Search

It is understood that atmospheric turbulence results in fluctuations in the received power of an electro-optical (EO) link, a phenomenon known as optical scintillation. The atmospheric variable relevant to optical scintillation is the structure function parameter (Cn2) which can be quantified through optical scintillation measurements or derived from measurements of high-rate sampled atmospheric turbulence, especially the temperature perturbations. In addition to this (Cn2) can be estimated using models, some of which are based on surface layer similarity theory. However, the near shore marine atmospheric surface layer (MASL) provides an optically heterogeneous and complex turbulent environment that can be difficult to model accurately. A better understanding of the characteristics of near shore surface layer scintillation will provide increased exploitation of the environment by current and future EO systems operating in littoral regions. In an effort to better determine the scintillation effects in the MASL, observations were taken during the 26-day Couple Air-Sea Processes and Electromagnetic ducting Research West coast (CASPER-West) field campaign in September - October 2017 off the coast of Pt Mugu, CA. In this paper, we introduce the CASPER-West EO component to include a description of the operating area, major platforms and major instruments relevant to EO measurements, and sampling strategy. We show comparisons of the derived (Cn2) from scalar perturbation measurements, bulk model parameterization, and from concurrent scintillation measurements between the R/V Sally Ride and R/P FLIP. Slant path optical links between a remotely piloted hexa-copter and the R/P FLIP were also available. Both stable and unstable thermal stratifications of the MASL were encountered throughout the campaign and we will discuss the observed differences between the experiment and those from current similarity theories in these different stability conditions.

The article of record as published may be found at http://dx.doi.org/10.1117/12.2263533 Analysis of bulk-skin sea surface temperature (SST) difference form the west and east coasts of United States is presented using the data collected from three field experiments. These experiments were conducted at offshore Duck, North Carolina and in the Monterey Bay of the California coastal region. Bulk SST measurements were made using conventional thermistors from a depth of one meter below the sea level. Infrared radiometers were used to measure the surface skin SST. Depending on measurement depth and prevailing conditions, the bulk SST can differ from skin SST by few tenths of a degree to O(1°C). Difference between bulk and skin SST arise from cools skin and warm layer effects. Bulk-skin SST difference (ΔSST) estimated from east coast observations varied from -0.46°C to 1.24°C. Here, the bulk SST was higher than skin SST most of the time during the observations. This indicates cool skin effect was the dominant factor determining the ΔSST in the east coast. For wind speeds less than 4 m s-1, we also noticed an increase in ΔSST. Additionally, for low winds (< 4 m s-1) ΔSST also varied diurnally with the occurrence of generally higher ΔSST in the nighttime in comparison with daytime. Moreover, increase in downwelling longwave radiation reduced the bulk-skin SST difference. ΔSST calculated from the observation in the Monterey bay varied between ~2.3° and ~-2.3°C. This was higher than the variability ΔSST observed at the east coast. Moreover, ΔSST variability observed at west coast was independent of wind speed. CASPER is funded by the Office of Naval Research (ONR) under its Multidisciplinary University Research Initiative (MURI) program, grant N0001416WX00469, under project managers Dr. Daniel Eleuterio and Steve Russell.

The Micro Rain Radar (MRR) a highly resolution radar operates at a frequency of 24 GHz installed at Thumba (8.5°N, 76.9°E) under Ka band propagation experiment is used extensively to characterize the tropical rain. This radar measurements of rain were obtained with fine spatial and temporal resolutions like One minute time resolution and 200 m height resolution. With this radar for the first time classification of precipitating systems are studied. With the presence or absence of bright band a radar signature of melting layer one can classify particular rain type as convective or stratiform. For present study MRR data from September 2005 onwards are collected. The main objective is to classify precipitation system into Stratiform and Convective with the presence or absence of Bright band. Another potential of this radar is ability to give information of vertical structure of fall velocity of hydrometeors. This also gives profiles of number concentration of various ranges of Drop sizes, liquid water content and rain rate for different heights. These results are compared with the collocated ground based Disdrometer. Attenuation at Microwave frequencies during the presence of rain is a serious concern to the communication. Once temporal and spatial information of DSD is known microwave attenuation can be studied. These results will be presented in this paper.

Enhanced aerosol loading over the Indo-Gangetic Plain (IGP) is a regular feature during winter months. In addition to the environmental degradation and reduced visibility, these aerosols can cause significant radiative impact also. In view of this, a campaign mode observation under ISRO-GBP was conducted in D ecember 2004 to characterize the aerosol properties over the IGP. As part of this, extensive measurements of aerosol BC were made from Kharagpur, an inland rural location lying at the eastern end of the Indo Gangetic Plain. It also lies close to several industrialized regions and area having lot of mining activities Results showed, extremely high BC co ncentration, often exceeding ~20 P g m -2 , prevailed during December. During this period, BC concentration also showed large diurnal vari ation. Simultaneous measuremen ts of the local atmospheric boundary layer height and wind fields revealed a very close association between the BC concentration and the ventilation coefficient (defined as the product of the boundary layer height and the transport wind). Back trajectory analyses using HYSPLIT revealed that in addition to the local boundary layer dynamics, the changes in the advection pathways also influence the concentration of BC. Keywords: Aerosols, BC, Atmospheric boundary layer, HYSPLIT

A case study of sea breeze circulation at a coastal region Thumba (8.5°N, 76.9°E) was carried out using Doppler Sodar, surface wind, temperature, humidity measurements and radiosonde ascents. The analysis of surface meteorological data showed that the onset of sea breeze on 12th April 2006 was at 0945 hrs. GPS sonde observation over sea at 1425 hrs and Radiosonde observation over land at 1730 showed a well developed sea breeze circulation over Thumba coast by afternoon hours. The vertical extent of sea breeze circulation was ~1000m over sea as well as on land. The Thermal Internal Boundary Layer (TIBL) depth associated with sea breeze circulation was about 400m at 8 km away from coast. The marine mixed layer height was ~500m about 12 km away from the coast. Numerical simulation of sea breeze was made using HRM (High Resolution Model) and compared the results with the observations.