely high frequency (10 Hz). Vertically profiling wire walkers (Pinkel et al. 2011), each equipped with temperature-pressure or CTD sensors, were deployed during leg 4 to measure the upper-ocean structure without ship effects in the top 20 m every 5 min and in the top 200 m every 20 min.
Surface and subsurface moorings (Fig. 5) were deployed along 78.5°E. Surface and subsurface moor- ings were deployed at 9.75°S, 1.5°S, and 0° during the IOP by R/V Revelle, while a subsurface mooring was deployed at 5°S, 78.1°E during the SOP by R/V Mirai. The location of 9.75°S was chosen because of a peak of the thermocline ridge in September based on the XBT measurement by R/V Revelle. Since both Revelle and Mirai occupied locations near RAMA moorings that have been deployed along 80.5°E (McPhaden et al. 2009), it is possible to evaluate the accuracy of long-term moored buoy data by comparing with the CTD and surface meteorological data. Moreover, such sustained monitoring systems deployed in the IO (Meyers and Boscolo 2006) provide invaluable information regarding how representative the field campaign period is.
Aircraft measurements. The aircraft measurements featured a unique standalone suite of instruments and the capability of extending the observations from the fixed locations of ships and atolls to a wider coverage in the vicinity of the field campaign domain. Two research airplanes par- ticipated in the campaign. One was the NOAA WP- 3D, based on Diego Garcia. It flew 12 missions from 11 November to
The other airplane was the SAFIRE Falcon-20, operated from
ARM Mobile Facility. The second ARM Mobile Facility (AMF2) was deployed on
At the Manus site, a scanning C-band Doppler radar was added, thanks to Recovery Act funds, prior to the field campaign, which paired up with SMART-R at Addu Atoll. This C-band radar at Manus is critical for the production of model forcing datasets where a net- work of radiosonde sites is not feasible (Xie et al. 2010).
Logistic and forecast support. During the field campaign, logistic supports were provided by the DYNAMO Project Office at the NCAR Earth Observing Labora- tory (EOL). EOL maintained the field catalog on the Internet. It includes all necessary information for the field operation and in-field data analysis, such as field reports from all observation sites that summarized instrument conditions, status of data collection and transmission, operational products such as satellite images and numerical forecasts, preliminary data analysis, and update of the operational schedule. Through this catalog, all participants had the same information of the field operation. Glitches (e.g., tardy transmission of radiosonde data to NWP centers via GTS) were quickly identified and addressed.
Real-time forecast support was provided to the field campaign by various operations and research centers, including NCEP, ECMWF, NRL, Meteo-France, JMA, and IMD. In addition, JAMSTEC provided experi- mental forecast by a high-resolution Nonhydrostatic Icosahedral Atmospheric Model (NICAM) with a regionally stretched grid system technique (
Related projects. In addition to routine soundings over the Indonesia Maritime Continent region, a 1-month intensive observation (HARIMAU2011) was conducted by Japanese and Indonesian research groups over the western
The U.S. DOE ARM facility in Darwin,
GenerAl conditionS dUrinG the cAmpAiGn. The general atmospheric and oceanic conditions during the field campaign are briefly sum- marized in this section. Their more detailed descrip- tions can be found in Gottschalck et al. (2013). A La Niña event took place in the Pacific, reaching its peak during November 2011-February 2012, with Niño- 3.4 SST anomalies of about -1°C. Meanwhile, a weak positive
Four intraseasonal and eastward-propagating large-scale convective events occurred over the tropical IO in late October, late November, late December, and March, respectively (Fig. 7). While these convective events unambiguously moved from the IO over the Maritime Continent, the October and November events barely reached the Pacific, partially because of the La Niña condition there. Nonetheless, they were undoubtedly part of the MJO, judged by either the real-time multivariate MJO (RMM) index (Wheeler and Hendon 2004) with its amplitude great- er than one and rotating counterclockwise (red and dark blue lines in the inlet of Fig. 7) or MJO spectral filtering (Wheeler and Weickmann 2001) applied to OLR (Fig. 7). We refer to these two events as MJO1 and MJO2, respectively. The December event can be identified as a weak MJO event by the spectral filtering of OLR alone (single red contour in Fig. 7). However, the RMM index does not recognize it as an indepen- dent MJO event for its lack of a clear counterclockwise rotation in the phase diagram (cyan in the inlet of Fig. 7). The cloud system related to MJO2 appeared to stagnate after it had passed over the Maritime Continent and then retreated westward. For the con- venience of narration, this December intraseasonal event is referred to as MJO3. This event is very telling and suggestive for future research; it requires a reas- sessment of the conventional MJO index. The March event was again unambiguously an MJO event (MJO4) and the strongest one among the four. Its cloud signals propagated eastward the farthest, passing the Manus site and reaching the date line.
An intriguing feature of the first three MJO events is their short intervals (~30 days), which is on the high- frequency end of intraseasonal oscillation (30-90 days). One possible reason is the fast circumnavigating propagation of the dynamic field (mostly at 200 hPa; see Gottschalck et al. 2013). The RMM phase diagram suggests that the short interval between MJO2 and MJO3 came from a hiccup of MJO2, and MJO3 was really a continuation of MJO2 after that. Another possible reason is that high-frequency MJO events tend to occur near the equator and their signals are strong after a positive IOD phase (such as in October-
Figure 8 shows the time- latitude cross section of the infrared radiation bright- ness temperature averaged over the IO intensive array (70°-80°E). The convec- tive center tended to move from the Northern Hemi- sphere in the early part of the field campaign to the Southern Hemisphere dur- ing the latter part of the campaign as indicated by a dashed arrow. This matches well the climatological sea- sonal migration in latitude of the ITCZ (Zhang 2001) and MJO activities (Zhang and Dong 2004) over the IO. Meanwhile, there were intraseasonal fluctuations in the latitudinal positions of convective peaks. Prior to the convective peaks of MJO1 and MJO2, there was a northward shift of con- vective signals toward the equator as indicated by solid arrows from roughly 10°S, the usual latitude of the ITCZ in the IO. The commonly defined convectively suppressed periods near and north of the equator prior to convective initiation of the two MJO events were actually periods of active convection in the ITCZ. Convective initiation of the two MJO events coincided with the northward shift of the ITCZ.
PreliminAry reSUltS. Here, we provide preliminary results based on observations collected by the field campaign.
Sounding observations. Time series of vertical profiles of relative humidity (RH) at the southern intensive array and
RH profiles at Manus from October to early February were domi- nated by synoptic-scale variability. The convective centers of the three MJO events before March did not reach Manus. The only obvious intraseasonal sig- nal during this time was a dry period coinciding with the convective initiation of MJO1 over Gan and Revelle during mid to late October. A similar pattern occurred again with a dry period in late February preceding a distinct moistening associated with the MJO4 migra- tion into the western Pacific (not shown).
The zonal wind (u) profiles (Fig. 10) near the equa- tor (Gan, Revelle, and Manus) generally exhibit a typi- cal gravest baroclinic structure with u of the opposite signs in the upper and lower troposphere, subject to variability on various time scales. Off the equator at Mirai and Diego Garcia, however, the u profiles were mostly barotropic and dominated by easterlies, with deep westerlies occasionally punctuating through the troposphere during October-November. The expected low-level westerlies during convective initiation of the MJO at Gan were deeper and stronger for MJO2 and MJO3 than MJO1. While the westerlies occurred after the passage of convective peak for MJO1, both occurred at the almost same time for MJO3. There were tendencies of descending easterlies from the upper to middle troposphere prior to the three MJO events at Gan and Revelle, which is equivalent to de- creases in the depth of low-level westerlies. Very strong and persistent surface westerlies were observed at both Gan and Revelle at the beginning of MJO2. About one week later an abrupt change from low-level/midlevel easterlies to westerlies can also be found at Diego Garcia. There was a sharp transition in the vertical structure of u at Manus near the end of 2011 from upper-level westerlies and low-level easterlies to the opposite. Since there was a possibility that the abrupt change of wind pattern over the Manus site may have been related to the Australian monsoon onset, these data might be used for studying the relationship between the MJO and the Australian monsoon.
Oceanic observations. The oceanic variability through the first two MJO events is exemplified by the time series of surface and subsurface measurement during legs 2 and 3 of Revelle (Fig. 11). Prior to their convec- tive initiation of MJO1 and MJO2, surface stress was weak. Under such calm surface conditions, diurnal heating of the ocean sur- face was large. Large diur- nal cycle in the mixed layer depth (thick black lines) occurred only in October, which was accompanied by strong diurnal turbu- lent mixing in the upper 50 m of the ocean. In mid to late November, however, the mixed layer remained very shallow without any significant diurnal cycle, de- spite strong diurnal heating at the surface (about 1°-2°C) and diurnal mixing at the 50-80-m depth. The east- ward strong surface current (Wyrtki jet) was maintained through most of October. It almost disappeared in mid-November, but quickly re-amplified into an ex- traordinarily strong one by the abrupt onset of surface westerlies on 24 November as MJO2 started at Revelle. This jet was able to main- tain its strength (~1 m s-1) even when surface wind quieted down (beginning of December) and lasted through a large portion of December. Shear-induced mixing was not confined to the mixed layer. There were multiple layers of tur- bulent mixing throughout both legs. In addition to generation of turbulent mix- ing through shear, another substantial effect of the Wyrtki jet is zonal advec- tion of surface salinity. Fresh surface water in October was replaced by an incur- sion of saline water from the
On 24 November, the WP-3D aircraft flew from Gan to Revelle and cap- tured the large-scale vertical cross sec- tion between the two using dropsondes (Fig. 12). There was an evident west-east westerly momentum transport downward from the middle to lower troposphere that was partially responsible for the sudden onset of surface wind stress experienced at Revelle. Accompanying this was an onset of a cold pool at Revelle. The sudden appearance of atmospheric forcing associ- ated with MJO2 and the abrupt oceanic response on this day and after are apparent in Fig. 11.
Radar observations. The C-band radars onboard Revelle and Mirai sampled cloud populations in two distinct climate regimes (Fig. 13), because of the latitudinal shift of the ITCZ and sea- sonal position of the MJO (Fig. 8). During the pre-onset stages of both MJO1 and MJO2, the Revelle radar re- corded a cloud population dominated by shallow and isolated deep convection under a generally suppressed condition of deep convection, and the Mirai radar captured a cloud population dominated by many deep convective clouds in the ITCZ. The cloud populations sampled by the two radars switched when MJO convec- tion had been initiated and became active at Revelle. Figure 13 also shows plenty of radar echoes during the periods that led to the convective initiation of the two MJO events when cloud-top IR temperature was relatively high (>280 K). This suggests the abundance of shallow, precipitating clouds in those periods.
An example of the observations from the radar super site at Addu Atoll is shown in Fig. 14. The same cloud system was observed simultaneously by the three radars on
Others. The field observations also revealed many other interesting and intriguing features during the cam- paign. For example, the aerosol measurement at Revelle indicates that the passage of MJO convection had a major impact on aerosol number, size and composition, and there was an aerosol regime change before and after convectively active episodes (DeWitt et al. 2013). A latitudinal meander of the SCTR during the IOP was suggested by measurements from Revelle (September, January) and
DAtA policy And ArchiVe. CINDY2011 and DYNAMO data policies require timely release of field observations for public use no later than
ConclUdinG remArkS. The 2011-12 MJO field campaign conducted in and around the tropi- cal
The 2011-12 MJO field campaign provided observations that are unique in several aspects in compar- ison to previous tropical field cam- paigns that aimed at interactions between atmospheric convection and its large-scale environment and between the atmosphere and ocean. It is the only one in the tropical IO with continuous time series of atmospheric and upper- ocean profiles. It is the first time the entire cloud population rang- ing from shallow nonprecipitating and precipitating clouds to deep convection with anvils were si- multaneously sampled by modern radars of different wavelengths over a tropical open ocean. It is also the first time observations were collected by identical instruments for two tropical climate regimes (the ITCZ and MJO) and from two oceans (the Indian and western Pacific Oceans). The instruments used in this field campaign are far superior to any previous campaigns of similar scope.
Data collected by this field cam- paign will benefit the study of the MJO and tropical atmospheric and oceanic processes in general for many years to come. It is very meritorious that the modeling community has been actively involved with the field campaign, from its planning to operation and postfield data analysis and applications. A close collaboration between experts of field data collection and modeling is the foundation for the legacy of this field campaign: using the observations in hypothesis testing and model development and improvement.
AcknoWledGmentS. We extend recognition and gratitude to all who contributed to the preparation and operation of the field campaign; the success of the field campaign would be impossible without their diligent and dedicated efforts. Nearly 100 students from seven coun- tries volunteered their time to help collect observations onboard ships and aircraft, as well as on the ground. The field campaign provided them with rare opportunities of career experience; they were part of the central force of the success of the field campaign. The DYNAMO Project Office, led by
View from Addu Atoll showing a mix of convective and cirroform clouds.
The UniqUeness of The indian ocean
The tropical Indian Ocean, together with the western Pacific, hosts the largest body of warm surface water on Earth, known as the warm pool.
ParTiciPaTing Programs
The 2011-12 MJO field campaign was initiated and organized internationally under the Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (CINDY2011). Researchers, including roughly 100 stu- dents, from more than 60 institutes of
Many made critical scientific contributions to the planning and operation of the field campaign (far too numerous to mention all here), especially
PiloT sTUdies
In the boreal fall of 2006, the field campaign MISMO was conducted to observe the atmosphere and ocean of the central equatorial Indian Ocean (Yoneyama et al. 2008). During 1½ months of this field campaign, its triangle observing array formed by two islands and a ship captured a transition period from convectively inactive to active phase of tropical intraseasonal variability. Its observational data reveal that eastward-propagating mesoscale cloud systems played an important role in moistening the middle and upper troposphere to assist the onset of large-scale convection (Katsumata et al. 2009), as suggested by theo- ries and numerical simulations (e.g., Raymond and Fuchs 2009; Maloney 2009; Sugiyama 2009). MISMO has also led to other lessons. A quadrilateral sounding array is needed to reduce observational errors in estimates of atmo- spheric heating and moisture budgets (Katsumata et al. 2011). In particular, it is important to evaluate the influ- ence of meridional advection associated with large-scale disturbances (
In January-
Data collected at the ARM Manus site demonstrated the utility of single point measurement in detecting vari- ous aspects of the MJO (Wang et al. 2010) and motivated a tropical western Pacific MJO campaign at the
Radar scanning sTraTegy
S-PolKa performed a combination of full horizontal scans (PPI) and vertical cross-sectional scans (RHI) as illustrated in the figure. The scanning strategy included 8 PPI elevation angles (from 0.5° to 11°) and 55 RHIs with scan angles of 0°- 45°. Of the 55 RHIs, 39 were toward the north to the east and 16 were toward the AMF2 site. Two special vertical scans over the KAZR had a wider range of scan angles 0°-60° (repre- sented by the transparent vertical cross section in the figure). The pattern repeated on a 15-min cycle. The maximum range for the PPI and RHI scans was 150 km for the S band.
The SMART-R performed full volume scans of 25 eleva- tion angles (from 0.5 to 33°) every 10 min, interspersed with a long-range, low-level PRF surveillance scan and an RHI scan over the KAZR. The maximum range for the PPI and RHI scans was 150 km and was extended to 300 km for the long-range surveillance.
Within each 10-min cycle, the C-band radars onboard R/V Revelle and Mirai performed a combination of full horizontal volume scans of about 8-9 min and vertical RHI scans of about 1-2 min to a range of 150 km. Every 30 min a 0.5° elevation low-level PRF surveillance scan to a range of 300 km was added to the RHI scan. The RHI scans targeted a specific cloud system at the scene. The horizontal scans of the Revelle C-band radar were in either deep (22 elevations from 0.8° to 21.5°) or shallow (22 elevations from 0.8° to 35.9°) modes, depending on whether deep or shallow clouds are present. The Mirai C-band radar kept the same 21 eleva- tions from 0.5° to 40° in its horizontal scans regardless of the cloud type at the scene.
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AffiliAtionS: yoneyama-
CorreSpondinG AUthor:
E-mail: [email protected]
The abstract for this ar ticle can be found in this issue, following the table of contents.
DOI:10.1175/BAMS-D-12-00157.1
A supplement to this article is available online (10.1175/BAMS-D-12-00157.2)
In final form
©2013
AppendiX: liSt of AcronymS And AbbreViAtionS.
ADCP Acoustic Doppler current profiler
AMF2 The second ARM Mobile Facility
AMIE ARM-MJO Investigation Experiment
ARM Atmospheric Radiation Measurement
AXBT Airborne expendable bathythermograph
AXCTD Airborne expendable CTD
BMKG Badan Meteorologi, Klimatologi, dan Geofisika (
BoM
BPPT Badan Pengkajian dan Penerapan Teknologi (
CINDY2011 Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011
CLIVAR Climate Variability and Predictability
CNES Centre National d'Etudes Spatiales,
CNRS Centre National de la Recherche Scientifique,
CPC Climate Prediction Center
CTD Conductivity-temperature-depth
DYNAMO Dynamics of the Madden-Julian Oscillation
GATE Global Atmospheric Research Program Atlantic Tropical Experiment
GOOS Global Ocean Observing System
GPS Global Positioning System
GTS Global Telecommunication System
HARIMAU Hydrometeorological Array for Intraseasonal Variability-Monsoon Automonitoring
ICPO International CLIVAR Project Office
IOD Indian Ocean Dipole
ISS Integrated Sounding System
ITCZ Intertropical convergence zone
KAZR Ka-band ARM Zenith Radar
LASP Littoral Air-Sea Process
MISMO Mirai Indian Ocean Cruise for the Study of the MJO-Convection Onset
MJO Madden-Julian oscillation
NRL
NSF
NWP Numerical weather prediction
OLR Outgoing longwave radiation
PPI Plan position indicator (radar scan with sweep of the azimuth angle while holding the antenna at a constant elevation angle)
PRF Pulse antenna repetition at a constant frequency elevation angle)
RAMA Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction
RMM Real-time antenna at multivariate a constant azimuth MJO angle)
SAFIRE Service des Avions Francais Instrumentes pour la Recherche en Environment (
S-PolKa S-band and Ka-band polarization Doppler radar
SCTR Seychelles-Chagos thermocline ridge
TOGA COARE Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment
Copyright: | (c) 2013 American Meteorological Society |
Wordcount: | 10959 |
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