We suspect the answer is a little bit of both these explanations. There is likely substantial under-reporting of severe weather in regions with either

Transcription

1 RELAMPAGO (Remote sensing of Electrification, Lightning, And Meso-scale/micro-scale Processes with Adaptive Ground Observations) - Relevance to NASA GPM GV Relampago means lightning in both Spanish and Portuguese. This name is subject to change, particularly as a NASA component of the program would focus on precipitation. Daniel Cecil, Timothy Lang, and Patrick Gatlin - NASA MSFC Steve Nesbitt - University of Illinois Kristen Rasmussen and Bob Houze University of Washington Several members of the GPM community (D. Cecil, T. Lang, S. Nesbitt, L. Machado, P. Salio, E. Zipser, R. Houze, K. Rasmussen, S. Rutledge) have conceived a field campaign to study intense convective systems in northern Argentina during late 2016 (target dates 1 Nov. 15 Dec.). This is intended as a multi-agency, multi-national effort. We have received positive feedback from NSF, with plans for a major ground-based facilities request. There is interest from NOAA, particularly for GOES-R cal-val and possibly JPSS cal-val and/or support from the NOAA Climate Program Office. Partners in Argentina and Brazil are confident about bringing observational resources as well as local expertise. We believe this is an excellent opportunity for a NASA GPM Ground Validation field campaign, contributing its unique assets while leveraging the observational capabilities of the other participants. At a minimum, several disdrometers and related ground-based rain measurement equipment should be deployed within range of the RELAMPAGO radars. A GPM satellite-simulator payload on a NASA ER-2 would allow appropriate connection between the detailed ground-based measurements and the satellite measurements for which the GPM community needs better understanding. Considering NOAA s interest in cal-val for its satellites, some cost sharing may be possible. Many thunderstorms in mid-latitude South America stand out in satellite observations as being among the strongest anywhere on earth in terms of satellite-based convective proxies, such as lightning flash rate per storm, prevalence for extremely tall, wide convective cores (with 40- dbz radar echoes extending well above 10 km altitude), and broad stratiform regions. These conditions lead to radar and passive microwave-based satellite precipitation retrievals being challenged by non-raleigh scattering effects, attenuation, and extremely low brightness temperatures (sometimes below 50 K at 85.5 GHz and 100 K at 37.0 GHz). Variations in surface emissivity further complicate physical and empirical passive microwave precipitation retrievals. Well-documented issues with the PR 2A25 near-surface precipitation estimates in deep convective storms over land have been partially attributed to errors in the drop size distribution parameter (ε), which tends to negatively bias Z-R calculations of rain rate. Recent studies have shown that deep convective storms in South America are particularly affected by this bias, likely resulting in an underestimate of the hydrologic impact of convective storms in this region. Despite the fact that satellite proxies for convective intensity and severe weather in subtropical South America rival or exceed those from the central United States, reports from the ground suggest that the frequency or violence of severe storms does not match that documented in the United States. Is this discrepancy a result of storms going under-observed or underreported because of issues such as low population density? Or do the storms have systematic differences in structural or microphysical characteristics, complicating the interpretation of satellite measurements and retrieval algorithms? Such differences may be brought on by unique storm environments (e.g., synoptic forcing, mesoscale dynamics, land surface conditions, aerosol environments).

2 We suspect the answer is a little bit of both these explanations. There is likely substantial under-reporting of severe weather in regions with either sparse population, or without an infrastructure designed to collect reports of severe weather. On the other hand, the damage produced by a relatively high frequency of significant tornadoes would be difficult to miss. If we identify and understand systematic differences in the storms, we can make strides towards improvement of microphysical models and remote sensing retrievals in intense thunderstorms with new information that might be applicable beyond this region. Can we identify ingredients that are missing from the intense thunderstorms of mid-latitude South America, and thereby improve the ability to distinguish between damaging severe thunderstorms and thunderstorms that appear intense but produce relatively little damage at the ground? This last question has implications for both forecasting natural hazards, and understanding weather and climate conditions associated with these natural hazards. A study in this region also applies to GPM via hydrology. This region of South America includes the La Plata Basin, with the Parana River as its main artery. It is one of the largest river basins on Earth and vital to the energy and agricultural production in central and southern South America. Land-atmosphere interaction may play a role in determining the structure of convective systems in the region. Much of the flooding along this river has been correlated with El-Nino occurrence, but on a shorter-time scale, intense convective events can be responsible for significant flooding. In addition, flash flooding and landslides are common along the slopes and foothills of the Andes, predictions of which rely on accurate prescription of precipitation and antecedent soil conditions. Can precipitation products be improved to more accurately constrain the hydrologic cycle for improved weather and climate prediction and natural hazard forecasting? Experiment Design: The experiment is to be conducted in austral spring, The timing allows for continuous total lightning measurements from the Geostationary Lightning Mapper, following the launch of GOES-R in late Steve Goodman from NOAA NESDIS is on the RELAMPAGO Science Steering Group in part to facilitate availability of GOES-R scanning. Figure 1 shows the study region and potential observing system configuration without NASA participation.

3 Figure 1. Potential observing facilities from international partners and NSF. i) Radiosondes: Red balloons and yellow bullseyes are radiosonde sites. Most of those in Brazil are currently operational; most of those in Argentina are to be requested from NSF and from international partners. Solid green lines mark inner and outer sounding arrays. ii) Radars: Blue circles are 200 km range from operational C-band dual-pol radars to be installed by Argentina by Red circles are 200 km range from a proposed NSF-requested S-PolKa and 50 km range from two dual-pol DOW radars. DOWs likely would not chase storms, but would pre-deploy based on forecast storm locations. iii) Lightning Mapping Array: White shading. To be provided by Brazil. Figure 2 adds NASA assets: NPOL radar to the northeast of the other radars, a sequence of sites for disdrometers and other surface-based rain measurements along a radial between NPOL and S-PolKa, D3R radar also located between NPOL and S-PolKa, and an indication of the ER-2 aircraft tentatively based in Buenos Aires. The D3R radar would be a particularly useful addition if DOW radars are not included by NSF, or if NPOL is not included by NASA. The annual frequency of occurrence of severe thunderstorms, as estimated using AMSR-E 36 GHz and 89 GHz satellite measurements, is shaded in the background. This estimation is adapted from Cecil and Blankenship (2012, J. Climate). No other place on earth has a greater frequency of satellite-indicated severe thunderstorms than this region of South America, according to the AMSR-E 36 GHz ice scattering signatures.

4 Figure 2. As in Figure 1, with addition of NASA NPOL radar and 200 km range ring in yellow, a sequence of disdrometer sites (white stars) along a radial between NPOL and S-PolKa, D3R radar and 50 km range circle in white, and NASA ER-2 tentatively based in Buenos Aires. Background shading is estimated frequency of severe thunderstorm occurrence, adapted from Cecil and Blankenship (2012). The preferred ER-2 payload for overflights of severe thunderstorms would include: Downward looking radar (EXRAD, EDOP, HIWRAP, or similar) Passive Microwave Radiometer(s) (AMPR, CoSMIR) Lightning / Electrification Package (GLM Airborne Simulator + LIP) Dropsondes If space and weight allows, other instrumentation may be desired for JPSS cal-val. This ER-2 payload would serve as a satellite simulator for GPM, providing the most effective linkage between satellite observables and the detailed ground-based measurements of the storms in this campaign. A dropsonde capability may offset the need for so many radiosonde sites as depicted in Figures 1-2. A major challenge for understanding the weather in this region is the sparseness of upper-air sites; ER-2 dropsondes would allow the flexibility to characterize the storm environments when storms do not occur in optimal locations for fixed radiosonde sites. Of course some fixed radiosonde sites would remain necessary in order to characterize the pre-storm environment before / between ER-2 flights. For the example ER-2 flight track in Figure 3, the ER-2 flies a radial between the NPOL and S- PolKa radars, over-flying the disdrometer and rain gauge sites. The ground radars would intersperse RHIs along this radial between sector scans or volume scans. The ER-2 could also fly transects across the convective line, or across particular cells, and drop sondes on the inflow

5 side. In this example, the flight track as drawn is about 1200 nautical miles including the leg from / to Buenos Aires. Several modules could be flown over a long-lived convective system before returning to base. Note that the population density in much of northern Argentina is quite low. This limits our options for logistics to support ground-based equipment in some places (e.g., forcing the placement of NPOL in Fig. 2 southeast from an ideal location fully covering the northern maximum in satellite-indicated severe thunderstorms). It does allow more freedom for dropsonde deployment. Dropsondes were released from the NOAA WP3D during the SALLJEX experiment in this region. Population centers would of course be avoided for dropsonde releases. Figure 3. As in Figure 2, with example ER-2 flight track (in purple) overlaid on TRMM 85 GHz H-pol brightness temperatures from orbit 68496, 1550 UTC 23 Nov 2009.