6A.1 ESTIMATION OF CONVECTIVE PLANETARY BOUNDARY LAYER EVOLUTION AND LAND-ATMOSPHERE INTERACTIONS FROM MODIS AND AIRS Joseph A. Santanello, Jr.*1,2, and Mark A. Friedl3 1ESSIC-UMCP, 2NASA-GSFC Hydrological Sciences Branch, 3Dept. of Geography & Environment, Boston Univ. 1. INTRODUCTION With these issues in mind, this paper examines atmospheric temperature profile retrievals from MODIS Land-atmosphere (L-A) interactions and coupling and AIRS, focusing on the potential utility of these remain weak links in current observational and sensors to infer PBL structure and evolution and, by modeling approaches to understanding and predicting extension, land surface properties and energy balance. the Earth-Atmosphere system. The degree to which the The results highlight the current utility and limitations of land impacts the atmosphere (and vice-versa) is difficult satellite remote sensing in the PBL and the potential for to quantify given the disparate resolutions and improving estimates and coupled modeling of the complexity of land surface and atmospheric models. relevant processes. However, the convective planetary boundary layer (PBL) serves as a short-term memory of land surface 2. BACKGROUND AND METHODOLOGY processes (through the integration of regional surface fluxes on diurnal scales), and therefore is diagnostic of 2.1 Sensor Development and Profile Retrieval the surface energy balance. Further, the PBL and land surface equilibrium reached each day describes the Instruments aboard geostationary and polar-orbiting degree of coupling and the impact of feedbacks within satellites have been used to observe and retrieve the L-A system. As such, knowledge of the diurnal information on the condition of the atmosphere and land evolution of the PBL can be instrumental in estimating surface for over 25 years (Menzel and Gumley 1998). surface fluxes and properties across regional scales as Radiometers and sounders measure infrared radiances well as quantifying and improving L-A representations in in multiple spectral bands, each of which is designed to coupled models. measure radiation received from a different level of the Sensors aboard two new polar-orbiting satellites atmosphere. Radiances are then combined with a first- offer the ability to monitor diurnal temperature and guess profile of atmospheric temperature and moisture moisture conditions in the convective planetary using a set of simulated regression relationships to boundary layer (0-4 km) at regional scales. The obtain the final retrieval product (Seemann et al. 2003; Moderate Resolution Imaging Spectroradiometer Chahine et al. 2001; Schmit et al. 2002; Menzel et al. (MODIS) aboard Terra and Aqua and the Atmospheric 2002). Prior to MODIS and AIRS, the ability of remote Infrared Sounder (AIRS) aboard Aqua are designed to sensing instruments to obtain profiles at resolutions measure radiances emitted from the lower troposphere required by current atmospheric and climate models and the land surface at unprecedented spatial and has been limited by insufficient bandwidth and retrieval spectral resolution (Menzel and Gumley 1998). algorithms. Therefore, atmospheric profiles retrieved from these The MODIS instrument was launched aboard EOS- sensors should be able to resolve daily temperature and Terra (MOD-T) on 18 December 1999 and EOS-Aqua moisture profiles in the PBL that previously could only (MOD-A) on 4 May 2002. MODIS was designed with be diagnosed using synoptic radiosonde networks. fine horizontal spatial resolution (5 km) that improves on The spatial resolution of MODIS and AIRS matches prior capabilities to monitor land surface temperature the typical integrating scale of the PBL (10-100 km) and and surface conditions, as well as the horizontal therefore offers the opportunity to monitor such gradients in these properties. MODIS also provides properties in a spatially continuous fashion. Previous better identification of cloud contamination, which is attempts to exploit the relationship between the PBL important for the profile retrieval process (Seemann et and the land surface have been hampered by al. 2003). Although it is not technically a sounding insufficient measurements (in time and space) and instrument, the 36 spectral bands of MODIS are able to incomplete understanding of the defining relationships retrieve vertical distribution of temperature in 20 among PBL and land surface properties (Diak and integrated layers, and the weighting functions near the Whipple 1993, 1994). However, through the surface are improved compared to GOES. However, combination of new remote sensing data and improved the MODIS retrieval algorithm still assumes that surface methodologies that are optimized for such data, the air and brightness temperatures are identical, which ability of the PBL to be used as an accurate proxy for limits the accuracy and vertical resolution near the land surface processes and conditions can now be surface, particularly in the PBL. reassessed. AIRS and the Advanced Microwave Sounding Unit ____________________________________________ (AMSU) and the Microwave Humidity Sounder of Brazil (HSB) were launched aboard EOS-Aqua on 4 May 2002 *Corresponding author address: Joseph A. Santanello, (Chahine et al. 2001). AIRS employs 2378 spectral Jr., Room 8, Bldg. 22, NASA-GSFC Code 614.3, channels (0.20 K SE) at 50 km horizontal resolution, Greenbelt, MD 20771; [email protected] and was designed based on the results of previous experiments using aircraft and instruments with high Atmospheric temperature and moisture profiles from spectral resolution (e.g. HIS; Diak et al. 1994). AIRS MOD-T and MOD-A were obtained and processed for vertical temperature profiles are specified to have an 44 clear-sky days in June and July 2003 at the ARM- accuracy of 1 K in 1-km thick layers, and are produced SGP central facility in Lamont, OK. Overpass times for for 28 vertical levels. The retrieval method assigns MOD-T and MOD-A ranged from 1630 to 1855 UTC trapezoidal weighting functions at low levels of the and from 1930 to 1955 UTC, respectively, depending on troposphere to resolve fine-scale variation in the exact orbital path of the satellite. MODIS standard temperature and moisture. These functions are used to temperature profiles are produced at 20 vertical levels, fine-tune an initial guess from synthetic regressions 7 of which are below 600 mb (620, 700, 780, 850, 920, applied in a fashion similar to MODIS retrievals (Fetzer 950, and 1000 mb). Support products (from which the et al. 2003; Susskind et al 2003), and are critical to standard products are generated) are available from profile accuracy and biases in the lower troposphere. MODIS at much finer vertical resolution (101 levels), but because MODIS is not a sounder there is little 2.2 Methods for Diagnosing L-A Interactions additional information in the support data (S. Seemann; pers. communication). Santanello et al. (2006, 2005) present a detailed examination of the relationships among PBL and land 3.2 AIRS surface properties from an empirical and modeling perspective. Traditional methods based on heat AIRS Level-2 temperature profiles were obtained conservation in the PBL were shown to be unsuccessful and processed for the same dates as MODIS at in diagnosing regional fluxes on diurnal scales due to Lamont, OK. AIRS daytime overpasses (AIRS-d) are incomplete parameterization of entrainment and identical to MOD-A, with 6 levels below 600 mb advection processes. As a result, alternative methods available from the standard product (600, 700, 850, were developed based on relationships between 925, 1000, 1100). The AIRS support product provides observable properties of the PBL and the land-surface. 17 levels below 600 mb (617, 639, 661, 683, 706, 729, In turn, a methodology was established that enables 753, 777, 802, 827, 852, 878, 904, 931, 958, 986, 1013 limited observations of PBL structure to be converted mb), but again there is little information in these into estimates of land surface energy balance and additional levels compared to the standard product. surface conditions. AIRS nighttime overpasses (AIRS-n) occur between Namely, the results presented in Santanello et al. 0730 and 0930 UTC, which is close to the timing of (2005) show that PBL height (h) can be estimated with morning radiosonde ascents (1130 UTC) at Lamont, reasonable accuracy using observations of initial OK. Therefore, AIRS-n retrievals should more closely reflect the bulk state of the early-morning lower atmospheric stability in the PBL (γ), diurnal change in 2 troposphere, which is highlighted by a morning surface meter or mixed-layer temperatures (∆θ), and near- inversion and, on occasion, a residual mixed-layer. surface soil moisture (w). More importantly, these Most importantly, stability in the mixed layer is relationships are only weakly dependent on soil and estimated from morning profiles of potential vegetation conditions since the PBL integrates these temperature, and is a significant predictor of PBL properties for a given location, an important growth. consideration for the application of remote sensing data. For both MODIS and AIRS data, estimated dry bulb This methodology was inverted to estimate soil moisture temperatures were first converted to potential from PBL structure, which was then linked directly to temperature and plotted against the pressure levels of sensible heat flux. Although the precise nature of the each product. In theory, the staggered overpass times relationships is site-specific, this strategy