Field Strength Calculations: Calculating

As stated in the previous post, one more piece of information is required to complete the puzzle of calculating received field strength. That is the millivolt per meter level at 1 kilometer from the station transmitter, eminating in your direction. Notice I said "eminating in your direction". It is not good enough to simply calculate the mV/m level at 1 kilometer for the station's overall power output. Two things must be accounted for that change that result and would make our field strength calculation inaccurate. They are:

1. Antenna efficiency. A mediumwave tower or array of towers will be more or less efficient depending on their radiation length(s). The FCC provides us with a figure called RMS Theoretical for every station's antenna array whether it be one tower or several, measured in mV/m. Reflected in this figure is the efficiency.

2. Pattern gain. Multiple tower arrays inherently have broadcast patterns. Meaning, of course, they aim to broadcast a majority of their signal in a certain direction to cover their market audience and/or avoid co-channel interference with another station. Where you are in relation to that pattern is important. If you are in the major lobe of a 50KW station, it may be pumping upwards of 100KW towards you, or more. If you are in a sharp pattern null, it may only be beaming hundreds of watts towards you. The amount of millivolts per meter "facing you" is the important figure. The FCC provides that as well, in their pattern plots.

There is only one case where we will need to do a simple extra calculation to arrive at the full millivolt per meter level for a station. That is for stations with a single tower only. I will explain why in just a minute.

So let's put together what we need. First, pick a station within reasonable distance you think you'd like to log. Note its frequency. Next, gather the following four things:

1. The ground conductivity in mS/m between you and the station. Use the M3 conductivity map. If the station path crosses a couple of zones, estimate the average ground conductivity for the entire path. The resultant figure should fall between 0.1 mS/m and 30 mS/m, or possibly higher if part of the path is over salt seawater.

2. The Ground Wave Field Strength Versus Distance graph for the frequency of the station, one of the 20 graphs published by the FCC. Several frequencies are usually grouped into one graph. The graphs are in .PDF form. Have your .PDF viewer ready.

3. You will need to find your distance to the station in kilometers, and also the reverse bearing from the station back to you. Many calculators exist on the web which will compute this information. The FCC has a good one, be sure to check out their calculator. These calculators require you to know the latitude and longitude of both your location and the station's location.

www.wikimapia.org is a great way to determine your home latitude and longitude as it has a crosshair defining the center of the map, and thus the latitude and longitude. Move the map to your exact location and read the latitude-longitude in the web browser's address bar.

The station's latitude and longitude can be found in a couple of ways. The FCC's AM Query web page allows us to query the station by call sign. The search output will display basic information like latitude and longitude. Click on the call sign link and you will be taken to the FCC's web page for the facility (station). Example: WHAM-1180 page.

4. The last item. Get the millivolt per meter value at 1 kilometer from the station transmitter, headed your way. The method of locating this figure will depend on whether the station has one antenna tower or multiple towers in its array.

Determine if the station uses a single tower or multiple towers for the service you are interested in. This information can be found on the FCC's web page for the facility (station), as shown just above.

Note that stations may have more than one entry on the page, one for each service they operate under, i.e., UNLIMITED, DAYTIME, NIGHTTIME, CRITICAL HOURS. Be sure you are looking at the correct service. Sometimes stations use a different number of towers for day and night.

mV/m for multiple towers.

The mV/m figure is gotten from the pattern data. It's simple.

Multiple tower arrays will give you the option to display the pattern plot. The pattern plot link will be under a heading that looks like this:

Horizontal Pattern at 1 km radius (Sections 73.150 and 73.152):
       Electric Field Strength pattern plot
       Pattern Data for WXXI

Either link will give us the information we need, though the "Electric Field Strength pattern plot" gives a nice graphic pattern plot for the station. Click one of the links.

RMS Theoretical values, and in some cases RMS Standard or even RMS Augmented values will be displayed for each five degrees of compass, 0-360. Find the compass bearing that most closely matches the return bearing from the station to you. We need to record one value only. Preferably, record the RMS Augmented value, if given. If not available, record the RMS Standard value. If not given, record the RMS Theoretical value. These values are in millivolts per meter and are the value of signal level the station presents towards you.

A quick definition of RMS Standard and RMS Augmented values. RMS Standard is essentially the RMS Theoretical value plus 5%. It is a "guard" against interference to other co-channel stations by overstating the RMS Theoretical calculated value. If stations have pattern augmentations, and many do, the RMS Augmented field will be present. Augmentations are enhancements or detractions to the theoretical pattern.

I'll use WXXI-1370 for the example. At night it runs 4 towers and has a roughly figure-8 pattern north-south. WXXI's return bearing to me is 204.7 degrees. Checking the FCC pattern plot for the station, we see that the 205 degree return azimuth presents a facing RMS Theoretical of 350.59 mV/m and a facing RMS Standard of 368.88 mV/m. We will use the RMS Standard value in the final calculation.

mV/m for single tower.

A special case requiring a simple calculation. We will calculate the mV/m figure from the RMS Theoretical value.

Again go to the FCC's web page for the facility (station), as above. The RMS Theoretical value will be on this page.

Note again that stations may have more than one entry on the page, one for each service they operate under, i.e., UNLIMITED, DAYTIME, NIGHTTIME, CRITICAL HOURS. Be sure you are looking at the correct service. Sometimes stations use a different number of towers for day and night.

The FCC computes all RMS Theoretical values from a formula of course. The values are calculated for a distance of 1 kilometer. The FCC formula used generates accurate millivolt per meter values (as published) for multiple tower arrays. Single tower arrays are a special case, however, in that the published mV/m value is always based on a 1 kilowatt output power calculation. Hence, the only published single tower mV/m values we can use are those of 1 KW stations. For all others, we will do a simple calculation to arrive at the correct mV/m value. Proof of this is simple. For example, check the FCC's published figures for my local WHAM-1180 station out of Rochester, NY. This 50KW station shows a calculated RMS Theoretical value at 1 kilometer of only 376.59 mV/m. Now of course this cannot be correct for a 50KW station, as a 1 KW station running a quarter wave (.250 wavelength) monopole has an exact calculated figure of 305.768 mV/m at 1 kilometer.

376.59 mV/m would, however, be correct for a 1 KW station using the same single tower antenna that WHAM uses (a .492 wavelength antenna).

To accurately calculate the mV/m figure for WHAM (or any other single tower station, including those 1 KW stations), the following formula must be applied:

(Power in KW, distance in KM):

mV/m = RMSTheoretical x SQRoot(Power/Distance)

Thus in WHAM's case:

2662.89 = 376.59 * SQRoot(50/1)

WHAM's actual RMS Theoretical value is 2662.89 mV/m. And since it is a single tower antenna having an omnidirectional pattern, it presents this value of signal in all directions. Use the value you calculate for your single tower station of interest as the mV/m value that the station presents towards you.

Making The Calculation

Now we have all of our information. Let's get busy. We will use the FCC's Ground Wave Field Strength Versus Distance graph to arrive at the received mV/m signal level. Proceed with the following steps.

1. To make them universal, the FCC's Ground Wave Field Strength Versus Distance graphs are based on 100 mV/m levels at 1 kilometer. We simply need to calculate how many 100s our mV/m value is. Just move the decimal point left two places. In WHAM's case, 2662.89 mV/m, 26.6289 (26.6289 x 100 = 2662.89). The multiplier value we will use for WHAM is 26.6289. In WXXI's case, 368.88 mV/m, 3.6888 (3.6888 x 100 = 368.88). The multiplier value we will use for WXXI is 3.6888.

2. Find the station distance in kilometers on the graph, usually at the bottom. The bottom range is 10 to 1000 kilometers. The top range is 0.1 to 50 kilometers.

3. Draw a trace upwards (or downwards if using the top scale) until you hit the ground conductivity value curve that matches the average ground conductivity between you and the station.

4. From the previous point, draw a trace leftward to the scale on the left side of the graph. This is the base millivolt per meter level based on 100 mV/m at 1 kilometer. Multiply this value by your multiplier value. In WHAM's case, multiply times 26.6289. In WXXI's case, multiply times 3.6888. This resultant value is the received field strength in millivolts per meter at your location.

There you have it. You have ballparked the approximate field strength of your station of interest. If done correctly, you should find this in fairly good agreement with V-Soft's figure if you are near the zipcode point they based their calculation on. With a list of expected receive field strengths for various stations, you can judge the approximate sensitivity of your receiver. After a few times trying this, you will find the calculation to be rather simple to do.

Hope you have enjoyed this series.

If you are interested in the history of field strength calculations, be sure to see Field Strength Calculations: A History on RADIO-TIMETRAVELLER.

Field Strength Calculations: Measurements

Continuing on with ground conductivity, the higher the conductivity the farther away the station's signal will be copyable. Study the accompanying graph showing the range of a 600 KHz signal at the 50KW power level at various ground conductivities. 50 kilowatts over good ground conductivity of 15 mS/m will produce a very copyable signal at a distance of 375 kilometers (233 miles). At an average to poor ground conductivity of 4 mS/m, coverage is reduced to under 200 kilometers. Excellent ground conductivity of 30 mS/m takes the same signal out to more than 500 kilometers! A purely over-seawater path (5000 mS/m) should result in a fair signal out to about 750 kilometers or some 465 miles.

Also study the graph of the transmitter with only 1KW output at 600 KHz. It gets out quite well considering its output is a mere one-fiftieth of its bigger brother! Its range is perhaps a third of the 50KW transmitter.

Take another look at the M3 map from the previous part in this series. The country is filled with pockets of different ground conductivities, some large in area, some small. The mid-section of the country has some of the best. A large portion of eastern Colorado and western Kansas are in the 15 mS/m range. Most of Kansas proper is an incredible 30 mS/m. Signals propagating eastward out of Colorado travel a long way. Northern Texas and Oklahoma also have great ground conductivity.

Frequency of operation makes an important difference in how far a signal travels. Propagation distance at the high end of the mediumwave band is less than half the distance of that at the low end for the same received signal strength. A study of the two accompanying graphs comparing the distance coverage of 600 KHz, 1100 KHz, and 1600 KHz signals clearly show this.

The common unit used in measuring received field strength is volts per meter, or usually, millivolts per meter "mV/m". This is also the FCC requirement. An odd term, millivolts (thousandths of a volt) per meter. We all know what voltage is, but per meter of what, exactly?

Volts per meter expresses the voltage that would be induced in a one meter long wire placed parallel to the lines of flux of the received signal (remember the electrical flux from a mediumwave tower is vertical, the magnetic horizontal). This induced voltage results from the movement of the flux across the wire.

It is important to note that the E (electrical) component of an electromagnetic field is measured in a single dimension. Why? The intensity-versus-distance relation is a straight inverse rule, not the inverse square law commonly used for calculating received power density. In the perfect environment of space, if you double the distance the signal has to travel, the received voltage (in volts/meter or fraction thereof) is halved. Ten times farther away results in 1/10 of the voltage. This is known as field strength. Power density, a different method of measuring received signal strength, follows the inverse square law. That is, the density is related to the inverse of the square of the distance.

In broadcast parlance, millivolts per meter is often referred to in a different context, that being "dBu", or more accurately, dBµV/m. This is decibels above or below 1 millionth of a volt per meter. It is a convenient way to represent field strength, as the decibel is simply a ratio of values. Be sure not to confuse this dBu (lowercase "u") with the Greek "mu" ("µ") on the new model DSP ultralight radios. They are different. These radios actually measure dBµV - voltage across antenna terminals at a certain impedance, not volts per meter.

The FCC offers a conversion calculator to convert from dBu to mV/m and back.

Or, you can figure it yourself by using the following formula:

• dBu = 20 * Log(mV/m * 1000)

To reverse the computation, converting dBu back to mV/m:

• mV/m = (10 ^ (dBu / 20)) / 1000

But let's put received millivolts per meter into practical application, something a little more understandable. Hatfield & Dawson, Consulting Electrical Engineers out of Seattle, WA have a wealth of interesting mediumwave engineering documents for perusal, floating about the web. This document seems to describe it best in terms the layman can understand.

From an engineering report by Hatfield & Dawson, 2002:

"MW radio signal strengths are measured in volts per meter (V/m). The FCC requires that MW radio stations provide a predicted 5 mV/m daytime signal and a 5 mV/m nighttime signal or a Nighttime Interference Free (NIF) signal, whichever is greater, over the city of license."

"MW radio receivers vary greatly in sensitivity and much has been written lately about the poor performance of MW receivers built today. The general practice for broadcaster use for coverage is 2 mV/m for coverage in vehicles, 5 mV/m to 25 mV/m for in home and 25 mV/m in downtown office buildings. On a Walkman-type portable radio, you may need as much as 5 millivolts (5 mV/m) of signal to have static-free reception. The reason for these recommended signal levels is to overcome the effects of interference. Sources of interference include fluorescent lights, computers, TVs, office equipment, overhead power lines, and other appliances operating near a radio that can overload the receiver. In a city core, stations generally need more signal than this because of heavy attenuation inside large steel structures like office buildings. In your home, depending on the location, type of radio, and the utilization of any external antennas, you can have good reception with signals between 1 mV/m and 25 mV/m."

radio-locator.com produces widely used antenna pattern plots, available to interested parties over the web. These depict the expected signal coverage of the mediumwave station. radio-locator divides the signal coverage area into three distinct ranges.

1. Local (red line), the area in which the field strength is 2.5 mV/m or greater, where "....you should be able to receive the radio station on almost any radio with moderately good to very good reception".

2. Distant (purple line), the area between 0.5 and 2.5 mV/m, where "....the signal of the radio station may be weak unless you have a good car radio or a good stereo with a good antenna. You may not be able to receive the station at all on Walkmans or other portable radios".

3. Fringe (blue line), the area between 0.15 and 0.5 mV/m, where "....the station's signal will be very weak. You may be able to receive this station if you have a very good radio with a good antenna, but it's possible that interference from other stations may prevent you from picking up these stations at all." This seems to agree with Hatfield and Dawson's report.

Another important factor in our quest to predict received signal strength is transmitter antenna efficiency. Size does matter. The better the antenna, the better the station gets out. Returning again to Hatfield and Dawson, now discussing mediumwave antennas:

"MW antenna heights are referenced to a wavelength (this only includes the radiating portion of the tower). In MW broadcasting, 5/8 wavelength (or 225°) antennas are more efficient than ¼ wave antennas. A ¼ wavelength (or 90°) antenna is near the lower end of acceptable antenna heights. Antenna heights much below ¼ wavelength are undesirable, as efficiencies decrease dramatically below this height. A 225° antenna provides the maximum coverage and is the theoretical maximum. The efficiency decreases for antennas taller than 225°, which results in reduced coverage. In summary, taller towers are more efficient and shorter towers decrease coverage and are more difficult to work with."

So back to our quest of received signal strength prediction. Few documents are available which demonstrate how to predict "real-world" surface propagation distances at mediumwave frequencies. Many analysts use vanilla formulas for calculating free space path loss using the inverse square law, computing the path loss (in dB) from transmitter to receiver. The path loss, in turn, is used to determine the received field strength value.

Unfortunately, free space path loss assumes a perfect environment, like you would find out in space or over a perfectly conducting earth. Be wary of cute little field strength calculators on the web, their resultant field strength figures are almost an order of magnitude higher than what is seen in real life. Formulas exist which will predict field strength at mediumwave frequencies, but the math is well beyond the average person's ability.

A simpler method exists to ballpark the figure we want. We need but one more piece of information to complete the puzzle. That is the millivolt per meter level at one kilometer from the station transmitter, emanating in your direction. Using that with the FCC's Ground Wave Field Strength Versus Distance graphs and the M3 conductivity map we can estimate the received signal level in mV/m to fairly good accuracy at our location for any station.

The next part of this article will show you how to do that. But let me leave you with this before we go. What information can we derive from the FCC graphs and other station data to maximize our daytime DX distance?

1. The lower frequencies propagate better per unit of distance. Stations near the low end of the broadcast band propagate nearly three times farther than ones at the highest end, for the same power output and same ground conductivity. The lesson: listen to the lower end of the MW band if you want extreme distance in reception.

2. Look for over-water paths. A local example: Ground conductivity around here in the Rochester, NY area is about 8 or a little less, tending towards the 6 mS/m figure judging from reception experience. Without passive loop assistance, normal daytime reception limits seem to max out at about 150 miles. That is, except for two stations: WJR-760, Detroit, MI and CKLW-800, Windsor, Ontario, Canada, near Detroit. These two are out at about 250 miles or about 400 kilometers. Why are they receivable? Most of their signal path is across water over the east-west length of Lake Erie into Rochester. Reception is routine on most simple radios with medium or better sensitivity.

3. Study station antenna patterns. The FCC web site is great for this. Virtually all stations with multiple towers have directional patterns and the FCC makes the pattern plot available in .PDF form. Study the plot and pay particular attention to your azimuth away from the station. Pick stations that push a lot of signal in your direction. They are the best prospects. Example: WXXI-1370 pattern

4. The radio-locator "fringe" 0.15 mV/m boundary seen on their plots is just that - fringe. Many stations are copyable at this boundary and beyond on a sensitive radio. Don't hesitate to try for them. Example: Denver stations KHOW-630 (only 5KW), KKZN-760 (50KW), and KOA-850 (50KW) all have excellent strength east to well past Hays, Kansas (300+ miles, or 483+ km) despite the fringe zone ending miles back towards the Kansas/Colorado state line.

The jury seems to be out on how far ground conductivity plays a role in daytime propagation. Some documents refer to the 55 kilometer figure, others to 150 kilometers. My bet is it is well beyond the 150 km figure as I have routinely heard stations at the 800 kilometer range during high daylight hours at all times of the year.

Next up: Calculating

Field Strength Calculations: Ground Conductivity

Ground (also called soil) conductivity plays a huge role in how far the mediumwave signal travels during the daytime. Lesser known to many, station frequency is also a factor, and maybe more of one than you would think. Though one can argue successfully that frequency is not a factor in the formula for calculating received signal strength, it indeed becomes relevant as you will see. In this series, let's explore ground conductivity and station frequency and see how they relate to "how far you can hear" on the mediumwave band during the daytime. We will end with a method to calculate approximate field strength for stations of interest.

Many years ago, ground conductivity measurements were compiled into a map titled "Estimated Effective Ground Conductivity in the United States" (Figure M3) by the FCC. This map is used for the allocations planning for placement of MW stations in the United States. The map presents optimistic ground conductivities and is used when measured conductivity is not available. This information has been used and accepted since it was compiled in 1954.

Soil conductance is measured in siemens per meter but most generally shown in millisiemens per meter. This is the mS/m designation you see in the accompanying chart. The siemens (symbolized S) is the Standard International (SI) unit of electrical conductance. The old term for this unit is the mho (ohm spelled backwards). Conductance (mho) is of course the opposite of resistance (ohm). As you can see, salt sea water provides the best conductance by far (5000 mS/m). The higher the value the better. Average soil runs 6-8 mS/m. Find your location on the map and see what your local conductance value is. Notice also that a distant station's receive path may transition across more than one zone.

Equally important, the FCC also produces a series of charts known as the "Ground Wave Field Strength Versus Distance" graphs. These 20 graphs in .PDF form are grouped by mediumwave channels in the 540-1700 KHz range, and allow prediction of received signal strength by cross-referencing the distance to the receiving location with the ground conductivity factor between you and the station. These charts cover soil conductivity ranges of 0.1 mS/m to 5000 mS/m. They are still in use today. The only working link I have for them is:

FCC Ground Wave Field Strength Versus Distance Graphs

Be sure to get the .PDF versions.

How well a mediumwave transmitter "gets out" is not only dependent on its power, frequency, and the ground conductivity between it and you, but also on the ground condition at its location. The following is a quote from the Standards of Good Engineering Practice Concerning Standard Broadcast Stations (550-1600 kc.), 1939, and is still relevant today:

"The ideal location of a broadcast transmitter is in a low area of marshy or 'crawfishy' soil or area, which is damp the maximum percentage of time and from which a clear view over the entire center of population may be had... The type and condition of the soil or earth immediately around a site is very important. Important, to an equal extent, is the soil or earth between the site and the principal area to be served. Sandy soil is considered the worst type, with glacial deposits and mineral-ore areas next. Alluvial, marshy areas and salt-water bogs have been found to have the least absorption of the signal."

All well and good. Our transmitter is well-located, emitting a good signal traveling over perhaps many kilometers or miles to our receiving location. We either hear it or we don't depending on the natural attenuation decay between us and the transmitter. But just how do we predict the outcome? How do we (abstractly) measure a mediumwave signal's strength at the receiving end? We will use these tools and others to find out.

Next up: Measurements

Signal Patterns - 670 KHz - American Southwest

Though I am back in New York for the summer, lets temporarily time travel back to the southwestern United States to January of this year. This article was written then but never posted.

January, 2011. Southwestern Arizona.

The Players:

KIRN-670 Simi Valley, CA 5KW 260.6mi
KMZQ-670 Las Vegas, NV 30KW 197.9mi
KBOI-670 Boise, ID 50KW 683.6mi
KLTT-670 Commerce City, CO 50KW 681.0mi

In the hour just after sunrise this time of year, little KIRN-670, Simi Valley, CA (5KW at 260.6 miles) is sometimes audible here, fading in and out weakly amongst a handful of stations. An ethnic station, KIRN (K-IRAN) plays a wonderful selection of Iranian music. KIRN has three main competitors at this time of day. The strongest and main signal heard during this hour is news-talk KBOI-670, Boise, ID (50KW at 683.6 miles). Weaker, though closer to me is Las Vegas, NV station KMZQ-670 (30KW at 197.9 miles), usually down in the mud for some reason. Last, christian affiliate KLTT-670 in suburban Denver's Commerce City (50KW at 681.0 miles) has already peaked about an hour before and is fading away for good as the sun heads west. Or is it?

KBOI in Boise disappears for good about one hour after sunrise. Then follows KIRN, farther west. As high-daylight emerges, left on frequency seems to be KMZQ in Las Vegas - weak, but audible throughout the day on a sensitive radio like a Sony 2010. KMZQ's pattern is directed mostly northwest (335 degrees), so most of its signal is funneled away from my location approximately four hours south of Las Vegas. It is sometimes weakly audible at certain times of day on the truck radio, a somewhat sensitive beast. Without an assist, most ULRs offer up only noise on this channel during daytime hours.

My loop of choice, a 24-inch passive loop, does wonders during the day. KMZQ-670 becomes clearly audible at medium strength on any radio. Rotate the loop a little to the east, and surprisingly Colorado's KLTT-670 is often present at varying ultra-weak to weak signal strength. KMZQ-670 is always in there, though. KLTT sometimes rises above and is nearly in the clear with proper nulling, particularly late in the morning. KLTT is an excellent DX catch here during daylight hours - at an astounding distance of 681 miles. Helping tremendously is KLTT's signal pattern. I am in the main lobe of its daytime pattern, which points roughly southwest (247 degrees). A resounding 5.0 dB pattern gain results in 161 kilowatts ERP being pumped this way after sunrise, crossing the high continental divide running through the center of Colorado. So far, KLTT-670 is my Arizona fixed location distance record for daytime DX. Two other personal records of longer distance are documented in a previous article.

Returning to 50KW outlet KBOI-670 in Boise, if we can receive 50KW KLTT-670 in Denver at 681 miles during daylight hours, why can't we receive KBOI at 683 miles? So far this station has only been audible during nighttime hours. Part of the problem here is KBOI's pattern. During the daytime, it is an omnidirectional one without gain. Secondly, and unfortunately, Las Vegas's KMZQ is also almost directly in-between KBOI and me. Null KMZQ, and I am nulling KBOI. Daytime reception will probably never happen.

Still I listen for little KIRN-670 over in Simi Valley. I have not caught it during daytime hours yet, but continue to try. The possibility exists that its 5KW signal could one day make the grade over the relatively short distance of only 260 miles. KMZQ in Las Vegas is a major problem, though. Little azimuth exists between these two stations from this location, making it hard to null KMZQ effectively enough to quiet the frequency. It is interesting that KLTT makes the grade all the way from Denver over the 681 mile path at 50KW, but KIRN cannot manage 260 miles with 5KW. Partly, KIRN's pattern is due south, and I am off the side of it. The return pattern loss is a negative 5.5 dB, so only 1384 effective watts are sent this way.

It would be nice to one day hear Chicago's 50KW WSCR-670, at 1530 miles distance from southwestern Arizona. It is on a bearing of 60 degrees, slightly east of Colorado's KLTT at 47 degrees. Looking at a grayline map, it might be possible to snatch WSCR at its local sunrise time, as KLTT is still at low power for the darkness period (at 700 watts), and Las Vegas's KMZQ is still at low power as well (600 watts). Evenings may be possible too. On another channel, WWL-870 in New Orleans is receivable here at 1437 miles many evenings, though it has less competition.

Check out the pattern plot for KMZQ. See how nicely KMZQ avoids KIRN and KLTT, fitting them exactly into the deepest nulls of its pattern. Nice work!

The Mystery Of The Missing Sunspots - Solved

The long dry-spell explained by NASA. One of the mysteries of the erratic nature of sunspot cycles has finally been solved. Back at the last solar minimum, sunspots virtually disappeared for a two year period - 2008 and 2009. Many wondered if they would ever return.

In March an article appeared in NASA Science News explaining the inter-relationship of previously-known solar plasma flows ("meridional flows"), plasma flowing in a constant loop from the surface of the sun, diving to the interior at the poles, then reemerging at the equator of the sun in a constant symphony of motion.

"Plasma currents deep inside the sun interfered with the formation of sunspots and prolonged solar minimum," says lead author Dibyendu Nandi of the Indian Institute of Science Education and Research in Kolkata. "Our conclusions are based on a new computer model of the sun's interior." Read more in this fascinating article, Researchers Crack The Mystery Of The Missing Sunspots. Maybe we are on the verge of being able to predict the length and intensity of solar cycles?